Re: [FFmpeg-devel] [PATCH v14 1/5] libavutil: Add wchartoutf8(), wchartoansi(), utf8toansi() and getenv_utf8()

["Martin Storsjö" <martin@martin.st>]

On Mon, 13 Jun 2022, Nil Admirari wrote:

> wchartoutf8() converts strings returned by WinAPI into UTF-8,
> which is FFmpeg's preffered encoding.
>
> Some external dependencies, such as AviSynth, are still
> not Unicode-enabled. utf8toansi() converts UTF-8 strings
> into ANSI in two steps: UTF-8 -> wchar_t -> ANSI.
> wchartoansi() is responsible for the second step of the conversion.
> Conversion in just one step is not supported by WinAPI.
>
> Since these character converting functions allocate the buffer
> of necessary size, they also facilitate the removal of MAX_PATH limit
> in places where fixed-size ANSI/WCHAR strings were used
> as filename buffers.
>
> getenv_utf8() wraps _wgetenv() converting its input from
> and its output to UTF-8. Compared to plain getenv(),
> getenv_utf8() requires a cleanup.
>
> Because of that, in places that only test the existence of
> an environment variable or compare its value with a string
> consisting entirely of ASCII characters, the use of plain getenv()
> is still preferred. (libavutil/log.c check_color_terminal()
> is an example of such a place.)
>
> Plain getenv() is also preffered in UNIX-only code,
> such as bktr.c, fbdev_common.c, oss.c in libavdevice
> or af_ladspa.c in libavfilter.
> ---
> libavutil/getenv_utf8.h    | 63 ++++++++++++++++++++++++++++++++++++++
> libavutil/wchar_filename.h | 51 ++++++++++++++++++++++++++++++
> 2 files changed, 114 insertions(+)
> create mode 100644 libavutil/getenv_utf8.h
>
> diff --git a/libavutil/getenv_utf8.h b/libavutil/getenv_utf8.h
> new file mode 100644
> index 0000000000..2c48a36355
> --- /dev/null
> +++ b/libavutil/getenv_utf8.h
> @@ -0,0 +1,63 @@
> +/*
> + * This file is part of FFmpeg.
> + *
> + * FFmpeg is free software; you can redistribute it and/or
> + * modify it under the terms of the GNU Lesser General Public
> + * License as published by the Free Software Foundation; either
> + * version 2.1 of the License, or (at your option) any later version.
> + *
> + * FFmpeg is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> + * Lesser General Public License for more details.
> + *
> + * You should have received a copy of the GNU Lesser General Public
> + * License along with FFmpeg; if not, write to the Free Software
> + * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
> + */
> +
> +#ifndef AVUTIL_GETENV_UTF8_H
> +#define AVUTIL_GETENV_UTF8_H
> +
> +#include <stdlib.h>
> +
> +#include "mem.h"
> +
> +#ifdef _WIN32
> +
> +#include "libavutil/wchar_filename.h"
> +
> +static inline char *getenv_utf8(const char *varname)
> +{
> +    wchar_t *varname_w, *var_w;
> +    char *var;
> +
> +    if (utf8towchar(varname, &varname_w))
> +        return NULL;
> +    if (!varname_w)
> +        return NULL;
> +
> +    var_w = _wgetenv(varname_w);
> +    av_free(varname_w);
> +
> +    if (!var_w)
> +        return NULL;
> +    if (wchartoutf8(var_w, &var))
> +        return NULL;
> +
> +    return var;
> +
> +    // No CP_ACP fallback compared to other *_utf8() functions:
> +    // non UTF-8 strings must not be returned.
> +}

Note, there are Windows configurations that entirely lack getenv() (and 
presumably _wgetenv() too), namely the Windows Store App / Windows Phone 
App API subsets for Windows 8.x. I think those functions were allowed 
again in Windows 10 though...

In configure, we have this:

check_func_headers stdlib.h getenv

enabled getenv || echo "#define getenv(x) NULL" >> $TMPH

I guess we'd might have to add getenv to e.g. the SYSTEM_FUNCS list, so 
we'd get a HAVE_GETENV in config.h - then we could make getenv_utf8 a 
no-op if HAVE_GETENV is 0.

(I'm not in a situation where I can test and investigate properly right 
now, I can maybe look closer into it later.)

// Martin


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