Implement chrome.downloads.onDeterminingFilename()

chrome/common/extensions/api/downloads.idl

Index: chrome/common/extensions/api/downloads.idl
diff --git a/chrome/common/extensions/api/downloads.idl b/chrome/common/extensions/api/downloads.idl
index b6ca8d6c204e46bdc9ef99a4f25a961d06c34c83..fa5629573bc38904685d36bda1d51364d17cb73f 100644
--- a/chrome/common/extensions/api/downloads.idl
+++ b/chrome/common/extensions/api/downloads.idl
@@ -12,6 +12,17 @@ namespace downloads {
     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 {
@@ -393,9 +404,6 @@ namespace downloads {
     // 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.
@@ -419,5 +427,15 @@ namespace downloads {
     // 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.

   };
 };