Merge pull request #7 from dogmatiq/context

Add functions for working with context deadlines.

context.go

@@ -0,0 +1,50 @@
+package linger
+
+import (
+	"context"
+	"time"
+)
+
+// FromContextDeadline returns the duration until the deadline of ctx is
+// reached.
+//
+// ok is false if ctx does not have a deadline.
+func FromContextDeadline(ctx context.Context) (d time.Duration, ok bool) {
+	if dl, ok := ctx.Deadline(); ok {
+		return time.Until(dl), true
+	}
+
+	return 0, false
+}
+
+// ContextWithTimeout returns a context with a deadline some duration after the
+// current time.
+//
+// The timeout duration is computed by finding the first of the supplied
+// durations that is positive. It uses a zero duration if none of the supplied
+// durations are positive.
+func ContextWithTimeout(
+	ctx context.Context,
+	durations ...time.Duration,
+) (context.Context, func()) {
+	return ContextWithTimeoutX(ctx, Identity, durations...)
+}
+
+// ContextWithTimeoutX returns a context with a deadline some duration after the
+// current time.
+//
+// The timeout duration is computed by finding the first of the supplied
+// durations that is positive, then applying the transform x. It uses a zero
+// duration if none of the supplied durations are positive.
+//
+// The transform can be used to apply jitter to the timeout duration, for
+// example, by using one of the built-in jitter transforms such as FullJitter()
+// or ProportionalJitter().
+func ContextWithTimeoutX(
+	ctx context.Context,
+	x DurationTransform,
+	durations ...time.Duration,
+) (context.Context, func()) {
+	d, _ := Coalesce(durations...)
+	return context.WithTimeout(ctx, x(d))
+}

context_test.go

@@ -0,0 +1,62 @@
+package linger_test
+
+import (
+	"context"
+	"time"
+
+	. "github.com/dogmatiq/linger"
+	. "github.com/onsi/ginkgo"
+	. "github.com/onsi/gomega"
+)
+
+var _ = Describe("func FromContextDeadline()", func() {
+	It("returns the time until the deadline of the context", func() {
+		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+		defer cancel()
+
+		d, ok := FromContextDeadline(ctx)
+		Expect(ok).To(BeTrue())
+		Expect(d).To(BeNumerically("~", 10*time.Second, 1*time.Second))
+	})
+
+	It("returns false if the context does not have a deadline", func() {
+		_, ok := FromContextDeadline(context.Background())
+		Expect(ok).To(BeFalse())
+	})
+})
+
+var _ = Describe("func ContextWithTimeout()", func() {
+	It("sets a timeout for the first positive duration", func() {
+		expect := time.Now().Add(10 * time.Second)
+		ctx, cancel := ContextWithTimeout(context.Background(), 0*time.Second, -1*time.Second, 10*time.Second)
+		defer cancel()
+
+		dl, ok := ctx.Deadline()
+		Expect(ok).To(BeTrue())
+		Expect(dl).To(BeTemporally("~", expect))
+	})
+
+	It("times out 'immediately' if none of the durations are positive", func() {
+		ctx, cancel := ContextWithTimeout(context.Background(), 0*time.Second, -1*time.Second)
+		defer cancel()
+
+		err := ctx.Err()
+		Expect(err).To(Equal(context.DeadlineExceeded))
+	})
+})
+
+var _ = Describe("func ContextWithTimeoutX()", func() {
+	It("applies the transform", func() {
+		x := func(t time.Duration) time.Duration {
+			return t / 2
+		}
+
+		expect := time.Now().Add(10 * time.Second)
+		ctx, cancel := ContextWithTimeoutX(context.Background(), x, 20*time.Second)
+		defer cancel()
+
+		dl, ok := ctx.Deadline()
+		Expect(ok).To(BeTrue())
+		Expect(dl).To(BeTemporally("~", expect))
+	})
+})