Add web worker JS API (#1993)

* Refactored the way worker polling is scheduled and errors are handled.
* Share the worker future as a Shared

js/workers.ts

@@ -1,33 +1,110 @@
 // Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
-import * as dispatch from "./dispatch";
+/* eslint-disable @typescript-eslint/no-explicit-any */
+import { sendAsync, sendSync } from "./dispatch";
 import * as msg from "gen/cli/msg_generated";
 import * as flatbuffers from "./flatbuffers";
 import { assert, log } from "./util";
+import { TextDecoder, TextEncoder } from "./text_encoding";
 import { window } from "./window";
 
-export async function postMessage(data: Uint8Array): Promise<void> {
+const encoder = new TextEncoder();
+const decoder = new TextDecoder();
+
+export function encodeMessage(data: any): Uint8Array {
+  const dataJson = JSON.stringify(data);
+  return encoder.encode(dataJson);
+}
+
+export function decodeMessage(dataIntArray: Uint8Array): any {
+  const dataJson = decoder.decode(dataIntArray);
+  return JSON.parse(dataJson);
+}
+
+function createWorker(specifier: string): number {
   const builder = flatbuffers.createBuilder();
-  msg.WorkerPostMessage.startWorkerPostMessage(builder);
-  const inner = msg.WorkerPostMessage.endWorkerPostMessage(builder);
-  const baseRes = await dispatch.sendAsync(
+  const specifier_ = builder.createString(specifier);
+  msg.CreateWorker.startCreateWorker(builder);
+  msg.CreateWorker.addSpecifier(builder, specifier_);
+  const inner = msg.CreateWorker.endCreateWorker(builder);
+  const baseRes = sendSync(builder, msg.Any.CreateWorker, inner);
+  assert(baseRes != null);
+  assert(
+    msg.Any.CreateWorkerRes === baseRes!.innerType(),
+    `base.innerType() unexpectedly is ${baseRes!.innerType()}`
+  );
+  const res = new msg.CreateWorkerRes();
+  assert(baseRes!.inner(res) != null);
+  return res.rid();
+}
+
+async function hostGetWorkerClosed(rid: number): Promise<void> {
+  const builder = flatbuffers.createBuilder();
+  msg.HostGetWorkerClosed.startHostGetWorkerClosed(builder);
+  msg.HostGetWorkerClosed.addRid(builder, rid);
+  const inner = msg.HostGetWorkerClosed.endHostGetWorkerClosed(builder);
+  await sendAsync(builder, msg.Any.HostGetWorkerClosed, inner);
+}
+
+function hostPostMessage(rid: number, data: any): void {
+  const dataIntArray = encodeMessage(data);
+  const builder = flatbuffers.createBuilder();
+  msg.HostPostMessage.startHostPostMessage(builder);
+  msg.HostPostMessage.addRid(builder, rid);
+  const inner = msg.HostPostMessage.endHostPostMessage(builder);
+  const baseRes = sendSync(
     builder,
-    msg.Any.WorkerPostMessage,
+    msg.Any.HostPostMessage,
     inner,
-    data
+    dataIntArray
   );
   assert(baseRes != null);
 }
 
-export async function getMessage(): Promise<null | Uint8Array> {
+async function hostGetMessage(rid: number): Promise<any> {
+  const builder = flatbuffers.createBuilder();
+  msg.HostGetMessage.startHostGetMessage(builder);
+  msg.HostGetMessage.addRid(builder, rid);
+  const inner = msg.HostGetMessage.endHostGetMessage(builder);
+  const baseRes = await sendAsync(builder, msg.Any.HostGetMessage, inner);
+  assert(baseRes != null);
+  assert(
+    msg.Any.HostGetMessageRes === baseRes!.innerType(),
+    `base.innerType() unexpectedly is ${baseRes!.innerType()}`
+  );
+  const res = new msg.HostGetMessageRes();
+  assert(baseRes!.inner(res) != null);
+
+  const dataArray = res.dataArray();
+  if (dataArray != null) {
+    return decodeMessage(dataArray);
+  } else {
+    return null;
+  }
+}
+
+// Stuff for workers
+export let onmessage: (e: { data: any }) => void = (): void => {};
+
+export function postMessage(data: any): void {
+  const dataIntArray = encodeMessage(data);
+  const builder = flatbuffers.createBuilder();
+  msg.WorkerPostMessage.startWorkerPostMessage(builder);
+  const inner = msg.WorkerPostMessage.endWorkerPostMessage(builder);
+  const baseRes = sendSync(
+    builder,
+    msg.Any.WorkerPostMessage,
+    inner,
+    dataIntArray
+  );
+  assert(baseRes != null);
+}
+
+export async function getMessage(): Promise<any> {
   log("getMessage");
   const builder = flatbuffers.createBuilder();
   msg.WorkerGetMessage.startWorkerGetMessage(builder);
   const inner = msg.WorkerGetMessage.endWorkerGetMessage(builder);
-  const baseRes = await dispatch.sendAsync(
-    builder,
-    msg.Any.WorkerGetMessage,
-    inner
-  );
+  const baseRes = await sendAsync(builder, msg.Any.WorkerGetMessage, inner);
   assert(baseRes != null);
   assert(
     msg.Any.WorkerGetMessageRes === baseRes!.innerType(),
@@ -37,14 +114,14 @@ export async function getMessage(): Promise<null | Uint8Array> {
   assert(baseRes!.inner(res) != null);
 
   const dataArray = res.dataArray();
-  if (dataArray == null) {
-    return null;
+  if (dataArray != null) {
+    return decodeMessage(dataArray);
   } else {
-    return new Uint8Array(dataArray!);
+    return null;
   }
 }
 
-let isClosing = false;
+export let isClosing = false;
 
 export function workerClose(): void {
   isClosing = true;
@@ -67,3 +144,45 @@ export async function workerMain(): Promise<void> {
     }
   }
 }
+
+export interface Worker {
+  onerror?: () => void;
+  onmessage?: (e: { data: any }) => void;
+  onmessageerror?: () => void;
+  postMessage(data: any): void;
+}
+
+export class WorkerImpl implements Worker {
+  private readonly rid: number;
+  private isClosing: boolean = false;
+  public onerror?: () => void;
+  public onmessage?: (data: any) => void;
+  public onmessageerror?: () => void;
+
+  constructor(specifier: string) {
+    this.rid = createWorker(specifier);
+    this.run();
+    hostGetWorkerClosed(this.rid).then(() => {
+      this.isClosing = true;
+    });
+  }
+
+  postMessage(data: any): void {
+    hostPostMessage(this.rid, data);
+  }
+
+  private async run(): Promise<void> {
+    while (!this.isClosing) {
+      const data = await hostGetMessage(this.rid);
+      if (data == null) {
+        log("worker got null message. quitting.");
+        break;
+      }
+      // TODO(afinch7) stop this from eating messages before onmessage has been assigned
+      if (this.onmessage) {
+        const event = { data };
+        this.onmessage(event);
+      }
+    }
+  }
+}