snapshot of https://github.com/grpc/grpc-go.git (master, 2026-09-15; blobs > 131072B omitted)

internal/xds/clients/xdsclient/clientimpl_watchers.go

@@ -0,0 +1,109 @@
+/*
+ *
+ * Copyright 2025 gRPC authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package xdsclient
+
+import (
+	"context"
+	"fmt"
+
+	"google.golang.org/grpc/internal/xds/clients/xdsclient/internal/xdsresource"
+)
+
+// wrappingWatcher is a wrapper around an xdsresource.ResourceWatcher that adds
+// the node ID to the error messages reported to the watcher.
+type wrappingWatcher struct {
+	ResourceWatcher
+	nodeID string
+}
+
+func (w *wrappingWatcher) AmbientError(err error, done func()) {
+	w.ResourceWatcher.AmbientError(fmt.Errorf("[xDS node id: %v]: %w", w.nodeID, err), done)
+}
+
+func (w *wrappingWatcher) ResourceError(err error, done func()) {
+	w.ResourceWatcher.ResourceError(fmt.Errorf("[xDS node id: %v]: %w", w.nodeID, err), done)
+}
+
+// WatchResource starts watching the specified resource.
+//
+// The watch fails to start if:
+//   - There is no ResourceType implementation for the given typeURL in the
+//     ResourceTypes field of the Config struct used to create the XDSClient.
+//   - The provided resourceName contains an authority that is not present in the
+//     Authorities field.
+//
+// The returned function cancels the watch and prevents future calls to the
+// watcher.
+func (c *XDSClient) WatchResource(typeURL, resourceName string, watcher ResourceWatcher) (cancel func()) {
+	// Return early if the client is already closed.
+	if c.done.HasFired() {
+		logger.Warningf("Watch registered for type %q, but client is closed", typeURL)
+		return func() {}
+	}
+
+	watcher = &wrappingWatcher{
+		ResourceWatcher: watcher,
+		nodeID:          c.config.Node.ID,
+	}
+
+	rType, ok := c.config.ResourceTypes[typeURL]
+	if !ok {
+		logger.Warningf("ResourceType implementation for resource type url %q is not found", rType.TypeURL)
+		c.serializer.TrySchedule(func(context.Context) {
+			watcher.ResourceError(fmt.Errorf("no ResourceType implementation found for typeURL %q", rType.TypeURL), func() {})
+		})
+		return func() {}
+	}
+
+	n := xdsresource.ParseName(resourceName)
+	a := c.getAuthorityForResource(n)
+	if a == nil {
+		logger.Warningf("Watch registered for name %q of type %q, authority %q is not found", rType.TypeName, resourceName, n.Authority)
+		c.serializer.TrySchedule(func(context.Context) {
+			watcher.ResourceError(fmt.Errorf("authority %q not found in the config for resource %q", n.Authority, resourceName), func() {})
+		})
+		return func() {}
+	}
+	// The watchResource method on the authority is invoked with n.String()
+	// instead of resourceName because n.String() canonicalizes the given name.
+	// So, two resource names which don't differ in the query string, but only
+	// differ in the order of context params will result in the same resource
+	// being watched by the authority.
+	return a.watchResource(rType, n.String(), watcher)
+}
+
+// Gets the authority for the given resource name.
+//
+// See examples in this section of the gRFC:
+// https://github.com/grpc/proposal/blob/master/A47-xds-federation.md#bootstrap-config-changes
+func (c *XDSClient) getAuthorityForResource(name *xdsresource.Name) *authority {
+	// For new-style resource names, always lookup the authorities map. If the
+	// name does not specify an authority, we will end up looking for an entry
+	// in the map with the empty string as the key.
+	if name.Scheme == xdsresource.FederationScheme {
+		return c.authorities[name.Authority]
+	}
+
+	// For old-style resource names, we use the top-level authority if the name
+	// does not specify an authority.
+	if name.Authority == "" {
+		return c.topLevelAuthority
+	}
+	return c.authorities[name.Authority]
+}