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From "Doug Cutting (JIRA)" <j...@apache.org>
Subject [jira] Commented: (HADOOP-136) Overlong UTF8's not handled well
Date Mon, 08 May 2006 18:57:21 GMT
    [ http://issues.apache.org/jira/browse/HADOOP-136?page=comments#action_12378493 ] 

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

I think we should aim for 100% back-compatibility.  Perhaps if the 16th bit is set, and the
next byte is invalid UTF-8 (e.g., a null) then we can assume the fourth byte is part of the
length, otherwise the third and fourth are payload data.  That would permit up to 2^23 bytes.
 In a subsequent release we could drop this "feature", permitting up to 2^31 bytes.  Could
something like that work?


> 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

>
> 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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