SSL_get_fd, SSL_get_rfd, SSL_get_wfd - get file descriptor linked to an SSL object

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       Licensed under the Apache License 2.0 (the "License").  You may not use this file  except  in  compliance
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       <https://www.openssl.org/source/license.html>.

3.5.0                                              2025-06-04                                   SSL_GET_FD(3SSL)

SSL_get_fd() returns the file descriptor which is linked to ssl.  SSL_get_rfd() and SSL_get_wfd() return
       the file descriptors for the read or the write channel, which can be different. If the read and the write
       channel are different, SSL_get_fd() will return the file descriptor of the read channel.

       SSL_get_fd, SSL_get_rfd, SSL_get_wfd - get file descriptor linked to an SSL object

       The following return values can occur:

       -1  The  operation  failed,  because  the  underlying  BIO  is not of the correct type (suitable for file
           descriptors).

       >=0 The file descriptor linked to ssl.

SSL_set_fd(3), ssl(7) , bio(7)

        #include <openssl/ssl.h>

        int SSL_get_fd(const SSL *ssl);
        int SSL_get_rfd(const SSL *ssl);
        int SSL_get_wfd(const SSL *ssl);