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_HANDOVER, ZMQ_ROUTER_MANDATORY, ZMQ_PROBE_ROUTER,
ZMQ_XPUB_VERBOSE, ZMQ_XPUB_VERBOSER, ZMQ_REQ_CORRELATE,
ZMQ_REQ_RELAXED, ZMQ_SNDHWM and ZMQ_RCVHWM, only take effect for
subsequent socket bind/connects.

Specifically, security options take effect for subsequent bind/connect calls,
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. For options taking a value of
type "character string", the provided byte data should either contain no zero
bytes, or end in a single zero byte (terminating ASCII NUL character).

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


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_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_CONNECT_RID: Assign the next outbound connection id 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_CONNECT_RID' option sets the peer id of the next host connected 
via the zmq_connect() call, and immediately readies that connection for 
data transfer with the named id.  This option applies only to the first
subsequent call to zmq_connect(), calls thereafter use default connection 
behaviour. 

Typical use is to set this socket option ahead of each zmq_connect() attempt 
to a new host. Each connection MUST be assigned a unique name. Assigning a 
name that is already in use is not allowed. 

Useful when connecting ROUTER to ROUTER, or STREAM to STREAM, as it 
allows for immediate sending to peers. Outbound id framing requirements 
for ROUTER and STREAM sockets apply.

The peer id should be from 1 to 255 bytes long and MAY NOT start with 
binary zero.

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


ZMQ_CONFLATE: Keep only last message
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If set, a socket shall keep only one message in its inbound/outbound
queue, this message being the last message received/the last message
to be sent. Ignores 'ZMQ_RCVHWM' and 'ZMQ_SNDHWM' options. Does not
support multi-part messages, in particular, only one part of it is kept
in the socket internal queue.

[horizontal]
Option value type:: int
Option value unit:: boolean
Default value:: 0 (false)
Applicable socket types:: ZMQ_PULL, ZMQ_PUSH, ZMQ_SUB, ZMQ_PUB, ZMQ_DEALER


ZMQ_CONNECT_TIMEOUT: Set connect() timeout
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets how long to wait before timing-out a connect() system call.
The connect() system call normally takes a long time before it returns a
time out error. Setting this option allows the library to time out the call
at an earlier interval.

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


ZMQ_CURVE_PUBLICKEY: Set CURVE public key
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the socket's long term public key. You must set this on CURVE client
sockets, see linkzmq:zmq_curve[7]. You can provide the key as 32 binary
bytes, or as a 40-character string encoded in the Z85 encoding format and
terminated in a null byte. The public key must always be used with the
matching secret key. To generate a public/secret key pair, use
linkzmq:zmq_curve_keypair[3]. To derive the public key from a secret key,
use linkzmq:zmq_curve_public[3].

NOTE: an option value size of 40 is supported for backwards compatibility,
though is deprecated.

[horizontal]
Option value type:: binary data or Z85 text string
Option value size:: 32 or 41
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 both CURVE
client and server sockets, see linkzmq:zmq_curve[7]. You can provide the
key as 32 binary bytes, or as a 40-character string encoded in the Z85
encoding format and terminated in a null byte. To generate a public/secret
key pair, use linkzmq:zmq_curve_keypair[3]. To derive the public key from
a secret key, use linkzmq:zmq_curve_public[3].

NOTE: an option value size of 40 is supported for backwards compatibility,
though is deprecated.

[horizontal]
Option value type:: binary data or Z85 text string
Option value size:: 32 or 41
Default value:: NULL
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 server's secret key using the
ZMQ_CURVE_SECRETKEY option. A server socket does not need to know
its own public key.

[horizontal]
Option value type:: int
Option value unit:: 0, 1
Default value:: 0
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 CURVE client
sockets, see linkzmq:zmq_curve[7]. You can provide the key as 32 binary
bytes, or as a 40-character string encoded in the Z85 encoding format and
terminated in a null byte. This key must have been generated together with
the server's secret key. To generate a public/secret key pair, use
linkzmq:zmq_curve_keypair[3].

NOTE: an option value size of 40 is supported for backwards compatibility,
though is deprecated.

[horizontal]
Option value type:: binary data or Z85 text string
Option value size:: 32 or 41
Default value:: NULL
Applicable socket types:: all, when using TCP transport


ZMQ_GSSAPI_PLAINTEXT: Disable GSSAPI encryption
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Defines whether communications on the socket will encrypted, see
linkzmq:zmq_gssapi[7]. A value of '1' means  that communications will be
plaintext.  A value of '0' means communications will be encrypted.

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


ZMQ_GSSAPI_PRINCIPAL: Set name of GSSAPI principal
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the name of the principal for whom GSSAPI credentials should be acquired.

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


ZMQ_GSSAPI_SERVER: Set GSSAPI server role
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Defines whether the socket will act as server for GSSAPI security, see
linkzmq:zmq_gssapi[7]. A value of '1' means the socket will act as GSSAPI
server. A value of '0' means the socket will act as GSSAPI client.

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


ZMQ_GSSAPI_SERVICE_PRINCIPAL: Set name of GSSAPI service principal
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the name of the principal of the GSSAPI server to which a GSSAPI client
intends to connect.

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


ZMQ_HANDSHAKE_IVL: Set maximum handshake interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_HANDSHAKE_IVL' option shall set the maximum handshake interval for
the specified 'socket'. Handshaking is the exchange of socket configuration
information (socket type, identity, security) that occurs when a connection
is first opened, only for connection-oriented transports. If handshaking does
not complete within the configured time, the connection shall be closed.
The value 0 means no handshake time limit.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 30000
Applicable socket types:: all but ZMQ_STREAM, only for connection-oriented transports


ZMQ_HEARTBEAT_IVL: Set interval between sending ZMTP heartbeats
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_HEARTBEAT_IVL' option shall set the interval between sending ZMTP heartbeats
for the specified 'socket'. If this option is set and is greater than 0, then a 'PING'
ZMTP command will be sent every 'ZMQ_HEARTBEAT_IVL' milliseconds.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 0
Applicable socket types:: all, when using connection-oriented transports


ZMQ_HEARTBEAT_TIMEOUT: Set timeout for ZMTP heartbeats
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_HEARTBEAT_TIMEOUT' option shall set how long to wait before timing-out a
connection after sending a 'PING' ZMTP command and not receiving any traffic. This
option is only valid if 'ZMQ_HEARTBEAT_IVL' is also set, and is greater than 0. The
connection will time out if there is no traffic received after sending the 'PING'
command, but the received traffic does not have to be a 'PONG' command - any received
traffic will cancel the timeout.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 0
Applicable socket types:: all, when using connection-oriented transports


ZMQ_HEARTBEAT_TTL: Set the TTL value for ZMTP heartbeats
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_HEARTBEAT_TTL' option shall set the timeout on the remote peer for ZMTP
heartbeats. If this option is greater than 0, the remote side shall time out the
connection if it does not receive any more traffic within the TTL period. This option
does not have any effect if 'ZMQ_HEARTBEAT_IVL' is not set or is 0. Internally, this
value is rounded down to the nearest decisecond, any value less than 100 will have
no effect.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: 0
Applicable socket types:: all, when using connection-oriented transports


ZMQ_IDENTITY: Set socket identity
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_IDENTITY' option shall set the identity of the specified 'socket'
when connecting to a ROUTER socket. The identity should be from 1 to 255
bytes long and may contain any values.

If two clients use the same identity when connecting to a ROUTER, the
results shall depend on the ZMQ_ROUTER_HANDOVER option setting. If that
is not set (or set to the default of zero), the ROUTER socket shall reject
clients trying to connect with an already-used identity. If that option
is set to 1, the ROUTER socket shall hand-over the connection to the new
client and disconnect the existing one.

[horizontal]
Option value type:: binary data
Option value unit:: N/A
Default value:: NULL
Applicable socket types:: ZMQ_REQ, ZMQ_REP, ZMQ_ROUTER, ZMQ_DEALER.


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_INVERT_MATCHING: Invert message filtering
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Reverses the filtering behavior of PUB-SUB sockets, when set to 1.

On 'PUB' and 'XPUB' sockets, this causes messages to be sent to all
connected sockets 'except' those subscribed to a prefix that matches
the message. On 'SUB' sockets, this causes only incoming messages that
do 'not' match any of the socket's subscriptions to be received by the user.

Whenever 'ZMQ_INVERT_MATCHING' is set to 1 on a 'PUB' socket, all 'SUB'
sockets connecting to it must also have the option set to 1. Failure to
do so will have the 'SUB' sockets reject everything the 'PUB' socket sends
them. 'XSUB' sockets do not need to do this because they do not filter
incoming messages.

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


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_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 disconnected with
linkzmq:zmq_disconnect[3] or closed with linkzmq:zmq_close[3], and further
affects the termination of the socket's context with linkzmq:zmq_ctx_term[3].
The following outlines the different behaviours:

* A value of '-1' specifies an infinite linger period. Pending
  messages shall not be discarded after a call to _zmq_disconnect()_ or
  _zmq_close()_; attempting to terminate the socket's context with _zmq_ctx_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 after a call to _zmq_disconnect()_ or _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_disconnect()_ or
  _zmq_close()_; attempting to terminate the socket's context with _zmq_ctx_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:: 30000 (thirty seconds)
Applicable socket types:: all


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_MULTICAST_MAXTPDU: Maximum transport data unit size for multicast packets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the maximum transport data unit size used for outbound multicast
packets.

This must be set at or below the minimum Maximum Transmission Unit (MTU) for
all network paths over which multicast reception is required.

[horizontal]
Option value type:: int
Option value unit:: bytes
Default value:: 1500
Applicable socket types:: all, when using multicast transports


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_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_USE_FD: Set the pre-allocated socket file descriptor
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
When set to a positive integer value before zmq_bind is called on the socket,
the socket shall use the corresponding file descriptor for connections over
TCP or IPC instead of allocating a new file descriptor.
Useful for writing systemd socket activated services. If set to -1 (default),
a new file descriptor will be allocated instead (default behaviour).

NOTE: if set after calling zmq_bind, this option shall have no effect.
NOTE: the file descriptor passed through MUST have been ran through the "bind"
      and "listen" system calls beforehand. Also, socket option that would
      normally be passed through zmq_setsockopt like TCP buffers length,
      IP_TOS or SO_REUSEADDR MUST be set beforehand by the caller, as they
      must be set before the socket is bound.

[horizontal]
Option value type:: int
Option value unit:: file descriptor
Default value:: -1
Applicable socket types:: all bound sockets, when using IPC or TCP transport


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_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_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 -1 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:: -1
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_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_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_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_REQ_CORRELATE: match replies with requests
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The default behaviour of REQ sockets is to rely on the ordering of messages to
match requests and responses and that is usually sufficient. When this option
is set to 1, the REQ socket will prefix outgoing messages with an extra frame
containing a request id. That means the full message is (request id, 0,
user frames...). The REQ socket will discard all incoming messages that don't
begin with these two frames.

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


ZMQ_REQ_RELAXED: relax strict alternation between request and reply
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
By default, a REQ socket does not allow initiating a new request with
_zmq_send(3)_ until the reply to the previous one has been received.
When set to 1, sending another message is allowed and previous replies will
be discarded if any. The request-reply state machine is reset and a new
request is sent to the next available peer.

If set to 1, also enable ZMQ_REQ_CORRELATE to ensure correct matching of
requests and replies. Otherwise a late reply to an aborted request can be
reported as the reply to the superseding request.

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


ZMQ_ROUTER_HANDOVER: handle duplicate client identities on ROUTER sockets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
If two clients use the same identity when connecting to a ROUTER, the
results shall depend on the ZMQ_ROUTER_HANDOVER option setting. If that
is not set (or set to the default of zero), the ROUTER socket shall reject
clients trying to connect with an already-used identity. If that option
is set to 1, the ROUTER socket shall hand-over the connection to the new
client and disconnect the existing one.

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


ZMQ_ROUTER_MANDATORY: accept only routable messages on ROUTER sockets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the ROUTER socket behaviour when an unroutable message is encountered. A
value of `0` is the default and discards the message silently when it cannot be
routed or the peers SNDHWM is reached.  A value of `1` returns an
'EHOSTUNREACH' error code if the message cannot be routed or 'EAGAIN' error
code if the SNDHWM is reached and ZMQ_DONTWAIT was used. Without ZMQ_DONTWAIT
it will block until the SNDTIMEO is reached or a spot in the send queue opens
up.

[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_SNDMORE
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).

NOTE: This option is deprecated, please use ZMQ_STREAM sockets instead.

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


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 -1 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:: -1
Applicable socket types:: all


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_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_STREAM_NOTIFY: send connect and disconnect notifications
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Enables connect and disconnect notifications on a STREAM socket, when set
to 1. When notifications are enabled, the socket delivers a zero-length
message when a peer connects or disconnects.

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


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_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_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_IDLE: Override TCP_KEEPIDLE (or TCP_KEEPALIVE on some OS)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Override 'TCP_KEEPIDLE' (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_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_MAXRT: Set TCP Maximum Retransmit Timeout
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On OSes where it is supported, sets how long before an unacknowledged TCP
retransmit times out. The system normally attempts many TCP retransmits
following an exponential backoff strategy. This means that after a network
outage, it may take a long time before the session can be re-established.
Setting this option allows the timeout to happen at a shorter interval.

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


ZMQ_TOS: Set the Type-of-Service on socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the ToS fields (Differentiated services (DS) and Explicit Congestion
Notification (ECN) field of the IP header. The ToS field is typically used
to specify a packets priority. The availability of this option is dependent
on intermediate network equipment that inspect the ToS field and provide a
path for low-delay, high-throughput, highly-reliable service, etc.

[horizontal]
Option value type:: int
Option value unit:: >0
Default value:: 0
Applicable socket types:: all, only for connection-oriented transports


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_XPUB_VERBOSE: pass subscribe messages on XPUB socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the 'XPUB' socket behaviour on new subscriptions. If enabled,
the socket passes all subscribe messages to the caller. If disabled,
these are not visible to the caller. The default is 0 (disabled).

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


ZMQ_XPUB_VERBOSER: pass subscribe and unsubscribe messages on XPUB socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the 'XPUB' socket behaviour on new subscriptions and ubsubscriptions.
If enabled, the socket passes all subscribe and unsubscribe messages to the
caller. If disabled, these are not visible to the caller. The default is 0
(disabled).

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


ZMQ_XPUB_MANUAL: change the subscription handling to manual
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the 'XPUB' socket subscription handling mode manual/automatic.
A value of '0' is the default and subscription requests will be handled automatically.
A value of '1' will change the subscription requests handling to manual, 
with manual mode subscription requests are not added to the subscription list.
To add subscription the user need to call setsockopt with ZMQ_SUBSCRIBE on XPUB socket.

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


ZMQ_XPUB_NODROP: do not silently drop messages if SENDHWM is reached
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the 'XPUB' socket behaviour to return error EAGAIN if SENDHWM is
reached and the message could not be send. 

A value of `0` is the default and drops the message silently when the peers
SNDHWM is reached.  A value of `1` returns an 'EAGAIN' error code if the
SNDHWM is reached and ZMQ_DONTWAIT was used.

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


ZMQ_XPUB_WELCOME_MSG: set welcome message that will be received by subscriber when connecting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets a welcome message the will be recieved by subscriber when connecting.
Subscriber must subscribe to the Welcome message before connecting.
Welcome message will also be sent on reconnecting.
For welcome message to work well user must poll on incoming subscription messages on the XPUB socket and handle them.

Use NULL and lenght of zero to disable welcome message.

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


ZMQ_ZAP_DOMAIN: Set RFC 27 authentication domain
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Sets the domain for ZAP (ZMQ RFC 27) authentication. For NULL security (the
default on all tcp:// connections), ZAP authentication only happens if you
set a non-empty domain. For PLAIN and CURVE security, ZAP requests are always
made, if there is a ZAP handler present. See http://rfc.zeromq.org/spec:27
for more details.

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


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.

NOTE: This option is deprecated, please use authentication via the ZAP API
and IP address whitelisting / blacklisting.

[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_IPC_FILTER_GID: Assign group ID filters to allow new IPC connections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Assign an arbitrary number of filters that will be applied for each new IPC
transport connection on a listening socket. If no IPC filters are applied, then
the IPC transport allows connections from any process. If at least one UID,
GID, or PID filter is applied then new connection credentials should be
matched. To clear all GID filters call zmq_setsockopt(socket,
ZMQ_IPC_FILTER_GID, NULL, 0).

NOTE: GID filters are only available on platforms supporting SO_PEERCRED or
LOCAL_PEERCRED socket options (currently only Linux and later versions of
OS X).

NOTE: This option is deprecated, please use authentication via the ZAP API
and IPC whitelisting / blacklisting.

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


ZMQ_IPC_FILTER_PID: Assign process ID filters to allow new IPC connections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Assign an arbitrary number of filters that will be applied for each new IPC
transport connection on a listening socket. If no IPC filters are applied, then
the IPC transport allows connections from any process. If at least one UID,
GID, or PID filter is applied then new connection credentials should be
matched. To clear all PID filters call zmq_setsockopt(socket,
ZMQ_IPC_FILTER_PID, NULL, 0).

NOTE: PID filters are only available on platforms supporting the SO_PEERCRED
socket option (currently only Linux).

NOTE: This option is deprecated, please use authentication via the ZAP API
and IPC whitelisting / blacklisting.

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


ZMQ_IPC_FILTER_UID: Assign user ID filters to allow new IPC connections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Assign an arbitrary number of filters that will be applied for each new IPC
transport connection on a listening socket. If no IPC filters are applied, then
the IPC transport allows connections from any process. If at least one UID,
GID, or PID filter is applied then new connection credentials should be
matched. To clear all UID filters call zmq_setsockopt(socket,
ZMQ_IPC_FILTER_UID, NULL, 0).

NOTE: UID filters are only available on platforms supporting SO_PEERCRED or
LOCAL_PEERCRED socket options (currently only Linux and later versions of
OS X).

NOTE: This option is deprecated, please use authentication via the ZAP API
and IPC whitelisting / blacklisting.

[horizontal]
Option value type:: uid_t
Option value unit:: N/A
Default value:: no filters (allow from all)
Applicable socket types:: all listening sockets, when using IPC 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_VMCI_BUFFER_SIZE: Set buffer size of the VMCI socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The `ZMQ_VMCI_BUFFER_SIZE` option shall set the size of the underlying
buffer for the socket. Used during negotiation before the connection is established.

[horizontal]
Option value type:: uint64_t
Option value unit:: bytes
Default value:: 65546
Applicable socket types:: all, when using VMCI transport


ZMQ_VMCI_BUFFER_MIN_SIZE: Set min buffer size of the VMCI socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The `ZMQ_VMCI_BUFFER_MIN_SIZE` option shall set the min size of the underlying
buffer for the socket. Used during negotiation before the connection is established.

[horizontal]
Option value type:: uint64_t
Option value unit:: bytes
Default value:: 128
Applicable socket types:: all, when using VMCI transport


ZMQ_VMCI_BUFFER_MAX_SIZE: Set max buffer size of the VMCI socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The `ZMQ_VMCI_BUFFER_MAX_SIZE` option shall set the max size of the underlying
buffer for the socket. Used during negotiation before the connection is established.

[horizontal]
Option value type:: uint64_t
Option value unit:: bytes
Default value:: 262144
Applicable socket types:: all, when using VMCI transport


ZMQ_VMCI_CONNECT_TIMEOUT: Set connection timeout of the VMCI socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The `ZMQ_VMCI_CONNECT_TIMEOUT` option shall set connection timeout
for the socket.

[horizontal]
Option value type:: int
Option value unit:: milliseconds
Default value:: -1
Applicable socket types:: all, when using VMCI 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
-------
This page was written by the 0MQ community. To make a change please
read the 0MQ Contribution Policy at <http://www.zeromq.org/docs:contributing>.