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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-136) Overlong UTF8's not handled well
Date Tue, 23 May 2006 17:38:30 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-136?page=comments#action_12412964 ] 

Doug Cutting commented on HADOOP-136:
-------------------------------------

If we can't fix the UTF8 class back-compatibly, then I'd prefer we provide a replacement class
and deprecate UTF8.  Long-term we don't want two classes around that do almost the same thing.
 We could name the new class Text or Chars.  It could use a variable number of bytes to indicate
its length, using the 1 byte for lengths less than 127, two-bytes for lengths less than 2^14,
etc., then encode the content with UTF-8.  Note that the length should be the number of bytes
of content, not the number of encoded characters.  Does this sound reasonable?


> Overlong UTF8's not handled well
> --------------------------------
>
>          Key: HADOOP-136
>          URL: http://issues.apache.org/jira/browse/HADOOP-136
>      Project: Hadoop
>         Type: Bug

>   Components: io
>     Reporter: Dick King
>     Priority: Minor
>  Attachments: largeutf8.patch
>
> When we feed an overlong string to the UTF8 constructor, two suboptimal things happen.
> First, we truncate to 0xffff/3 characters on the assumption that every character takes
three bytes in UTF8.  This can truncate strings that don't need it, and it can be overoptimistic
since there are characters that render as four bytes in UTF8.
> Second, the code doesn't actually handle four-byte characters.
> Third, there's a behavioral discontinuity.  If the string is "discovered" to be overlong
by the arbitrary limit described above, we truncate with a log message, otherwise we signal
a RuntimeException.  One feels that both forms of truncation should be treated alike.  However,
this issue is concealed by the second issue; the exception will never be thrown because UTF8.utf8Length
can't return more than three times the length of its input.
> I would recommend changing UTF8.utf8Length to let its caller know how many characters
of the input string will actually fit if there's an overflow [perhaps by returning the negative
of that number] and doing the truncation accurately as needed.
> -dk

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