SSL_HANDLE_EVENTS(3SSL) OpenSSL SSL_HANDLE_EVENTS(3SSL)
NAME
SSL_handle_events - advance asynchronous state machine and perform
network I/O
SYNOPSIS
#include <openssl/ssl.h>
int SSL_handle_events(SSL *ssl);
DESCRIPTION
SSL_handle_events() performs any internal processing which is due on an
SSL object. The exact operations performed by SSL_handle_events() vary
depending on what kind of protocol is being used with the given SSL
object. For example, SSL_handle_events() may handle timeout events which
have become due, or may attempt, to the extent currently possible, to
perform network I/O operations on one of the BIOs underlying the SSL
object.
The primary use case for SSL_handle_events() is to allow an application
which uses OpenSSL in nonblocking mode to give OpenSSL an opportunity to
handle timer events, or to respond to the availability of new data to be
read from an underlying BIO, or to respond to the opportunity to write
pending data to an underlying BIO.
SSL_handle_events() can be used only with the following types of SSL
object:
DTLS SSL objects
Using SSL_handle_events() on an SSL object being used with a DTLS
method allows timeout events to be handled properly. This is
equivalent to a call to DTLSv1_handle_timeout(3). Since
SSL_handle_events() handles a superset of the use cases of
DTLSv1_handle_timeout(3), it should be preferred for new
applications which do not require support for OpenSSL 3.1 or older.
When using DTLS, an application must call SSL_handle_events() as
indicated by calls to SSL_get_event_timeout(3); event handling is
not performed automatically by calls to other SSL functions such as
SSL_read(3) or SSL_write(3). Note that this is different to QUIC
which also performs event handling implicitly; see below.
QUIC connection SSL objects
Using SSL_handle_events() on an SSL object which represents a QUIC
connection allows timeout events to be handled properly, as well as
incoming network data to be processed, and queued outgoing network
data to be written, if the underlying BIO has the capacity to accept
it.
Ordinarily, when an application uses an SSL object in blocking mode,
it does not need to call SSL_handle_events() because OpenSSL
performs ticking internally on an automatic basis. However, if an
application uses a QUIC connection in nonblocking mode, it must at a
minimum ensure that SSL_handle_events() is called periodically to
allow timeout events to be handled. An application can find out when
it next needs to call SSL_handle_events() for this purpose (if at
all) by calling SSL_get_event_timeout(3).
Calling SSL_handle_events() on a QUIC connection SSL object being
used in blocking mode is not necessary unless no I/O calls (such as
SSL_read(3) or SSL_write(3)) will be made to the object for a
substantial period of time. So long as at least one call to the SSL
object is blocking, no such call is needed. However,
SSL_handle_events() may optionally be used on a QUIC connection
object if desired.
With the thread-assisted mode of operation
OSSL_QUIC_client_thread_method(3) it is unnecessary to call
SSL_handle_events() as the assist thread handles the QUIC connection
events.
Calling SSL_handle_events() on any other kind of SSL object is a no-op.
This is considered a success case.
Note that SSL_handle_events() supersedes the older
DTLSv1_handle_timeout(3) function for all use cases.
RETURN VALUES
Returns 1 on success and 0 on failure.
SEE ALSO
SSL_get_event_timeout(3), DTLSv1_handle_timeout(3), ssl(7)
HISTORY
The SSL_handle_events() function was added in OpenSSL 3.2.
COPYRIGHT
Copyright 2023 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>.
3.5.7 2026-06-09 SSL_HANDLE_EVENTS(3SSL)
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