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From "Roberto Tyley (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HARMONY-6637) [classlib] [archive] Inflater.inflate() short-circuits on zero-length request, finished() never true for a zero-length data source
Date Mon, 27 Sep 2010 14:37:33 GMT

    [ https://issues.apache.org/jira/browse/HARMONY-6637?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12915321#action_12915321
] 

Roberto Tyley commented on HARMONY-6637:
----------------------------------------

The infinite loop that occurs in Harmony is because inflater.finished() is never true - in
the RI, the flag would get set to true even if you were asking for the flation of zero bytes,
but in Harmony, if numBytes is zero, the flag will never get set.

byte[] buffer=new byte[numBytes]; // the developer knows how big the data is going to be,
that info is available to him through some other metadata
int numRead=0;
while (!inflater.finished()) { // reasonable assumption by the developer here!
    int inflatedChunkSize=inflater.inflate(buffer, numRead, buffer.length-numRead); // 'buffer.length-numRead'
is zero, harmony will not set the flag
    numRead+=inflatedChunkSize;;
}

... consequently, an infinite loop :-/



> [classlib] [archive] Inflater.inflate() short-circuits on zero-length request, finished()
never true for a zero-length data source
> ----------------------------------------------------------------------------------------------------------------------------------
>
>                 Key: HARMONY-6637
>                 URL: https://issues.apache.org/jira/browse/HARMONY-6637
>             Project: Harmony
>          Issue Type: Bug
>          Components: Classlib
>            Reporter: Roberto Tyley
>            Priority: Critical
>         Attachments: Main.java
>
>
> There's code in the inflate() method of classlib/modules/archive/src/main/java/java/util/zip/Inflater.java
(r926871 and earlier) which short-cuts the inflation if the parameter 'nbytes' is 0 - ie if
the caller is actually requesting zero bytes:
> if (nbytes == 0) {
>      return 0;     --- Don't do any work: DON'T UPDATE THE *FINISHED* FLAG!
> }
> While it seems reasonable, it is in fact incompatible with the RI (which *does* attempt
to process the deflated source data in the nbytes, and will update the finished() flag) -
and so causes problems with a common inflation loop scenario, where the code loops to populate
a destination byte-array of known size while inflater.finished() is not true. Even if the
destination byte-array is known to be zero-length (e.g. we're deflating a zero-length file),
the coder might still reasonably expect calling inflate() to set the finished() flag to true.
However, unlike the RI, Harmony implementation does not update the finished() flag, which
leads to an infinite loop or some other bad outcome.
> Bit short on time right now, will try to provide a better testcase and possibly a patch
at a later date.
> best regards,
> Roberto Tyley

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