SSL_set_fd, SSL_set_rfd, SSL_set_wfd - connect the SSL object with a file descriptor

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       Licensed under the Apache License 2.0 (the "License").  You may not use this file  except  in  compliance
       with  the  License.   You  can  obtain  a  copy  in  the  file  LICENSE  in the source distribution or at
       <https://www.openssl.org/source/license.html>.

3.5.0                                              2025-06-04                                   SSL_SET_FD(3SSL)

SSL_set_fd() sets the file descriptor fd as the input/output facility for the TLS/SSL (encrypted) side of
       ssl. fd will typically be the socket file descriptor of a network connection.

       When performing the operation, a socketBIO is automatically created to interface between the ssl and fd.
       The BIO and hence the SSL engine inherit the behaviour of fd. If fd is nonblocking, the ssl will also
       have nonblocking behaviour.

       When used on a QUIC connection SSL object, a datagramBIO is automatically created instead of a socketBIO. These functions fail if called on a QUIC stream SSL object.

       If there was already a BIO connected to ssl, BIO_free() will be called (for both the reading and writing
       side, if different).

       SSL_set_rfd() and SSL_set_wfd() perform the respective action, but only for the read channel or the write
       channel, which can be set independently.

       SSL_set_fd, SSL_set_rfd, SSL_set_wfd - connect the SSL object with a file descriptor

       On  Windows,  a  socket  handle  is  a  64-bit  data  type  (UINT_PTR), which leads to a compiler warning
       (conversion from  'SOCKET'  to  'int',  possible  loss  of  data)  when  passing  the  socket  handle  to
       SSL_set_*fd().  For  the  time  being, this warning can safely be ignored, because although the Microsoft
       documentation claims that the upper limit is  INVALID_SOCKET-1  (2^64  -  2),  in  practice  the  current
       socket()  implementation  returns  an index into the kernel handle table, the size of which is limited to
       2^24.

       The following return values can occur:

       0   The operation failed. Check the error stack to find out why.

       1   The operation succeeded.

SSL_get_fd(3), SSL_set_bio(3), SSL_connect(3), SSL_accept(3), SSL_shutdown(3), ssl(7) , bio(7)

        #include <openssl/ssl.h>

        int SSL_set_fd(SSL *ssl, int fd);
        int SSL_set_rfd(SSL *ssl, int fd);
        int SSL_set_wfd(SSL *ssl, int fd);