Re: [FFmpeg-devel] [PATCH] avformat/tls_openssl: fix warnings when openssl is lower version

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

Jack Lau via ffmpeg-devel:
> In higher versions (like openssl 1.1.1 and higher),
> the function signature is BIO *BIO_new_mem_buf(const void *buf, int len),
> so passing a const string doesn't cause an warnings.
> However, in lower versions of OpenSSL,
> the function signature becomes BIO *BIO_new_mem_buf(void *buf, int len),
> which leads to warnings.
> 
> OpenSSL guarantees that it will not modify the string,
> so it's safe to cast the pem_str to (void *) to avoid this warning.
> 
> Signed-off-by: Jack Lau <jacklau1222@qq.com>
> ---
>  libavformat/tls_openssl.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/tls_openssl.c b/libavformat/tls_openssl.c
> index 86e8935fee..5387e21df1 100644
> --- a/libavformat/tls_openssl.c
> +++ b/libavformat/tls_openssl.c
> @@ -415,7 +415,7 @@ error:
>   */
>  static EVP_PKEY *pkey_from_pem_string(const char *pem_str, int is_priv)
>  {
> -    BIO *mem = BIO_new_mem_buf(pem_str, -1);
> +    BIO *mem = BIO_new_mem_buf((void *)pem_str, -1);
>      if (!mem) {
>          av_log(NULL, AV_LOG_ERROR, "BIO_new_mem_buf failed\n");
>          return NULL;
> @@ -445,7 +445,7 @@ static EVP_PKEY *pkey_from_pem_string(const char *pem_str, int is_priv)
>   */
>  static X509 *cert_from_pem_string(const char *pem_str)
>  {
> -    BIO *mem = BIO_new_mem_buf(pem_str, -1);
> +    BIO *mem = BIO_new_mem_buf((void *)pem_str, -1);
>      if (!mem) {
>          av_log(NULL, AV_LOG_ERROR, "BIO_new_mem_buf failed\n");
>          return NULL;

Shouldn't this use #if checks to only cast const away when building for
old versions so that we do not forget to remove these casts when we drop
support for these old versions (and to avoid warnings when using
-Wcast-qual)?

- Andreas

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