transport: Prevent sending negative timeouts

internal/transport/http2_client.go

@@ -592,6 +592,9 @@ func (t *http2Client) createHeaderFields(ctx context.Context, callHdr *CallHdr)
 		// Send out timeout regardless its value. The server can detect timeout context by itself.
 		// TODO(mmukhi): Perhaps this field should be updated when actually writing out to the wire.
 		timeout := time.Until(dl)
+		if timeout <= 0 {
+			return nil, status.Error(codes.DeadlineExceeded, context.DeadlineExceeded.Error())
+		}
 		headerFields = append(headerFields, hpack.HeaderField{Name: "grpc-timeout", Value: grpcutil.EncodeDuration(timeout)})
 	}
 	for k, v := range authData {

test/end2end_test.go

@@ -5351,6 +5351,31 @@ func testRPCTimeout(t *testing.T, e env) {
 	}
 }
 
+// Tests that the client doesn't send a negative timeout to the server. If the
+// server receives a negative timeout, it would return an internal status. The
+// client checks the context error before starting a stream, however the context
+// may expire after this check and before the timeout is calculated.
+func (s) TestNegativeRPCTimeout(t *testing.T) {
+	server := stubserver.StartTestService(t, nil)
+	defer server.Stop()
+
+	if err := server.StartClient(); err != nil {
+		t.Fatalf("Failed to create client: %v", err)
+	}
+
+	// Try increasingly larger timeout values to trigger the condition when the
+	// context has expired while creating the grpc-timeout header.
+	for i := range 10 {
+		ctx, cancel := context.WithTimeout(context.Background(), time.Duration(i*100)*time.Nanosecond)
+		defer cancel()
+
+		client := server.Client
+		if _, err := client.EmptyCall(ctx, &testpb.Empty{}); status.Code(err) != codes.DeadlineExceeded {
+			t.Fatalf("TestService/EmptyCall(_, _) = _, %v; want <nil>, error code: %s", err, codes.DeadlineExceeded)
+		}
+	}
+}
+
 func (s) TestDisabledIOBuffers(t *testing.T) {
 	payload, err := newPayload(testpb.PayloadType_COMPRESSABLE, int32(60000))
 	if err != nil {