=pod =head1 NAME SSL_attach_stream, SSL_detach_stream, SSL_set_default_stream_mode, SSL_DEFAULT_STREAM_MODE_NONE, SSL_DEFAULT_STREAM_MODE_AUTO_BIDI, SSL_DEFAULT_STREAM_MODE_AUTO_UNI - manage the default stream for a QUIC connection =head1 SYNOPSIS #include int SSL_attach_stream(SSL *conn, SSL *stream); SSL *SSL_detach_stream(SSL *conn); #define SSL_DEFAULT_STREAM_MODE_NONE #define SSL_DEFAULT_STREAM_MODE_AUTO_BIDI #define SSL_DEFAULT_STREAM_MODE_AUTO_UNI int SSL_set_default_stream_mode(SSL *conn, uint32_t mode); =head1 DESCRIPTION A QUIC connection SSL object may have a default stream attached to it. A default stream is a QUIC stream to which calls to L and L made on a QUIC connection SSL object are redirected. Default stream handling allows legacy applications to use QUIC similarly to a traditional TLS connection. When not disabled, a default stream is automatically created on an outgoing connection once L or L is called. A QUIC stream must be explicitly designated as client-initiated or server-initiated up front. This broadly corresponds to whether an application protocol involves the client transmitting first, or the server transmitting first. As such, if L is called first (before any call to L) after establishing a connection, OpenSSL will wait for the server to open the first server-initiated stream, and then bind this as the default stream. Conversely, if L is called before any call to L, OpenSSL assumes the client wishes to transmit first, creates a client-initiated stream, and binds this as the default stream. By default, the default stream created is bidirectional. If a unidirectional stream is desired, or if the application wishes to disable default stream functionality, SSL_set_default_stream_mode() (discussed below) can be used to accomplish this. If a default stream is currently bound to a QUIC connection SSL object, it can be detached from that QUIC connection SSL object and used explicitly by calling SSL_detach_stream(), which detaches the default stream and returns it as an explicit QUIC stream SSL object. Once detached, the caller is responsible for managing the lifetime of the QUIC stream SSL object and must free it by calling L. The lifetime of a QUIC connection SSL object must exceed that of any subsidiary QUIC stream SSL objects; in other words, QUIC stream SSL objects must be freed before the parent QUIC connection SSL object is freed. When a QUIC connection SSL object has no default stream currently associated with it, for example because the default stream was detached or because default stream functionality was disabled, calls to functions which require a stream on the QUIC connection SSL object will fail. The act of detaching a stream from a QUIC connection SSL object can be reversed by calling SSL_attach_stream(). This can also be used to designate a stream obtained via L or L as the default stream. SSL_attach_stream() cannot be used if there is already a default stream associated with the QUIC connection SSL object; therefore, you may need to call SSL_detach_stream() first. It is recommended that new applications and applications which rely on multiple streams forego use of the default stream functionality, which is intended for legacy applications. SSL_set_default_stream_mode() can be used to configure or disable default stream handling. It can only be called on a QUIC connection SSL object prior to any default stream being created. If used, it is recommended to call it immediately after calling L, prior to initiating a connection. The argument B may be one of the following options: =over 4 =item SSL_DEFAULT_STREAM_MODE_AUTO_BIDI This is the default setting. If L is called prior to any call to L, a bidirectional client-initiated stream is created and bound as the default stream. If L is called prior to any call to L, OpenSSL waits for an incoming stream from the peer (causing L to block if the connection is in blocking mode), and then binds that stream as the default stream. Note that this incoming stream may be either bidirectional or unidirectional; thus, this setting does not guarantee presence of a bidirectional stream when L is called first. To determine the type of a stream after a call to L, use L. =item SSL_DEFAULT_STREAM_MODE_AUTO_UNI In this mode, if L is called prior to any call to L, a unidirectional client-initiated stream is created and bound as the default stream. The behaviour is otherwise identical to that of B. The behaviour when L is called prior to any call to L is unchanged. =item SSL_DEFAULT_STREAM_MODE_NONE Default stream creation is inhibited. This is the recommended mode of operation. L and L calls cannot be made on the QUIC connection SSL object directly. You must obtain streams using L or L in order to communicate with the peer. It is still possible to explicitly attach a stream as the default stream using SSL_attach_stream(). =back A default stream will not be automatically created on a QUIC connection SSL object if the default stream mode is set to B, or if the QUIC connection SSL object previously had a default stream which was detached using SSL_detach_stream(). L interacts significantly with the default stream functionality. =head1 RETURN VALUES SSL_detach_stream() returns a QUIC stream SSL object, or NULL if there is no default stream currently attached. SSL_attach_stream() returns 1 on success and 0 on failure. SSL_attach_stream() fails if a default stream is already attached to the QUIC connection SSL object. SSL_set_default_stream_mode() returns 1 on success and 0 on failure. SSL_set_default_stream_mode() fails if it is called after a default stream has already been established. These functions fail if called on a QUIC stream SSL object or on a non-QUIC SSL object. =head1 SEE ALSO L, L, L, L =head1 HISTORY These functions were added in OpenSSL 3.2. =head1 COPYRIGHT Copyright 2002-2023 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 L. =cut