Re: [musl] Broken freopen() does not reset fwide()

[Rich Felker <dalias@libc.org>]

On Tue, Aug 16, 2022 at 06:33:35PM +0000, Anonymousemail wrote:
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> 
>    I'm using musl based distribution.
>    The official example from https://en.cppreference.com/w/c/io/fwide is
>    malfunctioning, musl does not reset the fwide(), returns -1 (meaning BYTE
>    oriented).
> 
>    Output from example on musl:
>    1) A newly opened stream has no orientation.
>        no orientation
>    2) Establish byte orientation.
>        narrow orientation
>        narrow character read '#'
>        wide character read 'i'
>    3) Only freopen() can reset stream orientation.
>    4) A reopened stream has no orientation.
>        narrow orientation  <- problem detected here, should say "no
>    orientation"
>    5) Establish wide orientation.
>        narrow orientation
>        narrow character read '#'
>        wide character read 'i'
> 
>    Another simple example to reproduce the issue.:
>    #include <stdio.h>
>    #include <wchar.h>
>    #include <stdlib.h> // for EXIT_SUCCESS
>    #include <assert.h>
> 
>    int main() {
>        enum { narrow = -1, query = 0, wide = 1 };
>        FILE* test = fopen("test.bin", "r");
>        if(!test) {
>            puts("You need to have test.bin file.");
>            abort();
>        }
>        // establish NARROW orientation
>        fwide(test, narrow);
>        // reopen to reset, broken on musl
>        freopen("test.bin", "r", test);
>        assert(fwide(test, query) == 0); // will fail on musl
>        // CLEANUP
>        fclose(test);
>        // Exit the program
>        return EXIT_SUCCESS;
>    }
> 
>    -----
>    Save as main.c, run with
>    cc main.c
>    echo test >test.bin
>    ../a.out
> 
>    Will output
>    Assertion failed: fwide(test, query) == 0 (main2.c: main: 17)
>    Aborted

Indeed this looks like an oversight. I'll need to look at what it will
take to fix it. Naively, just f->wide = 0 before successful return in
freopen seems ok, but probably also f->locale needs to be set to 0 to
reset the encoding rule, and it might be necessary to null out some
buffer pointers to force future calls to stdio functions to reprobe
the width.

Thanks for the report.

BTW is there a way you can fix the mailer you're using? The plain text
version of your mail was not plain text, but was littered with html
entities (&nbsp; etc.) making it unreadable, so I rendered the html
version to text in order to be able to reply.

Rich