Hi:

1. What version of Go are you using (go version)?

   go version go1.6.2 darwin/amd64

2. What operating system and processor architecture are you using (go env)?

   GOARCH="amd64"
   GOOS="darwin"

3. What did you do?

   1. serving proxy requests by httputil.ReverseProxy
   2. about 10% of request are canceled by clients

4. What did you expect to see?

   no requests should occur any unexpected error.

5. What did you see instead?

   some normal(non-canceled) requests are affected by their former requests which are canceled by clients.

Finally I find this:

There is a goroutine here(in ServeHTTP): goroutine

this goroutine is used for receiving clientGone or reqDone signal, however, we assume this scene:

1. ServeHTTP start handling Request A(using underlying net.Conn C)
2. Request A was canceled by its client (sending sig to clientGone)
3. RoundTrip return error(may be use of closed network connection in go1.6- or other error in go1.6+)
4. ServeHTTP start to return and defer close(reqDone) is executed(close is non-block, so ServeHTTP may be return before the goroutine A receive close signal, but goroutine A is still alive)
5. net/http put net.Conn C to IdleConn
6. Request B arrived and net/http pick the same underlying net.Conn C
7. ServeHTTP start handling Request B (using the same underlying net.Conn C)
8. goroutine A got signal clientGone first, and then do CancelRequest which will close net.Conn C
9. Request B's RoundTrip return error cause its underlying conn is closed