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chrome/renderer/resources/extensions/file_browser_private_custom_bindings.js

Index: chrome/renderer/resources/extensions/file_browser_private_custom_bindings.js
diff --git a/chrome/renderer/resources/extensions/file_browser_private_custom_bindings.js b/chrome/renderer/resources/extensions/file_browser_private_custom_bindings.js
index df81bbaef14d54cfa7dc8844f46a6dd372d3ff16..e0b90c96fa1fb384e7eac1d9daa86ceca89b86f9 100644
--- a/chrome/renderer/resources/extensions/file_browser_private_custom_bindings.js
+++ b/chrome/renderer/resources/extensions/file_browser_private_custom_bindings.js
@@ -27,12 +27,17 @@ chromeHidden.registerCustomHook('fileBrowserPrivate', function(bindingsAPI) {
 
   apiFunctions.setCustomCallback('searchGData',
                                  function(name, request, response) {
-    if (response && !response.error && response) {
-      for (var i = 0; i < response.length; i++)
-       response[i] = GetExternalFileEntry(response[i]);
+    if (response && !response.error && response.entries) {
+      for (var i = 0; i < response.entries.length; i++)
+       response.entries[i] = GetExternalFileEntry(response.entries[i]);
     }
+
+    // So |request.callback| doesn't break if response is not defined.
+    if (!response)
+      response = {};

[asargent_no_longer_on_chrome, 2012/07/20 22:59:02]

nit: I think this technically breaks the contract of the API as specified in the
file_browser_private.json file, since |undefined| is not of type array / string
for entries and nextFeed respectively. The reason you may not be seeing a
problem with this is that having a custom callback skips the normal schema
validation that we do on callback dispatch. 

So, maybe do the following?

if (!response)
  response = {};
if (typeof(response.entries) == "undefined")
  response.entries = [];
if (typeof(response.nextFeed) == "undefined")
  response.nextFeed = "";

Alternatively, you can mark |entries| and |nextFeed| as optional in the
definition of the callback arguments in the file_browser_private.json file. 

[tbarzic, 2012/07/20 23:57:54]

Isn't the contract of the api already broken if !response is true, should we
really force array and string in that case? 
(afaik !response can legitimately happen if an error occurs in extension
function; in that case I think the function should return undefined).

maybe it would be better to just bail out here and continue with normal
validation (and break if there was no error)?

[asargent_no_longer_on_chrome, 2012/07/23 15:59:37]

It looks like the default behavior of handleResponse (defined in
chrome/renderer/resources/extensions/send_request.js) is to only validate
callback arguments if there was no error.

So I think it's actually fine to do as you suggest - just call the callback with
null or undefined. Note that the convention is also that the lastError property
should be set for the callback to examine
(http://code.google.com/chrome/extensions/extension.html#property-lastError). If
in your browser process ExtensionFunction subclass you've set the error_ member
variable and returned false from your RunImpl method, then lastError will be set
automatically to the value of error_. 

Otherwise you can manually set it here in the renderer by doing:

var lastError = require('lastError');
...

if (<something bad happened>) {
  lastError.set(<some string>)
}

[tbarzic, 2012/07/23 19:38:00]

ok, I'll leave it as it is then..

+
     if (request.callback)
-      request.callback(response);
+      request.callback(response.entries, response.nextFeed);
     request.callback = null;
   });
 });