net/http/httputil: make Switching Protocol requests (e.g. Websockets) cancelable

Ensures that a canceled client request for Switching Protocols
(e.g. h2c, Websockets) will cause the underlying connection to
be terminated.

Adds a goroutine in handleUpgradeResponse in order to select on
the incoming client request's context and appropriately cancel it.

Fixes #35559

Change-Id: I1238e18fd4cce457f034f78d9cdce0e7f93b8bf6
GitHub-Last-Rev: 3629c78493f667703ea99f9f4db5e63ddaaa0e6b
GitHub-Pull-Request: golang/go#38021
Reviewed-on: https://go-review.googlesource.com/c/go/+/224897
Run-TryBot: Emmanuel Odeke <emm.odeke@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/src/net/http/httputil/reverseproxy.go b/src/net/http/httputil/reverseproxy.go
index 4d6a085f60..eb17bef979 100644
--- a/src/net/http/httputil/reverseproxy.go
+++ b/src/net/http/httputil/reverseproxy.go
@@ -526,7 +526,20 @@ func (p *ReverseProxy) handleUpgradeResponse(rw http.ResponseWriter, req *http.R
 		p.getErrorHandler()(rw, req, fmt.Errorf("internal error: 101 switching protocols response with non-writable body"))
 		return
 	}
-	defer backConn.Close()
+
+	backConnCloseCh := make(chan bool)
+	go func() {
+		// Ensure that the cancelation of a request closes the backend.
+		// See issue https://golang.org/issue/35559.
+		select {
+		case <-req.Context().Done():
+		case <-backConnCloseCh:
+		}
+		backConn.Close()
+	}()
+
+	defer close(backConnCloseCh)
+
 	conn, brw, err := hj.Hijack()
 	if err != nil {
 		p.getErrorHandler()(rw, req, fmt.Errorf("Hijack failed on protocol switch: %v", err))