Re: [FFmpeg-devel] [PATCH v2 1/2] avformat/file: Add a specialized url_check callback for pipe protocol

[Neil Roberts <bpeeluk-at-yahoo.co.uk@ffmpeg.org>]

Bump.

Is anyone interested in looking at these two patches? I’m trying to get
into ffmpeg development and it would be nice to get some experience of
the full process of getting a patch landed. I don’t have commit rights.

Thanks in advance for any feedback.

Regards,
– Neil

Neil Roberts <bpeeluk-at-yahoo.co.uk@ffmpeg.org> writes:

> Using file_check for the pipe protocol doesn't make sense. For example,
> for a URL like “pipe:0” it would end up checking whether the “pipe:0”
> file exists. This patch instead makes it check the access modes on the
> corresponding file descriptor using fcntl on *nix and DuplicateHandle on
> Windows.
>
> v2: Use DuplicateHandle on Windows to check whether the duplicated
>     handle can have the corresponding access flags.
>
> Signed-off-by: Neil Roberts <bpeeluk@yahoo.co.uk>
> ---
>  libavformat/file.c | 74 ++++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 71 insertions(+), 3 deletions(-)
>
> diff --git a/libavformat/file.c b/libavformat/file.c
> index 98c9e81bcb..b3f7bc9282 100644
> --- a/libavformat/file.c
> +++ b/libavformat/file.c
> @@ -375,9 +375,8 @@ const URLProtocol ff_file_protocol = {
>  
>  #if CONFIG_PIPE_PROTOCOL
>  
> -static int pipe_open(URLContext *h, const char *filename, int flags)
> +static int pipe_get_fd(const char *filename, int flags)
>  {
> -    FileContext *c = h->priv_data;
>      int fd;
>      char *final;
>      av_strstart(filename, "pipe:", &filename);
> @@ -390,6 +389,14 @@ static int pipe_open(URLContext *h, const char *filename, int flags)
>              fd = 0;
>          }
>      }
> +
> +    return fd;
> +}
> +
> +static int pipe_open(URLContext *h, const char *filename, int flags)
> +{
> +    FileContext *c = h->priv_data;
> +    int fd = pipe_get_fd(filename, flags);
>  #if HAVE_SETMODE
>      setmode(fd, O_BINARY);
>  #endif
> @@ -398,13 +405,74 @@ static int pipe_open(URLContext *h, const char *filename, int flags)
>      return 0;
>  }
>  
> +static int pipe_check(URLContext *h, int mask)
> +{
> +    int fd = pipe_get_fd(h->filename, mask);
> +    int access = 0;
> +
> +#ifdef _WIN32
> +
> +    HANDLE pipe_handle = (HANDLE) _get_osfhandle(fd);
> +    HANDLE tmp_handle;
> +
> +    if (pipe_handle == INVALID_HANDLE_VALUE)
> +        return AVERROR(errno);
> +
> +    if (mask & AVIO_FLAG_READ &&
> +        DuplicateHandle(GetCurrentProcess(), /* hSourceProcessHandle */
> +                        pipe_handle,
> +                        GetCurrentProcess(), /* hTargetProcessHandle */
> +                        &tmp_handle,
> +                        FILE_READ_DATA,
> +                        FALSE, /* bInheritHandle */
> +                        0 /* options */)) {
> +        access |= AVIO_FLAG_READ;
> +        CloseHandle(tmp_handle);
> +    }
> +
> +    if (mask & AVIO_FLAG_WRITE &&
> +        DuplicateHandle(GetCurrentProcess(), /* hSourceProcessHandle */
> +                        pipe_handle,
> +                        GetCurrentProcess(), /* hTargetProcessHandle */
> +                        &tmp_handle,
> +                        FILE_WRITE_DATA,
> +                        FALSE, /* bInheritHandle */
> +                        0 /* options */)) {
> +        access |= AVIO_FLAG_WRITE;
> +        CloseHandle(tmp_handle);
> +    }
> +
> +#else /* _WIN32 */
> +
> +    int status_flags = fcntl(fd, F_GETFL);
> +
> +    if (status_flags == -1)
> +        return AVERROR(errno);
> +
> +    switch (status_flags & O_ACCMODE) {
> +    case O_RDONLY:
> +        access = AVIO_FLAG_READ;
> +        break;
> +    case O_WRONLY:
> +        access = AVIO_FLAG_WRITE;
> +        break;
> +    case O_RDWR:
> +        access = AVIO_FLAG_READ | AVIO_FLAG_WRITE;
> +        break;
> +    }
> +
> +#endif /* _WIN32 */
> +
> +    return access & mask;
> +}
> +
>  const URLProtocol ff_pipe_protocol = {
>      .name                = "pipe",
>      .url_open            = pipe_open,
>      .url_read            = file_read,
>      .url_write           = file_write,
>      .url_get_file_handle = file_get_handle,
> -    .url_check           = file_check,
> +    .url_check           = pipe_check,
>      .priv_data_size      = sizeof(FileContext),
>      .priv_data_class     = &pipe_class,
>      .default_whitelist   = "crypto,data"
> -- 
> 2.37.2
>
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