[Linear cache] rework watches and storage in the cache to make code m…

…ore common between delta and sotw (#11)

Following previous PRs on linear cache fixes in sotw, the implementation of linear cache has become more common between sotw and delta watches. This PR makes it clearer and reorganize the setup:
 - reorganize resource cache and watch tracking per resource, instead of per mode. This will enable changes like sotw using resource versions
 - avoid multiple marshaling of the resource when the version is already computed through marshaling (not in this PR, as potentially impactful on memory)
 - sotw and delta watches use a common model for their handling, with common code to compute subscription impact vs. cache. Only the generation of the response is different

Signed-off-by: Valerian Roche <[email protected]>

pkg/cache/v3/cache.go

@@ -56,12 +56,6 @@ type Subscription interface {
 	// This considers subtleties related to the current migration of wildcard definitions within the protocol.
 	// More details on the behavior of wildcard are present at https://www.envoyproxy.io/docs/envoy/latest/api-docs/xds_protocol#how-the-client-specifies-what-resources-to-return
 	IsWildcard() bool
-
-	// WatchesResources returns whether at least one of the resources provided is currently being watched by the subscription.
-	// It is currently only applicable to delta-xds.
-	// If the request is wildcard, it will always return true,
-	// otherwise it will compare the provided resources to the list of resources currently subscribed
-	WatchesResources(resourceNames map[string]struct{}) bool
 }
 
 // ConfigWatcher requests watches for configuration resources by a node, last

pkg/cache/v3/delta.go

@@ -22,12 +22,11 @@ import (
 
 // groups together resource-related arguments for the createDeltaResponse function
 type resourceContainer struct {
-	resourceMap   map[string]types.Resource
-	versionMap    map[string]string
-	systemVersion string
+	resourceMap map[string]types.Resource
+	versionMap  map[string]string
 }
 
-func createDeltaResponse(ctx context.Context, req *DeltaRequest, sub Subscription, resources resourceContainer) *RawDeltaResponse {
+func createDeltaResponse(ctx context.Context, req *DeltaRequest, sub Subscription, resources resourceContainer, cacheVersion string) *RawDeltaResponse {
 	// variables to build our response with
 	var nextVersionMap map[string]string
 	var filtered []types.Resource
@@ -81,7 +80,7 @@ func createDeltaResponse(ctx context.Context, req *DeltaRequest, sub Subscriptio
 		Resources:         filtered,
 		RemovedResources:  toRemove,
 		NextVersionMap:    nextVersionMap,
-		SystemVersionInfo: resources.systemVersion,
+		SystemVersionInfo: cacheVersion,
 		Ctx:               ctx,
 	}
 }