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,
+                        ignored_extraArgSchemas,
+                        opt_eventOptions) {
+  if (typeof eventName != 'string')
+    throw new Error('chrome.DownloadsEvent requires an event name.');
+  // onDeterminingFilename is the only special event in chrome.downloads.
+  if (eventName != 'downloads.onDeterminingFilename') {
+    return new chrome.Event(eventName, opt_argSchemas, opt_eventOptions);
+  }
+
+  this.eventName_ = eventName;
+  // ExtensionDownloadsEventRouter can't send a SuggestFilenameCallback, so
+  // slice it out of the event schema, leaving only the DownloadItem.
+  this.argSchemas_ = opt_argSchemas.slice(0, 1);
+  this.eventOptions_ = chromeHidden.parseEventOptions(opt_eventOptions);
+  this.subEvents_ = [];
+}
+
+// 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.subEvents_.length > 0);
+};
+
+DownloadsEvent.prototype.addListener = function(cb) {
+  if (!this.eventOptions_.supportsListeners)
+    throw new Error('This event does not support listeners.');
+  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 downloadItem = arguments[0];
+    // Copy the id so that extensions can't change downloadItem.id.
+    var downloadId = downloadItem.id;
+    var suggestable = true;
+    function suggest(result) {
+      if (!suggestable)
+        return;

[Matt Perry, 2013/02/22 01:43:43]

set suggestable to false here too

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

Done.

+      if ((typeof(result) == 'object') &&
+          result.filename &&
+          (typeof(result.filename) == 'string') &&
+          ((result.overwrite === undefined) ||
+           (typeof(result.overwrite) == 'boolean'))) {
+        chromeHidden.internalAPIs.downloadsInternal.determineFilename(
+            entry.determiner_id,
+            downloadId,
+            result.filename,
+            result.overwrite || false);
+      } else {
+        chromeHidden.internalAPIs.downloadsInternal.determineFilename(
+            entry.determiner_id,
+            downloadId);
+      }
+    }
+    try {
+      cb.apply(null, [downloadItem, suggest]);

[Matt Perry, 2013/02/22 01:43:43]

I'd recommend requiring the user to return true from the onDeterminingFilename
to indicate he wants to call |suggest| asynchronously. If they don't return
true, and suggest was not called, have it be an error and call determineFilename
yourself.

The reason is to make it explicit that the user intended to call |suggest|
asynchronously.

ex:
chrome.downloads.onDeterminingFilename.addListener(function(item, suggest) {
  if (item.filename.endsWith(".jpg")) {
    suggest("images/" + item.filename);
  } else {
    // handle asynchronously.
    window.setTimeout(function() { handle(item, suggest); }, 0);
    return true;
  }
});

Note that if I forget the "else" branch, chrome should call determineFilename
for me. The lack of return value helps chrome know when to do so.

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

Done.

+    } catch (e) {
+      chromeHidden.internalAPIs.downloadsInternal.determineFilename(
+          entry.determiner_id,
+          downloadId);
+      suggestable = false;
+      throw e;
+    }
+  };
+  this.subEvents_.push(entry);
+  entry.subEvent.addListener(entry.subEventCallback);
+};
+
+DownloadsEvent.prototype.removeListener = function(cb) {
+  if (!this.eventOptions_.supportsListeners)
+    throw new Error('This event does not support listeners.');
+  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) {
+  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);