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
#include <openssl/ssl.h>
#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);A QUIC connection SSL object may have a default stream attached to it. A default stream is a QUIC stream to which calls to SSL_read(3) and SSL_write(3) 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 SSL_read(3) or SSL_write(3) 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 SSL_read(3) is called first (before any call to SSL_write(3)) 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 SSL_write(3) is called before any call to SSL_read(3), 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.
When a QUIC connection SSL object has no default stream currently associated with it, for example because default stream functionality was disabled, calls to functions which require a stream on the QUIC connection SSL object (for example, SSL_read(3) and SSL_write(3)) will fail.
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 SSL_new(3), prior to initiating a connection. The argument mode may be one of the following options:
This is the default setting. If SSL_write(3) is called prior to any call to SSL_read(3), a bidirectional client-initiated stream is created and bound as the default stream. If SSL_read(3) is called prior to any call to SSL_write(3), OpenSSL waits for an incoming stream from the peer (causing SSL_read(3) 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 the presence of a bidirectional stream when SSL_read(3) is called first. To determine the type of a stream after a call to SSL_read(3), use SSL_get_stream_type(3).
In this mode, if SSL_write(3) is called prior to any call to SSL_read(3), a unidirectional client-initiated stream is created and bound as the default stream. The behaviour is otherwise identical to that of SSL_DEFAULT_STREAM_MODE_AUTO_BIDI. The behaviour when SSL_read(3) is called prior to any call to SSL_write(3) is unchanged.
Default stream creation is inhibited. This is the recommended mode of operation. SSL_read(3) and SSL_write(3) calls cannot be made on the QUIC connection SSL object directly. You must obtain streams using SSL_new_stream(3) or SSL_accept_stream(3) in order to communicate with the peer.
A default stream will not be automatically created on a QUIC connection SSL object if the default stream mode is set to SSL_DEFAULT_STREAM_MODE_NONE.
SSL_set_incoming_stream_policy(3) interacts significantly with the default stream functionality.
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.
SSL_new_stream(3), SSL_accept_stream(3), SSL_free(3), SSL_set_incoming_stream_policy(3)
These functions were added in OpenSSL 3.2.
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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.