net/http/internal/http2: make server write errors sticky

After encountering a write error on a server's connection,
remember the error and reuse it for future writes.
Fixes a rare flakiness in TestServerWriteByteTimeout,
where we can sometimes attempt to flush the write buffer
after encountering a write timeout.

Change-Id: I01649ae41185d6109180e222d4e8f8426a6a6964
Reviewed-on: https://go-review.googlesource.com/c/go/+/753720
Auto-Submit: Damien Neil <dneil@google.com>
Reviewed-by: Nicholas Husin <nsh@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Nicholas Husin <husin@google.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/src/net/http/internal/http2/http2.go b/src/net/http/internal/http2/http2.go
index ba93bb9479..edf34e1f77 100644
--- a/src/net/http/internal/http2/http2.go
+++ b/src/net/http/internal/http2/http2.go
@@ -258,6 +258,7 @@ type bufferedWriter struct {
 	conn        net.Conn      // immutable
 	bw          *bufio.Writer // non-nil when data is buffered
 	byteTimeout time.Duration // immutable, WriteByteTimeout
+	werr        error
 }
 
 func newBufferedWriter(conn net.Conn, timeout time.Duration) *bufferedWriter {
@@ -289,12 +290,16 @@ func (w *bufferedWriter) Available() int {
 }
 
 func (w *bufferedWriter) Write(p []byte) (n int, err error) {
+	if w.werr != nil {
+		return 0, w.werr
+	}
 	if w.bw == nil {
 		bw := bufWriterPool.Get().(*bufio.Writer)
 		bw.Reset((*bufferedWriterTimeoutWriter)(w))
 		w.bw = bw
 	}
-	return w.bw.Write(p)
+	n, w.werr = w.bw.Write(p)
+	return n, w.werr
 }
 
 func (w *bufferedWriter) Flush() error {
@@ -302,11 +307,14 @@ func (w *bufferedWriter) Flush() error {
 	if bw == nil {
 		return nil
 	}
-	err := bw.Flush()
+	if w.werr != nil {
+		return w.werr
+	}
+	w.werr = bw.Flush()
 	bw.Reset(nil)
 	bufWriterPool.Put(bw)
 	w.bw = nil
-	return err
+	return w.werr
 }
 
 type bufferedWriterTimeoutWriter bufferedWriter