doc/man3/SSL_get_value_uint.pod

=pod

=head1 NAME

SSL_get_value_uint, SSL_set_value_uint, SSL_get_generic_value_uint,
SSL_set_generic_value_uint, SSL_get_feature_request_uint,
SSL_set_feature_request_uint, SSL_get_feature_peer_request_uint,
SSL_get_feature_negotiated_uint, SSL_get_quic_stream_bidi_local_avail,
SSL_get_quic_stream_bidi_remote_avail, SSL_get_quic_stream_uni_local_avail,
SSL_get_quic_stream_uni_remote_avail, SSL_VALUE_CLASS_GENERIC,
SSL_VALUE_CLASS_FEATURE_REQUEST, SSL_VALUE_CLASS_FEATURE_PEER_REQUEST,
SSL_VALUE_CLASS_FEATURE_NEGOTIATED, SSL_VALUE_QUIC_STREAM_BIDI_LOCAL_AVAIL,
SSL_VALUE_QUIC_STREAM_BIDI_REMOTE_AVAIL, SSL_VALUE_QUIC_STREAM_UNI_LOCAL_AVAIL,
SSL_VALUE_QUIC_STREAM_UNI_REMOTE_AVAIL, SSL_VALUE_QUIC_IDLE_TIMEOUT,
SSL_VALUE_QUIC_UDP_PAYLOAD_SIZE_MAX, SSL_VALUE_QUIC_WINDOWCON,
SSL_VALUE_QUIC_WINDOWBSTR, SSL_VALUE_QUIC_WINDOWUSTR,
SSL_VALUE_QUIC_ACK_DELAY_EXPONENT, SSL_VALUE_QUIC_ACK_DELAY_MAX,
SSL_VALUE_EVENT_HANDLING_MODE,
SSL_VALUE_EVENT_HANDLING_MODE_INHERIT,
SSL_VALUE_EVENT_HANDLING_MODE_EXPLICIT,
SSL_VALUE_EVENT_HANDLING_MODE_IMPLICIT,
SSL_get_event_handling_mode,
SSL_set_event_handling_mode,
SSL_VALUE_STREAM_WRITE_BUF_SIZE,
SSL_get_stream_write_buf_size,
SSL_VALUE_STREAM_WRITE_BUF_USED,
SSL_get_stream_write_buf_used,
SSL_VALUE_STREAM_WRITE_BUF_AVAIL,
SSL_get_stream_write_buf_avail -
manage negotiable features and configuration values for an SSL object

=head1 SYNOPSIS

 #include <openssl/ssl.h>

 int SSL_get_value_uint(SSL *ssl, uint32_t class_, uint32_t id,
                        uint64_t *value);
 int SSL_set_value_uint(SSL *ssl, uint32_t class_, uint32_t id,
                        uint64_t value);

 #define SSL_VALUE_CLASS_GENERIC
 #define SSL_VALUE_CLASS_FEATURE_REQUEST
 #define SSL_VALUE_CLASS_FEATURE_PEER_REQUEST
 #define SSL_VALUE_CLASS_FEATURE_NEGOTIATED

 #define SSL_VALUE_QUIC_STREAM_BIDI_LOCAL_AVAIL
 #define SSL_VALUE_QUIC_STREAM_BIDI_REMOTE_AVAIL
 #define SSL_VALUE_QUIC_STREAM_UNI_LOCAL_AVAIL
 #define SSL_VALUE_QUIC_STREAM_UNI_REMOTE_AVAIL
 #define SSL_VALUE_QUIC_IDLE_TIMEOUT
 #define SSL_VALUE_QUIC_UDP_PAYLOAD_SIZE_MAX
 #define SSL_VALUE_QUIC_WINDOWCON
 #define SSL_VALUE_QUIC_WINDOWBSTR
 #define SSL_VALUE_QUIC_WINDOWUSTR
 #define SSL_VALUE_QUIC_ACK_DELAY_EXPONENT
 #define SSL_VALUE_QUIC_ACK_DELAY_MAX

 #define SSL_VALUE_EVENT_HANDLING_MODE
 #define SSL_VALUE_EVENT_HANDLING_MODE_INHERIT
 #define SSL_VALUE_EVENT_HANDLING_MODE_EXPLICIT
 #define SSL_VALUE_EVENT_HANDLING_MODE_IMPLICIT

 #define SSL_VALUE_STREAM_WRITE_BUF_SIZE
 #define SSL_VALUE_STREAM_WRITE_BUF_USED
 #define SSL_VALUE_STREAM_WRITE_BUF_AVAIL

The following convenience macros can also be used:

 int SSL_get_generic_value_uint(SSL *ssl, uint32_t id, uint64_t *value);
 int SSL_set_generic_value_uint(SSL *ssl, uint32_t id, uint64_t value);

 int SSL_get_feature_request_uint(SSL *ssl, uint32_t id, uint64_t *value);
 int SSL_set_feature_request_uint(SSL *ssl, uint32_t id, uint64_t value);

 int SSL_get_feature_peer_request_uint(SSL *ssl, uint32_t id, uint64_t *value);
 int SSL_get_feature_negotiated_uint(SSL *ssl, uint32_t id, uint64_t *value);

 int SSL_get_quic_stream_bidi_local_avail(SSL *ssl, uint64_t *value);
 int SSL_get_quic_stream_bidi_remote_avail(SSL *ssl, uint64_t *value);
 int SSL_get_quic_stream_uni_local_avail(SSL *ssl, uint64_t *value);
 int SSL_get_quic_stream_uni_remote_avail(SSL *ssl, uint64_t *value);

 int SSL_get_event_handling_mode(SSL *ssl, uint64_t *value);
 int SSL_set_event_handling_mode(SSL *ssl, uint64_t value);

 int SSL_get_stream_write_buf_size(SSL *ssl, uint64_t *value);
 int SSL_get_stream_write_buf_avail(SSL *ssl, uint64_t *value);
 int SSL_get_stream_write_buf_used(SSL *ssl, uint64_t *value);

=head1 DESCRIPTION

SSL_get_value_uint() and SSL_set_value_uint() provide access to configurable
parameters for a given SSL object. Amongst other things, they are used to
provide control over the feature negotiation process during establishment of a
connection, and access to statistics about that connection.

SSL_get_value_uint() and SSL_set_value_uint() get and set configurable values
within a given value class. The value classes are enumerated by
B<SSL_VALUE_CLASS> and are as follows:

=over 4

=item B<SSL_VALUE_CLASS_GENERIC>

Values in this class do not participate in the feature negotiation process. They
may represent connection parameters which do not participate in explicit
negotiation or provide connection statistics. Values in this class might be
read-write or read-only.

You can access values in this class using the convenience macros
SSL_get_generic_value_uint() and SSL_set_generic_value_uint() for brevity.

=item B<SSL_VALUE_CLASS_FEATURE_REQUEST>

Values in this class are read-write, and represent what the local party is
requesting during feature negotiation. Such a request will not necessarily be
honoured; see B<SSL_VALUE_CLASS_FEATURE_NEGOTIATED>.

A value in this class may become read-only in certain circumstances; for
example, after a connection has been established, for a value which cannot be
renegotiated after connection establishment. Setting a value in this class after
connection establishment represents a request for online renegotiation of the
specified feature.

You can access values in this class using the convenience macros
SSL_get_feature_request_uint() and SSL_set_feature_request_uint() for brevity.

=item B<SSL_VALUE_CLASS_FEATURE_PEER_REQUEST>

Values in this value class are read-only, and represent what was requested by a
peer during feature negotiation. Such a request has not necessarily been
honoured; see B<SSL_VALUE_CLASS_FEATURE_NEGOTIATED>.

You can access values in this class using the convenience macro
SSL_get_feature_peer_request_uint() for brevity.

=item B<SSL_VALUE_CLASS_FEATURE_NEGOTIATED>

Values in this value class are read-only, and represent the value which was
actually negotiated based on both local and peer input during feature
negotiation. This is the effective value in actual use.

Attempting to read a value in this class will generally fail if the feature
negotiation process has not yet completed and the value is therefore currently
unknown, unless the nature of the feature in question causes a provisional value
to be used prior to completion of feature negotiation, in which case that value
may be returned. If an online (post-handshake) renegotiation of a feature is
in progress, retrieving the negotiated value will continue to retrieve the
previous negotiated value until that process is completed. See the documentation
of specific values for full details of its behaviour.

You can access values in this class using the convenience macro
SSL_get_feature_negotiated_uint() for brevity.

=back

=head1 CONFIGURABLE VALUES FOR QUIC OBJECTS

The following configurable values are supported for QUIC SSL objects. Whether a
value is supported for a QUIC connection SSL object or a QUIC stream SSL object
is indicated in the heading for each value. Values supported for QUIC stream SSL
objects are also supported on QUIC connection SSL objects if they have a default
stream attached.

SSL_get_value() does not cause internal event processing to occur unless the
documentation for a specific value specifies otherwise.

=over 4

=item B<SSL_VALUE_QUIC_IDLE_TIMEOUT> (connection/listener object)

Negotiated feature value. This configures the desired QUIC idle timeout in
milliseconds, where 0 represents a lack of an idle timeout. This feature can
only be configured prior to connection establishment and cannot be subsequently
changed.

This release of OpenSSL uses a default value of 30 seconds. This default value
may change between releases of OpenSSL.

=item B<SSL_VALUE_QUIC_UDP_PAYLOAD_SIZE_MAX> (connection/listener object)

Feature (peer) request value. This configures the maximum UDP payload size in
bytes, corresponding to the QUIC max_udp_payload_size transport parameter
as defined in RFC 9000, Section 18.2. It limits the size of UDP datagrams the
local QUIC stack is willing to receive from the peer. It does not change the
maximum datagram payload size used on the transmit path. This feature can only
be configured prior to connection establishment and cannot be subsequently
changed. This value will be sent to the peer in the transport parameters.

This release of OpenSSL uses a default value of 1200 bytes. This default value
may change between releases of OpenSSL.

=item B<SSL_VALUE_QUIC_WINDOWCON> (connection/listener object)

Feature (peer) request value. This configures the initial QUIC connection-level
flow control receive window in bytes. This feature can only be configured prior
to connection establishment and cannot be subsequently changed. This value will
be sent to the peer in the transport parameters.

This release of OpenSSL uses a default value of 768 * 1024 bytes. This default
value may change between releases of OpenSSL.

=item B<SSL_VALUE_QUIC_WINDOWBSTR> (connection/listener object)

Feature (peer) request value. This sets the initial receive window size, in
bytes, for QUIC stream flow control on a bidirectional stream created by the
local endpoint. This feature can only be configured prior to connection
establishment and cannot be subsequently changed. This value will be sent to the
peer in the transport parameters.

This release of OpenSSL uses a default value of 512 * 1024 bytes. This default
value may change between releases of OpenSSL.

=item B<SSL_VALUE_QUIC_WINDOWUSTR> (connection/listener object)

As above, but configures the initial receive window size for QUIC stream flow
control on a unidirectional stream created by the remote endpoint.

=item B<SSL_VALUE_QUIC_ACK_DELAY_EXPONENT> (connection/listener object)

Feature (peer) request value. This configures the ACK delay exponent. This
feature can only be configured prior to connection establishment and cannot be
subsequently changed. This value will be sent to the peer in the transport
parameters.

This release of OpenSSL uses a default value of 3. This default value may change
between releases of OpenSSL.

=item B<SSL_VALUE_QUIC_ACK_DELAY_MAX> (connection/listener object)

Feature (peer) request value. This configures the maximum ACK delay in
milliseconds. This feature can only be configured prior to connection
establishment and cannot be subsequently changed. This value will be sent to the
peer in the transport parameters.

This release of OpenSSL uses a default value of 25 milliseconds. This default
value may change between releases of OpenSSL.

=item B<SSL_VALUE_QUIC_STREAM_BIDI_LOCAL_AVAIL> (connection object)

Generic read-only statistical value. The number of bidirectional,
locally-initiated streams available to be created (but not yet created). For
example, a value of 100 would mean that L<SSL_new_stream(3)> could be called 100
times to create 100 bidirectional streams before L<SSL_new_stream(3)> would
block or fail due to backpressure.

Can be queried using the convenience macro
SSL_get_quic_stream_bidi_local_avail().

=item B<SSL_VALUE_QUIC_STREAM_UNI_LOCAL_AVAIL> (connection object)

As above, but provides the number of unidirectional, locally-initiated streams
available to be created (but not yet created).

Can be queried using the convenience macro
SSL_get_quic_stream_uni_local_avail().

=item B<SSL_VALUE_QUIC_STREAM_BIDI_REMOTE_AVAIL> (connection object)

As above, but provides the number of bidirectional, remotely-initiated streams
available to be created (but not yet created) by the peer. This represents the
number of streams the local endpoint has authorised the peer to create in terms
of QUIC stream creation flow control.

Can be queried using the convenience macro
SSL_get_quic_stream_bidi_remote_avail().

=item B<SSL_VALUE_QUIC_STREAM_UNI_REMOTE_AVAIL> (connection object)

As above, but provides the number of unidirectional, remotely-initiated streams
available to be created (but not yet created).

Can be queried using the convenience macro
SSL_get_quic_stream_uni_remote_avail().

=item B<SSL_VALUE_EVENT_HANDLING_MODE> (connection or stream object)

Generic value. This is an integer value which takes one of the following values,
and determines the event handling mode in use:

=over 4

=item B<SSL_VALUE_EVENT_HANDLING_MODE_INHERIT>

When set, the event handling mode used is inherited from the value set on the
parent connection (for a stream), or, for a connection, defaults to the implicit
event handling model.

When a new connection is created, or a new stream is created or accepted, it
defaults to this setting.

=item B<SSL_VALUE_EVENT_HANDLING_MODE_IMPLICIT> (Implicit event handling)

If set to this value, the implicit event handling model is used. Under this
model, QUIC objects will automatically perform background event processing
(equivalent to a call to L<SSL_handle_events(3)>) when calls to I/O functions
such as L<SSL_read_ex(3)> or L<SSL_write_ex(3)> are made on a QUIC SSL object.
This helps to maintain the health of the QUIC connection and ensures that
incoming datagrams and timeout events are processed.

=item B<SSL_VALUE_EVENT_HANDLING_MODE_EXPLICIT> (Explicit event handling)

If set to this value, the explicit event handling model is used. Under this
model, B<nonblocking> calls to I/O functions such as L<SSL_read_ex(3)> or
L<SSL_write_ex(3)> do not result in the automatic processing of QUIC events. Any
new incoming network traffic is not handled; no new outgoing network traffic is
generated, and pending timeout events are not processed. This allows an
application to obtain greater control over the circumstances in which QUIC event
processing occurs. If this event handling model is used, it is the application's
responsibility to call L<SSL_handle_events(3)> as and when called for by the
QUIC implementation; see the L<SSL_get_rpoll_descriptor(3)> man page for more
information.

Selecting this model does not affect the operation of blocking I/O calls, which
will continue to use the implicit event handling model. Therefore, applications
using this model will generally want to disable blocking operation using
L<SSL_set_blocking_mode(3)>.

=back

Can be configured using the convenience macros SSL_get_event_handling_mode() and
SSL_set_event_handling_mode().

A call to SSL_set_value_uint() which causes this value to switch back to the
implicit event handling model does not in itself cause implicit event handling
to occur; such handling will occur on the next I/O API call. Equally, a call to
SSL_set_value_uint() which causes this value to switch to the explicit event
handling model will not cause event handling to occur before making that
transition.

This value controls whether implicit event handling occurs when making an I/O
API call on the SSL object it is set on. However, event processing is not
confined to state which relates to only that object. For example, if you
configure explicit event handling on QUIC stream SSL object "A" and configure
implicit event handling on QUIC stream SSL object "B", a call to an I/O function
on "B" may result in state changes to "A". In other words, if event handling
does happen as a result of an API call to an object related to a connection,
processing of background events (for example, received QUIC network traffic) may
also affect the state of any other object related to a connection.

=item B<SSL_VALUE_STREAM_WRITE_BUF_SIZE> (stream object)

Generic read-only statistical value. The size of the write buffer allocated to
hold data written to a stream with L<SSL_write_ex(3)> until it is transmitted
and subsequently acknowledged by the peer. This value may change at any time, as
buffer sizes are optimised in response to network conditions to optimise
throughput.

Can be queried using the convenience macro SSL_get_stream_write_buf_size().

=item B<SSL_VALUE_STREAM_WRITE_BUF_USED> (stream object)

Generic read-only statistical value. The number of bytes currently consumed
in the write buffer which have yet to be acknowledged by the peer. Successful
calls to L<SSL_write_ex(3)> which accept data cause this number to increase.
This number will then decrease as data is acknowledged by the peer.

Can be queried using the convenience macro SSL_get_stream_write_buf_used().

=item B<SSL_VALUE_STREAM_WRITE_BUF_AVAIL> (stream object)

Generic read-only statistical value. The number of bytes available in the write
buffer which have yet to be consumed by calls to L<SSL_write_ex(3)>. Successful
calls to L<SSL_write_ex(3)> which accept data cause this number to decrease.
This number will increase as data is acknowledged by the peer. It may also
change if the buffer is resized automatically to optimise throughput.

Can be queried using the convenience macro SSL_get_stream_write_buf_avail().

=back

No configurable values are currently defined for non-QUIC SSL objects.

=head1 RETURN VALUES

Returns 1 on success or 0 on failure. This function can fail for a number of
reasons:

=over 4

=item

An argument is invalid (e.g. NULL pointer or invalid class).

=item

The given value is not supported by the SSL object on which it was called.

=item

The given operation (get or set) is not supported by the specified
configurable value.

=item

You are trying to modify the given value and the value is not modifiable at this
time.

=back

=head1 SEE ALSO

L<SSL_ctrl(3)>, L<SSL_get_accept_stream_queue_len(3)>,
L<SSL_get_stream_read_state(3)>, L<SSL_get_stream_write_state(3)>,
L<SSL_get_stream_read_error_code(3)>, L<SSL_get_stream_write_error_code(3)>,
L<SSL_set_default_stream_mode(3)>, L<SSL_set_incoming_stream_policy(3)>

=head1 HISTORY

The values SSL_VALUE_QUIC_UDP_PAYLOAD_SIZE_MAX, SSL_VALUE_QUIC_WINDOWCON,
SSL_VALUE_QUIC_WINDOWBSTR, SSL_VALUE_QUIC_WINDOWUSTR,
SSL_VALUE_QUIC_ACK_DELAY_EXPONENT, and SSL_VALUE_QUIC_ACK_DELAY_MAX
were added in OpenSSL 4.1.

The remaining functions and values described here were all added in OpenSSL 3.3.

=head1 COPYRIGHT

Copyright 2002-2026 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