http2: don't reuse connections that are experiencing errors

When a request on a connection fails to complete successfully, mark the conn as doNotReuse. It's possible for requests to fail for reasons unrelated to connection health, but opening a new connection unnecessarily is less of an impact than reusing a dead connection. Fixes golang/go#59690 Change-Id: I40bf6cefae602ead70c3bcf2fe573cc13f34a385 Reviewed-on: https://go-review.googlesource.com/c/net/+/486156 Run-TryBot: Damien Neil <dneil@google.com> TryBot-Result: Gopher Robot <gobot@golang.org> Reviewed-by: Bryan Mills <bcmills@google.com>

Author: neild

http2/transport.go

@@ -1266,6 +1266,27 @@ func (cc *ClientConn) RoundTrip(req *http.Request) (*http.Response, error) {
 return res, nil
 }
 
+cancelRequest := func(cs *clientStream, err error) error {
+cs.cc.mu.Lock()
+defer cs.cc.mu.Unlock()
+cs.abortStreamLocked(err)
+if cs.ID != 0 {
+// This request may have failed because of a problem with the connection,
+// or for some unrelated reason. (For example, the user might have canceled
+// the request without waiting for a response.) Mark the connection as
+// not reusable, since trying to reuse a dead connection is worse than
+// unnecessarily creating a new one.
+//
+// If cs.ID is 0, then the request was never allocated a stream ID and
+// whatever went wrong was unrelated to the connection. We might have
+// timed out waiting for a stream slot when StrictMaxConcurrentStreams
+// is set, for example, in which case retrying on a different connection
+// will not help.
+cs.cc.doNotReuse = true
+}
+return err
+}
+
 for {
 select {
 case <-cs.respHeaderRecv:
@@ -1280,15 +1301,12 @@ func (cc *ClientConn) RoundTrip(req *http.Request) (*http.Response, error) {
 return handleResponseHeaders()
 default:
 waitDone()
-return nil, cs.abortErr
+return nil, cancelRequest(cs, cs.abortErr)
 }
 case <-ctx.Done():
-err := ctx.Err()
-cs.abortStream(err)
-return nil, err
+return nil, cancelRequest(cs, ctx.Err())
 case <-cs.reqCancel:
-cs.abortStream(errRequestCanceled)
-return nil, errRequestCanceled
+return nil, cancelRequest(cs, errRequestCanceled)
 }
 }
 }