http2: unconditionally recycle responseWriterState

CL 46008 fixed golang/go#20704 by not recycling the responseWriterState
if any previous Write call failed, as there could be outstanding
goroutines referencing the responseWriterState memory.

More recently, CL 467355 fixed a variant of the same issue by not
referencing that memory after exiting the Write call. This fix
supersedes the fix in CL 46008, as it is more general and does not
require the caller to know whether any previous Write calls failed.

This CL partially reverts CL 46008 just leaving the test case to ensure
that golang/go#20704 does not regress.

Change-Id: I18ea4d27420265a94cc7af21f1dffa3f7dc3bd34
Reviewed-on: https://go-review.googlesource.com/c/net/+/534315
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Damien Neil <dneil@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Run-TryBot: Quim Muntal <quimmuntal@gmail.com>
Commit-Queue: Damien Neil <dneil@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

http2/server.go

@@ -2549,7 +2549,6 @@ type responseWriterState struct {
 	wroteHeader   bool        // WriteHeader called (explicitly or implicitly). Not necessarily sent to user yet.
 	sentHeader    bool        // have we sent the header frame?
 	handlerDone   bool        // handler has finished
-	dirty         bool        // a Write failed; don't reuse this responseWriterState
 
 	sentContentLen int64 // non-zero if handler set a Content-Length header
 	wroteBytes     int64
@@ -2669,7 +2668,6 @@ func (rws *responseWriterState) writeChunk(p []byte) (n int, err error) {
 			date:          date,
 		})
 		if err != nil {
-			rws.dirty = true
 			return 0, err
 		}
 		if endStream {
@@ -2690,7 +2688,6 @@ func (rws *responseWriterState) writeChunk(p []byte) (n int, err error) {
 	if len(p) > 0 || endStream {
 		// only send a 0 byte DATA frame if we're ending the stream.
 		if err := rws.conn.writeDataFromHandler(rws.stream, p, endStream); err != nil {
-			rws.dirty = true
 			return 0, err
 		}
 	}
@@ -2702,9 +2699,6 @@ func (rws *responseWriterState) writeChunk(p []byte) (n int, err error) {
 			trailers:  rws.trailers,
 			endStream: true,
 		})
-		if err != nil {
-			rws.dirty = true
-		}
 		return len(p), err
 	}
 	return len(p), nil
@@ -2920,14 +2914,12 @@ func (rws *responseWriterState) writeHeader(code int) {
 			h.Del("Transfer-Encoding")
 		}
 
-		if rws.conn.writeHeaders(rws.stream, &writeResHeaders{
+		rws.conn.writeHeaders(rws.stream, &writeResHeaders{
 			streamID:    rws.stream.id,
 			httpResCode: code,
 			h:           h,
 			endStream:   rws.handlerDone && !rws.hasTrailers(),
-		}) != nil {
-			rws.dirty = true
-		}
+		})
 
 		return
 	}
@@ -2992,19 +2984,10 @@ func (w *responseWriter) write(lenData int, dataB []byte, dataS string) (n int,
 
 func (w *responseWriter) handlerDone() {
 	rws := w.rws
-	dirty := rws.dirty
 	rws.handlerDone = true
 	w.Flush()
 	w.rws = nil
-	if !dirty {
-		// Only recycle the pool if all prior Write calls to
-		// the serverConn goroutine completed successfully. If
-		// they returned earlier due to resets from the peer
-		// there might still be write goroutines outstanding
-		// from the serverConn referencing the rws memory. See
-		// issue 20704.
-		responseWriterStatePool.Put(rws)
-	}
+	responseWriterStatePool.Put(rws)
 }
 
 // Push errors.