[erlang-bugs] Bug in unicode characters_to_list trap

[Patrik Nyblom]

Hi again!

On 05/02/2013 10:48 AM, Patrik Nyblom wrote:
> Hi David!
>
> On 05/01/2013 06:35 PM, David Buckley wrote:
>> Simple test session:
>>
>> [ 17:28 ] bucko@REDACTED:~% erl
>> Erlang R15B01 (erts-5.9.1) [source] [64-bit] [smp:4:4] 
>> [async-threads:0] [hipe] [kernel-poll:false]
>>
>> Eshell V5.9.1  (abort with ^G)
>> 1> <<_, RR/binary>> = <<$a,164,161,$b>>.
>> <<"a¤¡b">>
>> 2> RR.
>> <<"¤¡b">>
>> 3> unicode:characters_to_list(RR).
>> {error,[],<<"a¤¡">>}
>> 4> unicode:characters_to_list(list_to_binary(binary_to_list(RR))).
>> {error,[],<<"¤¡b">>}
> Yep - that's a bug, no doubt...
> Can you try a source code patch when I've found a cure?
A small patch is attached, the full patch will of course also cointain a 
test case, but this is tha minimal fix.
It would be great if you would also test it, i will meanwhile prepare a 
fix in maint...
>>
>> I'm using Debian's default erlang build, but I've verified the bug on
>> various others, and can't see it in the release notes.
>>
>> Description: The latter two calls should return the dame value, as
>> list_to_binary(binary_to_list(RR)) =:= RR.
>>
>> I would guess that the code in erlang's guts is taking the falure offset
>> into the binary part as an offset into the full binary. At least, the
>> return values are consistent with this.
> Good guess, I agree.
And, you were absolutely right!
>>
>> Workaround is just to call list_to_binary(binary_to_list()) on your data
>> before calling unicode:characters_to_list on it. Or manually offsetting
>> into the binary yourself in the case of a failed parse.
>>
> Thanks!
> /Patrik
Cheers,
Patrik
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