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From "Markus Thies (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HTTPCORE-316) HeaderGroup clone removes headers from original
Date Sat, 09 Apr 2016 12:37:25 GMT

    [ https://issues.apache.org/jira/browse/HTTPCORE-316?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15233529#comment-15233529
] 

Markus Thies commented on HTTPCORE-316:
---------------------------------------

Well, maybe it was was not the best wording..., but I meant, clone(ing) from its theoretical
definition would only make shallow copies. That means, there should not be a copy made of
the List.
But the bug in the code is that the new clone is handled as if it was a real copy (instead
of a clone) and the headers are removed from the clone ( even I could not understand the intend
why the header of the clone should be cleared). Removing from the clone removed it also from
the original, what is not expected and considered as being the bug.

If any code would rely on the behavior that the new clone has no headers defined should not
use clone but a deep copy (actually copying the object).

The Unit test demonstrates perfectly the correct behavior!

> HeaderGroup clone removes headers from original
> -----------------------------------------------
>
>                 Key: HTTPCORE-316
>                 URL: https://issues.apache.org/jira/browse/HTTPCORE-316
>             Project: HttpComponents HttpCore
>          Issue Type: Bug
>          Components: HttpCore
>    Affects Versions: 4.2.2
>         Environment: All platforms
>            Reporter: Markus Thies
>              Labels: HeaderGroup, patch
>             Fix For: 4.2.3
>
>   Original Estimate: 2h
>  Remaining Estimate: 2h
>
> The class org.apache.http.message.HeaderGroup  provides a method clone().
> If clone is called the original object's headers are removed.
> The root cause of this is, that the class HeaderGroup has only one attribute (headers)
which is a List.
> As clone does a shallow copy the List is not cloned (that is correct).
> But within the method clone(), the headers of the newly created clone are removed (by
calling clear()) but they actually also clear the headers of the original object (since it
is not a copy).
> So this leads to very tricky problems in code where the headers are essential to be available
in the clone and in the original object.
> Original code:
>     public Object clone() throws CloneNotSupportedException {
>         HeaderGroup clone = (HeaderGroup) super.clone();
>         clone.headers.clear();
>         clone.headers.addAll(this.headers);
>         return clone;
>     }
> Corrected code:
>     public Object clone() throws CloneNotSupportedException {
>         HeaderGroup clone = (HeaderGroup) super.clone();
>         //BUG: would also clear the headers original 
>         //clone.headers.clear();
>         //clone.headers.addAll(this.headers);
>         return clone;
>     }



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