Add a helper for creating ChannelControlHelper children

Author: murgatroid99

packages/grpc-js-xds/src/load-balancer-eds.ts

@@ -185,14 +185,7 @@ export class EdsLoadBalancer implements LoadBalancer {
   private concurrentRequests: number = 0;
 
   constructor(private readonly channelControlHelper: ChannelControlHelper) {
-    this.childBalancer = new ChildLoadBalancerHandler({
-      createSubchannel: (subchannelAddress, subchannelArgs) =>
-        this.channelControlHelper.createSubchannel(
-          subchannelAddress,
-          subchannelArgs
-        ),
-      requestReresolution: () =>
-        this.channelControlHelper.requestReresolution(),
+    this.childBalancer = new ChildLoadBalancerHandler(experimental.createChildChannelControlHelper(this.channelControlHelper, {
       updateState: (connectivityState, originalPicker) => {
         if (this.latestEdsUpdate === null) {
           return;
@@ -243,7 +236,7 @@ export class EdsLoadBalancer implements LoadBalancer {
         };
         this.channelControlHelper.updateState(connectivityState, edsPicker);
       },
-    });
+    }));
     this.watcher = {
       onValidUpdate: (update) => {
         trace('Received EDS update for ' + this.edsServiceName + ': ' + JSON.stringify(update, undefined, 2));

packages/grpc-js-xds/src/load-balancer-lrs.ts

@@ -174,20 +174,14 @@ export class LrsLoadBalancer implements LoadBalancer {
   private localityStatsReporter: XdsClusterLocalityStats | null = null;
 
   constructor(private channelControlHelper: ChannelControlHelper) {
-    this.childBalancer = new ChildLoadBalancerHandler({
-      createSubchannel: (subchannelAddress, subchannelArgs) =>
-        channelControlHelper.createSubchannel(
-          subchannelAddress,
-          subchannelArgs
-        ),
-      requestReresolution: () => channelControlHelper.requestReresolution(),
+    this.childBalancer = new ChildLoadBalancerHandler(experimental.createChildChannelControlHelper(channelControlHelper, {
       updateState: (connectivityState: ConnectivityState, picker: Picker) => {
         if (this.localityStatsReporter !== null) {
           picker = new LoadReportingPicker(picker, this.localityStatsReporter);
         }
         channelControlHelper.updateState(connectivityState, picker);
       },
-    });
+    }));
   }
 
   updateAddressList(

packages/grpc-js-xds/src/load-balancer-priority.ts

@@ -139,23 +139,11 @@ export class PriorityLoadBalancer implements LoadBalancer {
     private failoverTimer: NodeJS.Timer | null = null;
     private deactivationTimer: NodeJS.Timer | null = null;
     constructor(private parent: PriorityLoadBalancer, private name: string) {
-      this.childBalancer = new ChildLoadBalancerHandler({
-        createSubchannel: (
-          subchannelAddress: SubchannelAddress,
-          subchannelArgs: ChannelOptions
-        ) => {
-          return this.parent.channelControlHelper.createSubchannel(
-            subchannelAddress,
-            subchannelArgs
-          );
-        },
+      this.childBalancer = new ChildLoadBalancerHandler(experimental.createChildChannelControlHelper(this.parent.channelControlHelper, {
         updateState: (connectivityState: ConnectivityState, picker: Picker) => {
           this.updateState(connectivityState, picker);
         },
-        requestReresolution: () => {
-          this.parent.channelControlHelper.requestReresolution();
-        },
-      });
+      }));
       this.picker = new QueuePicker(this.childBalancer);
     }
 

packages/grpc-js-xds/src/load-balancer-weighted-target.ts

@@ -168,17 +168,11 @@ export class WeightedTargetLoadBalancer implements LoadBalancer {
     private weight: number = 0;
 
     constructor(private parent: WeightedTargetLoadBalancer, private name: string) {
-      this.childBalancer = new ChildLoadBalancerHandler({
-        createSubchannel: (subchannelAddress, subchannelOptions) => {
-          return this.parent.channelControlHelper.createSubchannel(subchannelAddress, subchannelOptions);
-        },
-        updateState: (connectivityState, picker) => {
+      this.childBalancer = new ChildLoadBalancerHandler(experimental.createChildChannelControlHelper(this.parent.channelControlHelper, {
+        updateState: (connectivityState: ConnectivityState, picker: Picker) => {
           this.updateState(connectivityState, picker);
         },
-        requestReresolution: () => {
-          this.parent.channelControlHelper.requestReresolution();
-        }
-      });
+      }));
 
       this.picker = new QueuePicker(this.childBalancer);
     }

packages/grpc-js-xds/src/load-balancer-xds-cluster-manager.ts

@@ -131,17 +131,11 @@ class XdsClusterManager implements LoadBalancer {
     private childBalancer: ChildLoadBalancerHandler;
 
     constructor(private parent: XdsClusterManager, private name: string) {
-      this.childBalancer = new ChildLoadBalancerHandler({
-        createSubchannel: (subchannelAddress, subchannelOptions) => {
-          return this.parent.channelControlHelper.createSubchannel(subchannelAddress, subchannelOptions);
-        },
-        updateState: (connectivityState, picker) => {
+      this.childBalancer = new ChildLoadBalancerHandler(experimental.createChildChannelControlHelper(this.parent.channelControlHelper, {
+        updateState: (connectivityState: ConnectivityState, picker: Picker) => {
           this.updateState(connectivityState, picker);
         },
-        requestReresolution: () => {
-          this.parent.channelControlHelper.requestReresolution();
-        }
-      });
+      }));
 
       this.picker = new QueuePicker(this.childBalancer);
     }

packages/grpc-js/src/experimental.ts

@@ -12,6 +12,7 @@ export {
   LoadBalancer,
   LoadBalancingConfig,
   ChannelControlHelper,
+  createChildChannelControlHelper,
   registerLoadBalancerType,
   getFirstUsableConfig,
   validateLoadBalancingConfig,

packages/grpc-js/src/load-balancer.ts

@@ -52,6 +52,24 @@ export interface ChannelControlHelper {
   removeChannelzChild(child: ChannelRef | SubchannelRef): void;
 }
 
+/**
+ * Create a child ChannelControlHelper that overrides some methods of the
+ * parent while letting others pass through to the parent unmodified. This
+ * allows other code to create these children without needing to know about
+ * all of the methods to be passed through.
+ * @param parent 
+ * @param overrides 
+ */
+export function createChildChannelControlHelper(parent: ChannelControlHelper, overrides: Partial<ChannelControlHelper>): ChannelControlHelper {
+  return {
+    createSubchannel: overrides.createSubchannel?.bind(overrides) ?? parent.createSubchannel.bind(parent),
+    updateState: overrides.updateState?.bind(overrides) ?? parent.updateState.bind(parent),
+    requestReresolution: overrides.requestReresolution?.bind(overrides) ?? parent.requestReresolution.bind(parent),
+    addChannelzChild: overrides.addChannelzChild?.bind(overrides) ?? parent.addChannelzChild.bind(parent),
+    removeChannelzChild: overrides.removeChannelzChild?.bind(overrides) ?? parent.removeChannelzChild.bind(parent)
+  };
+}
+
 /**
  * Tracks one or more connected subchannels and determines which subchannel
  * each request should use.