From 29a6fd65adc049ffe4374a760fb601c67b5f9e97 Mon Sep 17 00:00:00 2001
From: Anthony Romano <anthony.romano@coreos.com>
Date: Fri, 17 Feb 2017 12:59:16 -0800
Subject: [PATCH] grpcproxy: only return ctx error in chan stream if recvc is
 empty

Since select{} won't prioritize, ctx.Done() can sometimes override
a pending message on recvc. Loop if recvc has messages instead.

Fixes #7340
---
 proxy/grpcproxy/chan_stream.go | 24 +++++++++++++++---------
 1 file changed, 15 insertions(+), 9 deletions(-)

diff --git a/proxy/grpcproxy/chan_stream.go b/proxy/grpcproxy/chan_stream.go
index 6a15b22ad6a..b1620bb05ec 100644
--- a/proxy/grpcproxy/chan_stream.go
+++ b/proxy/grpcproxy/chan_stream.go
@@ -116,17 +116,23 @@ func (s *chanStream) SendMsg(m interface{}) error {
 
 func (s *chanStream) RecvMsg(m interface{}) error {
 	v := m.(*interface{})
-	select {
-	case msg, ok := <-s.recvc:
-		if !ok {
-			return grpc.ErrClientConnClosing
+	for {
+		select {
+		case msg, ok := <-s.recvc:
+			if !ok {
+				return grpc.ErrClientConnClosing
+			}
+			if err, ok := msg.(error); ok {
+				return err
+			}
+			*v = msg
+			return nil
+		case <-s.ctx.Done():
 		}
-		if err, ok := msg.(error); ok {
-			return err
+		if len(s.recvc) == 0 {
+			// prioritize any pending recv messages over canceled context
+			break
 		}
-		*v = msg
-		return nil
-	case <-s.ctx.Done():
 	}
 	return s.ctx.Err()
 }