http2: avoid extended CONNECT hang when connection breaks during startup

Fixes golang/go#70658

Change-Id: Iaac5c7730a10afc8a8bb2e725746fa7387970582
Reviewed-on: https://go-review.googlesource.com/c/net/+/633277
Auto-Submit: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Antonio Ojea <aojea@google.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

http2/transport.go

@@ -2210,6 +2210,13 @@ func (rl *clientConnReadLoop) cleanup() {
 	}
 	cc.cond.Broadcast()
 	cc.mu.Unlock()
+
+	if !cc.seenSettings {
+		// If we have a pending request that wants extended CONNECT,
+		// let it continue and fail with the connection error.
+		cc.extendedConnectAllowed = true
+		close(cc.seenSettingsChan)
+	}
 }
 
 // countReadFrameError calls Transport.CountError with a string
@@ -2302,9 +2309,6 @@ func (rl *clientConnReadLoop) run() error {
 			if VerboseLogs {
 				cc.vlogf("http2: Transport conn %p received error from processing frame %v: %v", cc, summarizeFrame(f), err)
 			}
-			if !cc.seenSettings {
-				close(cc.seenSettingsChan)
-			}
 			return err
 		}
 	}

http2/transport_test.go

@@ -5914,3 +5914,24 @@ func TestExtendedConnectClientWithoutServerSupport(t *testing.T) {
 		t.Fatalf("expected error errExtendedConnectNotSupported, got: %v", err)
 	}
 }
+
+// Issue #70658: Make sure extended CONNECT requests don't get stuck if a
+// connection fails early in its lifetime.
+func TestExtendedConnectReadFrameError(t *testing.T) {
+	tc := newTestClientConn(t)
+	tc.wantFrameType(FrameSettings)
+	tc.wantFrameType(FrameWindowUpdate)
+
+	req, _ := http.NewRequest("CONNECT", "https://dummy.tld/", nil)
+	req.Header.Set(":protocol", "extended-connect")
+	rt := tc.roundTrip(req)
+	tc.wantIdle() // waiting for SETTINGS response
+
+	tc.closeWrite() // connection breaks without sending SETTINGS
+	if !rt.done() {
+		t.Fatalf("after connection closed: RoundTrip still running; want done")
+	}
+	if rt.err() == nil {
+		t.Fatalf("after connection closed: RoundTrip succeeded; want error")
+	}
+}