Implement chrome.downloads.onDeterminingFilename()

chrome/common/extensions/api/downloads.idl

 // Copyright (c) 2012 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.
 
 [permissions=downloads]
 namespace downloads {
   [inline_doc] dictionary HeaderNameValuePair {
     // Name of the HTTP header.
     DOMString name;
 
     // Value of the HTTP header.
     DOMString value;
   };
 
+  // $ref:onDeterminingFilename handlers may return a FilenameDetermination
+  // object in order to override a download's target filename.
+  dictionary FilenameDetermination {
+    // The download's new target filename.
+    DOMString filename;
+
+    // Whether to overwrite any existing files. Ignored if <code>filename</code>
+    // is unset.

[Randy Smith (Not in Mondays), 2013/01/14 21:02:29]

Sorry, probably still confused about syntax, but doesn't this imply that the
filename may be unset, and thus should have a ? after the type name?

[benjhayden, 2013/01/17 02:52:05]

Done.

[Randy Smith (Not in Mondays), 2013/01/17 19:15:42]

Still confused, Milo.  Does this mean that the extension will always set
filename, but it'll be a null string if the extension doesn't want to override
the path?

[benjhayden, 2013/01/18 20:59:50]

Not quite. See about L60 in
https://codereview.chromium.org/11574006/diff/70003/chrome/renderer/resources...
The handler may return |null|. If I could figure out how to get at this
dictionary from javascript, then I'd still only use it to validate what the
handler returns if it doesn't return null. Instead I just added a few extra
type-checks; see the latest PS.
By the time that this information gets to the browser process, yes, there's
always a |filename| parameter that may simply be empty.

Milo?

[Randy Smith (Not in Mondays), 2013/01/22 19:43:07]

Ok.
Bloom county reference/my quoting weirdness:
http://www.thecomicstrips.com/store/add_strip.php?iid=78410

+    boolean? overwrite;
+  };
+
   [inline_doc] enum HttpMethod {GET, POST};
 
   [inline_doc] dictionary DownloadOptions {
     // The URL to download.
     DOMString url;
 
     // A file path relative to the Downloads directory to contain the downloaded
     // file.
     DOMString? filename;
 
@@ skipping 361 matching lines @@
 
     // Show the downloaded file in its folder in a file manager.
     // |downloadId|: The identifier for the downloaded file.
     static void show(long downloadId);
 
     // Erase matching $ref:DownloadItem from history. An $ref:onErased event
     // will fire for each $ref:DownloadItem that matches <code>query</code>,
     // then <code>callback</code> will be called.
     static void erase(DownloadQuery query, optional EraseCallback callback);
 
-    // TODO(benjhayden) Comment.
-    [nodoc] static void setDestination(long downloadId, DOMString relativePath);
-
     // Prompt the user to either accept or cancel a dangerous download.
     // <code>acceptDanger()</code> does not automatically accept dangerous
     // downloads.
     [nodoc] static void acceptDanger(long downloadId);
 
     // Initiate dragging the downloaded file to another application.
     static void drag(long downloadId);
   };
 
   interface Events {
     // This event fires with the $ref:DownloadItem
     // object when a download begins.
     static void onCreated(DownloadItem downloadItem);
 
     // Fires with the <code>downloadId</code> when a download is erased from
     // history.
     // |downloadId|: The <code>id</code> of the $ref:DownloadItem that was erased.
     static void onErased(long downloadId);
 
     // When any of a $ref:DownloadItem's properties
     // except <code>bytesReceived</code> changes, this event fires with the
     // <code>downloadId</code> and an object containing the properties that changed.
     static void onChanged(DownloadDelta downloadDelta);
+
+    // During the filename determination process, extensions will be given the
+    // opportunity to override the target filename. Handlers may return null in
+    // order to allow the target filename to be used, or return a
+    // $ref:FilenameDetermination object in order to override the target
+    // filename. If more than one extension overrides the filename, then one
+    // extension will win. There is no way to predict or choose which extension
+    // will win. Users should be careful to not install extensions that may
+    // conflict.
+    static void onDeterminingFilename(DownloadItem downloadItem);

[Randy Smith (Not in Mondays), 2013/01/14 21:02:29]

This is solidly and definitely me not understanding the syntax, but if this
function can return something, should it be declared void?

[benjhayden, 2013/01/17 02:52:05]

The return values are always ignored in IDL.

   };
 };