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Date: Thu, 6 Sep 2012 14:03:07 +1100 (NCT)
From: "Jimmy Jarvis (JIRA)" <jira@apache.org>
To: callback-dev@incubator.apache.org
Message-ID: <549034274.42711.1346900587733.JavaMail.jiratomcat@arcas>
In-Reply-To: <1567442393.19746.1346374928107.JavaMail.jiratomcat@arcas>
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
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    [ https://issues.apache.org/jira/browse/CB-1318?page=3Dcom.atlassian.ji=
ra.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=3D1344937=
5#comment-13449375 ]=20

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 ID=
s. It would be unfortunate overhead to have to reinitialize our native logi=
c 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 ign=
oring unmatched callbacks. I agree seeing the plugin a Reset or Terminate m=
essage 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.
               =20
> Cordova Callback Logic Not Implemented Correctly -  Native Asynchronous C=
ompletion Can Call Wrong Logic in Javascript - Requires Non-recurring Uniqu=
e ID as Outlined
> -------------------------------------------------------------------------=
---------------------------------------------------------------------------=
----------------
>
>                 Key: CB-1318
>                 URL: https://issues.apache.org/jira/browse/CB-1318
>             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 async=
hronous callback that occurs when the calling context has changed.
> PROBLEM: Cordova callback logic can trigger the callback function of an u=
nrelated call from a different context. When a call from Javascript is made=
, Cordova generates a new callbackId, adds it to the cordova.callbacks arra=
y, and passes it along to the native code. Some time later, when the native=
 code completes the request, it injects javascript to call the callbackSucc=
ess or callbackError function. The respective callback handler looks up the=
 callback attributes from the cordova.callbacks array and executes the orig=
inal 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 t=
he same callbackId, even though the native code haS not yet completed the p=
rior request. This can occur upon a new page load or reload upon an empty h=
ref in an anchor tag. A call to native code from page1.html could trigger t=
he 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 =3D service + cordova.callbackId++;    // BUG: increme=
nting Id's can call unrelated callback logic
> // WITH THIS LINE
>         callbackId =3D service + ":" + 'xxxxxxxx-xxxx-4xxx-yxxx-xxxxxxxxx=
xxx'.replace(/[xy]/g, function(c) {var r =3D Math.random()*16|0,v=3Dc=3D=3D=
'x'?r:r&0x3|0x8;return v.toString(16);}); // Generate unique callbackID wit=
h 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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