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From "Jimmy Jarvis (JIRA)" <j...@apache.org>
Subject [jira] [Created] (CB-1318) Callback Logic Not Implemented Correctly - Native Asynchronous Completion Can Call Wrong Logic in Javascript - Requires Non-recurring Unique ID as Suggested
Date Fri, 31 Aug 2012 01:02:08 GMT
Jimmy Jarvis created CB-1318:
--------------------------------

             Summary: Callback Logic Not Implemented Correctly -  Native Asynchronous Completion
Can Call Wrong Logic in Javascript - Requires Non-recurring Unique ID as Suggested
                 Key: CB-1318
                 URL: https://issues.apache.org/jira/browse/CB-1318
             Project: Apache Cordova
          Issue Type: Bug
          Components: iOS
    Affects Versions: 2.0.0
            Reporter: Jimmy Jarvis
            Assignee: Shazron Abdullah
            Priority: Critical


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

// WITH THIS LINE
        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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