Apply suggestions from code review

Co-authored-by: Robert Knight <robertknight@gmail.com>

src/shared/port-finder.js

@@ -2,7 +2,7 @@ import { ListenerCollection } from './listener-collection';
 import { isMessageEqual, SOURCE as source } from './port-util';
 
 const MAX_WAIT_FOR_PORT = 1000 * 30;
-const POLLING_INTERVAL_FOR_PORT = 500;
+const POLLING_INTERVAL_FOR_PORT = 250;
 
 /**
  * @typedef {import('../types/annotator').Destroyable} Destroyable
@@ -12,8 +12,7 @@ const POLLING_INTERVAL_FOR_PORT = 500;
  */
 
 /**
- * PortFinder class should be used in frames that are not the `host` frame. It
- * helps to discover `MessagePort` on a specific channel.
+ * PortFinder helps to discover `MessagePort` on a specific channel.
  *
  * Channel nomenclature is `[frame1]-[frame2]` so that:
  *   - `port1` should be owned by/transferred to `frame1`, and
@@ -28,71 +27,42 @@ export class PortFinder {
     this._listeners = new ListenerCollection();
   }
 
-  // Two important characteristics of `MessagePort`:
-  // - it can only be used by one frame; the port is neutered if, after started to
-  //   be used to receive messages, the port is transferred to a different frame.
-  // - messages are queued until the other port is ready to listen (`port.start()`)
+  destroy() {
+    this._listeners.removeAll();
+  }
 
   /**
-   * `guest-host` communication
-   * @typedef {{channel: 'guest-host', hostFrame: Window, port: 'guest'}} options0
-   *
-   * `guest-sidebar` communication
-   * @typedef {{channel: 'guest-sidebar', hostFrame: Window, port: 'guest'}} options1
-   *
-   * `host-sidebar` communication
-   * @typedef {{channel: 'host-sidebar', hostFrame: Window, port: 'sidebar'}} options2
+   * Polls the hostFrame for a specific port and returns a Promise of the port.
    *
-   * `notebook-sidebar` communication
-   * @typedef {{channel: 'notebook-sidebar', hostFrame: Window, port: 'notebook'}} options3
-   *
-   * @param {options0|options1|options2|options3} options
+   * @param {object} options
+   *   @param {Channel} options.channel - requested channel
+   *   @param {Window} options.hostFrame - frame where the hypothesis client is
+   *     loaded and `PortProvider` is listening for messages
+   *   @param {Port} options.port - requested port
    * @return {Promise<MessagePort>}
    */
-  discover(options) {
-    const { channel, port } = options;
-    return new Promise((resolve, reject) => {
+  discover({ channel, hostFrame, port }) {
+    let isValidRequest = false;
     if (
       (channel === 'guest-host' && port === 'guest') ||
       (channel === 'guest-sidebar' && port === 'guest') ||
       (channel === 'host-sidebar' && port === 'sidebar') ||
       (channel === 'notebook-sidebar' && port === 'notebook')
     ) {
-        this._requestPort({
-          ...options,
-          reject,
-          resolve,
-        });
-        return;
+      isValidRequest = true;
     }
 
+    return new Promise((resolve, reject) => {
+      if (!isValidRequest) {
         reject(new Error('Invalid request of channel/port'));
-    });
+        return;
       }
 
-  /**
-   * @typedef RequestPortOptions
-   * @prop {Channel} channel - requested channel
-   * @prop {Window} hostFrame - the frame where the hypothesis client is loaded.
-   *   It is used to send a `window.postMessage`.
-   * @prop {Port} port - requested port
-   * @prop {(reason: Error) => void} reject - execute the `Promise.reject` in case
-   *   the `host` frame takes too long to answer the request.
-   * @prop {(port: MessagePort) => void} resolve - execute the `Promise.resolve`
-   *   when `host` frame successfully answers the request.
-   */
-
-  /**
-   * Register a listener for the port `offer` and sends a request for one port.
-   *
-   * @param {RequestPortOptions} options
-   */
-  _requestPort({ channel, hostFrame, port, reject, resolve }) {
       function postRequest() {
         hostFrame.postMessage({ channel, port, source, type: 'request' }, '*');
       }
 
-    const intervalId = window.setInterval(
+      const intervalId = setInterval(
         () => postRequest(),
         POLLING_INTERVAL_FOR_PORT
       );
@@ -106,40 +76,16 @@ export class PortFinder {
       }, MAX_WAIT_FOR_PORT);
 
       // TODO: It would be nice to remove the listener after receiving the port.
-    this._listeners.add(window, 'message', event =>
-      this._handlePortOffer(/** @type {MessageEvent} */ (event), {
-        intervalId,
-        message: { channel, port, source, type: 'offer' },
-        resolve,
-        timeoutId,
-      })
-    );
-
-    postRequest();
-  }
-
-  /**
-   * Resolve with a MessagePort when the `offer` message matches.
-   *
-   * @param {MessageEvent} event
-   * @param {object} options
-   *   @param {Message} options.message
-   *   @param {(port: MessagePort) => void} options.resolve
-   *   @param {number} options.timeoutId
-   *   @param {number} [options.intervalId]
-   */
-  _handlePortOffer(
-    { data, ports },
-    { message, resolve, timeoutId, intervalId }
-  ) {
-    if (isMessageEqual(data, message)) {
+      this._listeners.add(window, 'message', event => {
+        const { data, ports } = /** @type {MessageEvent} */ (event);
+        if (isMessageEqual(data, { channel, port, source, type: 'offer' })) {
           clearInterval(intervalId);
           clearTimeout(timeoutId);
           resolve(ports[0]);
         }
-  }
+      });
 
-  destroy() {
-    this._listeners.removeAll();
+      postRequest();
+    });
   }
 }

src/shared/port-util.js

 // Because there are many `postMessages` on the `host` frame, the SOURCE property
 // is added to the hypothesis `postMessages` to identify the provenance of the
 // message and avoid listening to messages that could have the same properties
-// but different source. This is not a is not a security feature but an
+// but different source. This is not a security feature but an
 // anti-collision mechanism.
 export const SOURCE = 'hypothesis';
 
 /**
+ * These types are the used in by `PortProvider` and `PortFinder` for the
+ * inter-frame discovery and communication processes.
  * @typedef {'guest-host'|'guest-sidebar'|'host-sidebar'|'notebook-sidebar'} Channel
  * @typedef {'guest'|'host'|'notebook'|'sidebar'} Port
  *

src/shared/test/port-finder-test.js

@@ -26,9 +26,46 @@ describe('PortFinder', () => {
     portFinder.destroy();
   });
 
+  describe('#destroy', () => {
+    it('ignores `offer` messages of ports', async () => {
+      let error;
+      const channel = 'host-sidebar';
+      const port = 'sidebar';
+      const { port1 } = new MessageChannel();
+      const clock = sinon.useFakeTimers();
+
+      try {
+        portFinder
+          .discover({
+            channel,
+            hostFrame: window,
+            port,
+          })
+          .catch(e => (error = e));
+        portFinder.destroy();
+        sendMessage({
+          data: { channel, port, source, type: 'offer' },
+          ports: [port1],
+        });
+        clock.tick(30000);
+      } finally {
+        clock.restore();
+      }
+
+      await delay(0);
+
+      assert.equal(
+        error.message,
+        "Unable to find 'sidebar' port on 'host-sidebar' channel"
+      );
+    });
+  });
+
+  describe('#discover', () => {
     [
       { channel: 'invalid', port: 'guest' },
       { channel: 'guest-host', port: 'invalid' },
+      { channel: 'guest-host', port: 'host' },
     ].forEach(({ channel, port }) =>
       it('rejects if requesting an invalid port', async () => {
         let error;
@@ -91,7 +128,7 @@ describe('PortFinder', () => {
         clock.restore();
       }
 
-    assert.callCount(window.postMessage, 61);
+      assert.callCount(window.postMessage, 121);
       assert.alwaysCalledWithExactly(
         window.postMessage,
         { channel, port, source, type: 'request' },
@@ -105,39 +142,5 @@ describe('PortFinder', () => {
         "Unable to find 'sidebar' port on 'host-sidebar' channel"
       );
     });
-
-  describe('#destroy', () => {
-    it('ignores `offer` messages of ports', async () => {
-      let error;
-      const channel = 'host-sidebar';
-      const port = 'sidebar';
-      const { port1 } = new MessageChannel();
-      const clock = sinon.useFakeTimers();
-
-      try {
-        portFinder
-          .discover({
-            channel,
-            hostFrame: window,
-            port,
-          })
-          .catch(e => (error = e));
-        portFinder.destroy();
-        sendMessage({
-          data: { channel, port, source, type: 'offer' },
-          ports: [port1],
-        });
-        clock.tick(30000);
-      } finally {
-        clock.restore();
-      }
-
-      await delay(0);
-
-      assert.equal(
-        error.message,
-        "Unable to find 'sidebar' port on 'host-sidebar' channel"
-      );
-    });
   });
 });

src/shared/test/port-provider-test.js

@@ -23,7 +23,8 @@ describe('PortProvider', () => {
 
   beforeEach(() => {
     sinon.stub(window, 'postMessage');
-    portProvider = new PortProvider(window.location.href);
+    portProvider = new PortProvider(window.location.origin);
+    portProvider.listen();
   });
 
   afterEach(() => {
@@ -31,6 +32,23 @@ describe('PortProvider', () => {
     portProvider.destroy();
   });
 
+  describe('#destroy', () => {
+    it('ignores valid port request if `PortFinder` has been destroyed', async () => {
+      portProvider.destroy();
+      sendMessage({
+        data: {
+          channel: 'host-sidebar',
+          port: 'sidebar',
+          source,
+          type: 'request',
+        },
+      });
+      await delay(0);
+
+      assert.notCalled(window.postMessage);
+    });
+  });
+
   describe('#getPort', () => {
     it('returns `null` if called with wrong arguments', () => {
       let hostPort;
@@ -59,20 +77,30 @@ describe('PortProvider', () => {
     });
   });
 
-  describe('#destroy', () => {
-    it('ignores valid port request if `PortFinder` has been destroyed', async () => {
+  describe('#listen', () => {
+    it('ignores all port request until start listening', async () => {
       portProvider.destroy();
-      sendMessage({
-        data: {
+      portProvider = new PortProvider(window.location.origin);
+      const data = {
         channel: 'host-sidebar',
         port: 'sidebar',
         source,
         type: 'request',
-        },
+      };
+      sendMessage({
+        data,
       });
       await delay(0);
 
       assert.notCalled(window.postMessage);
+
+      portProvider.listen();
+      sendMessage({
+        data,
+      });
+      await delay(0);
+
+      assert.calledOnce(window.postMessage);
     });
   });
 
@@ -94,7 +122,6 @@ describe('PortProvider', () => {
         data,
         source: new MessageChannel().port1,
       });
-
       await delay(0);
 
       assert.notCalled(window.postMessage);
@@ -132,7 +159,6 @@ describe('PortProvider', () => {
         data,
         origin: 'https://dummy.com',
       });
-
       await delay(0);
 
       assert.notCalled(window.postMessage);
@@ -148,7 +174,6 @@ describe('PortProvider', () => {
       sendMessage({
         data,
       });
-
       await delay(0);
 
       assert.calledWith(
@@ -217,7 +242,7 @@ describe('PortProvider', () => {
 
     it('sends the reciprocal port of the `guest-host` channel (via listener)', async () => {
       const handler = sinon.stub();
-      portProvider.addEventListener('onHostPortRequest', handler);
+      portProvider.on('hostPortRequest', handler);
       const data = {
         channel: 'guest-host',
         port: 'guest',