core: improve rpc protocol

- Ensure that pending requests are properly rejected when the underlying service channel is closed.
- Make  id-property from `NotificationMessage`s.  optional. Ids in notification are not strictly required and can be safely omitted.
- Rename `RpcConnectionFactory` to `RpcProtocolFactory` 
- Use a deferred in the `RpcProxyFactory` for protocol initialization

Part of #12581

packages/core/src/common/message-rpc/rpc-message-encoder.ts

@@ -51,7 +51,7 @@ export interface RequestMessage {
 
 export interface NotificationMessage {
     type: RpcMessageType.Notification;
-    id: number;
+    id?: number;
     method: string;
     args: any[];
 }
@@ -111,7 +111,7 @@ export interface RpcMessageDecoder {
 export interface RpcMessageEncoder {
     cancel(buf: WriteBuffer, requestId: number): void;
 
-    notification(buf: WriteBuffer, requestId: number, method: string, args: any[]): void
+    notification(buf: WriteBuffer, method: string, args: any[], id?: number): void
 
     request(buf: WriteBuffer, requestId: number, method: string, args: any[]): void
 
@@ -130,8 +130,8 @@ export class MsgPackMessageEncoder implements RpcMessageEncoder {
     cancel(buf: WriteBuffer, requestId: number): void {
         this.encode<CancelMessage>(buf, { type: RpcMessageType.Cancel, id: requestId });
     }
-    notification(buf: WriteBuffer, requestId: number, method: string, args: any[]): void {
-        this.encode<NotificationMessage>(buf, { type: RpcMessageType.Notification, id: requestId, method, args });
+    notification(buf: WriteBuffer, method: string, args: any[], id?: number): void {
+        this.encode<NotificationMessage>(buf, { type: RpcMessageType.Notification, method, args, id });
     }
     request(buf: WriteBuffer, requestId: number, method: string, args: any[]): void {
         this.encode<RequestMessage>(buf, { type: RpcMessageType.Request, id: requestId, method, args });

packages/core/src/common/message-rpc/rpc-protocol.ts

@@ -77,7 +77,11 @@ export class RpcProtocol {
         this.encoder = options.encoder ?? new MsgPackMessageEncoder();
         this.decoder = options.decoder ?? new MsgPackMessageDecoder();
         this.toDispose.push(this.onNotificationEmitter);
-        channel.onClose(() => this.toDispose.dispose());
+        channel.onClose(event => {
+            this.pendingRequests.forEach(pending => pending.reject(new Error(event.reason)));
+            this.pendingRequests.clear();
+            this.toDispose.dispose();
+        });
         this.toDispose.push(channel.onMessage(readBuffer => this.handleMessage(this.decoder.parse(readBuffer()))));
         this.mode = options.mode ?? 'default';
 
@@ -98,7 +102,7 @@ export class RpcProtocol {
                     return;
                 }
                 case RpcMessageType.Notification: {
-                    this.handleNotify(message.id, message.method, message.args);
+                    this.handleNotify(message.method, message.args, message.id);
                     return;
                 }
             }
@@ -179,7 +183,7 @@ export class RpcProtocol {
         }
 
         const output = this.channel.getWriteBuffer();
-        this.encoder.notification(output, this.nextMessageId++, method, args);
+        this.encoder.notification(output, method, args, this.nextMessageId++);
         output.commit();
     }
 
@@ -226,7 +230,7 @@ export class RpcProtocol {
         }
     }
 
-    protected async handleNotify(id: number, method: string, args: any[]): Promise<void> {
+    protected async handleNotify(method: string, args: any[], id?: number): Promise<void> {
         if (this.toDispose.disposed) {
             return;
         }

packages/core/src/common/messaging/proxy-factory.ts

@@ -23,6 +23,7 @@ import { Emitter, Event } from '../event';
 import { Channel } from '../message-rpc/channel';
 import { RequestHandler, RpcProtocol } from '../message-rpc/rpc-protocol';
 import { ConnectionHandler } from './handler';
+import { Deferred } from '../promise-util';
 
 export type JsonRpcServer<Client> = Disposable & {
     /**
@@ -55,11 +56,11 @@ export class JsonRpcConnectionHandler<T extends object> implements ConnectionHan
     }
 }
 /**
- * Factory for creating a new {@link RpcConnection} for a given chanel and {@link RequestHandler}.
+ * Factory for creating a new {@link RpcProtocol} for a given chanel and {@link RequestHandler}.
  */
-export type RpcConnectionFactory = (channel: Channel, requestHandler: RequestHandler) => RpcProtocol;
+export type RpcProtocolFactory = (channel: Channel, requestHandler: RequestHandler) => RpcProtocol;
 
-const defaultRPCConnectionFactory: RpcConnectionFactory = (channel, requestHandler) => new RpcProtocol(channel, requestHandler);
+const defaultRpcProtocolFactory: RpcProtocolFactory = (channel, requestHandler) => new RpcProtocol(channel, requestHandler);
 
 /**
  * Factory for JSON-RPC proxy objects.
@@ -109,25 +110,22 @@ export class JsonRpcProxyFactory<T extends object> implements ProxyHandler<T> {
     protected readonly onDidOpenConnectionEmitter = new Emitter<void>();
     protected readonly onDidCloseConnectionEmitter = new Emitter<void>();
 
-    protected connectionPromiseResolve: (connection: RpcProtocol) => void;
-    protected connectionPromise: Promise<RpcProtocol>;
+    protected rpcDeferred: Deferred<RpcProtocol>;
 
     /**
      * Build a new JsonRpcProxyFactory.
      *
      * @param target - The object to expose to JSON-RPC methods calls.  If this
      *   is omitted, the proxy won't be able to handle requests, only send them.
      */
-    constructor(public target?: any, protected rpcConnectionFactory = defaultRPCConnectionFactory) {
+    constructor(public target?: any, protected rpcProtocolFactory = defaultRpcProtocolFactory) {
         this.waitForConnection();
     }
 
     protected waitForConnection(): void {
-        this.connectionPromise = new Promise(resolve =>
-            this.connectionPromiseResolve = resolve
-        );
-        this.connectionPromise.then(connection => {
-            connection.channel.onClose(() => {
+        this.rpcDeferred = new Deferred<RpcProtocol>();
+        this.rpcDeferred.promise.then(protocol => {
+            protocol.channel.onClose(() => {
                 this.onDidCloseConnectionEmitter.fire(undefined);
                 // Wait for connection in case the backend reconnects
                 this.waitForConnection();
@@ -143,10 +141,10 @@ export class JsonRpcProxyFactory<T extends object> implements ProxyHandler<T> {
      * response.
      */
     listen(channel: Channel): void {
-        const connection = this.rpcConnectionFactory(channel, (meth, args) => this.onRequest(meth, ...args));
-        connection.onNotification(event => this.onNotification(event.method, ...event.args));
+        const protocol = this.rpcProtocolFactory(channel, (meth, args) => this.onRequest(meth, ...args));
+        protocol.onNotification(event => this.onNotification(event.method, ...event.args));
 
-        this.connectionPromiseResolve(connection);
+        this.rpcDeferred.resolve(protocol);
     }
 
     /**
@@ -249,7 +247,7 @@ export class JsonRpcProxyFactory<T extends object> implements ProxyHandler<T> {
         return (...args: any[]) => {
             const method = p.toString();
             const capturedError = new Error(`Request '${method}' failed`);
-            return this.connectionPromise.then(connection =>
+            return this.rpcDeferred.promise.then(connection =>
                 new Promise<void>((resolve, reject) => {
                     try {
                         if (isNotify) {