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From "Jimmy Jarvis (JIRA)" <>
Subject [jira] [Commented] (CB-1318) Cordova Callback Logic Not Implemented Correctly - Native Asynchronous Completion Can Call Wrong Logic in Javascript - Requires Non-recurring Unique ID as Outlined
Date Thu, 06 Sep 2012 03:03:07 GMT


Jimmy Jarvis commented on CB-1318:

JSON-P uses a unique callback identifier, similar to the proposed fix above, and is far more
reliable and easier to debug than reset with repeating IDs. It would be unfortunate overhead
to have to reinitialize our native logic every time a page reloads. The app would be come
far less responsive, at least for us. If a plugin is a bunch of stubs, it's not an big deal
as you say -- however, if it is a longer running setup process ---- I'd prefer ignoring unmatched
callbacks. I agree seeing the plugin a Reset or Terminate message would enable the plugin
authors an opportunity to do proper cleanup on pending requests, but even if they do not,
unique ID's (like JSON-P) are a better solution than repeating IDs.
> Cordova Callback Logic Not Implemented Correctly -  Native Asynchronous Completion Can
Call Wrong Logic in Javascript - Requires Non-recurring Unique ID as Outlined
> --------------------------------------------------------------------------------------------------------------------------------------------------------------------
>                 Key: CB-1318
>                 URL:
>             Project: Apache Cordova
>          Issue Type: Bug
>          Components: Android, iOS
>    Affects Versions: 2.0.0
>            Reporter: Jimmy Jarvis
>            Assignee: Shazron Abdullah
>            Priority: Critical
>             Fix For: 2.2.0
> This bug creates very difficult to find execution anomalies for any asynchronous callback
that occurs when the calling context has changed.
> PROBLEM: Cordova callback logic can trigger the callback function of an unrelated call
from a different context. When a call from Javascript is made, Cordova generates a new callbackId,
adds it to the cordova.callbacks array, and passes it along to the native code. Some time
later, when the native code completes the request, it injects javascript to call the callbackSuccess
or callbackError function. The respective callback handler looks up the callback attributes
from the cordova.callbacks array and executes the original caller's completion function. The
problem is each page, or reload of a page, resets the callbackId counter to zero and new calls
end up reusing the same callbackId, even though the native code haS not yet completed the
prior request. This can occur upon a new page load or reload upon an empty href in an anchor
tag. A call to native code from page1.html could trigger the completion routine on page2.html
because the native code has no context of the change on the other side of the bridge.
> SOLUTION: Replace the incrementing callbackId with a unique identifier to insure only
the caller's completion logic will be called. I have done this with a Pseudo-GUID generator.
Fix outlined below:
> // REPLACE THIS LINE in both cordova.2.0.0.js and cordova.ios.js
>         callbackId = service + cordova.callbackId++;    // BUG: incrementing Id's can
call unrelated callback logic
>         callbackId = service + ":" + 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxxxxx'.replace(/[xy]/g,
function(c) {var r = Math.random()*16|0,v=c=='x'?r:r&0x3|0x8;return v.toString(16);});
// Generate unique callbackID with Pseudo-GUID
> This fix insures no code will execute if the caller's context has changed and is a more
well formatted callbackId.

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