From e8c7f8efe9840275d4e5565ae3b924db5f2365c1 Mon Sep 17 00:00:00 2001
From: "dependabot[bot]" <49699333+dependabot[bot]@users.noreply.github.com>
Date: Wed, 25 Oct 2023 22:37:37 +0000
Subject: [PATCH] build(deps): bump google.golang.org/grpc from 1.55.0 to
 1.56.3

Bumps [google.golang.org/grpc](https://github.com/grpc/grpc-go) from 1.55.0 to 1.56.3.
- [Release notes](https://github.com/grpc/grpc-go/releases)
- [Commits](https://github.com/grpc/grpc-go/compare/v1.55.0...v1.56.3)

---
updated-dependencies:
- dependency-name: google.golang.org/grpc
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
---
 go.mod                                        |   2 +-
 go.sum                                        |   4 +-
 .../grpc/attributes/attributes.go             |  29 +
 .../grpc/balancer/balancer.go                 |   2 +-
 .../grpc/balancer_conn_wrappers.go            | 486 +++++++-------
 vendor/google.golang.org/grpc/call.go         |   5 +
 vendor/google.golang.org/grpc/clientconn.go   | 607 +++++++++++++-----
 vendor/google.golang.org/grpc/dialoptions.go  |  21 +
 vendor/google.golang.org/grpc/idle.go         | 287 +++++++++
 .../grpc/internal/binarylog/binarylog.go      |   3 +
 .../grpc/internal/binarylog/method_logger.go  |   9 +
 .../grpc/internal/buffer/unbounded.go         |  26 +-
 .../grpc/internal/envconfig/envconfig.go      |   4 +
 .../grpc/internal/envconfig/observability.go  |   6 +
 .../grpc/internal/envconfig/xds.go            |  19 +-
 .../grpc/internal/grpcrand/grpcrand.go        |  14 +
 .../internal/grpcsync/callback_serializer.go  |  64 +-
 .../grpc/internal/internal.go                 |  24 +
 .../grpc/internal/serviceconfig/duration.go   | 130 ++++
 .../grpc/internal/transport/handler_server.go |   2 +-
 .../grpc/internal/transport/http2_client.go   |   2 +-
 .../grpc/internal/transport/http2_server.go   |  21 +-
 .../grpc/internal/transport/transport.go      |   2 +-
 .../google.golang.org/grpc/picker_wrapper.go  |  38 +-
 vendor/google.golang.org/grpc/pickfirst.go    |  52 +-
 .../grpc/resolver/resolver.go                 |  16 +-
 .../grpc/resolver_conn_wrapper.go             | 229 ++++---
 vendor/google.golang.org/grpc/server.go       |  75 ++-
 .../google.golang.org/grpc/service_config.go  |  75 +--
 .../google.golang.org/grpc/status/status.go   |  29 +-
 vendor/google.golang.org/grpc/stream.go       |  29 +-
 vendor/google.golang.org/grpc/version.go      |   2 +-
 vendor/modules.txt                            |   2 +-
 33 files changed, 1648 insertions(+), 668 deletions(-)
 create mode 100644 vendor/google.golang.org/grpc/idle.go
 create mode 100644 vendor/google.golang.org/grpc/internal/serviceconfig/duration.go

diff --git a/go.mod b/go.mod
index 7f72e4f1..e8910b9c 100644
--- a/go.mod
+++ b/go.mod
@@ -26,7 +26,7 @@ require (
 	go.opentelemetry.io/contrib/instrumentation/gorilla/mux v0.7.0
 	go.uber.org/zap v1.24.0
 	gonum.org/v1/gonum v0.13.0
-	google.golang.org/grpc v1.55.0
+	google.golang.org/grpc v1.56.3
 	gopkg.in/yaml.v2 v2.4.0
 )
 
diff --git a/go.sum b/go.sum
index ed49bd46..995e35ff 100644
--- a/go.sum
+++ b/go.sum
@@ -222,8 +222,8 @@ google.golang.org/grpc v1.30.0/go.mod h1:N36X2cJ7JwdamYAgDz+s+rVMFjt3numwzf/HckM
 google.golang.org/grpc v1.33.1/go.mod h1:fr5YgcSWrqhRRxogOsw7RzIpsmvOZ6IcH4kBYTpR3n0=
 google.golang.org/grpc v1.36.0/go.mod h1:qjiiYl8FncCW8feJPdyg3v6XW24KsRHe+dy9BAGRRjU=
 google.golang.org/grpc v1.47.0/go.mod h1:vN9eftEi1UMyUsIF80+uQXhHjbXYbm0uXoFCACuMGWk=
-google.golang.org/grpc v1.55.0 h1:3Oj82/tFSCeUrRTg/5E/7d/W5A1tj6Ky1ABAuZuv5ag=
-google.golang.org/grpc v1.55.0/go.mod h1:iYEXKGkEBhg1PjZQvoYEVPTDkHo1/bjTnfwTeGONTY8=
+google.golang.org/grpc v1.56.3 h1:8I4C0Yq1EjstUzUJzpcRVbuYA2mODtEmpWiQoN/b2nc=
+google.golang.org/grpc v1.56.3/go.mod h1:I9bI3vqKfayGqPUAwGdOSu7kt6oIJLixfffKrpXqQ9s=
 google.golang.org/protobuf v0.0.0-20200109180630-ec00e32a8dfd/go.mod h1:DFci5gLYBciE7Vtevhsrf46CRTquxDuWsQurQQe4oz8=
 google.golang.org/protobuf v0.0.0-20200221191635-4d8936d0db64/go.mod h1:kwYJMbMJ01Woi6D6+Kah6886xMZcty6N08ah7+eCXa0=
 google.golang.org/protobuf v0.0.0-20200228230310-ab0ca4ff8a60/go.mod h1:cfTl7dwQJ+fmap5saPgwCLgHXTUD7jkjRqWcaiX5VyM=
diff --git a/vendor/google.golang.org/grpc/attributes/attributes.go b/vendor/google.golang.org/grpc/attributes/attributes.go
index 02f5dc53..3efca459 100644
--- a/vendor/google.golang.org/grpc/attributes/attributes.go
+++ b/vendor/google.golang.org/grpc/attributes/attributes.go
@@ -25,6 +25,11 @@
 // later release.
 package attributes
 
+import (
+	"fmt"
+	"strings"
+)
+
 // Attributes is an immutable struct for storing and retrieving generic
 // key/value pairs.  Keys must be hashable, and users should define their own
 // types for keys.  Values should not be modified after they are added to an
@@ -99,3 +104,27 @@ func (a *Attributes) Equal(o *Attributes) bool {
 	}
 	return true
 }
+
+// String prints the attribute map. If any key or values throughout the map
+// implement fmt.Stringer, it calls that method and appends.
+func (a *Attributes) String() string {
+	var sb strings.Builder
+	sb.WriteString("{")
+	first := true
+	for k, v := range a.m {
+		var key, val string
+		if str, ok := k.(interface{ String() string }); ok {
+			key = str.String()
+		}
+		if str, ok := v.(interface{ String() string }); ok {
+			val = str.String()
+		}
+		if !first {
+			sb.WriteString(", ")
+		}
+		sb.WriteString(fmt.Sprintf("%q: %q, ", key, val))
+		first = false
+	}
+	sb.WriteString("}")
+	return sb.String()
+}
diff --git a/vendor/google.golang.org/grpc/balancer/balancer.go b/vendor/google.golang.org/grpc/balancer/balancer.go
index 09d61dd1..8f00523c 100644
--- a/vendor/google.golang.org/grpc/balancer/balancer.go
+++ b/vendor/google.golang.org/grpc/balancer/balancer.go
@@ -286,7 +286,7 @@ type PickResult struct {
 	//
 	// LB policies with child policies are responsible for propagating metadata
 	// injected by their children to the ClientConn, as part of Pick().
-	Metatada metadata.MD
+	Metadata metadata.MD
 }
 
 // TransientFailureError returns e.  It exists for backward compatibility and
diff --git a/vendor/google.golang.org/grpc/balancer_conn_wrappers.go b/vendor/google.golang.org/grpc/balancer_conn_wrappers.go
index 0359956d..04b9ad41 100644
--- a/vendor/google.golang.org/grpc/balancer_conn_wrappers.go
+++ b/vendor/google.golang.org/grpc/balancer_conn_wrappers.go
@@ -25,14 +25,20 @@ import (
 	"sync"
 
 	"google.golang.org/grpc/balancer"
-	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/connectivity"
 	"google.golang.org/grpc/internal/balancer/gracefulswitch"
-	"google.golang.org/grpc/internal/buffer"
 	"google.golang.org/grpc/internal/channelz"
 	"google.golang.org/grpc/internal/grpcsync"
 	"google.golang.org/grpc/resolver"
-	"google.golang.org/grpc/status"
+)
+
+type ccbMode int
+
+const (
+	ccbModeActive = iota
+	ccbModeIdle
+	ccbModeClosed
+	ccbModeExitingIdle
 )
 
 // ccBalancerWrapper sits between the ClientConn and the Balancer.
@@ -49,192 +55,101 @@ import (
 // It uses the gracefulswitch.Balancer internally to ensure that balancer
 // switches happen in a graceful manner.
 type ccBalancerWrapper struct {
-	cc *ClientConn
-
-	// Since these fields are accessed only from handleXxx() methods which are
-	// synchronized by the watcher goroutine, we do not need a mutex to protect
-	// these fields.
+	// The following fields are initialized when the wrapper is created and are
+	// read-only afterwards, and therefore can be accessed without a mutex.
+	cc   *ClientConn
+	opts balancer.BuildOptions
+
+	// Outgoing (gRPC --> balancer) calls are guaranteed to execute in a
+	// mutually exclusive manner as they are scheduled in the serializer. Fields
+	// accessed *only* in these serializer callbacks, can therefore be accessed
+	// without a mutex.
 	balancer        *gracefulswitch.Balancer
 	curBalancerName string
 
-	updateCh *buffer.Unbounded // Updates written on this channel are processed by watcher().
-	resultCh *buffer.Unbounded // Results of calls to UpdateClientConnState() are pushed here.
-	closed   *grpcsync.Event   // Indicates if close has been called.
-	done     *grpcsync.Event   // Indicates if close has completed its work.
+	// mu guards access to the below fields. Access to the serializer and its
+	// cancel function needs to be mutex protected because they are overwritten
+	// when the wrapper exits idle mode.
+	mu               sync.Mutex
+	serializer       *grpcsync.CallbackSerializer // To serialize all outoing calls.
+	serializerCancel context.CancelFunc           // To close the seralizer at close/enterIdle time.
+	mode             ccbMode                      // Tracks the current mode of the wrapper.
 }
 
 // newCCBalancerWrapper creates a new balancer wrapper. The underlying balancer
 // is not created until the switchTo() method is invoked.
 func newCCBalancerWrapper(cc *ClientConn, bopts balancer.BuildOptions) *ccBalancerWrapper {
+	ctx, cancel := context.WithCancel(context.Background())
 	ccb := &ccBalancerWrapper{
-		cc:       cc,
-		updateCh: buffer.NewUnbounded(),
-		resultCh: buffer.NewUnbounded(),
-		closed:   grpcsync.NewEvent(),
-		done:     grpcsync.NewEvent(),
+		cc:               cc,
+		opts:             bopts,
+		serializer:       grpcsync.NewCallbackSerializer(ctx),
+		serializerCancel: cancel,
 	}
-	go ccb.watcher()
 	ccb.balancer = gracefulswitch.NewBalancer(ccb, bopts)
 	return ccb
 }
 
-// The following xxxUpdate structs wrap the arguments received as part of the
-// corresponding update. The watcher goroutine uses the 'type' of the update to
-// invoke the appropriate handler routine to handle the update.
-
-type ccStateUpdate struct {
-	ccs *balancer.ClientConnState
-}
-
-type scStateUpdate struct {
-	sc    balancer.SubConn
-	state connectivity.State
-	err   error
-}
-
-type exitIdleUpdate struct{}
-
-type resolverErrorUpdate struct {
-	err error
-}
-
-type switchToUpdate struct {
-	name string
-}
-
-type subConnUpdate struct {
-	acbw *acBalancerWrapper
-}
-
-// watcher is a long-running goroutine which reads updates from a channel and
-// invokes corresponding methods on the underlying balancer. It ensures that
-// these methods are invoked in a synchronous fashion. It also ensures that
-// these methods are invoked in the order in which the updates were received.
-func (ccb *ccBalancerWrapper) watcher() {
-	for {
-		select {
-		case u := <-ccb.updateCh.Get():
-			ccb.updateCh.Load()
-			if ccb.closed.HasFired() {
-				break
-			}
-			switch update := u.(type) {
-			case *ccStateUpdate:
-				ccb.handleClientConnStateChange(update.ccs)
-			case *scStateUpdate:
-				ccb.handleSubConnStateChange(update)
-			case *exitIdleUpdate:
-				ccb.handleExitIdle()
-			case *resolverErrorUpdate:
-				ccb.handleResolverError(update.err)
-			case *switchToUpdate:
-				ccb.handleSwitchTo(update.name)
-			case *subConnUpdate:
-				ccb.handleRemoveSubConn(update.acbw)
-			default:
-				logger.Errorf("ccBalancerWrapper.watcher: unknown update %+v, type %T", update, update)
-			}
-		case <-ccb.closed.Done():
-		}
-
-		if ccb.closed.HasFired() {
-			ccb.handleClose()
-			return
-		}
-	}
-}
-
 // updateClientConnState is invoked by grpc to push a ClientConnState update to
 // the underlying balancer.
-//
-// Unlike other methods invoked by grpc to push updates to the underlying
-// balancer, this method cannot simply push the update onto the update channel
-// and return. It needs to return the error returned by the underlying balancer
-// back to grpc which propagates that to the resolver.
 func (ccb *ccBalancerWrapper) updateClientConnState(ccs *balancer.ClientConnState) error {
-	ccb.updateCh.Put(&ccStateUpdate{ccs: ccs})
-
-	var res interface{}
-	select {
-	case res = <-ccb.resultCh.Get():
-		ccb.resultCh.Load()
-	case <-ccb.closed.Done():
-		// Return early if the balancer wrapper is closed while we are waiting for
-		// the underlying balancer to process a ClientConnState update.
-		return nil
-	}
-	// If the returned error is nil, attempting to type assert to error leads to
-	// panic. So, this needs to handled separately.
-	if res == nil {
-		return nil
-	}
-	return res.(error)
-}
-
-// handleClientConnStateChange handles a ClientConnState update from the update
-// channel and invokes the appropriate method on the underlying balancer.
-//
-// If the addresses specified in the update contain addresses of type "grpclb"
-// and the selected LB policy is not "grpclb", these addresses will be filtered
-// out and ccs will be modified with the updated address list.
-func (ccb *ccBalancerWrapper) handleClientConnStateChange(ccs *balancer.ClientConnState) {
-	if ccb.curBalancerName != grpclbName {
-		// Filter any grpclb addresses since we don't have the grpclb balancer.
-		var addrs []resolver.Address
-		for _, addr := range ccs.ResolverState.Addresses {
-			if addr.Type == resolver.GRPCLB {
-				continue
+	ccb.mu.Lock()
+	errCh := make(chan error, 1)
+	// Here and everywhere else where Schedule() is called, it is done with the
+	// lock held. But the lock guards only the scheduling part. The actual
+	// callback is called asynchronously without the lock being held.
+	ok := ccb.serializer.Schedule(func(_ context.Context) {
+		// If the addresses specified in the update contain addresses of type
+		// "grpclb" and the selected LB policy is not "grpclb", these addresses
+		// will be filtered out and ccs will be modified with the updated
+		// address list.
+		if ccb.curBalancerName != grpclbName {
+			var addrs []resolver.Address
+			for _, addr := range ccs.ResolverState.Addresses {
+				if addr.Type == resolver.GRPCLB {
+					continue
+				}
+				addrs = append(addrs, addr)
 			}
-			addrs = append(addrs, addr)
+			ccs.ResolverState.Addresses = addrs
 		}
-		ccs.ResolverState.Addresses = addrs
+		errCh <- ccb.balancer.UpdateClientConnState(*ccs)
+	})
+	if !ok {
+		// If we are unable to schedule a function with the serializer, it
+		// indicates that it has been closed. A serializer is only closed when
+		// the wrapper is closed or is in idle.
+		ccb.mu.Unlock()
+		return fmt.Errorf("grpc: cannot send state update to a closed or idle balancer")
 	}
-	ccb.resultCh.Put(ccb.balancer.UpdateClientConnState(*ccs))
+	ccb.mu.Unlock()
+
+	// We get here only if the above call to Schedule succeeds, in which case it
+	// is guaranteed that the scheduled function will run. Therefore it is safe
+	// to block on this channel.
+	err := <-errCh
+	if logger.V(2) && err != nil {
+		logger.Infof("error from balancer.UpdateClientConnState: %v", err)
+	}
+	return err
 }
 
 // updateSubConnState is invoked by grpc to push a subConn state update to the
 // underlying balancer.
 func (ccb *ccBalancerWrapper) updateSubConnState(sc balancer.SubConn, s connectivity.State, err error) {
-	// When updating addresses for a SubConn, if the address in use is not in
-	// the new addresses, the old ac will be tearDown() and a new ac will be
-	// created. tearDown() generates a state change with Shutdown state, we
-	// don't want the balancer to receive this state change. So before
-	// tearDown() on the old ac, ac.acbw (acWrapper) will be set to nil, and
-	// this function will be called with (nil, Shutdown). We don't need to call
-	// balancer method in this case.
-	if sc == nil {
-		return
-	}
-	ccb.updateCh.Put(&scStateUpdate{
-		sc:    sc,
-		state: s,
-		err:   err,
+	ccb.mu.Lock()
+	ccb.serializer.Schedule(func(_ context.Context) {
+		ccb.balancer.UpdateSubConnState(sc, balancer.SubConnState{ConnectivityState: s, ConnectionError: err})
 	})
-}
-
-// handleSubConnStateChange handles a SubConnState update from the update
-// channel and invokes the appropriate method on the underlying balancer.
-func (ccb *ccBalancerWrapper) handleSubConnStateChange(update *scStateUpdate) {
-	ccb.balancer.UpdateSubConnState(update.sc, balancer.SubConnState{ConnectivityState: update.state, ConnectionError: update.err})
-}
-
-func (ccb *ccBalancerWrapper) exitIdle() {
-	ccb.updateCh.Put(&exitIdleUpdate{})
-}
-
-func (ccb *ccBalancerWrapper) handleExitIdle() {
-	if ccb.cc.GetState() != connectivity.Idle {
-		return
-	}
-	ccb.balancer.ExitIdle()
+	ccb.mu.Unlock()
 }
 
 func (ccb *ccBalancerWrapper) resolverError(err error) {
-	ccb.updateCh.Put(&resolverErrorUpdate{err: err})
-}
-
-func (ccb *ccBalancerWrapper) handleResolverError(err error) {
-	ccb.balancer.ResolverError(err)
+	ccb.mu.Lock()
+	ccb.serializer.Schedule(func(_ context.Context) {
+		ccb.balancer.ResolverError(err)
+	})
+	ccb.mu.Unlock()
 }
 
 // switchTo is invoked by grpc to instruct the balancer wrapper to switch to the
@@ -248,24 +163,27 @@ func (ccb *ccBalancerWrapper) handleResolverError(err error) {
 // the ccBalancerWrapper keeps track of the current LB policy name, and skips
 // the graceful balancer switching process if the name does not change.
 func (ccb *ccBalancerWrapper) switchTo(name string) {
-	ccb.updateCh.Put(&switchToUpdate{name: name})
+	ccb.mu.Lock()
+	ccb.serializer.Schedule(func(_ context.Context) {
+		// TODO: Other languages use case-sensitive balancer registries. We should
+		// switch as well. See: https://github.com/grpc/grpc-go/issues/5288.
+		if strings.EqualFold(ccb.curBalancerName, name) {
+			return
+		}
+		ccb.buildLoadBalancingPolicy(name)
+	})
+	ccb.mu.Unlock()
 }
 
-// handleSwitchTo handles a balancer switch update from the update channel. It
-// calls the SwitchTo() method on the gracefulswitch.Balancer with a
-// balancer.Builder corresponding to name. If no balancer.Builder is registered
-// for the given name, it uses the default LB policy which is "pick_first".
-func (ccb *ccBalancerWrapper) handleSwitchTo(name string) {
-	// TODO: Other languages use case-insensitive balancer registries. We should
-	// switch as well. See: https://github.com/grpc/grpc-go/issues/5288.
-	if strings.EqualFold(ccb.curBalancerName, name) {
-		return
-	}
-
-	// TODO: Ensure that name is a registered LB policy when we get here.
-	// We currently only validate the `loadBalancingConfig` field. We need to do
-	// the same for the `loadBalancingPolicy` field and reject the service config
-	// if the specified policy is not registered.
+// buildLoadBalancingPolicy performs the following:
+//   - retrieve a balancer builder for the given name. Use the default LB
+//     policy, pick_first, if no LB policy with name is found in the registry.
+//   - instruct the gracefulswitch balancer to switch to the above builder. This
+//     will actually build the new balancer.
+//   - update the `curBalancerName` field
+//
+// Must be called from a serializer callback.
+func (ccb *ccBalancerWrapper) buildLoadBalancingPolicy(name string) {
 	builder := balancer.Get(name)
 	if builder == nil {
 		channelz.Warningf(logger, ccb.cc.channelzID, "Channel switches to new LB policy %q, since the specified LB policy %q was not registered", PickFirstBalancerName, name)
@@ -281,26 +199,114 @@ func (ccb *ccBalancerWrapper) handleSwitchTo(name string) {
 	ccb.curBalancerName = builder.Name()
 }
 
-// handleRemoveSucConn handles a request from the underlying balancer to remove
-// a subConn.
-//
-// See comments in RemoveSubConn() for more details.
-func (ccb *ccBalancerWrapper) handleRemoveSubConn(acbw *acBalancerWrapper) {
-	ccb.cc.removeAddrConn(acbw.getAddrConn(), errConnDrain)
+func (ccb *ccBalancerWrapper) close() {
+	channelz.Info(logger, ccb.cc.channelzID, "ccBalancerWrapper: closing")
+	ccb.closeBalancer(ccbModeClosed)
 }
 
-func (ccb *ccBalancerWrapper) close() {
-	ccb.closed.Fire()
-	<-ccb.done.Done()
+// enterIdleMode is invoked by grpc when the channel enters idle mode upon
+// expiry of idle_timeout. This call blocks until the balancer is closed.
+func (ccb *ccBalancerWrapper) enterIdleMode() {
+	channelz.Info(logger, ccb.cc.channelzID, "ccBalancerWrapper: entering idle mode")
+	ccb.closeBalancer(ccbModeIdle)
+}
+
+// closeBalancer is invoked when the channel is being closed or when it enters
+// idle mode upon expiry of idle_timeout.
+func (ccb *ccBalancerWrapper) closeBalancer(m ccbMode) {
+	ccb.mu.Lock()
+	if ccb.mode == ccbModeClosed || ccb.mode == ccbModeIdle {
+		ccb.mu.Unlock()
+		return
+	}
+
+	ccb.mode = m
+	done := ccb.serializer.Done
+	b := ccb.balancer
+	ok := ccb.serializer.Schedule(func(_ context.Context) {
+		// Close the serializer to ensure that no more calls from gRPC are sent
+		// to the balancer.
+		ccb.serializerCancel()
+		// Empty the current balancer name because we don't have a balancer
+		// anymore and also so that we act on the next call to switchTo by
+		// creating a new balancer specified by the new resolver.
+		ccb.curBalancerName = ""
+	})
+	if !ok {
+		ccb.mu.Unlock()
+		return
+	}
+	ccb.mu.Unlock()
+
+	// Give enqueued callbacks a chance to finish.
+	<-done
+	// Spawn a goroutine to close the balancer (since it may block trying to
+	// cleanup all allocated resources) and return early.
+	go b.Close()
 }
 
-func (ccb *ccBalancerWrapper) handleClose() {
-	ccb.balancer.Close()
-	ccb.done.Fire()
+// exitIdleMode is invoked by grpc when the channel exits idle mode either
+// because of an RPC or because of an invocation of the Connect() API. This
+// recreates the balancer that was closed previously when entering idle mode.
+//
+// If the channel is not in idle mode, we know for a fact that we are here as a
+// result of the user calling the Connect() method on the ClientConn. In this
+// case, we can simply forward the call to the underlying balancer, instructing
+// it to reconnect to the backends.
+func (ccb *ccBalancerWrapper) exitIdleMode() {
+	ccb.mu.Lock()
+	if ccb.mode == ccbModeClosed {
+		// Request to exit idle is a no-op when wrapper is already closed.
+		ccb.mu.Unlock()
+		return
+	}
+
+	if ccb.mode == ccbModeIdle {
+		// Recreate the serializer which was closed when we entered idle.
+		ctx, cancel := context.WithCancel(context.Background())
+		ccb.serializer = grpcsync.NewCallbackSerializer(ctx)
+		ccb.serializerCancel = cancel
+	}
+
+	// The ClientConn guarantees that mutual exclusion between close() and
+	// exitIdleMode(), and since we just created a new serializer, we can be
+	// sure that the below function will be scheduled.
+	done := make(chan struct{})
+	ccb.serializer.Schedule(func(_ context.Context) {
+		defer close(done)
+
+		ccb.mu.Lock()
+		defer ccb.mu.Unlock()
+
+		if ccb.mode != ccbModeIdle {
+			ccb.balancer.ExitIdle()
+			return
+		}
+
+		// Gracefulswitch balancer does not support a switchTo operation after
+		// being closed. Hence we need to create a new one here.
+		ccb.balancer = gracefulswitch.NewBalancer(ccb, ccb.opts)
+		ccb.mode = ccbModeActive
+		channelz.Info(logger, ccb.cc.channelzID, "ccBalancerWrapper: exiting idle mode")
+
+	})
+	ccb.mu.Unlock()
+
+	<-done
+}
+
+func (ccb *ccBalancerWrapper) isIdleOrClosed() bool {
+	ccb.mu.Lock()
+	defer ccb.mu.Unlock()
+	return ccb.mode == ccbModeIdle || ccb.mode == ccbModeClosed
 }
 
 func (ccb *ccBalancerWrapper) NewSubConn(addrs []resolver.Address, opts balancer.NewSubConnOptions) (balancer.SubConn, error) {
-	if len(addrs) <= 0 {
+	if ccb.isIdleOrClosed() {
+		return nil, fmt.Errorf("grpc: cannot create SubConn when balancer is closed or idle")
+	}
+
+	if len(addrs) == 0 {
 		return nil, fmt.Errorf("grpc: cannot create SubConn with empty address list")
 	}
 	ac, err := ccb.cc.newAddrConn(addrs, opts)
@@ -309,31 +315,35 @@ func (ccb *ccBalancerWrapper) NewSubConn(addrs []resolver.Address, opts balancer
 		return nil, err
 	}
 	acbw := &acBalancerWrapper{ac: ac, producers: make(map[balancer.ProducerBuilder]*refCountedProducer)}
-	acbw.ac.mu.Lock()
 	ac.acbw = acbw
-	acbw.ac.mu.Unlock()
 	return acbw, nil
 }
 
 func (ccb *ccBalancerWrapper) RemoveSubConn(sc balancer.SubConn) {
-	// Before we switched the ccBalancerWrapper to use gracefulswitch.Balancer, it
-	// was required to handle the RemoveSubConn() method asynchronously by pushing
-	// the update onto the update channel. This was done to avoid a deadlock as
-	// switchBalancer() was holding cc.mu when calling Close() on the old
-	// balancer, which would in turn call RemoveSubConn().
-	//
-	// With the use of gracefulswitch.Balancer in ccBalancerWrapper, handling this
-	// asynchronously is probably not required anymore since the switchTo() method
-	// handles the balancer switch by pushing the update onto the channel.
-	// TODO(easwars): Handle this inline.
+	if ccb.isIdleOrClosed() {
+		// It it safe to ignore this call when the balancer is closed or in idle
+		// because the ClientConn takes care of closing the connections.
+		//
+		// Not returning early from here when the balancer is closed or in idle
+		// leads to a deadlock though, because of the following sequence of
+		// calls when holding cc.mu:
+		// cc.exitIdleMode --> ccb.enterIdleMode --> gsw.Close -->
+		// ccb.RemoveAddrConn --> cc.removeAddrConn
+		return
+	}
+
 	acbw, ok := sc.(*acBalancerWrapper)
 	if !ok {
 		return
 	}
-	ccb.updateCh.Put(&subConnUpdate{acbw: acbw})
+	ccb.cc.removeAddrConn(acbw.ac, errConnDrain)
 }
 
 func (ccb *ccBalancerWrapper) UpdateAddresses(sc balancer.SubConn, addrs []resolver.Address) {
+	if ccb.isIdleOrClosed() {
+		return
+	}
+
 	acbw, ok := sc.(*acBalancerWrapper)
 	if !ok {
 		return
@@ -342,6 +352,10 @@ func (ccb *ccBalancerWrapper) UpdateAddresses(sc balancer.SubConn, addrs []resol
 }
 
 func (ccb *ccBalancerWrapper) UpdateState(s balancer.State) {
+	if ccb.isIdleOrClosed() {
+		return
+	}
+
 	// Update picker before updating state.  Even though the ordering here does
 	// not matter, it can lead to multiple calls of Pick in the common start-up
 	// case where we wait for ready and then perform an RPC.  If the picker is
@@ -352,6 +366,10 @@ func (ccb *ccBalancerWrapper) UpdateState(s balancer.State) {
 }
 
 func (ccb *ccBalancerWrapper) ResolveNow(o resolver.ResolveNowOptions) {
+	if ccb.isIdleOrClosed() {
+		return
+	}
+
 	ccb.cc.resolveNow(o)
 }
 
@@ -362,71 +380,31 @@ func (ccb *ccBalancerWrapper) Target() string {
 // acBalancerWrapper is a wrapper on top of ac for balancers.
 // It implements balancer.SubConn interface.
 type acBalancerWrapper struct {
+	ac *addrConn // read-only
+
 	mu        sync.Mutex
-	ac        *addrConn
 	producers map[balancer.ProducerBuilder]*refCountedProducer
 }
 
-func (acbw *acBalancerWrapper) UpdateAddresses(addrs []resolver.Address) {
-	acbw.mu.Lock()
-	defer acbw.mu.Unlock()
-	if len(addrs) <= 0 {
-		acbw.ac.cc.removeAddrConn(acbw.ac, errConnDrain)
-		return
-	}
-	if !acbw.ac.tryUpdateAddrs(addrs) {
-		cc := acbw.ac.cc
-		opts := acbw.ac.scopts
-		acbw.ac.mu.Lock()
-		// Set old ac.acbw to nil so the Shutdown state update will be ignored
-		// by balancer.
-		//
-		// TODO(bar) the state transition could be wrong when tearDown() old ac
-		// and creating new ac, fix the transition.
-		acbw.ac.acbw = nil
-		acbw.ac.mu.Unlock()
-		acState := acbw.ac.getState()
-		acbw.ac.cc.removeAddrConn(acbw.ac, errConnDrain)
-
-		if acState == connectivity.Shutdown {
-			return
-		}
+func (acbw *acBalancerWrapper) String() string {
+	return fmt.Sprintf("SubConn(id:%d)", acbw.ac.channelzID.Int())
+}
 
-		newAC, err := cc.newAddrConn(addrs, opts)
-		if err != nil {
-			channelz.Warningf(logger, acbw.ac.channelzID, "acBalancerWrapper: UpdateAddresses: failed to newAddrConn: %v", err)
-			return
-		}
-		acbw.ac = newAC
-		newAC.mu.Lock()
-		newAC.acbw = acbw
-		newAC.mu.Unlock()
-		if acState != connectivity.Idle {
-			go newAC.connect()
-		}
-	}
+func (acbw *acBalancerWrapper) UpdateAddresses(addrs []resolver.Address) {
+	acbw.ac.updateAddrs(addrs)
 }
 
 func (acbw *acBalancerWrapper) Connect() {
-	acbw.mu.Lock()
-	defer acbw.mu.Unlock()
 	go acbw.ac.connect()
 }
 
-func (acbw *acBalancerWrapper) getAddrConn() *addrConn {
-	acbw.mu.Lock()
-	defer acbw.mu.Unlock()
-	return acbw.ac
-}
-
-var errSubConnNotReady = status.Error(codes.Unavailable, "SubConn not currently connected")
-
 // NewStream begins a streaming RPC on the addrConn.  If the addrConn is not
-// ready, returns errSubConnNotReady.
+// ready, blocks until it is or ctx expires.  Returns an error when the context
+// expires or the addrConn is shut down.
 func (acbw *acBalancerWrapper) NewStream(ctx context.Context, desc *StreamDesc, method string, opts ...CallOption) (ClientStream, error) {
-	transport := acbw.ac.getReadyTransport()
-	if transport == nil {
-		return nil, errSubConnNotReady
+	transport, err := acbw.ac.getTransport(ctx)
+	if err != nil {
+		return nil, err
 	}
 	return newNonRetryClientStream(ctx, desc, method, transport, acbw.ac, opts...)
 }
diff --git a/vendor/google.golang.org/grpc/call.go b/vendor/google.golang.org/grpc/call.go
index 9e20e4d3..e6a1dc5d 100644
--- a/vendor/google.golang.org/grpc/call.go
+++ b/vendor/google.golang.org/grpc/call.go
@@ -27,6 +27,11 @@ import (
 //
 // All errors returned by Invoke are compatible with the status package.
 func (cc *ClientConn) Invoke(ctx context.Context, method string, args, reply interface{}, opts ...CallOption) error {
+	if err := cc.idlenessMgr.onCallBegin(); err != nil {
+		return err
+	}
+	defer cc.idlenessMgr.onCallEnd()
+
 	// allow interceptor to see all applicable call options, which means those
 	// configured as defaults from dial option as well as per-call options
 	opts = combine(cc.dopts.callOptions, opts)
diff --git a/vendor/google.golang.org/grpc/clientconn.go b/vendor/google.golang.org/grpc/clientconn.go
index 3a761424..95a7459b 100644
--- a/vendor/google.golang.org/grpc/clientconn.go
+++ b/vendor/google.golang.org/grpc/clientconn.go
@@ -24,7 +24,6 @@ import (
 	"fmt"
 	"math"
 	"net/url"
-	"reflect"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -69,6 +68,9 @@ var (
 	errConnDrain = errors.New("grpc: the connection is drained")
 	// errConnClosing indicates that the connection is closing.
 	errConnClosing = errors.New("grpc: the connection is closing")
+	// errConnIdling indicates the the connection is being closed as the channel
+	// is moving to an idle mode due to inactivity.
+	errConnIdling = errors.New("grpc: the connection is closing due to channel idleness")
 	// invalidDefaultServiceConfigErrPrefix is used to prefix the json parsing error for the default
 	// service config.
 	invalidDefaultServiceConfigErrPrefix = "grpc: the provided default service config is invalid"
@@ -134,17 +136,29 @@ func (dcs *defaultConfigSelector) SelectConfig(rpcInfo iresolver.RPCInfo) (*ires
 // e.g. to use dns resolver, a "dns:///" prefix should be applied to the target.
 func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *ClientConn, err error) {
 	cc := &ClientConn{
-		target:            target,
-		csMgr:             &connectivityStateManager{},
-		conns:             make(map[*addrConn]struct{}),
-		dopts:             defaultDialOptions(),
-		blockingpicker:    newPickerWrapper(),
-		czData:            new(channelzData),
-		firstResolveEvent: grpcsync.NewEvent(),
-	}
+		target: target,
+		csMgr:  &connectivityStateManager{},
+		conns:  make(map[*addrConn]struct{}),
+		dopts:  defaultDialOptions(),
+		czData: new(channelzData),
+	}
+
+	// We start the channel off in idle mode, but kick it out of idle at the end
+	// of this method, instead of waiting for the first RPC. Other gRPC
+	// implementations do wait for the first RPC to kick the channel out of
+	// idle. But doing so would be a major behavior change for our users who are
+	// used to seeing the channel active after Dial.
+	//
+	// Taking this approach of kicking it out of idle at the end of this method
+	// allows us to share the code between channel creation and exiting idle
+	// mode. This will also make it easy for us to switch to starting the
+	// channel off in idle, if at all we ever get to do that.
+	cc.idlenessState = ccIdlenessStateIdle
+
 	cc.retryThrottler.Store((*retryThrottler)(nil))
 	cc.safeConfigSelector.UpdateConfigSelector(&defaultConfigSelector{nil})
 	cc.ctx, cc.cancel = context.WithCancel(context.Background())
+	cc.exitIdleCond = sync.NewCond(&cc.mu)
 
 	disableGlobalOpts := false
 	for _, opt := range opts {
@@ -173,40 +187,11 @@ func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *
 		}
 	}()
 
-	pid := cc.dopts.channelzParentID
-	cc.channelzID = channelz.RegisterChannel(&channelzChannel{cc}, pid, target)
-	ted := &channelz.TraceEventDesc{
-		Desc:     "Channel created",
-		Severity: channelz.CtInfo,
-	}
-	if cc.dopts.channelzParentID != nil {
-		ted.Parent = &channelz.TraceEventDesc{
-			Desc:     fmt.Sprintf("Nested Channel(id:%d) created", cc.channelzID.Int()),
-			Severity: channelz.CtInfo,
-		}
-	}
-	channelz.AddTraceEvent(logger, cc.channelzID, 1, ted)
-	cc.csMgr.channelzID = cc.channelzID
+	// Register ClientConn with channelz.
+	cc.channelzRegistration(target)
 
-	if cc.dopts.copts.TransportCredentials == nil && cc.dopts.copts.CredsBundle == nil {
-		return nil, errNoTransportSecurity
-	}
-	if cc.dopts.copts.TransportCredentials != nil && cc.dopts.copts.CredsBundle != nil {
-		return nil, errTransportCredsAndBundle
-	}
-	if cc.dopts.copts.CredsBundle != nil && cc.dopts.copts.CredsBundle.TransportCredentials() == nil {
-		return nil, errNoTransportCredsInBundle
-	}
-	transportCreds := cc.dopts.copts.TransportCredentials
-	if transportCreds == nil {
-		transportCreds = cc.dopts.copts.CredsBundle.TransportCredentials()
-	}
-	if transportCreds.Info().SecurityProtocol == "insecure" {
-		for _, cd := range cc.dopts.copts.PerRPCCredentials {
-			if cd.RequireTransportSecurity() {
-				return nil, errTransportCredentialsMissing
-			}
-		}
+	if err := cc.validateTransportCredentials(); err != nil {
+		return nil, err
 	}
 
 	if cc.dopts.defaultServiceConfigRawJSON != nil {
@@ -249,15 +234,12 @@ func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *
 	}
 
 	// Determine the resolver to use.
-	resolverBuilder, err := cc.parseTargetAndFindResolver()
-	if err != nil {
+	if err := cc.parseTargetAndFindResolver(); err != nil {
 		return nil, err
 	}
-	cc.authority, err = determineAuthority(cc.parsedTarget.Endpoint(), cc.target, cc.dopts)
-	if err != nil {
+	if err = cc.determineAuthority(); err != nil {
 		return nil, err
 	}
-	channelz.Infof(logger, cc.channelzID, "Channel authority set to %q", cc.authority)
 
 	if cc.dopts.scChan != nil {
 		// Blocking wait for the initial service config.
@@ -275,57 +257,224 @@ func DialContext(ctx context.Context, target string, opts ...DialOption) (conn *
 		go cc.scWatcher()
 	}
 
+	// This creates the name resolver, load balancer, blocking picker etc.
+	if err := cc.exitIdleMode(); err != nil {
+		return nil, err
+	}
+
+	// Configure idleness support with configured idle timeout or default idle
+	// timeout duration. Idleness can be explicitly disabled by the user, by
+	// setting the dial option to 0.
+	cc.idlenessMgr = newIdlenessManager(cc, cc.dopts.idleTimeout)
+
+	// Return early for non-blocking dials.
+	if !cc.dopts.block {
+		return cc, nil
+	}
+
+	// A blocking dial blocks until the clientConn is ready.
+	for {
+		s := cc.GetState()
+		if s == connectivity.Idle {
+			cc.Connect()
+		}
+		if s == connectivity.Ready {
+			return cc, nil
+		} else if cc.dopts.copts.FailOnNonTempDialError && s == connectivity.TransientFailure {
+			if err = cc.connectionError(); err != nil {
+				terr, ok := err.(interface {
+					Temporary() bool
+				})
+				if ok && !terr.Temporary() {
+					return nil, err
+				}
+			}
+		}
+		if !cc.WaitForStateChange(ctx, s) {
+			// ctx got timeout or canceled.
+			if err = cc.connectionError(); err != nil && cc.dopts.returnLastError {
+				return nil, err
+			}
+			return nil, ctx.Err()
+		}
+	}
+}
+
+// addTraceEvent is a helper method to add a trace event on the channel. If the
+// channel is a nested one, the same event is also added on the parent channel.
+func (cc *ClientConn) addTraceEvent(msg string) {
+	ted := &channelz.TraceEventDesc{
+		Desc:     fmt.Sprintf("Channel %s", msg),
+		Severity: channelz.CtInfo,
+	}
+	if cc.dopts.channelzParentID != nil {
+		ted.Parent = &channelz.TraceEventDesc{
+			Desc:     fmt.Sprintf("Nested channel(id:%d) %s", cc.channelzID.Int(), msg),
+			Severity: channelz.CtInfo,
+		}
+	}
+	channelz.AddTraceEvent(logger, cc.channelzID, 0, ted)
+}
+
+// exitIdleMode moves the channel out of idle mode by recreating the name
+// resolver and load balancer.
+func (cc *ClientConn) exitIdleMode() error {
+	cc.mu.Lock()
+	if cc.conns == nil {
+		cc.mu.Unlock()
+		return errConnClosing
+	}
+	if cc.idlenessState != ccIdlenessStateIdle {
+		cc.mu.Unlock()
+		logger.Info("ClientConn asked to exit idle mode when not in idle mode")
+		return nil
+	}
+
+	defer func() {
+		// When Close() and exitIdleMode() race against each other, one of the
+		// following two can happen:
+		// - Close() wins the race and runs first. exitIdleMode() runs after, and
+		//   sees that the ClientConn is already closed and hence returns early.
+		// - exitIdleMode() wins the race and runs first and recreates the balancer
+		//   and releases the lock before recreating the resolver. If Close() runs
+		//   in this window, it will wait for exitIdleMode to complete.
+		//
+		// We achieve this synchronization using the below condition variable.
+		cc.mu.Lock()
+		cc.idlenessState = ccIdlenessStateActive
+		cc.exitIdleCond.Signal()
+		cc.mu.Unlock()
+	}()
+
+	cc.idlenessState = ccIdlenessStateExitingIdle
+	exitedIdle := false
+	if cc.blockingpicker == nil {
+		cc.blockingpicker = newPickerWrapper()
+	} else {
+		cc.blockingpicker.exitIdleMode()
+		exitedIdle = true
+	}
+
 	var credsClone credentials.TransportCredentials
 	if creds := cc.dopts.copts.TransportCredentials; creds != nil {
 		credsClone = creds.Clone()
 	}
-	cc.balancerWrapper = newCCBalancerWrapper(cc, balancer.BuildOptions{
-		DialCreds:        credsClone,
-		CredsBundle:      cc.dopts.copts.CredsBundle,
-		Dialer:           cc.dopts.copts.Dialer,
-		Authority:        cc.authority,
-		CustomUserAgent:  cc.dopts.copts.UserAgent,
-		ChannelzParentID: cc.channelzID,
-		Target:           cc.parsedTarget,
-	})
+	if cc.balancerWrapper == nil {
+		cc.balancerWrapper = newCCBalancerWrapper(cc, balancer.BuildOptions{
+			DialCreds:        credsClone,
+			CredsBundle:      cc.dopts.copts.CredsBundle,
+			Dialer:           cc.dopts.copts.Dialer,
+			Authority:        cc.authority,
+			CustomUserAgent:  cc.dopts.copts.UserAgent,
+			ChannelzParentID: cc.channelzID,
+			Target:           cc.parsedTarget,
+		})
+	} else {
+		cc.balancerWrapper.exitIdleMode()
+	}
+	cc.firstResolveEvent = grpcsync.NewEvent()
+	cc.mu.Unlock()
 
-	// Build the resolver.
-	rWrapper, err := newCCResolverWrapper(cc, resolverBuilder)
-	if err != nil {
-		return nil, fmt.Errorf("failed to build resolver: %v", err)
+	// This needs to be called without cc.mu because this builds a new resolver
+	// which might update state or report error inline which needs to be handled
+	// by cc.updateResolverState() which also grabs cc.mu.
+	if err := cc.initResolverWrapper(credsClone); err != nil {
+		return err
+	}
+
+	if exitedIdle {
+		cc.addTraceEvent("exiting idle mode")
 	}
+	return nil
+}
+
+// enterIdleMode puts the channel in idle mode, and as part of it shuts down the
+// name resolver, load balancer and any subchannels.
+func (cc *ClientConn) enterIdleMode() error {
 	cc.mu.Lock()
-	cc.resolverWrapper = rWrapper
+	if cc.conns == nil {
+		cc.mu.Unlock()
+		return ErrClientConnClosing
+	}
+	if cc.idlenessState != ccIdlenessStateActive {
+		logger.Error("ClientConn asked to enter idle mode when not active")
+		return nil
+	}
+
+	// cc.conns == nil is a proxy for the ClientConn being closed. So, instead
+	// of setting it to nil here, we recreate the map. This also means that we
+	// don't have to do this when exiting idle mode.
+	conns := cc.conns
+	cc.conns = make(map[*addrConn]struct{})
+
+	// TODO: Currently, we close the resolver wrapper upon entering idle mode
+	// and create a new one upon exiting idle mode. This means that the
+	// `cc.resolverWrapper` field would be overwritten everytime we exit idle
+	// mode. While this means that we need to hold `cc.mu` when accessing
+	// `cc.resolverWrapper`, it makes the code simpler in the wrapper. We should
+	// try to do the same for the balancer and picker wrappers too.
+	cc.resolverWrapper.close()
+	cc.blockingpicker.enterIdleMode()
+	cc.balancerWrapper.enterIdleMode()
+	cc.csMgr.updateState(connectivity.Idle)
+	cc.idlenessState = ccIdlenessStateIdle
 	cc.mu.Unlock()
 
-	// A blocking dial blocks until the clientConn is ready.
-	if cc.dopts.block {
-		for {
-			cc.Connect()
-			s := cc.GetState()
-			if s == connectivity.Ready {
-				break
-			} else if cc.dopts.copts.FailOnNonTempDialError && s == connectivity.TransientFailure {
-				if err = cc.connectionError(); err != nil {
-					terr, ok := err.(interface {
-						Temporary() bool
-					})
-					if ok && !terr.Temporary() {
-						return nil, err
-					}
-				}
-			}
-			if !cc.WaitForStateChange(ctx, s) {
-				// ctx got timeout or canceled.
-				if err = cc.connectionError(); err != nil && cc.dopts.returnLastError {
-					return nil, err
-				}
-				return nil, ctx.Err()
+	go func() {
+		cc.addTraceEvent("entering idle mode")
+		for ac := range conns {
+			ac.tearDown(errConnIdling)
+		}
+	}()
+	return nil
+}
+
+// validateTransportCredentials performs a series of checks on the configured
+// transport credentials. It returns a non-nil error if any of these conditions
+// are met:
+//   - no transport creds and no creds bundle is configured
+//   - both transport creds and creds bundle are configured
+//   - creds bundle is configured, but it lacks a transport credentials
+//   - insecure transport creds configured alongside call creds that require
+//     transport level security
+//
+// If none of the above conditions are met, the configured credentials are
+// deemed valid and a nil error is returned.
+func (cc *ClientConn) validateTransportCredentials() error {
+	if cc.dopts.copts.TransportCredentials == nil && cc.dopts.copts.CredsBundle == nil {
+		return errNoTransportSecurity
+	}
+	if cc.dopts.copts.TransportCredentials != nil && cc.dopts.copts.CredsBundle != nil {
+		return errTransportCredsAndBundle
+	}
+	if cc.dopts.copts.CredsBundle != nil && cc.dopts.copts.CredsBundle.TransportCredentials() == nil {
+		return errNoTransportCredsInBundle
+	}
+	transportCreds := cc.dopts.copts.TransportCredentials
+	if transportCreds == nil {
+		transportCreds = cc.dopts.copts.CredsBundle.TransportCredentials()
+	}
+	if transportCreds.Info().SecurityProtocol == "insecure" {
+		for _, cd := range cc.dopts.copts.PerRPCCredentials {
+			if cd.RequireTransportSecurity() {
+				return errTransportCredentialsMissing
 			}
 		}
 	}
+	return nil
+}
 
-	return cc, nil
+// channelzRegistration registers the newly created ClientConn with channelz and
+// stores the returned identifier in `cc.channelzID` and `cc.csMgr.channelzID`.
+// A channelz trace event is emitted for ClientConn creation. If the newly
+// created ClientConn is a nested one, i.e a valid parent ClientConn ID is
+// specified via a dial option, the trace event is also added to the parent.
+//
+// Doesn't grab cc.mu as this method is expected to be called only at Dial time.
+func (cc *ClientConn) channelzRegistration(target string) {
+	cc.channelzID = channelz.RegisterChannel(&channelzChannel{cc}, cc.dopts.channelzParentID, target)
+	cc.addTraceEvent("created")
+	cc.csMgr.channelzID = cc.channelzID
 }
 
 // chainUnaryClientInterceptors chains all unary client interceptors into one.
@@ -471,7 +620,9 @@ type ClientConn struct {
 	authority       string               // See determineAuthority().
 	dopts           dialOptions          // Default and user specified dial options.
 	channelzID      *channelz.Identifier // Channelz identifier for the channel.
+	resolverBuilder resolver.Builder     // See parseTargetAndFindResolver().
 	balancerWrapper *ccBalancerWrapper   // Uses gracefulswitch.balancer underneath.
+	idlenessMgr     idlenessManager
 
 	// The following provide their own synchronization, and therefore don't
 	// require cc.mu to be held to access them.
@@ -492,11 +643,31 @@ type ClientConn struct {
 	sc              *ServiceConfig             // Latest service config received from the resolver.
 	conns           map[*addrConn]struct{}     // Set to nil on close.
 	mkp             keepalive.ClientParameters // May be updated upon receipt of a GoAway.
+	idlenessState   ccIdlenessState            // Tracks idleness state of the channel.
+	exitIdleCond    *sync.Cond                 // Signalled when channel exits idle.
 
 	lceMu               sync.Mutex // protects lastConnectionError
 	lastConnectionError error
 }
 
+// ccIdlenessState tracks the idleness state of the channel.
+//
+// Channels start off in `active` and move to `idle` after a period of
+// inactivity. When moving back to `active` upon an incoming RPC, they
+// transition through `exiting_idle`. This state is useful for synchronization
+// with Close().
+//
+// This state tracking is mostly for self-protection. The idlenessManager is
+// expected to keep track of the state as well, and is expected not to call into
+// the ClientConn unnecessarily.
+type ccIdlenessState int8
+
+const (
+	ccIdlenessStateActive ccIdlenessState = iota
+	ccIdlenessStateIdle
+	ccIdlenessStateExitingIdle
+)
+
 // WaitForStateChange waits until the connectivity.State of ClientConn changes from sourceState or
 // ctx expires. A true value is returned in former case and false in latter.
 //
@@ -536,7 +707,10 @@ func (cc *ClientConn) GetState() connectivity.State {
 // Notice: This API is EXPERIMENTAL and may be changed or removed in a later
 // release.
 func (cc *ClientConn) Connect() {
-	cc.balancerWrapper.exitIdle()
+	cc.exitIdleMode()
+	// If the ClientConn was not in idle mode, we need to call ExitIdle on the
+	// LB policy so that connections can be created.
+	cc.balancerWrapper.exitIdleMode()
 }
 
 func (cc *ClientConn) scWatcher() {
@@ -705,6 +879,7 @@ func (cc *ClientConn) newAddrConn(addrs []resolver.Address, opts balancer.NewSub
 		dopts:        cc.dopts,
 		czData:       new(channelzData),
 		resetBackoff: make(chan struct{}),
+		stateChan:    make(chan struct{}),
 	}
 	ac.ctx, ac.cancel = context.WithCancel(cc.ctx)
 	// Track ac in cc. This needs to be done before any getTransport(...) is called.
@@ -798,9 +973,6 @@ func (ac *addrConn) connect() error {
 		ac.mu.Unlock()
 		return nil
 	}
-	// Update connectivity state within the lock to prevent subsequent or
-	// concurrent calls from resetting the transport more than once.
-	ac.updateConnectivityState(connectivity.Connecting, nil)
 	ac.mu.Unlock()
 
 	ac.resetTransport()
@@ -819,58 +991,62 @@ func equalAddresses(a, b []resolver.Address) bool {
 	return true
 }
 
-// tryUpdateAddrs tries to update ac.addrs with the new addresses list.
-//
-// If ac is TransientFailure, it updates ac.addrs and returns true. The updated
-// addresses will be picked up by retry in the next iteration after backoff.
-//
-// If ac is Shutdown or Idle, it updates ac.addrs and returns true.
-//
-// If the addresses is the same as the old list, it does nothing and returns
-// true.
-//
-// If ac is Connecting, it returns false. The caller should tear down the ac and
-// create a new one. Note that the backoff will be reset when this happens.
-//
-// If ac is Ready, it checks whether current connected address of ac is in the
-// new addrs list.
-//   - If true, it updates ac.addrs and returns true. The ac will keep using
-//     the existing connection.
-//   - If false, it does nothing and returns false.
-func (ac *addrConn) tryUpdateAddrs(addrs []resolver.Address) bool {
+// updateAddrs updates ac.addrs with the new addresses list and handles active
+// connections or connection attempts.
+func (ac *addrConn) updateAddrs(addrs []resolver.Address) {
 	ac.mu.Lock()
-	defer ac.mu.Unlock()
-	channelz.Infof(logger, ac.channelzID, "addrConn: tryUpdateAddrs curAddr: %v, addrs: %v", ac.curAddr, addrs)
+	channelz.Infof(logger, ac.channelzID, "addrConn: updateAddrs curAddr: %v, addrs: %v", ac.curAddr, addrs)
+
+	if equalAddresses(ac.addrs, addrs) {
+		ac.mu.Unlock()
+		return
+	}
+
+	ac.addrs = addrs
+
 	if ac.state == connectivity.Shutdown ||
 		ac.state == connectivity.TransientFailure ||
 		ac.state == connectivity.Idle {
-		ac.addrs = addrs
-		return true
+		// We were not connecting, so do nothing but update the addresses.
+		ac.mu.Unlock()
+		return
 	}
 
-	if equalAddresses(ac.addrs, addrs) {
-		return true
+	if ac.state == connectivity.Ready {
+		// Try to find the connected address.
+		for _, a := range addrs {
+			a.ServerName = ac.cc.getServerName(a)
+			if a.Equal(ac.curAddr) {
+				// We are connected to a valid address, so do nothing but
+				// update the addresses.
+				ac.mu.Unlock()
+				return
+			}
+		}
 	}
 
-	if ac.state == connectivity.Connecting {
-		return false
-	}
+	// We are either connected to the wrong address or currently connecting.
+	// Stop the current iteration and restart.
 
-	// ac.state is Ready, try to find the connected address.
-	var curAddrFound bool
-	for _, a := range addrs {
-		a.ServerName = ac.cc.getServerName(a)
-		if reflect.DeepEqual(ac.curAddr, a) {
-			curAddrFound = true
-			break
-		}
+	ac.cancel()
+	ac.ctx, ac.cancel = context.WithCancel(ac.cc.ctx)
+
+	// We have to defer here because GracefulClose => Close => onClose, which
+	// requires locking ac.mu.
+	if ac.transport != nil {
+		defer ac.transport.GracefulClose()
+		ac.transport = nil
 	}
-	channelz.Infof(logger, ac.channelzID, "addrConn: tryUpdateAddrs curAddrFound: %v", curAddrFound)
-	if curAddrFound {
-		ac.addrs = addrs
+
+	if len(addrs) == 0 {
+		ac.updateConnectivityState(connectivity.Idle, nil)
 	}
 
-	return curAddrFound
+	ac.mu.Unlock()
+
+	// Since we were connecting/connected, we should start a new connection
+	// attempt.
+	go ac.resetTransport()
 }
 
 // getServerName determines the serverName to be used in the connection
@@ -1023,39 +1199,40 @@ func (cc *ClientConn) Close() error {
 		cc.mu.Unlock()
 		return ErrClientConnClosing
 	}
+
+	for cc.idlenessState == ccIdlenessStateExitingIdle {
+		cc.exitIdleCond.Wait()
+	}
+
 	conns := cc.conns
 	cc.conns = nil
 	cc.csMgr.updateState(connectivity.Shutdown)
 
+	pWrapper := cc.blockingpicker
 	rWrapper := cc.resolverWrapper
-	cc.resolverWrapper = nil
 	bWrapper := cc.balancerWrapper
+	idlenessMgr := cc.idlenessMgr
 	cc.mu.Unlock()
 
 	// The order of closing matters here since the balancer wrapper assumes the
 	// picker is closed before it is closed.
-	cc.blockingpicker.close()
+	if pWrapper != nil {
+		pWrapper.close()
+	}
 	if bWrapper != nil {
 		bWrapper.close()
 	}
 	if rWrapper != nil {
 		rWrapper.close()
 	}
+	if idlenessMgr != nil {
+		idlenessMgr.close()
+	}
 
 	for ac := range conns {
 		ac.tearDown(ErrClientConnClosing)
 	}
-	ted := &channelz.TraceEventDesc{
-		Desc:     "Channel deleted",
-		Severity: channelz.CtInfo,
-	}
-	if cc.dopts.channelzParentID != nil {
-		ted.Parent = &channelz.TraceEventDesc{
-			Desc:     fmt.Sprintf("Nested channel(id:%d) deleted", cc.channelzID.Int()),
-			Severity: channelz.CtInfo,
-		}
-	}
-	channelz.AddTraceEvent(logger, cc.channelzID, 0, ted)
+	cc.addTraceEvent("deleted")
 	// TraceEvent needs to be called before RemoveEntry, as TraceEvent may add
 	// trace reference to the entity being deleted, and thus prevent it from being
 	// deleted right away.
@@ -1085,7 +1262,8 @@ type addrConn struct {
 	addrs   []resolver.Address // All addresses that the resolver resolved to.
 
 	// Use updateConnectivityState for updating addrConn's connectivity state.
-	state connectivity.State
+	state     connectivity.State
+	stateChan chan struct{} // closed and recreated on every state change.
 
 	backoffIdx   int // Needs to be stateful for resetConnectBackoff.
 	resetBackoff chan struct{}
@@ -1099,6 +1277,9 @@ func (ac *addrConn) updateConnectivityState(s connectivity.State, lastErr error)
 	if ac.state == s {
 		return
 	}
+	// When changing states, reset the state change channel.
+	close(ac.stateChan)
+	ac.stateChan = make(chan struct{})
 	ac.state = s
 	if lastErr == nil {
 		channelz.Infof(logger, ac.channelzID, "Subchannel Connectivity change to %v", s)
@@ -1124,7 +1305,8 @@ func (ac *addrConn) adjustParams(r transport.GoAwayReason) {
 
 func (ac *addrConn) resetTransport() {
 	ac.mu.Lock()
-	if ac.state == connectivity.Shutdown {
+	acCtx := ac.ctx
+	if acCtx.Err() != nil {
 		ac.mu.Unlock()
 		return
 	}
@@ -1152,15 +1334,14 @@ func (ac *addrConn) resetTransport() {
 	ac.updateConnectivityState(connectivity.Connecting, nil)
 	ac.mu.Unlock()
 
-	if err := ac.tryAllAddrs(addrs, connectDeadline); err != nil {
+	if err := ac.tryAllAddrs(acCtx, addrs, connectDeadline); err != nil {
 		ac.cc.resolveNow(resolver.ResolveNowOptions{})
 		// After exhausting all addresses, the addrConn enters
 		// TRANSIENT_FAILURE.
-		ac.mu.Lock()
-		if ac.state == connectivity.Shutdown {
-			ac.mu.Unlock()
+		if acCtx.Err() != nil {
 			return
 		}
+		ac.mu.Lock()
 		ac.updateConnectivityState(connectivity.TransientFailure, err)
 
 		// Backoff.
@@ -1175,13 +1356,13 @@ func (ac *addrConn) resetTransport() {
 			ac.mu.Unlock()
 		case <-b:
 			timer.Stop()
-		case <-ac.ctx.Done():
+		case <-acCtx.Done():
 			timer.Stop()
 			return
 		}
 
 		ac.mu.Lock()
-		if ac.state != connectivity.Shutdown {
+		if acCtx.Err() == nil {
 			ac.updateConnectivityState(connectivity.Idle, err)
 		}
 		ac.mu.Unlock()
@@ -1196,14 +1377,13 @@ func (ac *addrConn) resetTransport() {
 // tryAllAddrs tries to creates a connection to the addresses, and stop when at
 // the first successful one. It returns an error if no address was successfully
 // connected, or updates ac appropriately with the new transport.
-func (ac *addrConn) tryAllAddrs(addrs []resolver.Address, connectDeadline time.Time) error {
+func (ac *addrConn) tryAllAddrs(ctx context.Context, addrs []resolver.Address, connectDeadline time.Time) error {
 	var firstConnErr error
 	for _, addr := range addrs {
-		ac.mu.Lock()
-		if ac.state == connectivity.Shutdown {
-			ac.mu.Unlock()
+		if ctx.Err() != nil {
 			return errConnClosing
 		}
+		ac.mu.Lock()
 
 		ac.cc.mu.RLock()
 		ac.dopts.copts.KeepaliveParams = ac.cc.mkp
@@ -1217,7 +1397,7 @@ func (ac *addrConn) tryAllAddrs(addrs []resolver.Address, connectDeadline time.T
 
 		channelz.Infof(logger, ac.channelzID, "Subchannel picks a new address %q to connect", addr.Addr)
 
-		err := ac.createTransport(addr, copts, connectDeadline)
+		err := ac.createTransport(ctx, addr, copts, connectDeadline)
 		if err == nil {
 			return nil
 		}
@@ -1234,19 +1414,20 @@ func (ac *addrConn) tryAllAddrs(addrs []resolver.Address, connectDeadline time.T
 // createTransport creates a connection to addr. It returns an error if the
 // address was not successfully connected, or updates ac appropriately with the
 // new transport.
-func (ac *addrConn) createTransport(addr resolver.Address, copts transport.ConnectOptions, connectDeadline time.Time) error {
+func (ac *addrConn) createTransport(ctx context.Context, addr resolver.Address, copts transport.ConnectOptions, connectDeadline time.Time) error {
 	addr.ServerName = ac.cc.getServerName(addr)
-	hctx, hcancel := context.WithCancel(ac.ctx)
+	hctx, hcancel := context.WithCancel(ctx)
 
 	onClose := func(r transport.GoAwayReason) {
 		ac.mu.Lock()
 		defer ac.mu.Unlock()
 		// adjust params based on GoAwayReason
 		ac.adjustParams(r)
-		if ac.state == connectivity.Shutdown {
-			// Already shut down.  tearDown() already cleared the transport and
-			// canceled hctx via ac.ctx, and we expected this connection to be
-			// closed, so do nothing here.
+		if ctx.Err() != nil {
+			// Already shut down or connection attempt canceled.  tearDown() or
+			// updateAddrs() already cleared the transport and canceled hctx
+			// via ac.ctx, and we expected this connection to be closed, so do
+			// nothing here.
 			return
 		}
 		hcancel()
@@ -1265,7 +1446,7 @@ func (ac *addrConn) createTransport(addr resolver.Address, copts transport.Conne
 		ac.updateConnectivityState(connectivity.Idle, nil)
 	}
 
-	connectCtx, cancel := context.WithDeadline(ac.ctx, connectDeadline)
+	connectCtx, cancel := context.WithDeadline(ctx, connectDeadline)
 	defer cancel()
 	copts.ChannelzParentID = ac.channelzID
 
@@ -1282,7 +1463,7 @@ func (ac *addrConn) createTransport(addr resolver.Address, copts transport.Conne
 
 	ac.mu.Lock()
 	defer ac.mu.Unlock()
-	if ac.state == connectivity.Shutdown {
+	if ctx.Err() != nil {
 		// This can happen if the subConn was removed while in `Connecting`
 		// state. tearDown() would have set the state to `Shutdown`, but
 		// would not have closed the transport since ac.transport would not
@@ -1294,6 +1475,9 @@ func (ac *addrConn) createTransport(addr resolver.Address, copts transport.Conne
 		// The error we pass to Close() is immaterial since there are no open
 		// streams at this point, so no trailers with error details will be sent
 		// out. We just need to pass a non-nil error.
+		//
+		// This can also happen when updateAddrs is called during a connection
+		// attempt.
 		go newTr.Close(transport.ErrConnClosing)
 		return nil
 	}
@@ -1401,6 +1585,29 @@ func (ac *addrConn) getReadyTransport() transport.ClientTransport {
 	return nil
 }
 
+// getTransport waits until the addrconn is ready and returns the transport.
+// If the context expires first, returns an appropriate status.  If the
+// addrConn is stopped first, returns an Unavailable status error.
+func (ac *addrConn) getTransport(ctx context.Context) (transport.ClientTransport, error) {
+	for ctx.Err() == nil {
+		ac.mu.Lock()
+		t, state, sc := ac.transport, ac.state, ac.stateChan
+		ac.mu.Unlock()
+		if state == connectivity.Ready {
+			return t, nil
+		}
+		if state == connectivity.Shutdown {
+			return nil, status.Errorf(codes.Unavailable, "SubConn shutting down")
+		}
+
+		select {
+		case <-ctx.Done():
+		case <-sc:
+		}
+	}
+	return nil, status.FromContextError(ctx.Err()).Err()
+}
+
 // tearDown starts to tear down the addrConn.
 //
 // Note that tearDown doesn't remove ac from ac.cc.conns, so the addrConn struct
@@ -1552,7 +1759,14 @@ func (cc *ClientConn) connectionError() error {
 	return cc.lastConnectionError
 }
 
-func (cc *ClientConn) parseTargetAndFindResolver() (resolver.Builder, error) {
+// parseTargetAndFindResolver parses the user's dial target and stores the
+// parsed target in `cc.parsedTarget`.
+//
+// The resolver to use is determined based on the scheme in the parsed target
+// and the same is stored in `cc.resolverBuilder`.
+//
+// Doesn't grab cc.mu as this method is expected to be called only at Dial time.
+func (cc *ClientConn) parseTargetAndFindResolver() error {
 	channelz.Infof(logger, cc.channelzID, "original dial target is: %q", cc.target)
 
 	var rb resolver.Builder
@@ -1564,7 +1778,8 @@ func (cc *ClientConn) parseTargetAndFindResolver() (resolver.Builder, error) {
 		rb = cc.getResolver(parsedTarget.URL.Scheme)
 		if rb != nil {
 			cc.parsedTarget = parsedTarget
-			return rb, nil
+			cc.resolverBuilder = rb
+			return nil
 		}
 	}
 
@@ -1579,15 +1794,16 @@ func (cc *ClientConn) parseTargetAndFindResolver() (resolver.Builder, error) {
 	parsedTarget, err = parseTarget(canonicalTarget)
 	if err != nil {
 		channelz.Infof(logger, cc.channelzID, "dial target %q parse failed: %v", canonicalTarget, err)
-		return nil, err
+		return err
 	}
 	channelz.Infof(logger, cc.channelzID, "parsed dial target is: %+v", parsedTarget)
 	rb = cc.getResolver(parsedTarget.URL.Scheme)
 	if rb == nil {
-		return nil, fmt.Errorf("could not get resolver for default scheme: %q", parsedTarget.URL.Scheme)
+		return fmt.Errorf("could not get resolver for default scheme: %q", parsedTarget.URL.Scheme)
 	}
 	cc.parsedTarget = parsedTarget
-	return rb, nil
+	cc.resolverBuilder = rb
+	return nil
 }
 
 // parseTarget uses RFC 3986 semantics to parse the given target into a
@@ -1610,7 +1826,15 @@ func parseTarget(target string) (resolver.Target, error) {
 // - user specified authority override using `WithAuthority` dial option
 // - creds' notion of server name for the authentication handshake
 // - endpoint from dial target of the form "scheme://[authority]/endpoint"
-func determineAuthority(endpoint, target string, dopts dialOptions) (string, error) {
+//
+// Stores the determined authority in `cc.authority`.
+//
+// Returns a non-nil error if the authority returned by the transport
+// credentials do not match the authority configured through the dial option.
+//
+// Doesn't grab cc.mu as this method is expected to be called only at Dial time.
+func (cc *ClientConn) determineAuthority() error {
+	dopts := cc.dopts
 	// Historically, we had two options for users to specify the serverName or
 	// authority for a channel. One was through the transport credentials
 	// (either in its constructor, or through the OverrideServerName() method).
@@ -1627,25 +1851,58 @@ func determineAuthority(endpoint, target string, dopts dialOptions) (string, err
 	}
 	authorityFromDialOption := dopts.authority
 	if (authorityFromCreds != "" && authorityFromDialOption != "") && authorityFromCreds != authorityFromDialOption {
-		return "", fmt.Errorf("ClientConn's authority from transport creds %q and dial option %q don't match", authorityFromCreds, authorityFromDialOption)
+		return fmt.Errorf("ClientConn's authority from transport creds %q and dial option %q don't match", authorityFromCreds, authorityFromDialOption)
 	}
 
+	endpoint := cc.parsedTarget.Endpoint()
+	target := cc.target
 	switch {
 	case authorityFromDialOption != "":
-		return authorityFromDialOption, nil
+		cc.authority = authorityFromDialOption
 	case authorityFromCreds != "":
-		return authorityFromCreds, nil
+		cc.authority = authorityFromCreds
 	case strings.HasPrefix(target, "unix:") || strings.HasPrefix(target, "unix-abstract:"):
 		// TODO: remove when the unix resolver implements optional interface to
 		// return channel authority.
-		return "localhost", nil
+		cc.authority = "localhost"
 	case strings.HasPrefix(endpoint, ":"):
-		return "localhost" + endpoint, nil
+		cc.authority = "localhost" + endpoint
 	default:
 		// TODO: Define an optional interface on the resolver builder to return
 		// the channel authority given the user's dial target. For resolvers
 		// which don't implement this interface, we will use the endpoint from
 		// "scheme://authority/endpoint" as the default authority.
-		return endpoint, nil
+		cc.authority = endpoint
+	}
+	channelz.Infof(logger, cc.channelzID, "Channel authority set to %q", cc.authority)
+	return nil
+}
+
+// initResolverWrapper creates a ccResolverWrapper, which builds the name
+// resolver. This method grabs the lock to assign the newly built resolver
+// wrapper to the cc.resolverWrapper field.
+func (cc *ClientConn) initResolverWrapper(creds credentials.TransportCredentials) error {
+	rw, err := newCCResolverWrapper(cc, ccResolverWrapperOpts{
+		target:  cc.parsedTarget,
+		builder: cc.resolverBuilder,
+		bOpts: resolver.BuildOptions{
+			DisableServiceConfig: cc.dopts.disableServiceConfig,
+			DialCreds:            creds,
+			CredsBundle:          cc.dopts.copts.CredsBundle,
+			Dialer:               cc.dopts.copts.Dialer,
+		},
+		channelzID: cc.channelzID,
+	})
+	if err != nil {
+		return fmt.Errorf("failed to build resolver: %v", err)
 	}
+	// Resolver implementations may report state update or error inline when
+	// built (or right after), and this is handled in cc.updateResolverState.
+	// Also, an error from the resolver might lead to a re-resolution request
+	// from the balancer, which is handled in resolveNow() where
+	// `cc.resolverWrapper` is accessed. Hence, we need to hold the lock here.
+	cc.mu.Lock()
+	cc.resolverWrapper = rw
+	cc.mu.Unlock()
+	return nil
 }
diff --git a/vendor/google.golang.org/grpc/dialoptions.go b/vendor/google.golang.org/grpc/dialoptions.go
index cdc8263b..15a3d510 100644
--- a/vendor/google.golang.org/grpc/dialoptions.go
+++ b/vendor/google.golang.org/grpc/dialoptions.go
@@ -77,6 +77,7 @@ type dialOptions struct {
 	defaultServiceConfig        *ServiceConfig // defaultServiceConfig is parsed from defaultServiceConfigRawJSON.
 	defaultServiceConfigRawJSON *string
 	resolvers                   []resolver.Builder
+	idleTimeout                 time.Duration
 }
 
 // DialOption configures how we set up the connection.
@@ -655,3 +656,23 @@ func WithResolvers(rs ...resolver.Builder) DialOption {
 		o.resolvers = append(o.resolvers, rs...)
 	})
 }
+
+// WithIdleTimeout returns a DialOption that configures an idle timeout for the
+// channel. If the channel is idle for the configured timeout, i.e there are no
+// ongoing RPCs and no new RPCs are initiated, the channel will enter idle mode
+// and as a result the name resolver and load balancer will be shut down. The
+// channel will exit idle mode when the Connect() method is called or when an
+// RPC is initiated.
+//
+// By default this feature is disabled, which can also be explicitly configured
+// by passing zero to this function.
+//
+// # Experimental
+//
+// Notice: This API is EXPERIMENTAL and may be changed or removed in a
+// later release.
+func WithIdleTimeout(d time.Duration) DialOption {
+	return newFuncDialOption(func(o *dialOptions) {
+		o.idleTimeout = d
+	})
+}
diff --git a/vendor/google.golang.org/grpc/idle.go b/vendor/google.golang.org/grpc/idle.go
new file mode 100644
index 00000000..dc3dc72f
--- /dev/null
+++ b/vendor/google.golang.org/grpc/idle.go
@@ -0,0 +1,287 @@
+/*
+ *
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package grpc
+
+import (
+	"fmt"
+	"math"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+// For overriding in unit tests.
+var timeAfterFunc = func(d time.Duration, f func()) *time.Timer {
+	return time.AfterFunc(d, f)
+}
+
+// idlenessEnforcer is the functionality provided by grpc.ClientConn to enter
+// and exit from idle mode.
+type idlenessEnforcer interface {
+	exitIdleMode() error
+	enterIdleMode() error
+}
+
+// idlenessManager defines the functionality required to track RPC activity on a
+// channel.
+type idlenessManager interface {
+	onCallBegin() error
+	onCallEnd()
+	close()
+}
+
+type noopIdlenessManager struct{}
+
+func (noopIdlenessManager) onCallBegin() error { return nil }
+func (noopIdlenessManager) onCallEnd()         {}
+func (noopIdlenessManager) close()             {}
+
+// idlenessManagerImpl implements the idlenessManager interface. It uses atomic
+// operations to synchronize access to shared state and a mutex to guarantee
+// mutual exclusion in a critical section.
+type idlenessManagerImpl struct {
+	// State accessed atomically.
+	lastCallEndTime           int64 // Unix timestamp in nanos; time when the most recent RPC completed.
+	activeCallsCount          int32 // Count of active RPCs; -math.MaxInt32 means channel is idle or is trying to get there.
+	activeSinceLastTimerCheck int32 // Boolean; True if there was an RPC since the last timer callback.
+	closed                    int32 // Boolean; True when the manager is closed.
+
+	// Can be accessed without atomics or mutex since these are set at creation
+	// time and read-only after that.
+	enforcer idlenessEnforcer // Functionality provided by grpc.ClientConn.
+	timeout  int64            // Idle timeout duration nanos stored as an int64.
+
+	// idleMu is used to guarantee mutual exclusion in two scenarios:
+	// - Opposing intentions:
+	//   - a: Idle timeout has fired and handleIdleTimeout() is trying to put
+	//     the channel in idle mode because the channel has been inactive.
+	//   - b: At the same time an RPC is made on the channel, and onCallBegin()
+	//     is trying to prevent the channel from going idle.
+	// - Competing intentions:
+	//   - The channel is in idle mode and there are multiple RPCs starting at
+	//     the same time, all trying to move the channel out of idle. Only one
+	//     of them should succeed in doing so, while the other RPCs should
+	//     piggyback on the first one and be successfully handled.
+	idleMu       sync.RWMutex
+	actuallyIdle bool
+	timer        *time.Timer
+}
+
+// newIdlenessManager creates a new idleness manager implementation for the
+// given idle timeout.
+func newIdlenessManager(enforcer idlenessEnforcer, idleTimeout time.Duration) idlenessManager {
+	if idleTimeout == 0 {
+		return noopIdlenessManager{}
+	}
+
+	i := &idlenessManagerImpl{
+		enforcer: enforcer,
+		timeout:  int64(idleTimeout),
+	}
+	i.timer = timeAfterFunc(idleTimeout, i.handleIdleTimeout)
+	return i
+}
+
+// resetIdleTimer resets the idle timer to the given duration. This method
+// should only be called from the timer callback.
+func (i *idlenessManagerImpl) resetIdleTimer(d time.Duration) {
+	i.idleMu.Lock()
+	defer i.idleMu.Unlock()
+
+	if i.timer == nil {
+		// Only close sets timer to nil. We are done.
+		return
+	}
+
+	// It is safe to ignore the return value from Reset() because this method is
+	// only ever called from the timer callback, which means the timer has
+	// already fired.
+	i.timer.Reset(d)
+}
+
+// handleIdleTimeout is the timer callback that is invoked upon expiry of the
+// configured idle timeout. The channel is considered inactive if there are no
+// ongoing calls and no RPC activity since the last time the timer fired.
+func (i *idlenessManagerImpl) handleIdleTimeout() {
+	if i.isClosed() {
+		return
+	}
+
+	if atomic.LoadInt32(&i.activeCallsCount) > 0 {
+		i.resetIdleTimer(time.Duration(i.timeout))
+		return
+	}
+
+	// There has been activity on the channel since we last got here. Reset the
+	// timer and return.
+	if atomic.LoadInt32(&i.activeSinceLastTimerCheck) == 1 {
+		// Set the timer to fire after a duration of idle timeout, calculated
+		// from the time the most recent RPC completed.
+		atomic.StoreInt32(&i.activeSinceLastTimerCheck, 0)
+		i.resetIdleTimer(time.Duration(atomic.LoadInt64(&i.lastCallEndTime) + i.timeout - time.Now().UnixNano()))
+		return
+	}
+
+	// This CAS operation is extremely likely to succeed given that there has
+	// been no activity since the last time we were here.  Setting the
+	// activeCallsCount to -math.MaxInt32 indicates to onCallBegin() that the
+	// channel is either in idle mode or is trying to get there.
+	if !atomic.CompareAndSwapInt32(&i.activeCallsCount, 0, -math.MaxInt32) {
+		// This CAS operation can fail if an RPC started after we checked for
+		// activity at the top of this method, or one was ongoing from before
+		// the last time we were here. In both case, reset the timer and return.
+		i.resetIdleTimer(time.Duration(i.timeout))
+		return
+	}
+
+	// Now that we've set the active calls count to -math.MaxInt32, it's time to
+	// actually move to idle mode.
+	if i.tryEnterIdleMode() {
+		// Successfully entered idle mode. No timer needed until we exit idle.
+		return
+	}
+
+	// Failed to enter idle mode due to a concurrent RPC that kept the channel
+	// active, or because of an error from the channel. Undo the attempt to
+	// enter idle, and reset the timer to try again later.
+	atomic.AddInt32(&i.activeCallsCount, math.MaxInt32)
+	i.resetIdleTimer(time.Duration(i.timeout))
+}
+
+// tryEnterIdleMode instructs the channel to enter idle mode. But before
+// that, it performs a last minute check to ensure that no new RPC has come in,
+// making the channel active.
+//
+// Return value indicates whether or not the channel moved to idle mode.
+//
+// Holds idleMu which ensures mutual exclusion with exitIdleMode.
+func (i *idlenessManagerImpl) tryEnterIdleMode() bool {
+	i.idleMu.Lock()
+	defer i.idleMu.Unlock()
+
+	if atomic.LoadInt32(&i.activeCallsCount) != -math.MaxInt32 {
+		// We raced and lost to a new RPC. Very rare, but stop entering idle.
+		return false
+	}
+	if atomic.LoadInt32(&i.activeSinceLastTimerCheck) == 1 {
+		// An very short RPC could have come in (and also finished) after we
+		// checked for calls count and activity in handleIdleTimeout(), but
+		// before the CAS operation. So, we need to check for activity again.
+		return false
+	}
+
+	// No new RPCs have come in since we last set the active calls count value
+	// -math.MaxInt32 in the timer callback. And since we have the lock, it is
+	// safe to enter idle mode now.
+	if err := i.enforcer.enterIdleMode(); err != nil {
+		logger.Errorf("Failed to enter idle mode: %v", err)
+		return false
+	}
+
+	// Successfully entered idle mode.
+	i.actuallyIdle = true
+	return true
+}
+
+// onCallBegin is invoked at the start of every RPC.
+func (i *idlenessManagerImpl) onCallBegin() error {
+	if i.isClosed() {
+		return nil
+	}
+
+	if atomic.AddInt32(&i.activeCallsCount, 1) > 0 {
+		// Channel is not idle now. Set the activity bit and allow the call.
+		atomic.StoreInt32(&i.activeSinceLastTimerCheck, 1)
+		return nil
+	}
+
+	// Channel is either in idle mode or is in the process of moving to idle
+	// mode. Attempt to exit idle mode to allow this RPC.
+	if err := i.exitIdleMode(); err != nil {
+		// Undo the increment to calls count, and return an error causing the
+		// RPC to fail.
+		atomic.AddInt32(&i.activeCallsCount, -1)
+		return err
+	}
+
+	atomic.StoreInt32(&i.activeSinceLastTimerCheck, 1)
+	return nil
+}
+
+// exitIdleMode instructs the channel to exit idle mode.
+//
+// Holds idleMu which ensures mutual exclusion with tryEnterIdleMode.
+func (i *idlenessManagerImpl) exitIdleMode() error {
+	i.idleMu.Lock()
+	defer i.idleMu.Unlock()
+
+	if !i.actuallyIdle {
+		// This can happen in two scenarios:
+		// - handleIdleTimeout() set the calls count to -math.MaxInt32 and called
+		//   tryEnterIdleMode(). But before the latter could grab the lock, an RPC
+		//   came in and onCallBegin() noticed that the calls count is negative.
+		// - Channel is in idle mode, and multiple new RPCs come in at the same
+		//   time, all of them notice a negative calls count in onCallBegin and get
+		//   here. The first one to get the lock would got the channel to exit idle.
+		//
+		// Either way, nothing to do here.
+		return nil
+	}
+
+	if err := i.enforcer.exitIdleMode(); err != nil {
+		return fmt.Errorf("channel failed to exit idle mode: %v", err)
+	}
+
+	// Undo the idle entry process. This also respects any new RPC attempts.
+	atomic.AddInt32(&i.activeCallsCount, math.MaxInt32)
+	i.actuallyIdle = false
+
+	// Start a new timer to fire after the configured idle timeout.
+	i.timer = timeAfterFunc(time.Duration(i.timeout), i.handleIdleTimeout)
+	return nil
+}
+
+// onCallEnd is invoked at the end of every RPC.
+func (i *idlenessManagerImpl) onCallEnd() {
+	if i.isClosed() {
+		return
+	}
+
+	// Record the time at which the most recent call finished.
+	atomic.StoreInt64(&i.lastCallEndTime, time.Now().UnixNano())
+
+	// Decrement the active calls count. This count can temporarily go negative
+	// when the timer callback is in the process of moving the channel to idle
+	// mode, but one or more RPCs come in and complete before the timer callback
+	// can get done with the process of moving to idle mode.
+	atomic.AddInt32(&i.activeCallsCount, -1)
+}
+
+func (i *idlenessManagerImpl) isClosed() bool {
+	return atomic.LoadInt32(&i.closed) == 1
+}
+
+func (i *idlenessManagerImpl) close() {
+	atomic.StoreInt32(&i.closed, 1)
+
+	i.idleMu.Lock()
+	i.timer.Stop()
+	i.timer = nil
+	i.idleMu.Unlock()
+}
diff --git a/vendor/google.golang.org/grpc/internal/binarylog/binarylog.go b/vendor/google.golang.org/grpc/internal/binarylog/binarylog.go
index af03a40d..755fdebc 100644
--- a/vendor/google.golang.org/grpc/internal/binarylog/binarylog.go
+++ b/vendor/google.golang.org/grpc/internal/binarylog/binarylog.go
@@ -32,6 +32,9 @@ var grpclogLogger = grpclog.Component("binarylog")
 
 // Logger specifies MethodLoggers for method names with a Log call that
 // takes a context.
+//
+// This is used in the 1.0 release of gcp/observability, and thus must not be
+// deleted or changed.
 type Logger interface {
 	GetMethodLogger(methodName string) MethodLogger
 }
diff --git a/vendor/google.golang.org/grpc/internal/binarylog/method_logger.go b/vendor/google.golang.org/grpc/internal/binarylog/method_logger.go
index 56fcf008..6c3f6322 100644
--- a/vendor/google.golang.org/grpc/internal/binarylog/method_logger.go
+++ b/vendor/google.golang.org/grpc/internal/binarylog/method_logger.go
@@ -49,6 +49,9 @@ func (g *callIDGenerator) reset() {
 var idGen callIDGenerator
 
 // MethodLogger is the sub-logger for each method.
+//
+// This is used in the 1.0 release of gcp/observability, and thus must not be
+// deleted or changed.
 type MethodLogger interface {
 	Log(context.Context, LogEntryConfig)
 }
@@ -65,6 +68,9 @@ type TruncatingMethodLogger struct {
 }
 
 // NewTruncatingMethodLogger returns a new truncating method logger.
+//
+// This is used in the 1.0 release of gcp/observability, and thus must not be
+// deleted or changed.
 func NewTruncatingMethodLogger(h, m uint64) *TruncatingMethodLogger {
 	return &TruncatingMethodLogger{
 		headerMaxLen:  h,
@@ -145,6 +151,9 @@ func (ml *TruncatingMethodLogger) truncateMessage(msgPb *binlogpb.Message) (trun
 }
 
 // LogEntryConfig represents the configuration for binary log entry.
+//
+// This is used in the 1.0 release of gcp/observability, and thus must not be
+// deleted or changed.
 type LogEntryConfig interface {
 	toProto() *binlogpb.GrpcLogEntry
 }
diff --git a/vendor/google.golang.org/grpc/internal/buffer/unbounded.go b/vendor/google.golang.org/grpc/internal/buffer/unbounded.go
index 9f6a0c12..81c2f5fd 100644
--- a/vendor/google.golang.org/grpc/internal/buffer/unbounded.go
+++ b/vendor/google.golang.org/grpc/internal/buffer/unbounded.go
@@ -35,6 +35,7 @@ import "sync"
 // internal/transport/transport.go for an example of this.
 type Unbounded struct {
 	c       chan interface{}
+	closed  bool
 	mu      sync.Mutex
 	backlog []interface{}
 }
@@ -47,16 +48,18 @@ func NewUnbounded() *Unbounded {
 // Put adds t to the unbounded buffer.
 func (b *Unbounded) Put(t interface{}) {
 	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.closed {
+		return
+	}
 	if len(b.backlog) == 0 {
 		select {
 		case b.c <- t:
-			b.mu.Unlock()
 			return
 		default:
 		}
 	}
 	b.backlog = append(b.backlog, t)
-	b.mu.Unlock()
 }
 
 // Load sends the earliest buffered data, if any, onto the read channel
@@ -64,6 +67,10 @@ func (b *Unbounded) Put(t interface{}) {
 // value from the read channel.
 func (b *Unbounded) Load() {
 	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.closed {
+		return
+	}
 	if len(b.backlog) > 0 {
 		select {
 		case b.c <- b.backlog[0]:
@@ -72,7 +79,6 @@ func (b *Unbounded) Load() {
 		default:
 		}
 	}
-	b.mu.Unlock()
 }
 
 // Get returns a read channel on which values added to the buffer, via Put(),
@@ -80,6 +86,20 @@ func (b *Unbounded) Load() {
 //
 // Upon reading a value from this channel, users are expected to call Load() to
 // send the next buffered value onto the channel if there is any.
+//
+// If the unbounded buffer is closed, the read channel returned by this method
+// is closed.
 func (b *Unbounded) Get() <-chan interface{} {
 	return b.c
 }
+
+// Close closes the unbounded buffer.
+func (b *Unbounded) Close() {
+	b.mu.Lock()
+	defer b.mu.Unlock()
+	if b.closed {
+		return
+	}
+	b.closed = true
+	close(b.c)
+}
diff --git a/vendor/google.golang.org/grpc/internal/envconfig/envconfig.go b/vendor/google.golang.org/grpc/internal/envconfig/envconfig.go
index 5ba9d94d..80fd5c7d 100644
--- a/vendor/google.golang.org/grpc/internal/envconfig/envconfig.go
+++ b/vendor/google.golang.org/grpc/internal/envconfig/envconfig.go
@@ -36,6 +36,10 @@ var (
 	// "GRPC_RING_HASH_CAP".  This does not override the default bounds
 	// checking which NACKs configs specifying ring sizes > 8*1024*1024 (~8M).
 	RingHashCap = uint64FromEnv("GRPC_RING_HASH_CAP", 4096, 1, 8*1024*1024)
+	// PickFirstLBConfig is set if we should support configuration of the
+	// pick_first LB policy, which can be enabled by setting the environment
+	// variable "GRPC_EXPERIMENTAL_PICKFIRST_LB_CONFIG" to "true".
+	PickFirstLBConfig = boolFromEnv("GRPC_EXPERIMENTAL_PICKFIRST_LB_CONFIG", false)
 )
 
 func boolFromEnv(envVar string, def bool) bool {
diff --git a/vendor/google.golang.org/grpc/internal/envconfig/observability.go b/vendor/google.golang.org/grpc/internal/envconfig/observability.go
index 821dd0a7..dd314cfb 100644
--- a/vendor/google.golang.org/grpc/internal/envconfig/observability.go
+++ b/vendor/google.golang.org/grpc/internal/envconfig/observability.go
@@ -28,9 +28,15 @@ const (
 var (
 	// ObservabilityConfig is the json configuration for the gcp/observability
 	// package specified directly in the envObservabilityConfig env var.
+	//
+	// This is used in the 1.0 release of gcp/observability, and thus must not be
+	// deleted or changed.
 	ObservabilityConfig = os.Getenv(envObservabilityConfig)
 	// ObservabilityConfigFile is the json configuration for the
 	// gcp/observability specified in a file with the location specified in
 	// envObservabilityConfigFile env var.
+	//
+	// This is used in the 1.0 release of gcp/observability, and thus must not be
+	// deleted or changed.
 	ObservabilityConfigFile = os.Getenv(envObservabilityConfigFile)
 )
diff --git a/vendor/google.golang.org/grpc/internal/envconfig/xds.go b/vendor/google.golang.org/grpc/internal/envconfig/xds.go
index 3b17705b..02b4b6a1 100644
--- a/vendor/google.golang.org/grpc/internal/envconfig/xds.go
+++ b/vendor/google.golang.org/grpc/internal/envconfig/xds.go
@@ -61,11 +61,10 @@ var (
 	// have a brand new API on the server-side and users explicitly need to use
 	// the new API to get security integration on the server.
 	XDSClientSideSecurity = boolFromEnv("GRPC_XDS_EXPERIMENTAL_SECURITY_SUPPORT", true)
-	// XDSAggregateAndDNS indicates whether processing of aggregated cluster
-	// and DNS cluster is enabled, which can be enabled by setting the
-	// environment variable
-	// "GRPC_XDS_EXPERIMENTAL_ENABLE_AGGREGATE_AND_LOGICAL_DNS_CLUSTER" to
-	// "true".
+	// XDSAggregateAndDNS indicates whether processing of aggregated cluster and
+	// DNS cluster is enabled, which can be disabled by setting the environment
+	// variable "GRPC_XDS_EXPERIMENTAL_ENABLE_AGGREGATE_AND_LOGICAL_DNS_CLUSTER"
+	// to "false".
 	XDSAggregateAndDNS = boolFromEnv("GRPC_XDS_EXPERIMENTAL_ENABLE_AGGREGATE_AND_LOGICAL_DNS_CLUSTER", true)
 
 	// XDSRBAC indicates whether xDS configured RBAC HTTP Filter is enabled,
@@ -82,11 +81,15 @@ var (
 	XDSFederation = boolFromEnv("GRPC_EXPERIMENTAL_XDS_FEDERATION", true)
 
 	// XDSRLS indicates whether processing of Cluster Specifier plugins and
-	// support for the RLS CLuster Specifier is enabled, which can be enabled by
+	// support for the RLS CLuster Specifier is enabled, which can be disabled by
 	// setting the environment variable "GRPC_EXPERIMENTAL_XDS_RLS_LB" to
-	// "true".
-	XDSRLS = boolFromEnv("GRPC_EXPERIMENTAL_XDS_RLS_LB", false)
+	// "false".
+	XDSRLS = boolFromEnv("GRPC_EXPERIMENTAL_XDS_RLS_LB", true)
 
 	// C2PResolverTestOnlyTrafficDirectorURI is the TD URI for testing.
 	C2PResolverTestOnlyTrafficDirectorURI = os.Getenv("GRPC_TEST_ONLY_GOOGLE_C2P_RESOLVER_TRAFFIC_DIRECTOR_URI")
+	// XDSCustomLBPolicy indicates whether Custom LB Policies are enabled, which
+	// can be disabled by setting the environment variable
+	// "GRPC_EXPERIMENTAL_XDS_CUSTOM_LB_CONFIG" to "false".
+	XDSCustomLBPolicy = boolFromEnv("GRPC_EXPERIMENTAL_XDS_CUSTOM_LB_CONFIG", true)
 )
diff --git a/vendor/google.golang.org/grpc/internal/grpcrand/grpcrand.go b/vendor/google.golang.org/grpc/internal/grpcrand/grpcrand.go
index 517ea706..d08e3e90 100644
--- a/vendor/google.golang.org/grpc/internal/grpcrand/grpcrand.go
+++ b/vendor/google.golang.org/grpc/internal/grpcrand/grpcrand.go
@@ -72,3 +72,17 @@ func Uint64() uint64 {
 	defer mu.Unlock()
 	return r.Uint64()
 }
+
+// Uint32 implements rand.Uint32 on the grpcrand global source.
+func Uint32() uint32 {
+	mu.Lock()
+	defer mu.Unlock()
+	return r.Uint32()
+}
+
+// Shuffle implements rand.Shuffle on the grpcrand global source.
+var Shuffle = func(n int, f func(int, int)) {
+	mu.Lock()
+	defer mu.Unlock()
+	r.Shuffle(n, f)
+}
diff --git a/vendor/google.golang.org/grpc/internal/grpcsync/callback_serializer.go b/vendor/google.golang.org/grpc/internal/grpcsync/callback_serializer.go
index 79993d34..37b8d411 100644
--- a/vendor/google.golang.org/grpc/internal/grpcsync/callback_serializer.go
+++ b/vendor/google.golang.org/grpc/internal/grpcsync/callback_serializer.go
@@ -20,6 +20,7 @@ package grpcsync
 
 import (
 	"context"
+	"sync"
 
 	"google.golang.org/grpc/internal/buffer"
 )
@@ -31,15 +32,26 @@ import (
 //
 // This type is safe for concurrent access.
 type CallbackSerializer struct {
+	// Done is closed once the serializer is shut down completely, i.e all
+	// scheduled callbacks are executed and the serializer has deallocated all
+	// its resources.
+	Done chan struct{}
+
 	callbacks *buffer.Unbounded
+	closedMu  sync.Mutex
+	closed    bool
 }
 
 // NewCallbackSerializer returns a new CallbackSerializer instance. The provided
 // context will be passed to the scheduled callbacks. Users should cancel the
 // provided context to shutdown the CallbackSerializer. It is guaranteed that no
-// callbacks will be executed once this context is canceled.
+// callbacks will be added once this context is canceled, and any pending un-run
+// callbacks will be executed before the serializer is shut down.
 func NewCallbackSerializer(ctx context.Context) *CallbackSerializer {
-	t := &CallbackSerializer{callbacks: buffer.NewUnbounded()}
+	t := &CallbackSerializer{
+		Done:      make(chan struct{}),
+		callbacks: buffer.NewUnbounded(),
+	}
 	go t.run(ctx)
 	return t
 }
@@ -48,18 +60,60 @@ func NewCallbackSerializer(ctx context.Context) *CallbackSerializer {
 //
 // Callbacks are expected to honor the context when performing any blocking
 // operations, and should return early when the context is canceled.
-func (t *CallbackSerializer) Schedule(f func(ctx context.Context)) {
+//
+// Return value indicates if the callback was successfully added to the list of
+// callbacks to be executed by the serializer. It is not possible to add
+// callbacks once the context passed to NewCallbackSerializer is cancelled.
+func (t *CallbackSerializer) Schedule(f func(ctx context.Context)) bool {
+	t.closedMu.Lock()
+	defer t.closedMu.Unlock()
+
+	if t.closed {
+		return false
+	}
 	t.callbacks.Put(f)
+	return true
 }
 
 func (t *CallbackSerializer) run(ctx context.Context) {
+	var backlog []func(context.Context)
+
+	defer close(t.Done)
 	for ctx.Err() == nil {
 		select {
 		case <-ctx.Done():
-			return
-		case callback := <-t.callbacks.Get():
+			// Do nothing here. Next iteration of the for loop will not happen,
+			// since ctx.Err() would be non-nil.
+		case callback, ok := <-t.callbacks.Get():
+			if !ok {
+				return
+			}
 			t.callbacks.Load()
 			callback.(func(ctx context.Context))(ctx)
 		}
 	}
+
+	// Fetch pending callbacks if any, and execute them before returning from
+	// this method and closing t.Done.
+	t.closedMu.Lock()
+	t.closed = true
+	backlog = t.fetchPendingCallbacks()
+	t.callbacks.Close()
+	t.closedMu.Unlock()
+	for _, b := range backlog {
+		b(ctx)
+	}
+}
+
+func (t *CallbackSerializer) fetchPendingCallbacks() []func(context.Context) {
+	var backlog []func(context.Context)
+	for {
+		select {
+		case b := <-t.callbacks.Get():
+			backlog = append(backlog, b.(func(context.Context)))
+			t.callbacks.Load()
+		default:
+			return backlog
+		}
+	}
 }
diff --git a/vendor/google.golang.org/grpc/internal/internal.go b/vendor/google.golang.org/grpc/internal/internal.go
index 836b6a3b..42ff39c8 100644
--- a/vendor/google.golang.org/grpc/internal/internal.go
+++ b/vendor/google.golang.org/grpc/internal/internal.go
@@ -60,6 +60,9 @@ var (
 	GetServerCredentials interface{} // func (*grpc.Server) credentials.TransportCredentials
 	// CanonicalString returns the canonical string of the code defined here:
 	// https://github.com/grpc/grpc/blob/master/doc/statuscodes.md.
+	//
+	// This is used in the 1.0 release of gcp/observability, and thus must not be
+	// deleted or changed.
 	CanonicalString interface{} // func (codes.Code) string
 	// DrainServerTransports initiates a graceful close of existing connections
 	// on a gRPC server accepted on the provided listener address. An
@@ -69,20 +72,35 @@ var (
 	// AddGlobalServerOptions adds an array of ServerOption that will be
 	// effective globally for newly created servers. The priority will be: 1.
 	// user-provided; 2. this method; 3. default values.
+	//
+	// This is used in the 1.0 release of gcp/observability, and thus must not be
+	// deleted or changed.
 	AddGlobalServerOptions interface{} // func(opt ...ServerOption)
 	// ClearGlobalServerOptions clears the array of extra ServerOption. This
 	// method is useful in testing and benchmarking.
+	//
+	// This is used in the 1.0 release of gcp/observability, and thus must not be
+	// deleted or changed.
 	ClearGlobalServerOptions func()
 	// AddGlobalDialOptions adds an array of DialOption that will be effective
 	// globally for newly created client channels. The priority will be: 1.
 	// user-provided; 2. this method; 3. default values.
+	//
+	// This is used in the 1.0 release of gcp/observability, and thus must not be
+	// deleted or changed.
 	AddGlobalDialOptions interface{} // func(opt ...DialOption)
 	// DisableGlobalDialOptions returns a DialOption that prevents the
 	// ClientConn from applying the global DialOptions (set via
 	// AddGlobalDialOptions).
+	//
+	// This is used in the 1.0 release of gcp/observability, and thus must not be
+	// deleted or changed.
 	DisableGlobalDialOptions interface{} // func() grpc.DialOption
 	// ClearGlobalDialOptions clears the array of extra DialOption. This
 	// method is useful in testing and benchmarking.
+	//
+	// This is used in the 1.0 release of gcp/observability, and thus must not be
+	// deleted or changed.
 	ClearGlobalDialOptions func()
 	// JoinDialOptions combines the dial options passed as arguments into a
 	// single dial option.
@@ -93,9 +111,15 @@ var (
 
 	// WithBinaryLogger returns a DialOption that specifies the binary logger
 	// for a ClientConn.
+	//
+	// This is used in the 1.0 release of gcp/observability, and thus must not be
+	// deleted or changed.
 	WithBinaryLogger interface{} // func(binarylog.Logger) grpc.DialOption
 	// BinaryLogger returns a ServerOption that can set the binary logger for a
 	// server.
+	//
+	// This is used in the 1.0 release of gcp/observability, and thus must not be
+	// deleted or changed.
 	BinaryLogger interface{} // func(binarylog.Logger) grpc.ServerOption
 
 	// NewXDSResolverWithConfigForTesting creates a new xds resolver builder using
diff --git a/vendor/google.golang.org/grpc/internal/serviceconfig/duration.go b/vendor/google.golang.org/grpc/internal/serviceconfig/duration.go
new file mode 100644
index 00000000..11d82afc
--- /dev/null
+++ b/vendor/google.golang.org/grpc/internal/serviceconfig/duration.go
@@ -0,0 +1,130 @@
+/*
+ *
+ * Copyright 2023 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package serviceconfig
+
+import (
+	"encoding/json"
+	"fmt"
+	"math"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// Duration defines JSON marshal and unmarshal methods to conform to the
+// protobuf JSON spec defined [here].
+//
+// [here]: https://protobuf.dev/reference/protobuf/google.protobuf/#duration
+type Duration time.Duration
+
+func (d Duration) String() string {
+	return fmt.Sprint(time.Duration(d))
+}
+
+// MarshalJSON converts from d to a JSON string output.
+func (d Duration) MarshalJSON() ([]byte, error) {
+	ns := time.Duration(d).Nanoseconds()
+	sec := ns / int64(time.Second)
+	ns = ns % int64(time.Second)
+
+	var sign string
+	if sec < 0 || ns < 0 {
+		sign, sec, ns = "-", -1*sec, -1*ns
+	}
+
+	// Generated output always contains 0, 3, 6, or 9 fractional digits,
+	// depending on required precision.
+	str := fmt.Sprintf("%s%d.%09d", sign, sec, ns)
+	str = strings.TrimSuffix(str, "000")
+	str = strings.TrimSuffix(str, "000")
+	str = strings.TrimSuffix(str, ".000")
+	return []byte(fmt.Sprintf("\"%ss\"", str)), nil
+}
+
+// UnmarshalJSON unmarshals b as a duration JSON string into d.
+func (d *Duration) UnmarshalJSON(b []byte) error {
+	var s string
+	if err := json.Unmarshal(b, &s); err != nil {
+		return err
+	}
+	if !strings.HasSuffix(s, "s") {
+		return fmt.Errorf("malformed duration %q: missing seconds unit", s)
+	}
+	neg := false
+	if s[0] == '-' {
+		neg = true
+		s = s[1:]
+	}
+	ss := strings.SplitN(s[:len(s)-1], ".", 3)
+	if len(ss) > 2 {
+		return fmt.Errorf("malformed duration %q: too many decimals", s)
+	}
+	// hasDigits is set if either the whole or fractional part of the number is
+	// present, since both are optional but one is required.
+	hasDigits := false
+	var sec, ns int64
+	if len(ss[0]) > 0 {
+		var err error
+		if sec, err = strconv.ParseInt(ss[0], 10, 64); err != nil {
+			return fmt.Errorf("malformed duration %q: %v", s, err)
+		}
+		// Maximum seconds value per the durationpb spec.
+		const maxProtoSeconds = 315_576_000_000
+		if sec > maxProtoSeconds {
+			return fmt.Errorf("out of range: %q", s)
+		}
+		hasDigits = true
+	}
+	if len(ss) == 2 && len(ss[1]) > 0 {
+		if len(ss[1]) > 9 {
+			return fmt.Errorf("malformed duration %q: too many digits after decimal", s)
+		}
+		var err error
+		if ns, err = strconv.ParseInt(ss[1], 10, 64); err != nil {
+			return fmt.Errorf("malformed duration %q: %v", s, err)
+		}
+		for i := 9; i > len(ss[1]); i-- {
+			ns *= 10
+		}
+		hasDigits = true
+	}
+	if !hasDigits {
+		return fmt.Errorf("malformed duration %q: contains no numbers", s)
+	}
+
+	if neg {
+		sec *= -1
+		ns *= -1
+	}
+
+	// Maximum/minimum seconds/nanoseconds representable by Go's time.Duration.
+	const maxSeconds = math.MaxInt64 / int64(time.Second)
+	const maxNanosAtMaxSeconds = math.MaxInt64 % int64(time.Second)
+	const minSeconds = math.MinInt64 / int64(time.Second)
+	const minNanosAtMinSeconds = math.MinInt64 % int64(time.Second)
+
+	if sec > maxSeconds || (sec == maxSeconds && ns >= maxNanosAtMaxSeconds) {
+		*d = Duration(math.MaxInt64)
+	} else if sec < minSeconds || (sec == minSeconds && ns <= minNanosAtMinSeconds) {
+		*d = Duration(math.MinInt64)
+	} else {
+		*d = Duration(sec*int64(time.Second) + ns)
+	}
+	return nil
+}
diff --git a/vendor/google.golang.org/grpc/internal/transport/handler_server.go b/vendor/google.golang.org/grpc/internal/transport/handler_server.go
index fbee581b..98f80e3f 100644
--- a/vendor/google.golang.org/grpc/internal/transport/handler_server.go
+++ b/vendor/google.golang.org/grpc/internal/transport/handler_server.go
@@ -453,7 +453,7 @@ func (ht *serverHandlerTransport) IncrMsgSent() {}
 
 func (ht *serverHandlerTransport) IncrMsgRecv() {}
 
-func (ht *serverHandlerTransport) Drain() {
+func (ht *serverHandlerTransport) Drain(debugData string) {
 	panic("Drain() is not implemented")
 }
 
diff --git a/vendor/google.golang.org/grpc/internal/transport/http2_client.go b/vendor/google.golang.org/grpc/internal/transport/http2_client.go
index 5216998a..326bf084 100644
--- a/vendor/google.golang.org/grpc/internal/transport/http2_client.go
+++ b/vendor/google.golang.org/grpc/internal/transport/http2_client.go
@@ -1337,7 +1337,7 @@ func (t *http2Client) handleGoAway(f *http2.GoAwayFrame) {
 
 // setGoAwayReason sets the value of t.goAwayReason based
 // on the GoAway frame received.
-// It expects a lock on transport's mutext to be held by
+// It expects a lock on transport's mutex to be held by
 // the caller.
 func (t *http2Client) setGoAwayReason(f *http2.GoAwayFrame) {
 	t.goAwayReason = GoAwayNoReason
diff --git a/vendor/google.golang.org/grpc/internal/transport/http2_server.go b/vendor/google.golang.org/grpc/internal/transport/http2_server.go
index 4b406b8c..ec4eef21 100644
--- a/vendor/google.golang.org/grpc/internal/transport/http2_server.go
+++ b/vendor/google.golang.org/grpc/internal/transport/http2_server.go
@@ -171,15 +171,10 @@ func NewServerTransport(conn net.Conn, config *ServerConfig) (_ ServerTransport,
 		ID:  http2.SettingMaxFrameSize,
 		Val: http2MaxFrameLen,
 	}}
-	// TODO(zhaoq): Have a better way to signal "no limit" because 0 is
-	// permitted in the HTTP2 spec.
-	maxStreams := config.MaxStreams
-	if maxStreams == 0 {
-		maxStreams = math.MaxUint32
-	} else {
+	if config.MaxStreams != math.MaxUint32 {
 		isettings = append(isettings, http2.Setting{
 			ID:  http2.SettingMaxConcurrentStreams,
-			Val: maxStreams,
+			Val: config.MaxStreams,
 		})
 	}
 	dynamicWindow := true
@@ -258,7 +253,7 @@ func NewServerTransport(conn net.Conn, config *ServerConfig) (_ ServerTransport,
 		framer:            framer,
 		readerDone:        make(chan struct{}),
 		writerDone:        make(chan struct{}),
-		maxStreams:        maxStreams,
+		maxStreams:        config.MaxStreams,
 		inTapHandle:       config.InTapHandle,
 		fc:                &trInFlow{limit: uint32(icwz)},
 		state:             reachable,
@@ -1166,12 +1161,12 @@ func (t *http2Server) keepalive() {
 			if val <= 0 {
 				// The connection has been idle for a duration of keepalive.MaxConnectionIdle or more.
 				// Gracefully close the connection.
-				t.Drain()
+				t.Drain("max_idle")
 				return
 			}
 			idleTimer.Reset(val)
 		case <-ageTimer.C:
-			t.Drain()
+			t.Drain("max_age")
 			ageTimer.Reset(t.kp.MaxConnectionAgeGrace)
 			select {
 			case <-ageTimer.C:
@@ -1318,14 +1313,14 @@ func (t *http2Server) RemoteAddr() net.Addr {
 	return t.remoteAddr
 }
 
-func (t *http2Server) Drain() {
+func (t *http2Server) Drain(debugData string) {
 	t.mu.Lock()
 	defer t.mu.Unlock()
 	if t.drainEvent != nil {
 		return
 	}
 	t.drainEvent = grpcsync.NewEvent()
-	t.controlBuf.put(&goAway{code: http2.ErrCodeNo, debugData: []byte{}, headsUp: true})
+	t.controlBuf.put(&goAway{code: http2.ErrCodeNo, debugData: []byte(debugData), headsUp: true})
 }
 
 var goAwayPing = &ping{data: [8]byte{1, 6, 1, 8, 0, 3, 3, 9}}
@@ -1367,7 +1362,7 @@ func (t *http2Server) outgoingGoAwayHandler(g *goAway) (bool, error) {
 	// originated before the GoAway reaches the client.
 	// After getting the ack or timer expiration send out another GoAway this
 	// time with an ID of the max stream server intends to process.
-	if err := t.framer.fr.WriteGoAway(math.MaxUint32, http2.ErrCodeNo, []byte{}); err != nil {
+	if err := t.framer.fr.WriteGoAway(math.MaxUint32, http2.ErrCodeNo, g.debugData); err != nil {
 		return false, err
 	}
 	if err := t.framer.fr.WritePing(false, goAwayPing.data); err != nil {
diff --git a/vendor/google.golang.org/grpc/internal/transport/transport.go b/vendor/google.golang.org/grpc/internal/transport/transport.go
index 1b7d7fab..aa1c8965 100644
--- a/vendor/google.golang.org/grpc/internal/transport/transport.go
+++ b/vendor/google.golang.org/grpc/internal/transport/transport.go
@@ -726,7 +726,7 @@ type ServerTransport interface {
 	RemoteAddr() net.Addr
 
 	// Drain notifies the client this ServerTransport stops accepting new RPCs.
-	Drain()
+	Drain(debugData string)
 
 	// IncrMsgSent increments the number of message sent through this transport.
 	IncrMsgSent()
diff --git a/vendor/google.golang.org/grpc/picker_wrapper.go b/vendor/google.golang.org/grpc/picker_wrapper.go
index c525dc07..02f97595 100644
--- a/vendor/google.golang.org/grpc/picker_wrapper.go
+++ b/vendor/google.golang.org/grpc/picker_wrapper.go
@@ -36,6 +36,7 @@ import (
 type pickerWrapper struct {
 	mu         sync.Mutex
 	done       bool
+	idle       bool
 	blockingCh chan struct{}
 	picker     balancer.Picker
 }
@@ -47,7 +48,11 @@ func newPickerWrapper() *pickerWrapper {
 // updatePicker is called by UpdateBalancerState. It unblocks all blocked pick.
 func (pw *pickerWrapper) updatePicker(p balancer.Picker) {
 	pw.mu.Lock()
-	if pw.done {
+	if pw.done || pw.idle {
+		// There is a small window where a picker update from the LB policy can
+		// race with the channel going to idle mode. If the picker is idle here,
+		// it is because the channel asked it to do so, and therefore it is sage
+		// to ignore the update from the LB policy.
 		pw.mu.Unlock()
 		return
 	}
@@ -63,10 +68,8 @@ func (pw *pickerWrapper) updatePicker(p balancer.Picker) {
 //   - wraps the done function in the passed in result to increment the calls
 //     failed or calls succeeded channelz counter before invoking the actual
 //     done function.
-func doneChannelzWrapper(acw *acBalancerWrapper, result *balancer.PickResult) {
-	acw.mu.Lock()
-	ac := acw.ac
-	acw.mu.Unlock()
+func doneChannelzWrapper(acbw *acBalancerWrapper, result *balancer.PickResult) {
+	ac := acbw.ac
 	ac.incrCallsStarted()
 	done := result.Done
 	result.Done = func(b balancer.DoneInfo) {
@@ -152,14 +155,14 @@ func (pw *pickerWrapper) pick(ctx context.Context, failfast bool, info balancer.
 			return nil, balancer.PickResult{}, status.Error(codes.Unavailable, err.Error())
 		}
 
-		acw, ok := pickResult.SubConn.(*acBalancerWrapper)
+		acbw, ok := pickResult.SubConn.(*acBalancerWrapper)
 		if !ok {
 			logger.Errorf("subconn returned from pick is type %T, not *acBalancerWrapper", pickResult.SubConn)
 			continue
 		}
-		if t := acw.getAddrConn().getReadyTransport(); t != nil {
+		if t := acbw.ac.getReadyTransport(); t != nil {
 			if channelz.IsOn() {
-				doneChannelzWrapper(acw, &pickResult)
+				doneChannelzWrapper(acbw, &pickResult)
 				return t, pickResult, nil
 			}
 			return t, pickResult, nil
@@ -187,6 +190,25 @@ func (pw *pickerWrapper) close() {
 	close(pw.blockingCh)
 }
 
+func (pw *pickerWrapper) enterIdleMode() {
+	pw.mu.Lock()
+	defer pw.mu.Unlock()
+	if pw.done {
+		return
+	}
+	pw.idle = true
+}
+
+func (pw *pickerWrapper) exitIdleMode() {
+	pw.mu.Lock()
+	defer pw.mu.Unlock()
+	if pw.done {
+		return
+	}
+	pw.blockingCh = make(chan struct{})
+	pw.idle = false
+}
+
 // dropError is a wrapper error that indicates the LB policy wishes to drop the
 // RPC and not retry it.
 type dropError struct {
diff --git a/vendor/google.golang.org/grpc/pickfirst.go b/vendor/google.golang.org/grpc/pickfirst.go
index fc91b4d2..abe266b0 100644
--- a/vendor/google.golang.org/grpc/pickfirst.go
+++ b/vendor/google.golang.org/grpc/pickfirst.go
@@ -19,11 +19,15 @@
 package grpc
 
 import (
+	"encoding/json"
 	"errors"
 	"fmt"
 
 	"google.golang.org/grpc/balancer"
 	"google.golang.org/grpc/connectivity"
+	"google.golang.org/grpc/internal/envconfig"
+	"google.golang.org/grpc/internal/grpcrand"
+	"google.golang.org/grpc/serviceconfig"
 )
 
 // PickFirstBalancerName is the name of the pick_first balancer.
@@ -43,10 +47,28 @@ func (*pickfirstBuilder) Name() string {
 	return PickFirstBalancerName
 }
 
+type pfConfig struct {
+	serviceconfig.LoadBalancingConfig `json:"-"`
+
+	// If set to true, instructs the LB policy to shuffle the order of the list
+	// of addresses received from the name resolver before attempting to
+	// connect to them.
+	ShuffleAddressList bool `json:"shuffleAddressList"`
+}
+
+func (*pickfirstBuilder) ParseConfig(js json.RawMessage) (serviceconfig.LoadBalancingConfig, error) {
+	cfg := &pfConfig{}
+	if err := json.Unmarshal(js, cfg); err != nil {
+		return nil, fmt.Errorf("pickfirst: unable to unmarshal LB policy config: %s, error: %v", string(js), err)
+	}
+	return cfg, nil
+}
+
 type pickfirstBalancer struct {
 	state   connectivity.State
 	cc      balancer.ClientConn
 	subConn balancer.SubConn
+	cfg     *pfConfig
 }
 
 func (b *pickfirstBalancer) ResolverError(err error) {
@@ -69,7 +91,8 @@ func (b *pickfirstBalancer) ResolverError(err error) {
 }
 
 func (b *pickfirstBalancer) UpdateClientConnState(state balancer.ClientConnState) error {
-	if len(state.ResolverState.Addresses) == 0 {
+	addrs := state.ResolverState.Addresses
+	if len(addrs) == 0 {
 		// The resolver reported an empty address list. Treat it like an error by
 		// calling b.ResolverError.
 		if b.subConn != nil {
@@ -82,12 +105,23 @@ func (b *pickfirstBalancer) UpdateClientConnState(state balancer.ClientConnState
 		return balancer.ErrBadResolverState
 	}
 
+	if state.BalancerConfig != nil {
+		cfg, ok := state.BalancerConfig.(*pfConfig)
+		if !ok {
+			return fmt.Errorf("pickfirstBalancer: received nil or illegal BalancerConfig (type %T): %v", state.BalancerConfig, state.BalancerConfig)
+		}
+		b.cfg = cfg
+	}
+
+	if envconfig.PickFirstLBConfig && b.cfg != nil && b.cfg.ShuffleAddressList {
+		grpcrand.Shuffle(len(addrs), func(i, j int) { addrs[i], addrs[j] = addrs[j], addrs[i] })
+	}
 	if b.subConn != nil {
-		b.cc.UpdateAddresses(b.subConn, state.ResolverState.Addresses)
+		b.cc.UpdateAddresses(b.subConn, addrs)
 		return nil
 	}
 
-	subConn, err := b.cc.NewSubConn(state.ResolverState.Addresses, balancer.NewSubConnOptions{})
+	subConn, err := b.cc.NewSubConn(addrs, balancer.NewSubConnOptions{})
 	if err != nil {
 		if logger.V(2) {
 			logger.Errorf("pickfirstBalancer: failed to NewSubConn: %v", err)
@@ -119,7 +153,6 @@ func (b *pickfirstBalancer) UpdateSubConnState(subConn balancer.SubConn, state b
 		}
 		return
 	}
-	b.state = state.ConnectivityState
 	if state.ConnectivityState == connectivity.Shutdown {
 		b.subConn = nil
 		return
@@ -132,11 +165,21 @@ func (b *pickfirstBalancer) UpdateSubConnState(subConn balancer.SubConn, state b
 			Picker:            &picker{result: balancer.PickResult{SubConn: subConn}},
 		})
 	case connectivity.Connecting:
+		if b.state == connectivity.TransientFailure {
+			// We stay in TransientFailure until we are Ready. See A62.
+			return
+		}
 		b.cc.UpdateState(balancer.State{
 			ConnectivityState: state.ConnectivityState,
 			Picker:            &picker{err: balancer.ErrNoSubConnAvailable},
 		})
 	case connectivity.Idle:
+		if b.state == connectivity.TransientFailure {
+			// We stay in TransientFailure until we are Ready. Also kick the
+			// subConn out of Idle into Connecting. See A62.
+			b.subConn.Connect()
+			return
+		}
 		b.cc.UpdateState(balancer.State{
 			ConnectivityState: state.ConnectivityState,
 			Picker:            &idlePicker{subConn: subConn},
@@ -147,6 +190,7 @@ func (b *pickfirstBalancer) UpdateSubConnState(subConn balancer.SubConn, state b
 			Picker:            &picker{err: state.ConnectionError},
 		})
 	}
+	b.state = state.ConnectivityState
 }
 
 func (b *pickfirstBalancer) Close() {
diff --git a/vendor/google.golang.org/grpc/resolver/resolver.go b/vendor/google.golang.org/grpc/resolver/resolver.go
index 6215e5ef..353c10b6 100644
--- a/vendor/google.golang.org/grpc/resolver/resolver.go
+++ b/vendor/google.golang.org/grpc/resolver/resolver.go
@@ -22,13 +22,13 @@ package resolver
 
 import (
 	"context"
+	"fmt"
 	"net"
 	"net/url"
 	"strings"
 
 	"google.golang.org/grpc/attributes"
 	"google.golang.org/grpc/credentials"
-	"google.golang.org/grpc/internal/pretty"
 	"google.golang.org/grpc/serviceconfig"
 )
 
@@ -124,7 +124,7 @@ type Address struct {
 	Attributes *attributes.Attributes
 
 	// BalancerAttributes contains arbitrary data about this address intended
-	// for consumption by the LB policy.  These attribes do not affect SubConn
+	// for consumption by the LB policy.  These attributes do not affect SubConn
 	// creation, connection establishment, handshaking, etc.
 	BalancerAttributes *attributes.Attributes
 
@@ -151,7 +151,17 @@ func (a Address) Equal(o Address) bool {
 
 // String returns JSON formatted string representation of the address.
 func (a Address) String() string {
-	return pretty.ToJSON(a)
+	var sb strings.Builder
+	sb.WriteString(fmt.Sprintf("{Addr: %q, ", a.Addr))
+	sb.WriteString(fmt.Sprintf("ServerName: %q, ", a.ServerName))
+	if a.Attributes != nil {
+		sb.WriteString(fmt.Sprintf("Attributes: %v, ", a.Attributes.String()))
+	}
+	if a.BalancerAttributes != nil {
+		sb.WriteString(fmt.Sprintf("BalancerAttributes: %v", a.BalancerAttributes.String()))
+	}
+	sb.WriteString("}")
+	return sb.String()
 }
 
 // BuildOptions includes additional information for the builder to create
diff --git a/vendor/google.golang.org/grpc/resolver_conn_wrapper.go b/vendor/google.golang.org/grpc/resolver_conn_wrapper.go
index 05a9d4e0..b408b368 100644
--- a/vendor/google.golang.org/grpc/resolver_conn_wrapper.go
+++ b/vendor/google.golang.org/grpc/resolver_conn_wrapper.go
@@ -19,11 +19,11 @@
 package grpc
 
 import (
+	"context"
 	"strings"
 	"sync"
 
 	"google.golang.org/grpc/balancer"
-	"google.golang.org/grpc/credentials"
 	"google.golang.org/grpc/internal/channelz"
 	"google.golang.org/grpc/internal/grpcsync"
 	"google.golang.org/grpc/internal/pretty"
@@ -31,129 +31,192 @@ import (
 	"google.golang.org/grpc/serviceconfig"
 )
 
+// resolverStateUpdater wraps the single method used by ccResolverWrapper to
+// report a state update from the actual resolver implementation.
+type resolverStateUpdater interface {
+	updateResolverState(s resolver.State, err error) error
+}
+
 // ccResolverWrapper is a wrapper on top of cc for resolvers.
 // It implements resolver.ClientConn interface.
 type ccResolverWrapper struct {
-	cc         *ClientConn
-	resolverMu sync.Mutex
-	resolver   resolver.Resolver
-	done       *grpcsync.Event
-	curState   resolver.State
+	// The following fields are initialized when the wrapper is created and are
+	// read-only afterwards, and therefore can be accessed without a mutex.
+	cc                  resolverStateUpdater
+	channelzID          *channelz.Identifier
+	ignoreServiceConfig bool
+	opts                ccResolverWrapperOpts
+	serializer          *grpcsync.CallbackSerializer // To serialize all incoming calls.
+	serializerCancel    context.CancelFunc           // To close the serializer, accessed only from close().
+
+	// All incoming (resolver --> gRPC) calls are guaranteed to execute in a
+	// mutually exclusive manner as they are scheduled on the serializer.
+	// Fields accessed *only* in these serializer callbacks, can therefore be
+	// accessed without a mutex.
+	curState resolver.State
+
+	// mu guards access to the below fields.
+	mu       sync.Mutex
+	closed   bool
+	resolver resolver.Resolver // Accessed only from outgoing calls.
+}
 
-	incomingMu sync.Mutex // Synchronizes all the incoming calls.
+// ccResolverWrapperOpts wraps the arguments to be passed when creating a new
+// ccResolverWrapper.
+type ccResolverWrapperOpts struct {
+	target     resolver.Target       // User specified dial target to resolve.
+	builder    resolver.Builder      // Resolver builder to use.
+	bOpts      resolver.BuildOptions // Resolver build options to use.
+	channelzID *channelz.Identifier  // Channelz identifier for the channel.
 }
 
 // newCCResolverWrapper uses the resolver.Builder to build a Resolver and
 // returns a ccResolverWrapper object which wraps the newly built resolver.
-func newCCResolverWrapper(cc *ClientConn, rb resolver.Builder) (*ccResolverWrapper, error) {
+func newCCResolverWrapper(cc resolverStateUpdater, opts ccResolverWrapperOpts) (*ccResolverWrapper, error) {
+	ctx, cancel := context.WithCancel(context.Background())
 	ccr := &ccResolverWrapper{
-		cc:   cc,
-		done: grpcsync.NewEvent(),
-	}
-
-	var credsClone credentials.TransportCredentials
-	if creds := cc.dopts.copts.TransportCredentials; creds != nil {
-		credsClone = creds.Clone()
-	}
-	rbo := resolver.BuildOptions{
-		DisableServiceConfig: cc.dopts.disableServiceConfig,
-		DialCreds:            credsClone,
-		CredsBundle:          cc.dopts.copts.CredsBundle,
-		Dialer:               cc.dopts.copts.Dialer,
-	}
-
-	var err error
-	// We need to hold the lock here while we assign to the ccr.resolver field
-	// to guard against a data race caused by the following code path,
-	// rb.Build-->ccr.ReportError-->ccr.poll-->ccr.resolveNow, would end up
-	// accessing ccr.resolver which is being assigned here.
-	ccr.resolverMu.Lock()
-	defer ccr.resolverMu.Unlock()
-	ccr.resolver, err = rb.Build(cc.parsedTarget, ccr, rbo)
+		cc:                  cc,
+		channelzID:          opts.channelzID,
+		ignoreServiceConfig: opts.bOpts.DisableServiceConfig,
+		opts:                opts,
+		serializer:          grpcsync.NewCallbackSerializer(ctx),
+		serializerCancel:    cancel,
+	}
+
+	// Cannot hold the lock at build time because the resolver can send an
+	// update or error inline and these incoming calls grab the lock to schedule
+	// a callback in the serializer.
+	r, err := opts.builder.Build(opts.target, ccr, opts.bOpts)
 	if err != nil {
+		cancel()
 		return nil, err
 	}
+
+	// Any error reported by the resolver at build time that leads to a
+	// re-resolution request from the balancer is dropped by grpc until we
+	// return from this function. So, we don't have to handle pending resolveNow
+	// requests here.
+	ccr.mu.Lock()
+	ccr.resolver = r
+	ccr.mu.Unlock()
+
 	return ccr, nil
 }
 
 func (ccr *ccResolverWrapper) resolveNow(o resolver.ResolveNowOptions) {
-	ccr.resolverMu.Lock()
-	if !ccr.done.HasFired() {
-		ccr.resolver.ResolveNow(o)
+	ccr.mu.Lock()
+	defer ccr.mu.Unlock()
+
+	// ccr.resolver field is set only after the call to Build() returns. But in
+	// the process of building, the resolver may send an error update which when
+	// propagated to the balancer may result in a re-resolution request.
+	if ccr.closed || ccr.resolver == nil {
+		return
 	}
-	ccr.resolverMu.Unlock()
+	ccr.resolver.ResolveNow(o)
 }
 
 func (ccr *ccResolverWrapper) close() {
-	ccr.resolverMu.Lock()
-	ccr.resolver.Close()
-	ccr.done.Fire()
-	ccr.resolverMu.Unlock()
+	ccr.mu.Lock()
+	if ccr.closed {
+		ccr.mu.Unlock()
+		return
+	}
+
+	channelz.Info(logger, ccr.channelzID, "Closing the name resolver")
+
+	// Close the serializer to ensure that no more calls from the resolver are
+	// handled, before actually closing the resolver.
+	ccr.serializerCancel()
+	ccr.closed = true
+	r := ccr.resolver
+	ccr.mu.Unlock()
+
+	// Give enqueued callbacks a chance to finish.
+	<-ccr.serializer.Done
+
+	// Spawn a goroutine to close the resolver (since it may block trying to
+	// cleanup all allocated resources) and return early.
+	go r.Close()
+}
+
+// serializerScheduleLocked is a convenience method to schedule a function to be
+// run on the serializer while holding ccr.mu.
+func (ccr *ccResolverWrapper) serializerScheduleLocked(f func(context.Context)) {
+	ccr.mu.Lock()
+	ccr.serializer.Schedule(f)
+	ccr.mu.Unlock()
 }
 
+// UpdateState is called by resolver implementations to report new state to gRPC
+// which includes addresses and service config.
 func (ccr *ccResolverWrapper) UpdateState(s resolver.State) error {
-	ccr.incomingMu.Lock()
-	defer ccr.incomingMu.Unlock()
-	if ccr.done.HasFired() {
+	errCh := make(chan error, 1)
+	ok := ccr.serializer.Schedule(func(context.Context) {
+		ccr.addChannelzTraceEvent(s)
+		ccr.curState = s
+		if err := ccr.cc.updateResolverState(ccr.curState, nil); err == balancer.ErrBadResolverState {
+			errCh <- balancer.ErrBadResolverState
+			return
+		}
+		errCh <- nil
+	})
+	if !ok {
+		// The only time when Schedule() fail to add the callback to the
+		// serializer is when the serializer is closed, and this happens only
+		// when the resolver wrapper is closed.
 		return nil
 	}
-	ccr.addChannelzTraceEvent(s)
-	ccr.curState = s
-	if err := ccr.cc.updateResolverState(ccr.curState, nil); err == balancer.ErrBadResolverState {
-		return balancer.ErrBadResolverState
-	}
-	return nil
+	return <-errCh
 }
 
+// ReportError is called by resolver implementations to report errors
+// encountered during name resolution to gRPC.
 func (ccr *ccResolverWrapper) ReportError(err error) {
-	ccr.incomingMu.Lock()
-	defer ccr.incomingMu.Unlock()
-	if ccr.done.HasFired() {
-		return
-	}
-	channelz.Warningf(logger, ccr.cc.channelzID, "ccResolverWrapper: reporting error to cc: %v", err)
-	ccr.cc.updateResolverState(resolver.State{}, err)
+	ccr.serializerScheduleLocked(func(_ context.Context) {
+		channelz.Warningf(logger, ccr.channelzID, "ccResolverWrapper: reporting error to cc: %v", err)
+		ccr.cc.updateResolverState(resolver.State{}, err)
+	})
 }
 
-// NewAddress is called by the resolver implementation to send addresses to gRPC.
+// NewAddress is called by the resolver implementation to send addresses to
+// gRPC.
 func (ccr *ccResolverWrapper) NewAddress(addrs []resolver.Address) {
-	ccr.incomingMu.Lock()
-	defer ccr.incomingMu.Unlock()
-	if ccr.done.HasFired() {
-		return
-	}
-	ccr.addChannelzTraceEvent(resolver.State{Addresses: addrs, ServiceConfig: ccr.curState.ServiceConfig})
-	ccr.curState.Addresses = addrs
-	ccr.cc.updateResolverState(ccr.curState, nil)
+	ccr.serializerScheduleLocked(func(_ context.Context) {
+		ccr.addChannelzTraceEvent(resolver.State{Addresses: addrs, ServiceConfig: ccr.curState.ServiceConfig})
+		ccr.curState.Addresses = addrs
+		ccr.cc.updateResolverState(ccr.curState, nil)
+	})
 }
 
 // NewServiceConfig is called by the resolver implementation to send service
 // configs to gRPC.
 func (ccr *ccResolverWrapper) NewServiceConfig(sc string) {
-	ccr.incomingMu.Lock()
-	defer ccr.incomingMu.Unlock()
-	if ccr.done.HasFired() {
-		return
-	}
-	channelz.Infof(logger, ccr.cc.channelzID, "ccResolverWrapper: got new service config: %s", sc)
-	if ccr.cc.dopts.disableServiceConfig {
-		channelz.Info(logger, ccr.cc.channelzID, "Service config lookups disabled; ignoring config")
-		return
-	}
-	scpr := parseServiceConfig(sc)
-	if scpr.Err != nil {
-		channelz.Warningf(logger, ccr.cc.channelzID, "ccResolverWrapper: error parsing service config: %v", scpr.Err)
-		return
-	}
-	ccr.addChannelzTraceEvent(resolver.State{Addresses: ccr.curState.Addresses, ServiceConfig: scpr})
-	ccr.curState.ServiceConfig = scpr
-	ccr.cc.updateResolverState(ccr.curState, nil)
+	ccr.serializerScheduleLocked(func(_ context.Context) {
+		channelz.Infof(logger, ccr.channelzID, "ccResolverWrapper: got new service config: %s", sc)
+		if ccr.ignoreServiceConfig {
+			channelz.Info(logger, ccr.channelzID, "Service config lookups disabled; ignoring config")
+			return
+		}
+		scpr := parseServiceConfig(sc)
+		if scpr.Err != nil {
+			channelz.Warningf(logger, ccr.channelzID, "ccResolverWrapper: error parsing service config: %v", scpr.Err)
+			return
+		}
+		ccr.addChannelzTraceEvent(resolver.State{Addresses: ccr.curState.Addresses, ServiceConfig: scpr})
+		ccr.curState.ServiceConfig = scpr
+		ccr.cc.updateResolverState(ccr.curState, nil)
+	})
 }
 
+// ParseServiceConfig is called by resolver implementations to parse a JSON
+// representation of the service config.
 func (ccr *ccResolverWrapper) ParseServiceConfig(scJSON string) *serviceconfig.ParseResult {
 	return parseServiceConfig(scJSON)
 }
 
+// addChannelzTraceEvent adds a channelz trace event containing the new
+// state received from resolver implementations.
 func (ccr *ccResolverWrapper) addChannelzTraceEvent(s resolver.State) {
 	var updates []string
 	var oldSC, newSC *ServiceConfig
@@ -172,5 +235,5 @@ func (ccr *ccResolverWrapper) addChannelzTraceEvent(s resolver.State) {
 	} else if len(ccr.curState.Addresses) == 0 && len(s.Addresses) > 0 {
 		updates = append(updates, "resolver returned new addresses")
 	}
-	channelz.Infof(logger, ccr.cc.channelzID, "Resolver state updated: %s (%v)", pretty.ToJSON(s), strings.Join(updates, "; "))
+	channelz.Infof(logger, ccr.channelzID, "Resolver state updated: %s (%v)", pretty.ToJSON(s), strings.Join(updates, "; "))
 }
diff --git a/vendor/google.golang.org/grpc/server.go b/vendor/google.golang.org/grpc/server.go
index 76d152a6..8869cc90 100644
--- a/vendor/google.golang.org/grpc/server.go
+++ b/vendor/google.golang.org/grpc/server.go
@@ -115,12 +115,6 @@ type serviceInfo struct {
 	mdata       interface{}
 }
 
-type serverWorkerData struct {
-	st     transport.ServerTransport
-	wg     *sync.WaitGroup
-	stream *transport.Stream
-}
-
 // Server is a gRPC server to serve RPC requests.
 type Server struct {
 	opts serverOptions
@@ -145,7 +139,7 @@ type Server struct {
 	channelzID *channelz.Identifier
 	czData     *channelzData
 
-	serverWorkerChannel chan *serverWorkerData
+	serverWorkerChannel chan func()
 }
 
 type serverOptions struct {
@@ -177,6 +171,7 @@ type serverOptions struct {
 }
 
 var defaultServerOptions = serverOptions{
+	maxConcurrentStreams:  math.MaxUint32,
 	maxReceiveMessageSize: defaultServerMaxReceiveMessageSize,
 	maxSendMessageSize:    defaultServerMaxSendMessageSize,
 	connectionTimeout:     120 * time.Second,
@@ -387,6 +382,9 @@ func MaxSendMsgSize(m int) ServerOption {
 // MaxConcurrentStreams returns a ServerOption that will apply a limit on the number
 // of concurrent streams to each ServerTransport.
 func MaxConcurrentStreams(n uint32) ServerOption {
+	if n == 0 {
+		n = math.MaxUint32
+	}
 	return newFuncServerOption(func(o *serverOptions) {
 		o.maxConcurrentStreams = n
 	})
@@ -567,24 +565,19 @@ const serverWorkerResetThreshold = 1 << 16
 // [1] https://github.com/golang/go/issues/18138
 func (s *Server) serverWorker() {
 	for completed := 0; completed < serverWorkerResetThreshold; completed++ {
-		data, ok := <-s.serverWorkerChannel
+		f, ok := <-s.serverWorkerChannel
 		if !ok {
 			return
 		}
-		s.handleSingleStream(data)
+		f()
 	}
 	go s.serverWorker()
 }
 
-func (s *Server) handleSingleStream(data *serverWorkerData) {
-	defer data.wg.Done()
-	s.handleStream(data.st, data.stream, s.traceInfo(data.st, data.stream))
-}
-
 // initServerWorkers creates worker goroutines and a channel to process incoming
 // connections to reduce the time spent overall on runtime.morestack.
 func (s *Server) initServerWorkers() {
-	s.serverWorkerChannel = make(chan *serverWorkerData)
+	s.serverWorkerChannel = make(chan func())
 	for i := uint32(0); i < s.opts.numServerWorkers; i++ {
 		go s.serverWorker()
 	}
@@ -895,7 +888,7 @@ func (s *Server) drainServerTransports(addr string) {
 	s.mu.Lock()
 	conns := s.conns[addr]
 	for st := range conns {
-		st.Drain()
+		st.Drain("")
 	}
 	s.mu.Unlock()
 }
@@ -943,21 +936,26 @@ func (s *Server) serveStreams(st transport.ServerTransport) {
 	defer st.Close(errors.New("finished serving streams for the server transport"))
 	var wg sync.WaitGroup
 
+	streamQuota := newHandlerQuota(s.opts.maxConcurrentStreams)
 	st.HandleStreams(func(stream *transport.Stream) {
 		wg.Add(1)
+
+		streamQuota.acquire()
+		f := func() {
+			defer streamQuota.release()
+			defer wg.Done()
+			s.handleStream(st, stream, s.traceInfo(st, stream))
+		}
+
 		if s.opts.numServerWorkers > 0 {
-			data := &serverWorkerData{st: st, wg: &wg, stream: stream}
 			select {
-			case s.serverWorkerChannel <- data:
+			case s.serverWorkerChannel <- f:
 				return
 			default:
 				// If all stream workers are busy, fallback to the default code path.
 			}
 		}
-		go func() {
-			defer wg.Done()
-			s.handleStream(st, stream, s.traceInfo(st, stream))
-		}()
+		go f()
 	}, func(ctx context.Context, method string) context.Context {
 		if !EnableTracing {
 			return ctx
@@ -1046,7 +1044,7 @@ func (s *Server) addConn(addr string, st transport.ServerTransport) bool {
 	if s.drain {
 		// Transport added after we drained our existing conns: drain it
 		// immediately.
-		st.Drain()
+		st.Drain("")
 	}
 
 	if s.conns[addr] == nil {
@@ -1856,7 +1854,7 @@ func (s *Server) GracefulStop() {
 	if !s.drain {
 		for _, conns := range s.conns {
 			for st := range conns {
-				st.Drain()
+				st.Drain("graceful_stop")
 			}
 		}
 		s.drain = true
@@ -2052,3 +2050,32 @@ func validateSendCompressor(name, clientCompressors string) error {
 	}
 	return fmt.Errorf("client does not support compressor %q", name)
 }
+
+// atomicSemaphore implements a blocking, counting semaphore. acquire should be
+// called synchronously; release may be called asynchronously.
+type atomicSemaphore struct {
+	n    int64
+	wait chan struct{}
+}
+
+func (q *atomicSemaphore) acquire() {
+	if atomic.AddInt64(&q.n, -1) < 0 {
+		// We ran out of quota.  Block until a release happens.
+		<-q.wait
+	}
+}
+
+func (q *atomicSemaphore) release() {
+	// N.B. the "<= 0" check below should allow for this to work with multiple
+	// concurrent calls to acquire, but also note that with synchronous calls to
+	// acquire, as our system does, n will never be less than -1.  There are
+	// fairness issues (queuing) to consider if this was to be generalized.
+	if atomic.AddInt64(&q.n, 1) <= 0 {
+		// An acquire was waiting on us.  Unblock it.
+		q.wait <- struct{}{}
+	}
+}
+
+func newHandlerQuota(n uint32) *atomicSemaphore {
+	return &atomicSemaphore{n: int64(n), wait: make(chan struct{}, 1)}
+}
diff --git a/vendor/google.golang.org/grpc/service_config.go b/vendor/google.golang.org/grpc/service_config.go
index f22acace..0df11fc0 100644
--- a/vendor/google.golang.org/grpc/service_config.go
+++ b/vendor/google.golang.org/grpc/service_config.go
@@ -23,8 +23,6 @@ import (
 	"errors"
 	"fmt"
 	"reflect"
-	"strconv"
-	"strings"
 	"time"
 
 	"google.golang.org/grpc/codes"
@@ -106,8 +104,8 @@ type healthCheckConfig struct {
 
 type jsonRetryPolicy struct {
 	MaxAttempts          int
-	InitialBackoff       string
-	MaxBackoff           string
+	InitialBackoff       internalserviceconfig.Duration
+	MaxBackoff           internalserviceconfig.Duration
 	BackoffMultiplier    float64
 	RetryableStatusCodes []codes.Code
 }
@@ -129,50 +127,6 @@ type retryThrottlingPolicy struct {
 	TokenRatio float64
 }
 
-func parseDuration(s *string) (*time.Duration, error) {
-	if s == nil {
-		return nil, nil
-	}
-	if !strings.HasSuffix(*s, "s") {
-		return nil, fmt.Errorf("malformed duration %q", *s)
-	}
-	ss := strings.SplitN((*s)[:len(*s)-1], ".", 3)
-	if len(ss) > 2 {
-		return nil, fmt.Errorf("malformed duration %q", *s)
-	}
-	// hasDigits is set if either the whole or fractional part of the number is
-	// present, since both are optional but one is required.
-	hasDigits := false
-	var d time.Duration
-	if len(ss[0]) > 0 {
-		i, err := strconv.ParseInt(ss[0], 10, 32)
-		if err != nil {
-			return nil, fmt.Errorf("malformed duration %q: %v", *s, err)
-		}
-		d = time.Duration(i) * time.Second
-		hasDigits = true
-	}
-	if len(ss) == 2 && len(ss[1]) > 0 {
-		if len(ss[1]) > 9 {
-			return nil, fmt.Errorf("malformed duration %q", *s)
-		}
-		f, err := strconv.ParseInt(ss[1], 10, 64)
-		if err != nil {
-			return nil, fmt.Errorf("malformed duration %q: %v", *s, err)
-		}
-		for i := 9; i > len(ss[1]); i-- {
-			f *= 10
-		}
-		d += time.Duration(f)
-		hasDigits = true
-	}
-	if !hasDigits {
-		return nil, fmt.Errorf("malformed duration %q", *s)
-	}
-
-	return &d, nil
-}
-
 type jsonName struct {
 	Service string
 	Method  string
@@ -201,7 +155,7 @@ func (j jsonName) generatePath() (string, error) {
 type jsonMC struct {
 	Name                    *[]jsonName
 	WaitForReady            *bool
-	Timeout                 *string
+	Timeout                 *internalserviceconfig.Duration
 	MaxRequestMessageBytes  *int64
 	MaxResponseMessageBytes *int64
 	RetryPolicy             *jsonRetryPolicy
@@ -252,15 +206,10 @@ func parseServiceConfig(js string) *serviceconfig.ParseResult {
 		if m.Name == nil {
 			continue
 		}
-		d, err := parseDuration(m.Timeout)
-		if err != nil {
-			logger.Warningf("grpc: unmarshaling service config %s: %v", js, err)
-			return &serviceconfig.ParseResult{Err: err}
-		}
 
 		mc := MethodConfig{
 			WaitForReady: m.WaitForReady,
-			Timeout:      d,
+			Timeout:      (*time.Duration)(m.Timeout),
 		}
 		if mc.RetryPolicy, err = convertRetryPolicy(m.RetryPolicy); err != nil {
 			logger.Warningf("grpc: unmarshaling service config %s: %v", js, err)
@@ -312,18 +261,10 @@ func convertRetryPolicy(jrp *jsonRetryPolicy) (p *internalserviceconfig.RetryPol
 	if jrp == nil {
 		return nil, nil
 	}
-	ib, err := parseDuration(&jrp.InitialBackoff)
-	if err != nil {
-		return nil, err
-	}
-	mb, err := parseDuration(&jrp.MaxBackoff)
-	if err != nil {
-		return nil, err
-	}
 
 	if jrp.MaxAttempts <= 1 ||
-		*ib <= 0 ||
-		*mb <= 0 ||
+		jrp.InitialBackoff <= 0 ||
+		jrp.MaxBackoff <= 0 ||
 		jrp.BackoffMultiplier <= 0 ||
 		len(jrp.RetryableStatusCodes) == 0 {
 		logger.Warningf("grpc: ignoring retry policy %v due to illegal configuration", jrp)
@@ -332,8 +273,8 @@ func convertRetryPolicy(jrp *jsonRetryPolicy) (p *internalserviceconfig.RetryPol
 
 	rp := &internalserviceconfig.RetryPolicy{
 		MaxAttempts:          jrp.MaxAttempts,
-		InitialBackoff:       *ib,
-		MaxBackoff:           *mb,
+		InitialBackoff:       time.Duration(jrp.InitialBackoff),
+		MaxBackoff:           time.Duration(jrp.MaxBackoff),
 		BackoffMultiplier:    jrp.BackoffMultiplier,
 		RetryableStatusCodes: make(map[codes.Code]bool),
 	}
diff --git a/vendor/google.golang.org/grpc/status/status.go b/vendor/google.golang.org/grpc/status/status.go
index 53910fb7..bcf2e4d8 100644
--- a/vendor/google.golang.org/grpc/status/status.go
+++ b/vendor/google.golang.org/grpc/status/status.go
@@ -77,11 +77,18 @@ func FromProto(s *spb.Status) *Status {
 // FromError returns a Status representation of err.
 //
 //   - If err was produced by this package or implements the method `GRPCStatus()
-//     *Status`, or if err wraps a type satisfying this, the appropriate Status is
-//     returned.  For wrapped errors, the message returned contains the entire
-//     err.Error() text and not just the wrapped status.
+//     *Status` and `GRPCStatus()` does not return nil, or if err wraps a type
+//     satisfying this, the Status from `GRPCStatus()` is returned.  For wrapped
+//     errors, the message returned contains the entire err.Error() text and not
+//     just the wrapped status. In that case, ok is true.
 //
-//   - If err is nil, a Status is returned with codes.OK and no message.
+//   - If err is nil, a Status is returned with codes.OK and no message, and ok
+//     is true.
+//
+//   - If err implements the method `GRPCStatus() *Status` and `GRPCStatus()`
+//     returns nil (which maps to Codes.OK), or if err wraps a type
+//     satisfying this, a Status is returned with codes.Unknown and err's
+//     Error() message, and ok is false.
 //
 //   - Otherwise, err is an error not compatible with this package.  In this
 //     case, a Status is returned with codes.Unknown and err's Error() message,
@@ -92,10 +99,24 @@ func FromError(err error) (s *Status, ok bool) {
 	}
 	type grpcstatus interface{ GRPCStatus() *Status }
 	if gs, ok := err.(grpcstatus); ok {
+		if gs.GRPCStatus() == nil {
+			// Error has status nil, which maps to codes.OK. There
+			// is no sensible behavior for this, so we turn it into
+			// an error with codes.Unknown and discard the existing
+			// status.
+			return New(codes.Unknown, err.Error()), false
+		}
 		return gs.GRPCStatus(), true
 	}
 	var gs grpcstatus
 	if errors.As(err, &gs) {
+		if gs.GRPCStatus() == nil {
+			// Error wraps an error that has status nil, which maps
+			// to codes.OK.  There is no sensible behavior for this,
+			// so we turn it into an error with codes.Unknown and
+			// discard the existing status.
+			return New(codes.Unknown, err.Error()), false
+		}
 		p := gs.GRPCStatus().Proto()
 		p.Message = err.Error()
 		return status.FromProto(p), true
diff --git a/vendor/google.golang.org/grpc/stream.go b/vendor/google.golang.org/grpc/stream.go
index d1226a41..10092685 100644
--- a/vendor/google.golang.org/grpc/stream.go
+++ b/vendor/google.golang.org/grpc/stream.go
@@ -123,6 +123,9 @@ type ClientStream interface {
 	// calling RecvMsg on the same stream at the same time, but it is not safe
 	// to call SendMsg on the same stream in different goroutines. It is also
 	// not safe to call CloseSend concurrently with SendMsg.
+	//
+	// It is not safe to modify the message after calling SendMsg. Tracing
+	// libraries and stats handlers may use the message lazily.
 	SendMsg(m interface{}) error
 	// RecvMsg blocks until it receives a message into m or the stream is
 	// done. It returns io.EOF when the stream completes successfully. On
@@ -152,6 +155,11 @@ type ClientStream interface {
 // If none of the above happen, a goroutine and a context will be leaked, and grpc
 // will not call the optionally-configured stats handler with a stats.End message.
 func (cc *ClientConn) NewStream(ctx context.Context, desc *StreamDesc, method string, opts ...CallOption) (ClientStream, error) {
+	if err := cc.idlenessMgr.onCallBegin(); err != nil {
+		return nil, err
+	}
+	defer cc.idlenessMgr.onCallEnd()
+
 	// allow interceptor to see all applicable call options, which means those
 	// configured as defaults from dial option as well as per-call options
 	opts = combine(cc.dopts.callOptions, opts)
@@ -469,7 +477,7 @@ func (a *csAttempt) newStream() error {
 	// It is safe to overwrite the csAttempt's context here, since all state
 	// maintained in it are local to the attempt. When the attempt has to be
 	// retried, a new instance of csAttempt will be created.
-	if a.pickResult.Metatada != nil {
+	if a.pickResult.Metadata != nil {
 		// We currently do not have a function it the metadata package which
 		// merges given metadata with existing metadata in a context. Existing
 		// function `AppendToOutgoingContext()` takes a variadic argument of key
@@ -479,7 +487,7 @@ func (a *csAttempt) newStream() error {
 		// in a form passable to AppendToOutgoingContext(), or create a version
 		// of AppendToOutgoingContext() that accepts a metadata.MD.
 		md, _ := metadata.FromOutgoingContext(a.ctx)
-		md = metadata.Join(md, a.pickResult.Metatada)
+		md = metadata.Join(md, a.pickResult.Metadata)
 		a.ctx = metadata.NewOutgoingContext(a.ctx, md)
 	}
 
@@ -1265,14 +1273,19 @@ func newNonRetryClientStream(ctx context.Context, desc *StreamDesc, method strin
 	as.p = &parser{r: s}
 	ac.incrCallsStarted()
 	if desc != unaryStreamDesc {
-		// Listen on cc and stream contexts to cleanup when the user closes the
-		// ClientConn or cancels the stream context.  In all other cases, an error
-		// should already be injected into the recv buffer by the transport, which
-		// the client will eventually receive, and then we will cancel the stream's
-		// context in clientStream.finish.
+		// Listen on stream context to cleanup when the stream context is
+		// canceled.  Also listen for the addrConn's context in case the
+		// addrConn is closed or reconnects to a different address.  In all
+		// other cases, an error should already be injected into the recv
+		// buffer by the transport, which the client will eventually receive,
+		// and then we will cancel the stream's context in
+		// addrConnStream.finish.
 		go func() {
+			ac.mu.Lock()
+			acCtx := ac.ctx
+			ac.mu.Unlock()
 			select {
-			case <-ac.ctx.Done():
+			case <-acCtx.Done():
 				as.finish(status.Error(codes.Canceled, "grpc: the SubConn is closing"))
 			case <-ctx.Done():
 				as.finish(toRPCErr(ctx.Err()))
diff --git a/vendor/google.golang.org/grpc/version.go b/vendor/google.golang.org/grpc/version.go
index 853ce0e3..3cc75406 100644
--- a/vendor/google.golang.org/grpc/version.go
+++ b/vendor/google.golang.org/grpc/version.go
@@ -19,4 +19,4 @@
 package grpc
 
 // Version is the current grpc version.
-const Version = "1.55.0"
+const Version = "1.56.3"
diff --git a/vendor/modules.txt b/vendor/modules.txt
index bbc95ddd..e2a16f92 100644
--- a/vendor/modules.txt
+++ b/vendor/modules.txt
@@ -198,7 +198,7 @@ gonum.org/v1/gonum/mat
 # google.golang.org/genproto v0.0.0-20230410155749-daa745c078e1
 ## explicit; go 1.19
 google.golang.org/genproto/googleapis/rpc/status
-# google.golang.org/grpc v1.55.0
+# google.golang.org/grpc v1.56.3
 ## explicit; go 1.17
 google.golang.org/grpc
 google.golang.org/grpc/attributes