chore: extract backend server util (#419)

src/backend.ts

@@ -0,0 +1,135 @@
+/**
+ * Copyright (c) Microsoft Corporation.
+ *
+ * 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.
+ */
+
+import { spawn } from 'child_process';
+import { findNode } from './utils';
+import * as vscodeTypes from './vscodeTypes';
+import EventEmitter from 'events';
+import { WebSocketTransport } from './transport';
+
+export class BackendServer<T extends BackendClient> {
+  private _vscode: vscodeTypes.VSCode;
+  private _args: string[];
+  private _cwd: string;
+  private _envProvider: () => NodeJS.ProcessEnv;
+  private _clientFactory: () => T;
+
+  constructor(vscode: vscodeTypes.VSCode, args: string[], cwd: string, envProvider: () => NodeJS.ProcessEnv, clientFactory: () => T) {
+    this._vscode = vscode;
+    this._args = args;
+    this._cwd = cwd;
+    this._envProvider = envProvider;
+    this._clientFactory = clientFactory;
+  }
+
+  async start(): Promise<T | null> {
+    const node = await findNode(this._vscode, this._cwd);
+    const serverProcess = spawn(node, this._args, {
+      cwd: this._cwd,
+      stdio: 'pipe',
+      env: {
+        ...process.env,
+        ...this._envProvider(),
+      },
+    });
+
+    const client = this._clientFactory();
+
+    serverProcess.stderr?.on('data', () => {});
+    serverProcess.on('error', error => {
+      client._onErrorEvent.fire(error);
+    });
+
+    return new Promise(fulfill => {
+      serverProcess.stdout?.on('data', async data => {
+        const match = data.toString().match(/Listening on (.*)/);
+        if (!match)
+          return;
+        const wse = match[1];
+        await client._connect(wse);
+        fulfill(client);
+      });
+      serverProcess.on('exit', () => {
+        fulfill(null);
+        client._onCloseEvent.fire();
+      });
+    });
+  }
+}
+
+export class BackendClient extends EventEmitter {
+  private static _lastId = 0;
+  private _callbacks = new Map<number, { fulfill: (a: any) => void, reject: (e: Error) => void }>();
+  private _transport!: WebSocketTransport;
+  wsEndpoint!: string;
+
+  readonly onClose: vscodeTypes.Event<void>;
+  readonly _onCloseEvent: vscodeTypes.EventEmitter<void>;
+  readonly onError: vscodeTypes.Event<Error>;
+  readonly _onErrorEvent: vscodeTypes.EventEmitter<Error>;
+
+  constructor(vscode: vscodeTypes.VSCode) {
+    super();
+    this._onCloseEvent = new vscode.EventEmitter();
+    this.onClose = this._onCloseEvent.event;
+    this._onErrorEvent = new vscode.EventEmitter();
+    this.onError = this._onErrorEvent.event;
+  }
+
+  rewriteWsEndpoint(wsEndpoint: string): string {
+    return wsEndpoint;
+  }
+
+  rewriteWsHeaders(headers: Record<string, string>): Record<string, string> {
+    return headers;
+  }
+
+  async _connect(wsEndpoint: string) {
+    this.wsEndpoint = wsEndpoint;
+    this._transport = await WebSocketTransport.connect(this.rewriteWsEndpoint(wsEndpoint), this.rewriteWsHeaders({}));
+    this._transport.onmessage = (message: any) => {
+      if (!message.id) {
+        this.emit(message.method, message.params);
+        return;
+      }
+      const pair = this._callbacks.get(message.id);
+      if (!pair)
+        return;
+      this._callbacks.delete(message.id);
+      if (message.error) {
+        const error = new Error(message.error.error?.message || message.error.value);
+        error.stack = message.error.error?.stack;
+        pair.reject(error);
+      } else {
+        pair.fulfill(message.result);
+      }
+    };
+    await this.initialize();
+  }
+
+  async initialize() { }
+
+  requestGracefulTermination() { }
+
+  protected send(method: string, params: any = {}): Promise<any> {
+    return new Promise((fulfill, reject) => {
+      const id = ++BackendClient._lastId;
+      const command = { id, guid: 'DebugController', method, params, metadata: {} };
+      this._transport.send(command as any);
+      this._callbacks.set(id, { fulfill, reject });
+    });
+  }
+}