fix: wrap `onRequestFinished` to use promises

Fixes #249.

This updates `browser.devtools.network.onRequestFinished` to emit an
object with a promisified `getContent()` property. This brings the
polyfill implementation in line with Firefox's implementation, although
MDN documentation is still inaccurate at the moment.

Also updates some out of date documentation with `makeCallback()` and
`wrapAsyncFunction()`.

src/browser-polyfill.js

@@ -77,13 +77,17 @@ if (typeof browser === "undefined" || Object.getPrototypeOf(browser) !== Object.
      *        promise.
      * @param {function} promise.resolve
      *        The promise's resolution function.
-     * @param {function} promise.rejection
+     * @param {function} promise.reject
      *        The promise's rejection function.
      * @param {object} metadata
      *        Metadata about the wrapped method which has created the callback.
-     * @param {integer} metadata.maxResolvedArgs
-     *        The maximum number of arguments which may be passed to the
-     *        callback created by the wrapped async function.
+     * @param {boolean} metadata.singleCallbackArg
+     *        Whether or not the promise is resolved with only the first
+     *        argument of the callback, alternatively an array of all the
+     *        callback arguments is resolved. By default, if the callback
+     *        function is invoked with only a single argument, that will be
+     *        resolved to the promise, while all arguments will be resolved as
+     *        an array if multiple are given.
      *
      * @returns {function}
      *        The generated callback function.
@@ -118,9 +122,13 @@ if (typeof browser === "undefined" || Object.getPrototypeOf(browser) !== Object.
      *        The maximum number of arguments which may be passed to the
      *        function. If called with more than this number of arguments, the
      *        wrapper will raise an exception.
-     * @param {integer} metadata.maxResolvedArgs
-     *        The maximum number of arguments which may be passed to the
-     *        callback created by the wrapped async function.
+     * @param {boolean} metadata.singleCallbackArg
+     *        Whether or not the promise is resolved with only the first
+     *        argument of the callback, alternatively an array of all the
+     *        callback arguments is resolved. By default, if the callback
+     *        function is invoked with only a single argument, that will be
+     *        resolved to the promise, while all arguments will be resolved as
+     *        an array if multiple are given.
      *
      * @returns {function(object, ...*)}
      *       The generated wrapper function.
@@ -345,6 +353,30 @@ if (typeof browser === "undefined" || Object.getPrototypeOf(browser) !== Object.
       },
     });
 
+    const onRequestFinishedWrappers = new DefaultWeakMap(listener => {
+      if (typeof listener !== "function") {
+        return listener;
+      }
+
+      /**
+       * Wraps an onRequestFinished listener function so that it will return a
+       * `getContent()` property which returns a `Promise` rather than using a
+       * callback API.
+       *
+       * @param {object} req
+       *        The HAR entry object representing the network request.
+       */
+      return function onRequestFinished(req) {
+        const wrappedReq = wrapObject(req, {} /* wrappers */, {
+          getContent: {
+            minArgs: 0,
+            maxArgs: 0,
+          },
+        });
+        listener(wrappedReq);
+      };
+    });
+
     // Keep track if the deprecation warning has been logged at least once.
     let loggedSendResponseDeprecationWarning = false;
 
@@ -480,6 +512,11 @@ if (typeof browser === "undefined" || Object.getPrototypeOf(browser) !== Object.
     };
 
     const staticWrappers = {
+      devtools: {
+        network: {
+          onRequestFinished: wrapEvent(onRequestFinishedWrappers),
+        },
+      },
       runtime: {
         onMessage: wrapEvent(onMessageWrappers),
         onMessageExternal: wrapEvent(onMessageWrappers),

test/test-onRequestFinished.js

@@ -0,0 +1,119 @@
+"use strict";
+
+const {deepEqual, equal, ok} = require("chai").assert;
+const sinon = require("sinon");
+
+const {setupTestDOMWindow} = require("./setup");
+
+describe("browser-polyfill", () => {
+  describe("wrapped devtools.network.onRequestFinished listener", () => {
+    it("does not wrap the listener if it is not a function", () => {
+      const fakeChrome = {
+        devtools: {
+          network: {
+            onRequestFinished: {
+              addListener: sinon.spy(),
+            },
+          },
+        },
+      };
+
+      return setupTestDOMWindow(fakeChrome).then(window => {
+        const fakeNonFunctionListener = {fake: "non function listener"};
+
+        const browserOnRequestFinished = window.browser.devtools.network.onRequestFinished;
+        browserOnRequestFinished.addListener(fakeNonFunctionListener);
+
+        const fakeChromeOnRequestFinished = fakeChrome.devtools.network.onRequestFinished;
+        deepEqual(
+          fakeChromeOnRequestFinished.addListener.firstCall.args[0],
+          fakeNonFunctionListener,
+          "The non-function listener has not been wrapped"
+        );
+      });
+    });
+
+    it("promisifies the result", () => {
+      const fakeChrome = {
+        devtools: {
+          network: {
+            onRequestFinished: {
+              addListener: sinon.spy(),
+              hasListener: sinon.stub(),
+              removeListener: sinon.spy(),
+            },
+          },
+        },
+      };
+
+      return setupTestDOMWindow(fakeChrome).then(window => {
+        const listener = sinon.spy();
+
+        const browserOnRequestFinished = window.browser.devtools.network.onRequestFinished;
+        browserOnRequestFinished.addListener(listener);
+
+        const fakeChromeOnRequestFinished = fakeChrome.devtools.network.onRequestFinished;
+        ok(fakeChromeOnRequestFinished.addListener.calledOnce,
+           "devtools.network.onRequestFinished.addListener has been called once");
+
+        const wrappedListener = fakeChromeOnRequestFinished.addListener.firstCall.args[0];
+        wrappedListener({
+          getContent(cb) {
+            cb("<html>...</html>", "text/html; charset=utf8");
+          },
+        });
+
+        ok(listener.calledOnce, "listener has been called once");
+
+        const req = listener.firstCall.args[0];
+        return req.getContent().then(([content, encodingOrMimeType]) => {
+          equal(content, "<html>...</html>");
+          // On Chrome this is the encoding ('' or 'base64') while on Firefox
+          // this is the MIME type of the resource.
+          // See: https://github.com/mozilla/webextension-polyfill/issues/249#issuecomment-740000461
+          equal(encodingOrMimeType, "text/html; charset=utf8");
+        });
+      });
+    });
+
+    it("promisifies the result with a wrapped Request object", () => {
+      const fakeChrome = {
+        devtools: {
+          network: {
+            onRequestFinished: {
+              addListener: sinon.spy(),
+              hasListener: sinon.stub(),
+              removeListener: sinon.spy(),
+            },
+          },
+        },
+      };
+
+      return setupTestDOMWindow(fakeChrome).then(window => {
+        const listener = sinon.spy();
+
+        const browserOnRequestFinished = window.browser.devtools.network.onRequestFinished;
+        browserOnRequestFinished.addListener(listener);
+
+        const fakeChromeOnRequestFinished = fakeChrome.devtools.network.onRequestFinished;
+        ok(fakeChromeOnRequestFinished.addListener.calledOnce,
+           "devtools.network.onRequestFinished.addListener has been called once");
+
+        const request = Object.create({
+          inheritedProp: true,
+          getContent(cb) {
+            cb("", "");
+          },
+        });
+
+        const wrappedListener = fakeChromeOnRequestFinished.addListener.firstCall.args[0];
+        wrappedListener(request);
+
+        ok(listener.calledOnce, "listener has been called once");
+
+        const req = listener.firstCall.args[0];
+        ok(req.inheritedProp, "Wrapped request inherited prototype properties");
+      });
+    });
+  });
+});