Re: [FFmpeg-devel] [PATCH v17 1/5] libavutil: Add wchartoutf8(), wchartoansi(), utf8toansi() and getenv_utf8()

[Andreas Rheinhardt <andreas.rheinhardt@outlook.com>]

Nil Admirari:
> 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.
> ---
>  configure                  |  1 +
>  libavutil/getenv_utf8.h    | 71 ++++++++++++++++++++++++++++++++++++++
>  libavutil/wchar_filename.h | 51 +++++++++++++++++++++++++++
>  3 files changed, 123 insertions(+)
>  create mode 100644 libavutil/getenv_utf8.h
> 
> diff --git a/configure b/configure
> index 3dca1c4bd3..fa37a74531 100755
> --- a/configure
> +++ b/configure
> @@ -2272,6 +2272,7 @@ SYSTEM_FUNCS="
>      fcntl
>      getaddrinfo
>      getauxval
> +    getenv
>      gethrtime
>      getopt
>      GetModuleHandle
> diff --git a/libavutil/getenv_utf8.h b/libavutil/getenv_utf8.h
> new file mode 100644
> index 0000000000..161e3e6202
> --- /dev/null
> +++ b/libavutil/getenv_utf8.h
> @@ -0,0 +1,71 @@
> +/*
> + * 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 HAVE_GETENV
> +
> +#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.
> +}
> +
> +#else
> +
> +static inline char *getenv_utf8(const char *varname)
> +{
> +    return av_strdup(getenv(varname));

This forces allocations and frees in scenarios where this is wholly
unnecessary. This can be avoided by adding a custom deallocator for
strings returned via getenv_utf8: Namely a define/wrapper around av_free
in the _WIN32 and a no-op else.

> +}
> +
> +#endif // _WIN32
> +
> +#else
> +
> +#define getenv_utf8(x) NULL
> +
> +#endif // HAVE_GETENV
> +
> +#endif // AVUTIL_GETENV_UTF8_H
> diff --git a/libavutil/wchar_filename.h b/libavutil/wchar_filename.h
> index f36d9dfea3..a6d71e52e5 100644
> --- a/libavutil/wchar_filename.h
> +++ b/libavutil/wchar_filename.h
> @@ -41,6 +41,57 @@ static inline int utf8towchar(const char *filename_utf8, wchar_t **filename_w)
>      return 0;
>  }
>  
> +av_warn_unused_result
> +static inline int wchartocp(unsigned int code_page, const wchar_t *filename_w,
> +                            char **filename)
> +{
> +    DWORD flags = code_page == CP_UTF8 ? WC_ERR_INVALID_CHARS : 0;
> +    int num_chars = WideCharToMultiByte(code_page, flags, filename_w, -1,
> +                                        NULL, 0, NULL, NULL);
> +    if (num_chars <= 0) {
> +        *filename = NULL;
> +        return 0;
> +    }
> +    *filename = av_malloc_array(num_chars, sizeof *filename);
> +    if (!*filename) {
> +        errno = ENOMEM;
> +        return -1;
> +    }
> +    WideCharToMultiByte(code_page, flags, filename_w, -1,
> +                        *filename, num_chars, NULL, NULL);
> +    return 0;
> +}
> +
> +av_warn_unused_result
> +static inline int wchartoutf8(const wchar_t *filename_w, char **filename)
> +{
> +    return wchartocp(CP_UTF8, filename_w, filename);
> +}
> +
> +av_warn_unused_result
> +static inline int wchartoansi(const wchar_t *filename_w, char **filename)
> +{
> +    return wchartocp(CP_ACP, filename_w, filename);
> +}
> +
> +av_warn_unused_result
> +static inline int utf8toansi(const char *filename_utf8, char **filename)
> +{
> +    wchar_t *filename_w = NULL;
> +    int ret = -1;
> +    if (utf8towchar(filename_utf8, &filename_w))
> +        return -1;
> +
> +    if (!filename_w) {
> +        *filename = NULL;
> +        return 0;
> +    }
> +
> +    ret = wchartoansi(filename_w, filename);
> +    av_free(filename_w);
> +    return ret;
> +}
> +
>  /**
>   * Checks for extended path prefixes for which normalization needs to be skipped.
>   * see .NET6: PathInternal.IsExtended()

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