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Date: Tue, 27 Feb 2018 15:19:40 -0500
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com, Steffen Nurpmeso <steffen@...oden.eu>
Subject: Re: Re: iconv failure (ISO-2022-JP) since musl update on
 AlpineLinux

On Tue, Feb 27, 2018 at 08:44:32PM +0100, Steffen Nurpmeso wrote:
> Hi.
> 
> Rich Felker wrote:
> 
> sorry i did not get this :)

Sorry I neglected to keep you CC'd.

> but i wrote:
>  ||After updating to musl-1.1.19-r0 there i saw test failures for the
>  ||MUA i maintain, namely regarding the mentioned charset.  I will
>  ||attach a file to reproduce.  (Am not subscribed.)
>  ...
>  ||  #?0[steffen@...on steffen]$ cksum in.utf 
>  ||  1259742080 686 in.utf
>  ||  #?0[steffen@...on steffen]$ iconv -f utf8 -t iso-2022-jp <in.utf|cksum
>  ||  2184132317 536
>  ||  #?0[steffen@...on steffen]$ iconv --version
>  ||  iconv (GNU libiconv 1.11)
>  ||..
>  ||  #?0[steffen@...ex tmp]$ cksum in.utf 
>  ||  1259742080 686 in.utf
>  ||  #?0[steffen@...ex tmp]$ iconv -f utf8 -t iso-2022-jp <in.utf|cksum 
>  ||  209789743 1736
>  ||  #?0[steffen@...ex tmp]$ apk info --who-owns /usr/bin/iconv 
>  ||  /usr/bin/iconv is owned by musl-utils-1.1.19-r0
> 
>  |Does the data round-trip correctly? I don't think you can expect
> 
> Ok, i see what you mean, yes, musl iconv(1) can roundtrip.  But..
> But for one the error is new (though i actually have forgotten
> whether the test ever ran on a musl box or only on BSD and glibc
> Linux boxes, but if i recall, it did run, and then it did succeed,
> definetely), and then...
> 
>  |bitwise match between outputs of different ISO-2022-JP converters,
>  |unless perhaps they both guarantee minimality, because the ISO-2022-JP
>  |representation of a string is highly nonunique.
>  |
>  |In particular musl's to-ISO-2022-JP converter is stateless and always
>  |generates shifts in/out around every non-ASCII character. Of course
>  |this is highly suboptimal, but in the worst case (where the caller
>  |calls iconv one character at a time) the iconv API can't do any better
>  |because strings are required to end in the unshifted state, and the
>  |iconv API doesn't have any method to "finalize" a conversion. This
>  |implies that every time iconv returns with non-ASCII as the most
>  |recent output character, it must be followed by a shift back to the
>  |initial (ASCII) state.
>  |
>  |We could improve this in the case of batch conversions by overwriting
>  |the previous shift-back-to-initial and skipping the next shift if the
>  |character set of the next character to output matches the previous
>  |one, but that only works within a single batch call, since iconv can't
>  |write outside the buffer passed to it for the current call. This is an
>  |improvement I think I want to make, since it would improve typical
>  |output size a lot, but the cost is output determinism under different
>  |chunking by the caller.
> 
> Well...  In my cases the MUA fails to convert to ISO-2022-JP at
> all, because an iconv(3) error happens.  And when i instrument my
> code like
> 
>      for(;;){
>         size_t sz;
> 
>   fprintf(stderr, "iconv(3): in %lu out: %lu\n",*inbleft,*outbleft);
>   fprintf(stderr, "     in<%.*s>\n",(int)*inbleft,*inb);
>         sz = iconv(cd, __INBCAST(inb), inbleft, outb, outbleft);
>         if(sz > 0 && !(icf & n_ICONV_IGN_NOREVERSE)){
>   fprintf(stderr, "iconv(3) returned 0x%lX: %s\n",(ul_i)sz,strerror(errno));
>            err = n_ERR_NOENT;
>            goto jleave;
>         }
>         if(sz != (size_t)-1)
>            break;
> 
> then i get
> 
>   #?1[steffen@...ex nail.git]$ v mae-test-behave_iconv_mbyte_base64-2
>   ICONV 2
>   iconv(3): in 220 out: 427
>        in<シジュウカラ科(シジュウカラか、学名 Paridae)は、鳥類スズメ目の科である。シジュウカラ(四十雀)と総称されるが、狭義にはこの1種をシジュウカラと呼ぶ。
>   >
>   iconv(3) returned 0xFFFFFFFFFFFFFFFF: Argument list too long
>   ICONV 2 err: 2
> 
> And that is somehow ooops?  Interestingly if i call iconv(1) only
> on these 220 bytes i can roundtrip that, too.  Hmmm.  ...
> I thought maybe it is because of the tcc(1) compiler i use, but
> i can reproduce this with AlpineLinux gcc(1), too.  I don't know.

I think the test is just using an output buffer that's under the
worst-case size needed for conversion to ISO-2022-JP. The E2BIG error
is specified for "Input conversion stopped due to lack of space in the
output buffer" and is not really an error; is just means the
conversion stopped before reaching the end and you need to resume with
a new buffer for the remainder of the conversion.

Rich

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