http2: fix incorrect panic

Previously, we panic'd on sending WINDOW_UPDATE on the half-closed-local state. However, the RFC allows sending WINDOW_UPDATE in this state, so we should no panic. Change-Id: I702b2d5ad525837d7b8c650b7a2ed3f16371be63 Reviewed-on: https://go-review.googlesource.com/34498 Run-TryBot: Tom Bergan <tombergan@google.com> Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Author: tombergan

http2/server.go

@@ -936,9 +936,15 @@ func (sc *serverConn) startFrameWrite(wr FrameWriteRequest) {
 if st != nil {
 switch st.state {
 case stateHalfClosedLocal:
-panic("internal error: attempt to send frame on half-closed-local stream")
+switch wr.write.(type) {
+case StreamError, handlerPanicRST, writeWindowUpdate:
+// RFC 7540 Section 5.1 allows sending RST_STREAM, PRIORITY, and WINDOW_UPDATE
+// in this state. (We never send PRIORITY from the server, so that is not checked.)
+default:
+panic(fmt.Sprintf("internal error: attempt to send frame on a half-closed-local stream: %v", wr))
+}
 case stateClosed:
-panic(fmt.Sprintf("internal error: attempt to send a write %v on a closed stream", wr))
+panic(fmt.Sprintf("internal error: attempt to send frame a closed stream: %v", wr))
 }
 }
 if wpp, ok := wr.write.(*writePushPromise); ok {