openssl/doc/man3/SSL_set_fd.pod

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=pod
=head1 NAME
SSL_set_fd, SSL_set_rfd, SSL_set_wfd - connect the SSL object with a file descriptor
=head1 SYNOPSIS
#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);
=head1 DESCRIPTION
SSL_set_fd() sets the file descriptor B<fd> as the input/output facility
for the TLS/SSL (encrypted) side of B<ssl>. B<fd> will typically be the
socket file descriptor of a network connection.
When performing the operation, a B<socket BIO> is automatically created to
interface between the B<ssl> and B<fd>. The BIO and hence the SSL engine
inherit the behaviour of B<fd>. If B<fd> is nonblocking, the B<ssl> will
also have nonblocking behaviour.
If there was already a BIO connected to B<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.
=head1 RETURN VALUES
The following return values can occur:
=over 4
=item Z<>0
The operation failed. Check the error stack to find out why.
=item Z<>1
The operation succeeded.
=back
=head1 NOTES
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.
=head1 SEE ALSO
L<SSL_get_fd(3)>, L<SSL_set_bio(3)>,
L<SSL_connect(3)>, L<SSL_accept(3)>,
L<SSL_shutdown(3)>, L<ssl(7)> , L<bio(7)>
=head1 COPYRIGHT
Copyright 2000-2021 The OpenSSL Project Authors. All Rights Reserved.
Licensed under the OpenSSL license (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
L<https://www.openssl.org/source/license.html>.
=cut