libzmq/doc/zmq_setsockopt.txt

zmq_setsockopt(3)
=================


NAME
----

zmq_setsockopt - set 0MQ socket options


SYNOPSIS
--------
*int zmq_setsockopt (void '*socket', int 'option_name', const void '*option_value', size_t 'option_len');*

Caution: All options, with the exception of ZMQ_SUBSCRIBE, ZMQ_UNSUBSCRIBE,
ZMQ_LINGER, ZMQ_ROUTER_MANDATORY, ZMQ_PROBE_ROUTER, ZMQ_XPUB_VERBOSE only 
take effect for subsequent socket bind/connects. Specifically, security 
options take effect for subsequent binds/connects and can be changed at any 
time to affect subsequent binds and/or connects.

DESCRIPTION
-----------
The _zmq_setsockopt()_ function shall set the option specified by the
'option_name' argument to the value pointed to by the 'option_value' argument
for the 0MQ socket pointed to by the 'socket' argument. The 'option_len'
argument is the size of the option value in bytes.

The following socket options can be set with the _zmq_setsockopt()_ function:


ZMQ_SNDHWM: Set high water mark for outbound messages
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_SNDHWM' option shall set the high water mark for outbound messages on
the specified 'socket'. The high water mark is a hard limit on the maximum
number of outstanding messages 0MQ shall queue in memory for any single peer
that the specified 'socket' is communicating with. A value of zero means no
limit.

If this limit has been reached the socket shall enter an exceptional state and
depending on the socket type, 0MQ shall take appropriate action such as
blocking or dropping sent messages. Refer to the individual socket descriptions
in linkzmq:zmq_socket[3] for details on the exact action taken for each socket
type.

NOTE: 0MQ does not guarantee that the socket will accept as many as ZMQ_SNDHWM
messages, and the actual limit may be as much as 60-70% lower depending on the
flow of messages on the socket.

[horizontal]
Option value type:: int
Option value unit:: messages
Default value:: 1000
Applicable socket types:: all


ZMQ_RCVHWM: Set high water mark for inbound messages
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RCVHWM' option shall set the high water mark for inbound messages on
the specified 'socket'. The high water mark is a hard limit on the maximum
number of outstanding messages 0MQ shall queue in memory for any single peer
that the specified 'socket' is communicating with. A value of zero means no
limit.

If this limit has been reached the socket shall enter an exceptional state and
depending on the socket type, 0MQ shall take appropriate action such as
blocking or dropping sent messages. Refer to the individual socket descriptions
in linkzmq:zmq_socket[3] for details on the exact action taken for each socket
type.

[horizontal]
Option value type:: int
Option value unit:: messages
Default value:: 1000
Applicable socket types:: all


ZMQ_AFFINITY: Set I/O thread affinity
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_AFFINITY' option shall set the I/O thread affinity for newly created
connections on the specified 'socket'.

Affinity determines which threads from the 0MQ I/O thread pool associated with
the socket's _context_ shall handle newly created connections.  A value of zero
specifies no affinity, meaning that work shall be distributed fairly among all
0MQ I/O threads in the thread pool. For non-zero values, the lowest bit
corresponds to thread 1, second lowest bit to thread 2 and so on.  For example,
a value of 3 specifies that subsequent connections on 'socket' shall be handled
exclusively by I/O threads 1 and 2.

See also linkzmq:zmq_init[3] for details on allocating the number of I/O
threads for a specific _context_.

[horizontal]
Option value type:: uint64_t
Option value unit:: N/A (bitmap)
Default value:: 0
Applicable socket types:: N/A


ZMQ_SUBSCRIBE: Establish message filter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_SUBSCRIBE' option shall establish a new message filter on a 'ZMQ_SUB'
socket. Newly created 'ZMQ_SUB' sockets shall filter out all incoming messages,
therefore you should call this option to establish an initial message filter.

An empty 'option_value' of length zero shall subscribe to all incoming
messages. A non-empty 'option_value' shall subscribe to all messages beginning
with the specified prefix. Multiple filters may be attached to a single
'ZMQ_SUB' socket, in which case a message shall be accepted if it matches at
least one filter.

[horizontal]
Option value type:: binary data
Option value unit:: N/A
Default value:: N/A
Applicable socket types:: ZMQ_SUB


ZMQ_UNSUBSCRIBE: Remove message filter
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_UNSUBSCRIBE' option shall remove an existing message filter on a
'ZMQ_SUB' socket. The filter specified must match an existing filter previously
established with the 'ZMQ_SUBSCRIBE' option. If the socket has several
instances of the same filter attached the 'ZMQ_UNSUBSCRIBE' option shall remove
only one instance, leaving the rest in place and functional.

[horizontal]
Option value type:: binary data
Option value unit:: N/A
Default value:: N/A
Applicable socket types:: ZMQ_SUB


ZMQ_IDENTITY: Set socket identity
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_IDENTITY' option shall set the identity of the specified 'socket'.
Socket identity is used only by request/reply pattern. Namely, it can be used
in tandem with ROUTER socket to route messages to the peer with specific
identity.

Identity should be at least one byte and at most 255 bytes long. Identities
starting with binary zero are reserved for use by 0MQ infrastructure.

If two peers use the same identity when connecting to a third peer, the
results shall be undefined.

[horizontal]
Option value type:: binary data
Option value unit:: N/A
Default value:: NULL
Applicable socket types:: all


ZMQ_RATE: Set multicast data rate
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RATE' option shall set the maximum send or receive data rate for
multicast transports such as linkzmq:zmq_pgm[7] using the specified 'socket'.

[horizontal]
Option value type:: int
Option value unit:: kilobits per second
Default value:: 100
Applicable socket types:: all, when using multicast transports


ZMQ_RECOVERY_IVL: Set multicast recovery interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RECOVERY_IVL' option shall set the recovery interval for multicast
transports using the specified 'socket'. The recovery interval determines the
maximum time in milliseconds that a receiver can be absent from a multicast
group before unrecoverable data loss will occur.

CAUTION: Exercise care when setting large recovery intervals as the data
needed for recovery will be held in memory. For example, a 1 minute recovery
interval at a data rate of 1Gbps requires a 7GB in-memory buffer.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 10000
Applicable socket types:: all, when using multicast transports

ZMQ_SNDBUF: Set kernel transmit buffer size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_SNDBUF' option shall set the underlying kernel transmit buffer size
for the 'socket' to the specified size in bytes.  A value of zero means leave
the OS default unchanged. For details please refer to your operating system
documentation for the 'SO_SNDBUF' socket option.

[horizontal]
Option value type:: int
Option value unit:: bytes
Default value:: 0
Applicable socket types:: all


ZMQ_RCVBUF: Set kernel receive buffer size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RCVBUF' option shall set the underlying kernel receive buffer size for
the 'socket' to the specified size in bytes.  A value of zero means leave the
OS default unchanged. For details refer to your operating system documentation
for the 'SO_RCVBUF' socket option.

[horizontal]
Option value type:: int
Option value unit:: bytes
Default value:: 0
Applicable socket types:: all


ZMQ_LINGER: Set linger period for socket shutdown
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_LINGER' option shall set the linger period for the specified 'socket'.
The linger period determines how long pending messages which have yet to be
sent to a peer shall linger in memory after a socket is closed with
linkzmq:zmq_close[3], and further affects the termination of the socket's
context with linkzmq:zmq_term[3]. The following outlines the different
behaviours:

* The default value of '-1' specifies an infinite linger period. Pending
  messages shall not be discarded after a call to _zmq_close()_; attempting to
  terminate the socket's context with _zmq_term()_ shall block until all
  pending messages have been sent to a peer.

* The value of '0' specifies no linger period. Pending messages shall be
  discarded immediately when the socket is closed with _zmq_close()_.

* Positive values specify an upper bound for the linger period in milliseconds.
  Pending messages shall not be discarded after a call to _zmq_close()_;
  attempting to terminate the socket's context with _zmq_term()_ shall block
  until either all pending messages have been sent to a peer, or the linger
  period expires, after which any pending messages shall be discarded.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: -1 (infinite)
Applicable socket types:: all


ZMQ_RECONNECT_IVL: Set reconnection interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RECONNECT_IVL' option shall set the initial reconnection interval for
the specified 'socket'.  The reconnection interval is the period 0MQ
shall wait between attempts to reconnect disconnected peers when using
connection-oriented transports. The value -1 means no reconnection.

NOTE: The reconnection interval may be randomized by 0MQ to prevent
reconnection storms in topologies with a large number of peers per socket.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 100
Applicable socket types:: all, only for connection-oriented transports


ZMQ_RECONNECT_IVL_MAX: Set maximum reconnection interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RECONNECT_IVL_MAX' option shall set the maximum reconnection interval 
for the specified 'socket'.  This is the maximum period 0MQ shall wait between
attempts to reconnect. On each reconnect attempt, the previous interval shall be
doubled untill ZMQ_RECONNECT_IVL_MAX is reached. This allows for exponential
backoff strategy. Default value means no exponential backoff is performed and
reconnect interval calculations are only based on ZMQ_RECONNECT_IVL.

NOTE:  Values less than ZMQ_RECONNECT_IVL will be ignored.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 0 (only use ZMQ_RECONNECT_IVL)
Applicable socket types:: all, only for connection-oriented transports


ZMQ_BACKLOG: Set maximum length of the queue of outstanding connections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_BACKLOG' option shall set the maximum length of the queue of
outstanding peer connections for the specified 'socket'; this only applies to
connection-oriented transports. For details refer to your operating system
documentation for the 'listen' function.

[horizontal]
Option value type:: int
Option value unit:: connections
Default value:: 100
Applicable socket types:: all, only for connection-oriented transports.


ZMQ_MAXMSGSIZE: Maximum acceptable inbound message size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Limits the size of the inbound message. If a peer sends a message larger than
ZMQ_MAXMSGSIZE it is disconnected. Value of -1 means 'no limit'.

[horizontal]
Option value type:: int64_t
Option value unit:: bytes
Default value:: -1
Applicable socket types:: all


ZMQ_MULTICAST_HOPS: Maximum network hops for multicast packets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the time-to-live field in every multicast packet sent from this socket.
The default is 1 which means that the multicast packets don't leave the local
network.

[horizontal]
Option value type:: int
Option value unit:: network hops
Default value:: 1
Applicable socket types:: all, when using multicast transports


ZMQ_RCVTIMEO: Maximum time before a recv operation returns with EAGAIN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the timeout for receive operation on the socket. If the value is `0`,
_zmq_recv(3)_ will return immediately, with a EAGAIN error if there is no
message to receive. If the value is `-1`, it will block until a message is
available. For all other values, it will wait for a message for that amount
of time before returning with an EAGAIN error.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: -1 (infinite)
Applicable socket types:: all


ZMQ_SNDTIMEO: Maximum time before a send operation returns with EAGAIN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the timeout for send operation on the socket. If the value is `0`,
_zmq_send(3)_ will return immediately, with a EAGAIN error if the message
cannot be sent. If the value is `-1`, it will block until the message is sent.
For all other values, it will try to send the message for that amount of time
before returning with an EAGAIN error.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: -1 (infinite)
Applicable socket types:: all


ZMQ_IPV6: Enable IPv6 on socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Set the IPv6 option for the socket. A value of `1` means IPv6 is
enabled on the socket, while `0` means the socket will use only IPv4.
When IPv6 is enabled the socket will connect to, or accept connections
from, both IPv4 and IPv6 hosts.

[horizontal]
Option value type:: int
Option value unit:: boolean
Default value:: 0 (false)
Applicable socket types:: all, when using TCP transports.


ZMQ_IPV4ONLY: Use IPv4-only on socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Set the IPv4-only option for the socket. This option is deprecated.
Please use the ZMQ_IPV6 option.

[horizontal]
Option value type:: int
Option value unit:: boolean
Default value:: 1 (true)
Applicable socket types:: all, when using TCP transports.


ZMQ_IMMEDIATE: Queue messages only to completed connections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

By default queues will fill on outgoing connections even if the connection has
not completed. This can lead to "lost" messages on sockets with round-robin
routing (REQ, PUSH, DEALER). If this option is set to `1`, messages shall be
queued only to completed connections. This will cause the socket to block if
there are no other connections, but will prevent queues from filling on pipes
awaiting connection.

[horizontal]
Option value type:: int
Option value unit:: boolean
Default value:: 0 (false)
Applicable socket types:: all, only for connection-oriented transports.


ZMQ_ROUTER_MANDATORY: accept only routable messages on ROUTER sockets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the ROUTER socket behavior when an unroutable message is encountered. A 
value of `0` is the default and discards the message silently when it cannot be 
routed.  A value of `1` returns an 'EHOSTUNREACH' error code if the message
cannot be routed.

[horizontal]
Option value type:: int
Option value unit:: 0, 1
Default value:: 0
Applicable socket types:: ZMQ_ROUTER


ZMQ_ROUTER_RAW: switch ROUTER socket to raw mode
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the raw mode on the ROUTER, when set to 1. When the ROUTER socket is in
raw mode, and when using the tcp:// transport, it will read and write TCP data
without 0MQ framing. This lets 0MQ applications talk to non-0MQ applications.
When using raw mode, you cannot set explicit identities, and the ZMQ_MSGMORE
flag is ignored when sending data messages. In raw mode you can close a specific
connection by sending it a zero-length message (following the identity frame).

[horizontal]
Option value type:: int
Option value unit:: 0, 1
Default value:: 0
Applicable socket types:: ZMQ_ROUTER


ZMQ_PROBE_ROUTER: bootstrap connections to ROUTER sockets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

When set to 1, the socket will automatically send an empty message when a 
new connection is made or accepted. You may set this on REQ, DEALER, or 
ROUTER sockets connected to a ROUTER socket. The application must filter
such empty messages. The ZMQ_PROBE_ROUTER option in effect provides the 
ROUTER application with an event signaling the arrival of a new peer.

NOTE: do not set this option on a socket that talks to any other socket
types: the results are undefined.

[horizontal]
Option value type:: int
Option value unit:: 0, 1
Default value:: 0
Applicable socket types:: ZMQ_ROUTER, ZMQ_DEALER, ZMQ_REQ


ZMQ_XPUB_VERBOSE: provide all subscription messages on XPUB sockets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the 'XPUB' socket behavior on new subscriptions and unsubscriptions. 
A value of '0' is the default and passes only new subscription messages to 
upstream. A value of '1' passes all subscription messages upstream.

[horizontal]
Option value type:: int
Option value unit:: 0, 1
Default value:: 0
Applicable socket types:: ZMQ_XPUB


ZMQ_TCP_KEEPALIVE: Override SO_KEEPALIVE socket option
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Override 'SO_KEEPALIVE' socket option(where supported by OS).
The default value of `-1` means to skip any overrides and leave it to OS default.

[horizontal]
Option value type:: int
Option value unit:: -1,0,1
Default value:: -1 (leave to OS default)
Applicable socket types:: all, when using TCP transports.


ZMQ_TCP_KEEPALIVE_IDLE: Override TCP_KEEPCNT(or TCP_KEEPALIVE on some OS)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Override 'TCP_KEEPCNT'(or 'TCP_KEEPALIVE' on some OS) socket option (where 
supported by OS). The default value of `-1` means to skip any overrides and 
leave it to OS default.

[horizontal]
Option value type:: int
Option value unit:: -1,>0
Default value:: -1 (leave to OS default)
Applicable socket types:: all, when using TCP transports.


ZMQ_TCP_KEEPALIVE_CNT: Override TCP_KEEPCNT socket option
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Override 'TCP_KEEPCNT' socket option(where supported by OS). The default 
value of `-1` means to skip any overrides and leave it to OS default.

[horizontal]
Option value type:: int
Option value unit:: -1,>0
Default value:: -1 (leave to OS default)
Applicable socket types:: all, when using TCP transports.


ZMQ_TCP_KEEPALIVE_INTVL: Override TCP_KEEPINTVL socket option
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Override 'TCP_KEEPINTVL' socket option(where supported by OS). The default 
value of `-1` means to skip any overrides and leave it to OS default.

[horizontal]
Option value type:: int
Option value unit:: -1,>0
Default value:: -1 (leave to OS default)
Applicable socket types:: all, when using TCP transports.


ZMQ_TCP_ACCEPT_FILTER: Assign filters to allow new TCP connections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Assign an arbitrary number of filters that will be applied for each new TCP 
transport connection on a listening socket. If no filters are applied, then 
the TCP transport allows connections from any IP address. If at least one 
filter is applied then new connection source ip should be matched. To clear 
all filters call zmq_setsockopt(socket, ZMQ_TCP_ACCEPT_FILTER, NULL, 0). 
Filter is a null-terminated string with ipv6 or ipv4 CIDR.

[horizontal]
Option value type:: binary data
Option value unit:: N/A
Default value:: no filters (allow from all)
Applicable socket types:: all listening sockets, when using TCP transports.


ZMQ_PLAIN_SERVER: Set PLAIN server role
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Defines whether the socket will act as server for PLAIN security, see
linkzmq:zmq_plain[7]. A value of '1' means the socket will act as
PLAIN server. A value of '0' means the socket will not act as PLAIN
server, and its security role then depends on other option settings.
Setting this to '0' shall reset the socket security to NULL.

[horizontal]
Option value type:: int
Option value unit:: 0, 1
Default value:: 0
Applicable socket types:: all, when using TCP transport


ZMQ_PLAIN_USERNAME: Set PLAIN security username
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the username for outgoing connections over TCP or IPC. If you set this
to a non-null value, the security mechanism used for connections shall be 
PLAIN, see linkzmq:zmq_plain[7]. If you set this to a null value, the security 
mechanism used for connections shall be NULL, see linkzmq:zmq_null[3].

[horizontal]
Option value type:: character string
Option value unit:: N/A
Default value:: not set
Applicable socket types:: all, when using TCP transport


ZMQ_PLAIN_PASSWORD: Set PLAIN security password
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the password for outgoing connections over TCP or IPC. If you set this
to a non-null value, the security mechanism used for connections shall be 
PLAIN, see linkzmq:zmq_plain[7]. If you set this to a null value, the security 
mechanism used for connections shall be NULL, see linkzmq:zmq_null[3].

[horizontal]
Option value type:: character string
Option value unit:: N/A
Default value:: not set
Applicable socket types:: all, when using TCP transport


ZMQ_CURVE_SERVER: Set CURVE server role
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Defines whether the socket will act as server for CURVE security, see
linkzmq:zmq_curve[7]. A value of '1' means the socket will act as
CURVE server. A value of '0' means the socket will not act as CURVE
server, and its security role then depends on other option settings.
Setting this to '0' shall reset the socket security to NULL. When you
set this you must also set the ZMQ_CURVE_PUBLICKEY option.

[horizontal]
Option value type:: int
Option value unit:: 0, 1
Default value:: 0
Applicable socket types:: all, when using TCP transport


ZMQ_CURVE_PUBLICKEY: Set CURVE public key
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the socket's long term public key. You must set this on a CURVE
client or server socket, see linkzmq:zmq_curve[7]. The key is 32 bytes.
For servers, it must be persisted and shared through some unspecified
secure mechanism to clients.

[horizontal]
Option value type:: binary data
Option value size:: 32
Default value:: NULL
Applicable socket types:: all, when using TCP transport


ZMQ_CURVE_SECRETKEY: Set CURVE secret key
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the socket's long term secret key. You must set this on a CURVE
client socket, see linkzmq:zmq_curve[7]. The key is 32 bytes.

[horizontal]
Option value type:: binary data
Option value size:: 32
Default value:: NULL
Applicable socket types:: all, when using TCP transport


ZMQ_CURVE_SERVERKEY: Set CURVE server key
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sets the socket's long term server key. You must set this on a CURVE
client socket, see linkzmq:zmq_curve[7]. The key is 32 bytes. This
key must be the same as the public key set on the server socket.

[horizontal]
Option value type:: binary data
Option value size:: 32
Default value:: NULL
Applicable socket types:: all, when using TCP transport


RETURN VALUE
------------
The _zmq_setsockopt()_ function shall return zero if successful. Otherwise it
shall return `-1` and set 'errno' to one of the values defined below.

ERRORS
------
*EINVAL*::
The requested option _option_name_ is unknown, or the requested _option_len_ or
_option_value_ is invalid.
*ETERM*::
The 0MQ 'context' associated with the specified 'socket' was terminated.
*ENOTSOCK*::
The provided 'socket' was invalid.
*EINTR*::
The operation was interrupted by delivery of a signal.


EXAMPLE
-------
.Subscribing to messages on a 'ZMQ_SUB' socket
----
/* Subscribe to all messages */
rc = zmq_setsockopt (socket, ZMQ_SUBSCRIBE, "", 0);
assert (rc == 0);
/* Subscribe to messages prefixed with "ANIMALS.CATS" */
rc = zmq_setsockopt (socket, ZMQ_SUBSCRIBE, "ANIMALS.CATS", 12);
----

.Setting I/O thread affinity
----
int64_t affinity;
/* Incoming connections on TCP port 5555 shall be handled by I/O thread 1 */
affinity = 1;
rc = zmq_setsockopt (socket, ZMQ_AFFINITY, &affinity, sizeof (affinity));
assert (rc);
rc = zmq_bind (socket, "tcp://lo:5555");
assert (rc);
/* Incoming connections on TCP port 5556 shall be handled by I/O thread 2 */
affinity = 2;
rc = zmq_setsockopt (socket, ZMQ_AFFINITY, &affinity, sizeof (affinity));
assert (rc);
rc = zmq_bind (socket, "tcp://lo:5556");
assert (rc);
----


SEE ALSO
--------
linkzmq:zmq_getsockopt[3]
linkzmq:zmq_socket[3]
linkzmq:zmq_plain[7]
linkzmq:zmq_curve[7]
linkzmq:zmq[7]


AUTHORS
-------
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read the 0MQ Contribution Policy at <http://www.zeromq.org/docs:contributing>.