[PATCH] setlocale: Fail if iconv module for charset is not present [BZ #27996]

[Siddhesh Poyarekar]

On 7/17/21 1:58 AM, Carlos O'Donell wrote:
>> +
>> +  struct gconv_module *root = __gconv_modules_db;
>> +
>> +  while (root != NULL)
>> +    {
>> +      int cmpres;
>> +
>> +      cmpres = strcmp (name, root->from_string);
> 
> I think this is incomplete.
> 
> (a) We must have a converter that goes from name->INTERNAL.
> (b) We must have a converter that goes from INTERNAL->name.
> 
> You are only checking for (a) here, which means we can read
> input of the charset, but we can't write it out via printf
> and I don't think that would match user expectations.

Hmm, I had assumed that the presence of name->INTERNAL implies the 
presence of INTERNAL->name.  If we had to be properly general purpose 
then the check ought to confirm that we can actually find a 
transformation from name->INTERNAL and back:

===========
if (__gconv_find_transform ("INTERNAL", name, &steps, &nsteps,
                             0) != __GCONV_OK)
   return false;

__gconv_close_transform (steps, nsteps);

if (__gconv_find_transform (name, "INTERNAL", &steps, &nsteps,
                             0) != __GCONV_OK)
   return false;

__gconv_close_transform (steps, nsteps);

return true;
===========

Does that sound right?

Siddhesh