=pod

=head1 NAME

SSL_CTX_set_new_pending_conn_cb, SSL_set_new_pending_conn_cb_fn - callback function to report creation of QUIC connection SSL objects 

=head1 SYNOPSIS

 typedef int (*SSL_set_new_pending_conn_cb_fn)(SSL_CTX *c, SSL *new_ssl,
                                               void *arg);
 void SSL_CTX_set_new_pending_conn_cb(SSL_CTX *c,
                                     SSL_set_new_pending_conn_cb_fn *f,
                                     void *arg);

=head1 DESCRIPTION

SSL_CTX_set_new_pending_conn_cb() sets the new_pending_conn callback function and
associated application data argument I<arg>.  When using the QUIC transport, TLS
handshake processing may occur independently from the thread which accepts the
connection that the handshake is establishing.  As such, B<SSL> objects
representing the connection may be allocated and initialized prior to a call to
SSL_accept_connection().  This registered callback may be used to decorate the 
preallocated B<SSL> object or create other associations with its parent
B<SSL> prior to a call to SSL_accept_connection().

=head1 RETURN VALUES

SSL_CTX_set_new_pending_conn_cb() returns no value.

SSL_set_new_pending_conn_cb_fn() returns an integer value.  A return value of
0 indicates that the QUIC stack must discard this newly created B<SSL> object,
implying that the associated new connection will not be available for handling
on a subsequent call to SSL_accept_connection().  A nonzero return
value is treated as success, allowing the new connection to be enqueued to the
accept queue.

=head1 SEE ALSO

L<SSL_set_ex_data(3)>

=head1 NOTES

Callbacks in QUIC connections have some limitations to them that should be taken
into consideration when writing an application.

=over 4

QUIC connections may begin processing prior to when an application calls
SSL_accept_connection() on them.  As such, it may occur that callbacks are
delivered to applications' registered TLS callbacks prior to those SSL objects
being returned in SSL_accept_connection().  Applications should expect this
possibility.

In particular no references should be held on SSL objects passed to callbacks
for QUIC connections until such time as they are returned through a call to
SSL_accept_connection.

=back

=head1 HISTORY

SSL_CTX_set_new_pending_conn_cb() was added in OpenSSL 3.5

=head1 COPYRIGHT

Copyright 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
L<https://www.openssl.org/source/license.html>.

=cut
