Implement chrome.downloads.onDeterminingFilename()

chrome/renderer/resources/extensions/downloads_custom_bindings.js

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Custom bindings for the downloads API.
+
+var downloadsNatives = requireNative('downloads');
+var chromeHidden = requireNative('chrome_hidden').GetChromeHidden();
+var sendRequest = require('sendRequest').sendRequest;
+
+function DownloadsEvent(eventName, opt_argSchemas, opt_extraArgSchemas,
+                        opt_eventOptions) {
+  if (typeof eventName != 'string')
+    throw new Error('chrome.DownloadsEvent requires an event name.');
+
+  this.eventName_ = eventName;
+  this.determiningFilename_ = (eventName == 'downloads.onDeterminingFilename');
+  this.argSchemas_ = opt_argSchemas;
+  this.extraArgSchemas_ = opt_extraArgSchemas;
+  this.eventOptions_ = chromeHidden.parseEventOptions(opt_eventOptions);
+  if (this.determiningFilename_) {
+    this.subEvents_ = [];
+  } else {
+    this.actualEvent_ =
+        new chrome.Event(eventName, opt_argSchemas, opt_eventOptions);

[Matt Perry, 2013/02/05 20:49:39]

I'm not a JS expert, but I believe it's possible to just do "return new
chrome.Event(...);"

That way you only use a DownloadsEvent for onDeterminingFilename.

[benjhayden, 2013/02/05 21:12:19]

Unfortunately, registerCustomEvent does 'new DownloadsEvent'. DownloadsEvent is
an object class, not a function.

[Matt Perry, 2013/02/05 21:57:10]

I know, but I think it still works. For example, this code works for me:
function Parent(x) { this.x_ = x; }
function Child(x) { return new Parent(x); }
y = new Child(7);  // y is a Parent

[benjhayden, 2013/02/21 22:29:33]

8-O
...
Done.

+  }
+}
+
+// Test if the given callback is registered for this event.
+DownloadsEvent.prototype.hasListener = function(cb) {
+  if (!this.eventOptions_.supportsListeners)
+    throw new Error('This event does not support listeners.');
+  return this.findListener_(cb) > -1;
+};
+
+// Test if any callbacks are registered for this event.
+DownloadsEvent.prototype.hasListeners = function() {
+  if (!this.eventOptions_.supportsListeners)
+    throw new Error('This event does not support listeners.');
+  return (this.determiningFilename_ ? (this.subEvents_.length > 0) :
+                                      this.actualEvent_.hasListeners());
+};
+
+DownloadsEvent.prototype.addListener = function(cb) {
+  if (!this.eventOptions_.supportsListeners)
+    throw new Error('This event does not support listeners.');
+  if (!this.determiningFilename_) {
+    this.actualEvent_.addListener(cb);
+    return;
+  }
+  var entry = {callback: cb};
+  entry.determiner_id = downloadsNatives.GetFilenameDeterminerId();
+  entry.subEvent = new chrome.Event(
+      this.eventName_ + '/' + entry.determiner_id, this.argSchemas_);
+  chromeHidden.internalAPIs.downloadsInternal.addFilenameDeterminer(
+      entry.determiner_id);
+  entry.subEventCallback = function() {
+    var download_id = arguments[0].id;
+    try {
+      var result = cb.apply(null, arguments);
+      if ((typeof(result) == 'object') &&
+          result.filename &&
+          (typeof(result.filename) == 'string') &&
+          ((result.overwrite === undefined) ||
+           (typeof(result.overwrite) == 'boolean'))) {
+        chromeHidden.internalAPIs.downloadsInternal.determineFilename(
+            entry.determiner_id,
+            download_id,
+            result.filename,
+            result.overwrite || false);
+      } else {
+        chromeHidden.internalAPIs.downloadsInternal.determineFilename(
+            entry.determiner_id,
+            download_id);
+      }
+    } catch (e) {
+      chromeHidden.internalAPIs.downloadsInternal.determineFilename(
+          entry.determiner_id,
+          download_id);
+      throw e;
+    }
+  };
+  this.subEvents_.push(entry);
+  entry.subEvent.addListener(entry.subEventCallback);
+};
+
+DownloadsEvent.prototype.removeListener = function(cb) {

[Matt Perry, 2013/02/07 00:10:13]

This is only called when the extension explicitly calls it. You should also
handle the case where the extension page unloads, otherwise you could have an
event registered in the browser that doesn't exist. This can happen if an
extension popup adds a DownloadsEvent listener, for example. When the popup goes
away, we should remove the filename determiner.

The webRequest API handles this by hooking into EventRouter::OnListenerRemoved,
which is called on page unload as a result of chrome.Event.prototype.detach_.

[benjhayden, 2013/02/21 22:29:33]

I already Observe NOTIFICATION_EXTENSION_UNLOADED. Is there a reason that I
should use EventRouter::OnListenerRemoved instead?

[Matt Perry, 2013/02/21 23:07:49]

Yes - in the case of a popup closing, for example. The extension will not be
unloaded, but the listener will be removed.

[benjhayden, 2013/02/22 20:43:23]

Done -- I assumed that I should also use OnListenerAdded instead of
AddFilenameDeterminer. Is that assumption correct?

+  if (!this.eventOptions_.supportsListeners)
+    throw new Error('This event does not support listeners.');
+  if (!this.determiningFilename_) {
+    this.actualEvent_.removeListener(cb);
+    return;
+  }
+  var idx;
+  while ((idx = this.findListener_(cb)) >= 0) {
+    var e = this.subEvents_[idx];
+    e.subEvent.removeListener(e.subEventCallback);
+    chromeHidden.internalAPIs.downloadsInternal.removeFilenameDeterminer(
+        e.determiner_id);
+    if (e.subEvent.hasListeners()) {
+      console.error('Internal error: subEvent has orphaned listeners.');
+    }
+    this.subEvents_.splice(idx, 1);
+  }
+};
+
+DownloadsEvent.prototype.findListener_ = function(cb) {
+  if (!this.determiningFilename_) {
+    return this.actualEvent_.findListener(cb);
+  }
+  for (var i in this.subEvents_) {
+    var e = this.subEvents_[i];
+    if (e.callback === cb) {
+      if (e.subEvent.findListener_(e.subEventCallback) > -1)
+        return i;
+      console.error('Internal error: subEvent has no callback.');
+    }
+  }
+
+  return -1;
+};
+
+DownloadsEvent.prototype.addRules = function(rules, opt_cb) {
+  if (!this.eventOptions_.supportsRules)
+    throw new Error('This event does not support rules.');
+  this.eventForRules_.addRules(rules, opt_cb);
+}
+
+DownloadsEvent.prototype.removeRules = function(ruleIdentifiers, opt_cb) {
+  if (!this.eventOptions_.supportsRules)
+    throw new Error('This event does not support rules.');
+  this.eventForRules_.removeRules(ruleIdentifiers, opt_cb);
+}
+
+DownloadsEvent.prototype.getRules = function(ruleIdentifiers, cb) {
+  if (!this.eventOptions_.supportsRules)
+    throw new Error('This event does not support rules.');
+  this.eventForRules_.getRules(ruleIdentifiers, cb);
+}
+
+chromeHidden.registerCustomEvent('downloads', DownloadsEvent);