SSL_SET_BLOCKING_MODE(3ossl) OpenSSL SSL_SET_BLOCKING_MODE(3ossl)
NAME
SSL_set_blocking_mode, SSL_get_blocking_mode - configure blocking mode
for a QUIC SSL object
SYNOPSIS
#include <openssl/ssl.h>
int SSL_set_blocking_mode(SSL *s, int blocking);
int SSL_get_blocking_mode(SSL *s);
DESCRIPTION
SSL_set_blocking_mode(3) can be used to enable or disable blocking mode
on a QUIC connection SSL object. By default, blocking is enabled,
unless the SSL object is configured to use an underlying read or write
BIO which cannot provide a poll descriptor (see
BIO_get_rpoll_descriptor(3)), as blocking mode cannot be supported in
this case.
To enable blocking mode, call SSL_set_blocking_mode(3) with blocking set
to 1; to disable it, call SSL_set_blocking_mode(3) with blocking set to
0.
To retrieve the current blocking mode, call SSL_get_blocking_mode().
Blocking mode means that calls such as SSL_read() and SSL_write() will
block until the requested operation can be performed. In nonblocking
mode, these calls will fail if the requested operation cannot be
performed immediately; see SSL_get_error(3).
These functions are only applicable to QUIC connection SSL objects.
Other kinds of SSL object, such as those for TLS, automatically
function in blocking or nonblocking mode based on whether the
underlying network read and write BIOs provided to the SSL object are
themselves configured in nonblocking mode.
Where a QUIC connection SSL object is used in nonblocking mode, an
application is responsible for ensuring that the SSL object is ticked
regularly; see SSL_handle_events(3).
Blocking mode is disabled automatically if the application provides a
QUIC connection SSL object with a network BIO which cannot support
blocking mode. To re-enable blocking mode in this case, an application
must set a network BIO which can support blocking mode and explicitly
call SSL_set_blocking_mode(3).
RETURN VALUES
SSL_set_blocking_mode(3) returns 1 on success and 0 on failure. The
function fails if called on an SSL object which does not represent a
QUIC connection, or if blocking mode cannot be used for the given
connection.
SSL_get_blocking_mode() returns 1 if blocking is currently enabled. It
returns -1 if called on an unsupported SSL object.
SEE ALSO
SSL_handle_events(3), SSL_poll(3), openssl-quic(7),
openssl-quic-concurrency(7), ssl(7)
HISTORY
The SSL_set_blocking_mode(3) and SSL_get_blocking_mode() functions were
added in OpenSSL 3.2.
COPYRIGHT
Copyright 2022-2025 The OpenSSL Project Authors. All Rights Reserved.
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 2025-04-10 SSL_SET_BLOCKING_MODE(3ossl)
openssl 3.5.0 - Generated Wed Apr 30 16:38:17 CDT 2025