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