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 a 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>.

3.4.1                                              2025-04-03                            SSL_HANDLE_EVENTS(3SSL)