x-callback-url spec, R2 – new “x-cancel” parameter

We’ve gotten feedback that there are use cases for x-callback-url where the user is given the option to “cancel” the requested operation. Previous versions of the spec offered only parameters for success and error, so we added the “x-callback” parameter to the spec to support the case where the user wants to cancel and be returned to the source app. See the spec for details.

A call to iOS Twitter client developers!

With Instapaper’s x-callback-url support available, I hope people will start to see some of the cool possibilities for more complex handoffs between iOS apps. The next big thing I’d really like to see is for Twitter clients to extend their URL schemes to support x-callback-url, particularly to allow the user to jump over to post a tweet, and then be returned to what they were doing in their original app.

Most of the major iOS Twitter clients already support incoming URLs for status updates. For example, if you want to send a status update to Twitteriffic, just call:


For Twitter:


This is strictly a one-way call, however. Why not use x-callback-url to allow passing a return callback for after the user edits and sends the tweet. For example:


NOTE: arguments should be URL encoded, but were not for legibility.

This could work very much like the existing support in the Twitter app, opening the compose window with the text pre-entered — but after the user taps “Send” and the tweet is successfully posted, fire the callback URL and return the user to where they started.

With this sort of support available, it would be easy for apps to add “Share” functionality that lets their user take advantage of the accounts their users already have setup in their Twitter client, along with all the great composing tools, without forcing the user having leave their app with no clear way back.

If you think this is a cool idea, contact the developer of your favorite Twitter client and let them know. And tell them we’d be happy to help with testing!