fix(transport): dispatch messages in separate tasks (#841)

Fixes a bug in our pipe, and the same one in the non-standard `ws` module. Our protocol messages are I/O events, and therefore they should each be executed in their own task.

src/platform.ts

@@ -276,6 +276,42 @@ export function fetchUrl(url: string): Promise<string> {
   });
 }
 
+// See https://joel.tools/microtasks/
+export function makeWaitForNextTask() {
+  assert(isNode, 'Waitng for the next task is only supported in nodejs');
+  if (parseInt(process.versions.node, 10) >= 11)
+    return setImmediate;
+
+  // Unlike Node 11, Node 10 and less have a bug with Task and MicroTask execution order:
+  // - https://github.com/nodejs/node/issues/22257
+  //
+  // So we can't simply run setImmediate to dispatch code in a following task.
+  // However, we can run setImmediate from-inside setImmediate to make sure we're getting
+  // in the following task.
+
+  let spinning = false;
+  const callbacks: (() => void)[] = [];
+  const loop = () => {
+    const callback = callbacks.shift();
+    if (!callback) {
+      spinning = false;
+      return;
+    }
+    setImmediate(loop);
+    // Make sure to call callback() as the last thing since it's
+    // untrusted code that might throw.
+    callback();
+  };
+
+  return (callback: () => void) => {
+    callbacks.push(callback);
+    if (!spinning) {
+      spinning = true;
+      setImmediate(loop);
+    }
+  };
+}
+
 export class WebSocketTransport implements ConnectionTransport {
   private _ws: WebSocket;
 
@@ -292,10 +328,19 @@ export class WebSocketTransport implements ConnectionTransport {
       this._ws.addEventListener('open', () => fulfill());
       this._ws.addEventListener('error', event => reject(new Error(event.toString())));
     });
+    // The 'ws' module in node sometimes sends us multiple messages in a single task.
+    // In Web, all IO callbacks (e.g. WebSocket callbacks)
+    // are dispatched into separate tasks, so there's no need
+    // to do anything extra.
+    const messageWrap: (cb :() => void) => void = isNode ? makeWaitForNextTask() : cb => cb();
+
     this._ws.addEventListener('message', event => {
+      messageWrap(() => {
         if (this.onmessage)
           this.onmessage.call(null, event.data);
       });
+    });
+
     this._ws.addEventListener('close', event => {
       if (this.onclose)
         this.onclose.call(null);

src/server/pipeTransport.ts

@@ -17,11 +17,13 @@
 
 import { debugError, helper, RegisteredListener } from '../helper';
 import { ConnectionTransport } from '../transport';
+import { makeWaitForNextTask } from '../platform';
 
 export class PipeTransport implements ConnectionTransport {
   private _pipeWrite: NodeJS.WritableStream | null;
   private _pendingMessage = '';
   private _eventListeners: RegisteredListener[];
+  private _waitForNextTask = makeWaitForNextTask();
   onmessage?: (message: string) => void;
   onclose?: () => void;
 
@@ -52,14 +54,19 @@ export class PipeTransport implements ConnectionTransport {
       return;
     }
     const message = this._pendingMessage + buffer.toString(undefined, 0, end);
+    this._waitForNextTask(() => {
       if (this.onmessage)
         this.onmessage.call(null, message);
+    });
 
     let start = end + 1;
     end = buffer.indexOf('\0', start);
     while (end !== -1) {
+      const message = buffer.toString(undefined, start, end);
+      this._waitForNextTask(() => {
         if (this.onmessage)
-        this.onmessage.call(null, buffer.toString(undefined, start, end));
+          this.onmessage.call(null, message);
+      });
       start = end + 1;
       end = buffer.indexOf('\0', start);
     }