net/http: don't cancel Dials when requests are canceled

Currently, when a Transport creates a new connection for a request,
it uses the request's Context to make the Dial. If a request
times out or is canceled before a Dial completes, the Dial is
canceled.

Change this so that the lifetime of a Dial call is not bound
by the request that originated it.

This change avoids a scenario where a Transport can start and
then cancel many Dial calls in rapid succession:

  - Request starts a Dial.
  - A previous request completes, making its connection available.
  - The new request uses the now-idle connection, and completes.
  - The request Context is canceled, and the Dial is aborted.

Fixes #59017

Change-Id: I996ffabc56d3b1b43129cbfd9b3e9ea7d53d263c
Reviewed-on: https://go-review.googlesource.com/c/go/+/576555
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Cherry Mui <cherryyz@google.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/net/http/export_test.go b/src/net/http/export_test.go
index 8a6f4f192f..56ebda180b 100644
--- a/src/net/http/export_test.go
+++ b/src/net/http/export_test.go
@@ -86,6 +86,14 @@ func SetPendingDialHooks(before, after func()) {
 
 func SetTestHookServerServe(fn func(*Server, net.Listener)) { testHookServerServe = fn }
 
+func SetTestHookProxyConnectTimeout(t *testing.T, f func(context.Context, time.Duration) (context.Context, context.CancelFunc)) {
+	orig := testHookProxyConnectTimeout
+	t.Cleanup(func() {
+		testHookProxyConnectTimeout = orig
+	})
+	testHookProxyConnectTimeout = f
+}
+
 func NewTestTimeoutHandler(handler Handler, ctx context.Context) Handler {
 	return &timeoutHandler{
 		handler:     handler,