grpc-js: Propagate connectivity error information to request errors

Author: murgatroid99

packages/grpc-js/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@grpc/grpc-js",
-  "version": "1.9.5",
+  "version": "1.9.6",
   "description": "gRPC Library for Node - pure JS implementation",
   "homepage": "https://grpc.io/",
   "repository": "https://github.com/grpc/grpc-node/tree/master/packages/grpc-js",

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

@@ -153,9 +153,11 @@ export class PickFirstLoadBalancer implements LoadBalancer {
   private subchannelStateListener: ConnectivityStateListener = (
     subchannel,
     previousState,
-    newState
+    newState,
+    keepaliveTime,
+    errorMessage
   ) => {
-    this.onSubchannelStateUpdate(subchannel, previousState, newState);
+    this.onSubchannelStateUpdate(subchannel, previousState, newState, errorMessage);
   };
   /**
    * Timer reference for the timer tracking when to start
@@ -172,6 +174,12 @@ export class PickFirstLoadBalancer implements LoadBalancer {
    */
   private stickyTransientFailureMode = false;
 
+  /**
+   * The most recent error reported by any subchannel as it transitioned to
+   * TRANSIENT_FAILURE.
+   */
+  private lastError: string | null = null;
+
   /**
    * Load balancer that attempts to connect to each backend in the address list
    * in order, and picks the first one that connects, using it for every
@@ -200,7 +208,7 @@ export class PickFirstLoadBalancer implements LoadBalancer {
       if (this.stickyTransientFailureMode) {
         this.updateState(
           ConnectivityState.TRANSIENT_FAILURE,
-          new UnavailablePicker()
+          new UnavailablePicker({details: `No connection established. Last error: ${this.lastError}`})
         );
       } else {
         this.updateState(ConnectivityState.CONNECTING, new QueuePicker(this));
@@ -241,7 +249,8 @@ export class PickFirstLoadBalancer implements LoadBalancer {
   private onSubchannelStateUpdate(
     subchannel: SubchannelInterface,
     previousState: ConnectivityState,
-    newState: ConnectivityState
+    newState: ConnectivityState,
+    errorMessage?: string
   ) {
     if (this.currentPick?.realSubchannelEquals(subchannel)) {
       if (newState !== ConnectivityState.READY) {
@@ -258,6 +267,9 @@ export class PickFirstLoadBalancer implements LoadBalancer {
         }
         if (newState === ConnectivityState.TRANSIENT_FAILURE) {
           child.hasReportedTransientFailure = true;
+          if (errorMessage) {
+            this.lastError = errorMessage;
+          }
           this.maybeEnterStickyTransientFailureMode();
           if (index === this.currentSubchannelIndex) {
             this.startNextSubchannelConnecting(index + 1);

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

@@ -105,18 +105,24 @@ export class RoundRobinLoadBalancer implements LoadBalancer {
 
   private currentReadyPicker: RoundRobinPicker | null = null;
 
+  private lastError: string | null = null;
+
   constructor(private readonly channelControlHelper: ChannelControlHelper) {
     this.subchannelStateListener = (
       subchannel: SubchannelInterface,
       previousState: ConnectivityState,
-      newState: ConnectivityState
+      newState: ConnectivityState,
+      keepaliveTime: number,
+      errorMessage?: string
     ) => {
       this.calculateAndUpdateState();
-
       if (
         newState === ConnectivityState.TRANSIENT_FAILURE ||
         newState === ConnectivityState.IDLE
       ) {
+        if (errorMessage) {
+          this.lastError = errorMessage;
+        }
         this.channelControlHelper.requestReresolution();
         subchannel.startConnecting();
       }
@@ -157,7 +163,7 @@ export class RoundRobinLoadBalancer implements LoadBalancer {
     ) {
       this.updateState(
         ConnectivityState.TRANSIENT_FAILURE,
-        new UnavailablePicker()
+        new UnavailablePicker({details: `No connection established. Last error: ${this.lastError}`})
       );
     } else {
       this.updateState(ConnectivityState.IDLE, new QueuePicker(this));

packages/grpc-js/src/picker.ts

@@ -97,16 +97,13 @@ export interface Picker {
  */
 export class UnavailablePicker implements Picker {
   private status: StatusObject;
-  constructor(status?: StatusObject) {
-    if (status !== undefined) {
-      this.status = status;
-    } else {
-      this.status = {
-        code: Status.UNAVAILABLE,
-        details: 'No connection established',
-        metadata: new Metadata(),
-      };
-    }
+  constructor(status?: Partial<StatusObject>) {
+    this.status = {
+      code: Status.UNAVAILABLE,
+      details: 'No connection established',
+      metadata: new Metadata(),
+      ...status,
+    };
   }
   pick(pickArgs: PickArgs): TransientFailurePickResult {
     return {

packages/grpc-js/src/subchannel-interface.ts

@@ -23,7 +23,8 @@ export type ConnectivityStateListener = (
   subchannel: SubchannelInterface,
   previousState: ConnectivityState,
   newState: ConnectivityState,
-  keepaliveTime: number
+  keepaliveTime: number,
+  errorMessage?: string
 ) => void;
 
 /**

packages/grpc-js/src/subchannel.ts

@@ -250,7 +250,8 @@ export class Subchannel {
         error => {
           this.transitionToState(
             [ConnectivityState.CONNECTING],
-            ConnectivityState.TRANSIENT_FAILURE
+            ConnectivityState.TRANSIENT_FAILURE,
+            `${error}`
           );
         }
       );
@@ -265,7 +266,8 @@ export class Subchannel {
    */
   private transitionToState(
     oldStates: ConnectivityState[],
-    newState: ConnectivityState
+    newState: ConnectivityState,
+    errorMessage?: string
   ): boolean {
     if (oldStates.indexOf(this.connectivityState) === -1) {
       return false;
@@ -318,7 +320,7 @@ export class Subchannel {
         throw new Error(`Invalid state: unknown ConnectivityState ${newState}`);
     }
     for (const listener of this.stateListeners) {
-      listener(this, previousState, newState, this.keepaliveTime);
+      listener(this, previousState, newState, this.keepaliveTime, errorMessage);
     }
     return true;
   }

packages/grpc-js/src/transport.ts

@@ -741,6 +741,7 @@ export class Http2SubchannelConnector implements SubchannelConnector {
         connectionOptions
       );
       this.session = session;
+      let errorMessage = 'Failed to connect';
       session.unref();
       session.once('connect', () => {
         session.removeAllListeners();
@@ -749,10 +750,14 @@ export class Http2SubchannelConnector implements SubchannelConnector {
       });
       session.once('close', () => {
         this.session = null;
-        reject();
+        // Leave time for error event to happen before rejecting
+        setImmediate(() => {
+          reject(`${errorMessage} (${new Date().toISOString()})`);
+        });
       });
       session.once('error', error => {
-        this.trace('connection failed with error ' + (error as Error).message);
+        errorMessage = (error as Error).message;
+        this.trace('connection failed with error ' + errorMessage);
       });
     });
   }