server: allow 0s grpc-timeout header values, as java is known to be able to send them (#8439) (#8440)

Author: dfawley

internal/transport/http2_server.go

@@ -600,10 +600,24 @@ func (t *http2Server) operateHeaders(ctx context.Context, frame *http2.MetaHeade
 return nil
 }
 }
+
+if s.ctx.Err() != nil {
+// Early abort in case the timeout was zero or so low it already fired.
+t.controlBuf.put(&earlyAbortStream{
+httpStatus: http.StatusOK,
+streamID: s.id,
+contentSubtype: s.contentSubtype,
+status: status.New(codes.DeadlineExceeded, context.DeadlineExceeded.Error()),
+rst: !frame.StreamEnded(),
+})
+return nil
+}
+
 t.activeStreams[streamID] = s
 if len(t.activeStreams) == 1 {
 t.idle = time.Time{}
 }
+
 // Start a timer to close the stream on reaching the deadline.
 if timeoutSet {
 // We need to wait for s.cancel to be updated before calling

internal/transport/http_util.go

@@ -200,9 +200,6 @@ func decodeTimeout(s string) (time.Duration, error) {
 if err != nil {
 return 0, err
 }
-if t == 0 {
-return 0, fmt.Errorf("transport: timeout must be positive: %q", s)
-}
 const maxHours = math.MaxInt64 / uint64(time.Hour)
 if d == time.Hour && t > maxHours {
 // This timeout would overflow math.MaxInt64; clamp it.

internal/transport/http_util_test.go

@@ -56,9 +56,9 @@ func (s) TestDecodeTimeout(t *testing.T) {
 {"1", 0, true},
 {"", 0, true},
 {"9a1S", 0, true},
-{"0S", 0, true}, // PROTOCOL-HTTP2.md requires positive integers
-{"00000000S", 0, true},
-{"000000000S", 0, true},
+{"0S", 0, false}, // PROTOCOL-HTTP2.md requires positive integers, but we allow it to timeout instead
+{"00000000S", 0, false},
+{"000000000S", 0, true}, // PROTOCOL-HTTP2.md allows at most 8 digits
 } {
 d, err := decodeTimeout(test.s)
 gotErr := err != nil