=pod

=head1 NAME

SSL_new_stream, SSL_STREAM_FLAG_UNI, SSL_STREAM_FLAG_NO_BLOCK,
SSL_STREAM_FLAG_ADVANCE - create a new locally-initiated QUIC stream

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 #define SSL_STREAM_FLAG_UNI          (1U << 0)
 #define SSL_STREAM_FLAG_NO_BLOCK     (1U << 1)
 #define SSL_STREAM_FLAG_ADVANCE      (1U << 2)
 SSL *SSL_new_stream(SSL *ssl, uint64_t flags);

=head1 DESCRIPTION

The SSL_new_stream() function, when passed a QUIC connection SSL object, creates
a new locally-initiated bidirectional or unidirectional QUIC stream and returns
the newly created QUIC stream SSL object.

If the B<SSL_STREAM_FLAG_UNI> flag is passed, a unidirectional stream is
created; else a bidirectional stream is created.

To retrieve the stream ID of the newly created stream, use
L<SSL_get_stream_id(3)>.

It is the caller's responsibility to free the QUIC stream SSL object using
L<SSL_free(3)>. The lifetime of the QUIC connection SSL object must exceed that
of the QUIC stream SSL object; in other words, the QUIC stream SSL object must
be freed first.

Once a stream has been created using SSL_new_stream(), it may be used in the
normal way using L<SSL_read(3)> and L<SSL_write(3)>.

This function can only be used to create stream objects for locally-initiated
streams. To accept incoming streams initiated by a peer, use
L<SSL_accept_stream(3)>.

Calling SSL_new_stream() if there is no default stream already present
inhibits the future creation of a default stream. See L<openssl-quic(7)>.

The creation of new streams is subject to flow control by the QUIC protocol. If
it is currently not possible to create a new locally initiated stream of the
specified type, a call to SSL_new_stream() will either block (if the connection
is configured in blocking mode) until a new stream can be created, or otherwise
return NULL.

This function operates in blocking mode if the QUIC connection SSL object is
configured in blocking mode (see L<SSL_set_blocking_mode(3)>). It may also be
used in nonblocking mode on a connection configured in blocking mode by passing
the flag B<SSL_STREAM_FLAG_NO_BLOCK>.

The flag B<SSL_STREAM_FLAG_ADVANCE> may be used to create a QUIC stream SSL
object even if a new QUIC stream cannot yet be opened due to flow control. The
caller may begin to use the new stream and fill the write buffer of the stream
by calling L<SSL_write(3)>. However, no actual stream data (or QUIC frames
regarding the stream) will be sent until QUIC flow control allows it. Any queued
data will be sent as soon as a peer permits it. There is no guarantee the stream
will be eventually created; for example, the connection could fail, or a peer
might simply decide never to increase the number of allowed streams for the
remainder of the connection lifetime.

=head1 RETURN VALUES

SSL_new_stream() returns a new stream object, or NULL on error.

This function fails if called on a QUIC stream SSL object or on a non-QUIC SSL
object.

SSL_new_stream() may also fail if the underlying connection has reached the
maximum stream count, based on the B<max_streams_bidi> or B<max_streams_uni>
transport parameter values negotiated with the peer.  In this event the NULL
return will be accompanied by an error on the error stack (obtainable via
ERR_get_error()), which will contain a reason code of
B<SSL_R_STREAM_COUNT_LIMITED>.  When this error is encountered, the operation
may be retried.  It is recommended that, prior to retry, the error stack be
cleared via a call to ERR_clear_error(), and that the TLS state machine be
activated via a call to SSL_handle_events() to process any potential updates
from the server allowing additional streams to be created.

=head1 SEE ALSO

L<SSL_accept_stream(3)>, L<SSL_free(3)>

=head1 HISTORY

SSL_new_stream() was added in OpenSSL 3.2.

=head1 COPYRIGHT

Copyright 2002-2025 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
