libzmq/doc/zmq_getsockopt.txt

zmq_getsockopt(3)
=================


NAME
----

zmq_getsockopt - get 0MQ socket options


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


DESCRIPTION
-----------
The _zmq_getsockopt()_ function shall retrieve the value for the option
specified by the 'option_name' argument for the 0MQ socket pointed to by the
'socket' argument, and store it in the buffer pointed to by the 'option_value'
argument. The 'option_len' argument is the size in bytes of the buffer pointed
to by 'option_value'; upon successful completion _zmq_getsockopt()_ shall
modify the 'option_len' argument to indicate the actual size of the option
value stored in the buffer.

The following options can be retrieved with the _zmq_getsockopt()_ function:


ZMQ_AFFINITY: Retrieve I/O thread affinity
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_AFFINITY' option shall retrieve 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: Retrieve maximum length of the queue of outstanding connections
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_BACKLOG' option shall retrieve 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_BINDTODEVICE: Retrieve name of device the socket is bound to
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_BINDTODEVICE' option retrieves the name of the device this socket is
bound to, eg. an interface or VRF. If a socket is bound to an interface, only
packets received from that interface are processed by the socket. If device
is a VRF device, then subsequent binds/connects to that socket use addresses
in the VRF routing table.

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


ZMQ_CONNECT_TIMEOUT: Retrieve connect() timeout
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retrieves 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: Retrieve current CURVE public key
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Retrieves the current long term public key for the socket. You can
provide either a 32 byte buffer, to retrieve the binary key value, or
a 41 byte buffer, to retrieve the key in a printable Z85 format.
NOTE: to fetch a printable key, the buffer must be 41 bytes large
to hold the 40-char key value and one null byte.

[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: Retrieve current CURVE secret key
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Retrieves the current long term secret key for the socket. You can
provide either a 32 byte buffer, to retrieve the binary key value, or
a 41 byte buffer, to retrieve the key in a printable Z85 format.
NOTE: to fetch a printable key, the buffer must be 41 bytes large
to hold the 40-char key value and one null byte.

[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_SERVERKEY: Retrieve current CURVE server key
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Retrieves the current server key for the client socket. You can
provide either a 32 byte buffer, to retrieve the binary key value, or
a 41-byte buffer, to retrieve the key in a printable Z85 format.
NOTE: to fetch a printable key, the buffer must be 41 bytes large
to hold the 40-char key value and one null byte.

[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_EVENTS: Retrieve socket event state
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_EVENTS' option shall retrieve the event state for the specified
'socket'.  The returned value is a bit mask constructed by OR'ing a combination
of the following event flags:

*ZMQ_POLLIN*::
Indicates that at least one message may be received from the specified socket
without blocking.

*ZMQ_POLLOUT*::
Indicates that at least one message may be sent to the specified socket without
blocking.

The combination of a file descriptor returned by the 'ZMQ_FD' option being
ready for reading but no actual events returned by a subsequent retrieval of
the 'ZMQ_EVENTS' option is valid; applications should simply ignore this case
and restart their polling operation/event loop.

[horizontal]
Option value type:: int
Option value unit:: N/A (flags)
Default value:: N/A
Applicable socket types:: all


ZMQ_FD: Retrieve file descriptor associated with the socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_FD' option shall retrieve the file descriptor associated with the
specified 'socket'. The returned file descriptor can be used to integrate the
socket into an existing event loop; the 0MQ library shall signal any pending
events on the socket in an _edge-triggered_ fashion by making the file
descriptor become ready for reading.

NOTE: The ability to read from the returned file descriptor does not
necessarily indicate that messages are available to be read from, or can be
written to, the underlying socket; applications must retrieve the actual event
state with a subsequent retrieval of the 'ZMQ_EVENTS' option.

NOTE: The returned file descriptor is also used internally by the 'zmq_send'
and 'zmq_recv' functions. As the descriptor is edge triggered, applications
must update the state of 'ZMQ_EVENTS' after each invocation of 'zmq_send'
or 'zmq_recv'.To be more explicit: after calling 'zmq_send' the socket may
become readable (and vice versa) without triggering a read event on the
file descriptor.

CAUTION: The returned file descriptor is intended for use with a 'poll' or
similar system call only. Applications must never attempt to read or write data
to it directly, neither should they try to close it.

[horizontal]
Option value type:: int on POSIX systems, SOCKET on Windows
Option value unit:: N/A
Default value:: N/A
Applicable socket types:: all


ZMQ_GSSAPI_PLAINTEXT: Retrieve GSSAPI plaintext or encrypted status
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Returns the 'ZMQ_GSSAPI_PLAINTEXT' option, if any, previously set on the
socket.  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 or IPC transports


ZMQ_GSSAPI_PRINCIPAL: Retrieve the name of the GSSAPI principal
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_GSSAPI_PRINCIPAL' option shall retrieve the principal name set for the
GSSAPI security mechanism. The returned value shall be a NULL-terminated string
and MAY be empty. The returned size SHALL include the terminating null byte.

[horizontal]
Option value type:: NULL-terminated character string
Option value unit:: N/A
Default value:: null string
Applicable socket types:: all, when using TCP or IPC transports


ZMQ_GSSAPI_SERVER: Retrieve current GSSAPI server role
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Returns the 'ZMQ_GSSAPI_SERVER' option, if any, previously set on the socket.

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


ZMQ_GSSAPI_SERVICE_PRINCIPAL: Retrieve the name of the GSSAPI service principal
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_GSSAPI_SERVICE_PRINCIPAL' option shall retrieve the principal name of
the GSSAPI server to which a GSSAPI client socket intends to connect.  The
returned value shall be a NULL-terminated string and MAY be empty. The returned
size SHALL include the terminating null byte.

[horizontal]
Option value type:: NULL-terminated character string
Option value unit:: N/A
Default value:: null string
Applicable socket types:: all, when using TCP or IPC transports

ZMQ_GSSAPI_SERVICE_PRINCIPAL_NAMETYPE: Retrieve nametype for service principal
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Returns the 'ZMQ_GSSAPI_SERVICE_PRINCIPAL_NAMETYPE' option, if any, previously
set on the socket.  A value of 'ZMQ_GSSAPI_NT_HOSTBASED' (0) means the name
specified with 'ZMQ_GSSAPI_SERVICE_PRINCIPAL' is interpreted as a host based
name.  A value of 'ZMQ_GSSAPI_NT_USER_NAME' (1) means it is interpreted as
a local user name.  A value of 'ZMQ_GSSAPI_NT_KRB5_PRINCIPAL' (2) means it
is interpreted as an unparsed principal name string (valid only with the
krb5 GSSAPI mechanism).

[horizontal]
Option value type:: int
Option value unit:: 0, 1, 2
Default value:: 0 (ZMQ_GSSAPI_NT_HOSTBASED)
Applicable socket types:: all, when using TCP or IPC transports

ZMQ_GSSAPI_PRINCIPAL_NAMETYPE: Retrieve nametype for service principal
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Returns the 'ZMQ_GSSAPI_PRINCIPAL_NAMETYPE' option, if any, previously
set on the socket.  A value of 'ZMQ_GSSAPI_NT_HOSTBASED' (0) means the name
specified with 'ZMQ_GSSAPI_PRINCIPAL' is interpreted as a host based
name.  A value of 'ZMQ_GSSAPI_NT_USER_NAME' (1) means it is interpreted as
a local user name.  A value of 'ZMQ_GSSAPI_NT_KRB5_PRINCIPAL' (2) means it
is interpreted as an unparsed principal name string (valid only with the
krb5 GSSAPI mechanism).

[horizontal]
Option value type:: int
Option value unit:: 0, 1, 2
Default value:: 0 (ZMQ_GSSAPI_NT_HOSTBASED)
Applicable socket types:: all, when using TCP or IPC transports

ZMQ_HANDSHAKE_IVL: Retrieve maximum handshake interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_HANDSHAKE_IVL' option shall retrieve the maximum handshake interval
for the specified 'socket'. Handshaking is the exchange of socket configuration
information (socket type, routing id, 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_IDENTITY: Retrieve socket identity
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This option name is now deprecated. Use ZMQ_ROUTING_ID instead.
ZMQ_IDENTITY remains as an alias for now.


ZMQ_IMMEDIATE: Retrieve attach-on-connect value
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retrieve the state of the attach on connect value. If set to `1`, will delay the
attachment of a pipe on connect until the underlying connection has completed.
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, primarily when using TCP/IPC transports.


ZMQ_INVERT_MATCHING: Retrieve inverted filtering status
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Returns the value of the 'ZMQ_INVERT_MATCHING' option. A value of `1`
means the socket uses inverted prefix matching.

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_IPV4ONLY: Retrieve IPv4-only socket override status
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retrieve 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_IPV6: Retrieve IPv6 socket status
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retrieve 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_LAST_ENDPOINT: Retrieve the last endpoint set
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_LAST_ENDPOINT' option shall retrieve the last endpoint bound for
TCP and IPC transports. The returned value will be a string in the form of
a ZMQ DSN. Note that if the TCP host is INADDR_ANY, indicated by a *, then
the returned address will be 0.0.0.0 (for IPv4).
Note: not supported on GNU/Hurd with IPC due to non-working getsockname().

[horizontal]
Option value type:: NULL-terminated character string
Option value unit:: N/A
Default value:: NULL
Applicable socket types:: all, when binding TCP or IPC transports


ZMQ_LINGER: Retrieve linger period for socket shutdown
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_LINGER' option shall retrieve 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_ctx_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_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 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_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:: -1 (infinite)
Applicable socket types:: all


ZMQ_MAXMSGSIZE: Maximum acceptable inbound message size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The option shall retrieve limit for the inbound messages. 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_MECHANISM: Retrieve current security mechanism
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_MECHANISM' option shall retrieve the current security mechanism
for the socket.

[horizontal]
Option value type:: int
Option value unit:: ZMQ_NULL, ZMQ_PLAIN, ZMQ_CURVE, or ZMQ_GSSAPI
Default value:: ZMQ_NULL
Applicable socket types:: all, when using TCP or IPC transports


ZMQ_MULTICAST_HOPS: Maximum network hops for multicast packets
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The option shall retrieve time-to-live used for outbound multicast packets.
The default of 1 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
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_MULTICAST_MAXTPDU' option shall retrieve 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: Retrieve current password
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_PLAIN_PASSWORD' option shall retrieve the last password set for
the PLAIN security mechanism. The returned value shall be a NULL-terminated
string and MAY be empty. The returned size SHALL include the terminating
null byte.

[horizontal]
Option value type:: NULL-terminated character string
Option value unit:: N/A
Default value:: null string
Applicable socket types:: all, when using TCP or IPC transports


ZMQ_PLAIN_SERVER: Retrieve current PLAIN server role
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Returns the 'ZMQ_PLAIN_SERVER' option, if any, previously set on the socket.

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


ZMQ_PLAIN_USERNAME: Retrieve current PLAIN username
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_PLAIN_USERNAME' option shall retrieve the last username set for
the PLAIN security mechanism. The returned value shall be a NULL-terminated
string and MAY be empty. The returned size SHALL include the terminating
null byte.

[horizontal]
Option value type:: NULL-terminated character string
Option value unit:: N/A
Default value:: null string
Applicable socket types:: all, when using TCP or IPC transports


ZMQ_USE_FD: Retrieve the pre-allocated socket file descriptor
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_USE_FD' option shall retrieve the pre-allocated file
descriptor that has been assigned to a ZMQ socket, if any. -1 shall be
returned if a pre-allocated file descriptor was not set for the socket.

[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_PRIORITY: Retrieve the Priority on socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets the protocol-defined priority for all packets to be sent on this
socket, where supported by the OS.

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


ZMQ_RATE: Retrieve multicast data rate
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RATE' option shall retrieve the maximum send or receive data rate for
multicast transports 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: Retrieve kernel receive buffer size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RCVBUF' option shall retrieve the underlying kernel receive buffer
size for the specified 'socket'. 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:: 8192
Applicable socket types:: all


ZMQ_RCVHWM: Retrieve high water mark for inbound messages
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RCVHWM' option shall return 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_RCVMORE: More message data parts to follow
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RCVMORE' option shall return True (1) if the message part last
received from the 'socket' was a data part with more parts to follow. If there
are no data parts to follow, this option shall return False (0).

Refer to linkzmq:zmq_send[3] and linkzmq:zmq_recv[3] for a detailed description
of multi-part messages.

[horizontal]
Option value type:: int
Option value unit:: boolean
Default value:: N/A
Applicable socket types:: all


ZMQ_RCVTIMEO: Maximum time before a socket operation returns with EAGAIN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retrieve the timeout for recv 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: Retrieve reconnection interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RECONNECT_IVL' option shall retrieve 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: DEPRECATED
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RECONNECT_IVL_MAX option is an empty stub that only returns an
*EOPNOTSUPP* error, as the author did not provide a relicense agreement for
the Mozilla Public License v2 relicense of libzmq.


ZMQ_RECONNECT_STOP: Retrieve condition where reconnection will stop
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RECONNECT_STOP' option shall retrieve the conditions under which
automatic reconnection will stop.

The 'ZMQ_RECONNECT_STOP_CONN_REFUSED' option will stop reconnection when 0MQ
receives the ECONNREFUSED return code from the connect.  This indicates that
there is no code bound to the specified endpoint.

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


ZMQ_RECOVERY_IVL: Get multicast recovery interval
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_RECOVERY_IVL' option shall retrieve 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.

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


ZMQ_ROUTING_ID: Retrieve socket routing id
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_ROUTING_ID' option shall retrieve the routing id of the specified 'socket'.
Routing ids are used only by the request/reply pattern. Specifically, it can be used
in tandem with ROUTER socket to route messages to the peer with a specific
routing id.

A routing id must be at least one byte and at most 255 bytes long. Identities
starting with a zero byte are reserved for use by the 0MQ infrastructure.

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


ZMQ_SNDBUF: Retrieve kernel transmit buffer size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_SNDBUF' option shall retrieve the underlying kernel transmit buffer
size for the specified 'socket'. For details refer to your operating system
documentation for the 'SO_SNDBUF' socket option.

[horizontal]
Option value type:: int
Option value unit:: bytes
Default value:: 8192
Applicable socket types:: all


ZMQ_SNDHWM: Retrieves high water mark for outbound messages
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_SNDHWM' option shall return 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.

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


ZMQ_SNDTIMEO: Maximum time before a socket operation returns with EAGAIN
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retrieve 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_SOCKS_PROXY: Retrieve SOCKS5 proxy address
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_SOCKS_PROXY' option shall retrieve the SOCKS5 proxy address in string
format. The returned value shall be a NULL-terminated string and MAY be empty.
The returned size SHALL include the terminating null byte.

[horizontal]
Option value type:: NULL-terminated character string
Option value unit:: N/A
Default value:: null string
Applicable socket types:: all, when using TCP transports


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: Retrieve Max TCP Retransmit Timeout
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
On OSes where it is supported, retrieves 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_THREAD_SAFE: Retrieve socket thread safety
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_THREAD_SAFE' option shall retrieve a boolean value indicating whether
or not the socket is threadsafe. See linkzmq:zmq_socket[3] for which sockets are
thread-safe.

[horizontal]
Option value type:: int
Option value unit:: boolean
Applicable socket types:: all


ZMQ_TOS: Retrieve the Type-of-Service socket override status
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retrieve the IP_TOS option for the socket.

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


ZMQ_TYPE: Retrieve socket type
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_TYPE' option shall retrieve the socket type for the specified
'socket'.  The socket type is specified at socket creation time and
cannot be modified afterwards.

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


ZMQ_ZAP_DOMAIN: Retrieve RFC 27 authentication domain
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

The 'ZMQ_ZAP_DOMAIN' option shall retrieve the last ZAP domain set for
the socket. The returned value shall be a NULL-terminated string and MAY
be empty. An empty string means that ZAP authentication is disabled.
The returned size SHALL include the terminating null byte.

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


ZMQ_ZAP_ENFORCE_DOMAIN: Retrieve ZAP domain handling mode
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The 'ZMQ_ZAP_ENFORCE_DOMAIN' option shall retrieve the flag that determines
whether a ZAP domain is strictly required or not.

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


ZMQ_VMCI_BUFFER_SIZE: Retrieve buffer size of the VMCI socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The `ZMQ_VMCI_BUFFER_SIZE` option shall retrieve 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: Retrieve min buffer size of the VMCI socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The `ZMQ_VMCI_BUFFER_MIN_SIZE` option shall retrieve 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: Retrieve max buffer size of the VMCI socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The `ZMQ_VMCI_BUFFER_MAX_SIZE` option shall retrieve 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: Retrieve connection timeout of the VMCI socket
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The `ZMQ_VMCI_CONNECT_TIMEOUT` option shall retrieve 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


ZMQ_MULTICAST_LOOP: Retrieve multicast local loopback configuration
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retrieve the current multicast loopback configuration. A value of `1`
means that the multicast packets sent on this socket will be looped
back to local listening interface.

[horizontal]
Option value type:: int
Option value unit:: 0, 1
Default value:: 1
Applicable socket types:: ZMQ_RADIO, when using UDP multicast transport


ZMQ_ROUTER_NOTIFY: Retrieve router socket notification settings
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retrieve the current notification settings of a router socket. The returned
value is a bitmask composed of ZMQ_NOTIFY_CONNECT and ZMQ_NOTIFY_DISCONNECT
flags, meaning connect and disconnect notifications are enabled, respectively.
A value of '0' means the notifications are off.

NOTE: in DRAFT state, not yet available in stable releases.

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


ZMQ_IN_BATCH_SIZE: Maximal receive batch size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets the maximal amount of messages that can be received in a single
'recv' system call.

Cannot be zero.

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: messages
Default value:: 8192
Applicable socket types:: All, when using TCP, IPC, PGM or NORM transport.


ZMQ_OUT_BATCH_SIZE: Maximal send batch size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets the maximal amount of messages that can be sent in a single
'send' system call.

Cannot be zero.

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: messages
Default value:: 8192
Applicable socket types:: All, when using TCP, IPC, PGM or NORM transport.


ZMQ_TOPICS_COUNT: Number of topic subscriptions received
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets the number of topic (prefix) subscriptions either
* received on a (X)PUB socket from all the connected (X)SUB sockets or
* acknowledged on an (X)SUB socket from all the connected (X)PUB sockets

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: N/A
Default value:: 0
Applicable socket types:: ZMQ_PUB, ZMQ_XPUB, ZMQ_SUB, ZMQ_XSUB


ZMQ_NORM_MODE: Retrieve NORM Sender Mode
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets the NORM sender mode to control the operation of the NORM transport. NORM
supports fixed rate operation (0='ZMQ_NORM_FIXED'), congestion control mode 
(1='ZMQ_NORM_CC'), loss-tolerant congestion control (2='ZMQ_NORM_CCL'), explicit
congestion notification (ECN)-enabled congestion control (3='ZMQ_NORM_CCE'), and
ECN-only congestion control (4='ZMQ_NORM_CCE_ECNONLY'). The default value is 
TCP-friendly congestion control mode. Fixed rate mode (using datarate set by
'ZMQ_RATE') offers better performance, but care must be taken to prevent data
loss.

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: 0, 1, 2, 3, 4
Default value:: 1 ('ZMQ_NORM_CC')
Applicable socket types:: All, when using NORM transport.


ZMQ_NORM_UNICAST_NACK: Retrieve NORM Unicast NACK mode
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Retrieves status of NORM unicast NACK mode setting for multicast receivers. If
set, NORM receiver will send Negative ACKnowledgements (NACKs) back to the
sender using unicast instead of multicast.  NORM transport endpoints specifying
a unicast address will use unicast NACKs by default (without setting
'ZMQ_NORM_UNICAST_NACK').

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: boolean
Default value:: 0 (false)
Applicable socket types:: All, when using NORM transport.


ZMQ_NORM_BUFFER_SIZE: Retrieve NORM buffer size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets NORM buffer size for NORM transport sender, receiver, and stream.

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: kilobytes
Default value:: 2048
Applicable socket types:: All, when using NORM transport.


ZMQ_NORM_SEGMENT_SIZE: Retrieve NORM segment size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets NORM sender segment size, which is the maximum message payload size of
individual NORM messages (ZMQ messages may be split over multiple NORM
messages).  Ideally, this value should fit within the system/network maximum
transmission unit (MTU) after accounting for additional NORM message headers
(up to 48 bytes).

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: bytes
Default value:: 1400
Applicable socket types:: All, when using NORM transport.


ZMQ_NORM_BLOCK_SIZE: Retrieve NORM block size
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets NORM sender block size, which is the number of segments in a NORM FEC
coding block. NORM repair operations take place at block boundaries. Maximum
value is 255, but parity packets ('ZMQ_NORM_NUM_PARITY') are limited to a value
of (255 - 'ZMQ_NORM_BLOCK_SIZE'). Minimum value is ('ZMQ_NORM_NUM_PARITY' + 1).
Effective value may be different based on the settings of 'ZMQ_NORM_NUM_PARITY'
and 'ZMQ_NORM_NUM_AUTOPARITY' if invalid settings are provided.

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: >0, <=255
Default value:: 16
Applicable socket types:: All, when using NORM transport.


ZMQ_NORM_NUM_PARITY: Retrieve NORM parity segment setting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets the maximum number of NORM parity symbol segments that the sender is
willing to calculate per FEC coding block for the purpose of reparing lost data.
Maximum value is 255, but is further limited to a value of
(255 - 'ZMQ_NORM_BLOCK_SIZE'). Minimum value is 'ZMQ_NORM_NUM_AUTOPARITY'.
Effective value may be different based on the setting of
'ZMQ_NORM_NUM_AUTOPARITY' if invalid settings are provided.

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: >0, <255
Default value:: 4
Applicable socket types:: All, when using NORM transport.


ZMQ_NORM_NUM_AUTOPARITY: Retrieve proactive NORM parity segment setting
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets the number of NORM parity symbol segments that the sender will proactively
send at the end of each FEC coding block. By default, no proactive parity
segments will be sent; instead, parity segments will only be sent in response to
repair requests (NACKs). Maximum value is 255, but is further limited to a 
maximum value of 'ZMQ_NORM_NUM_PARITY'.

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: >=0, <255
Default value:: 0
Applicable socket types:: All, when using NORM transport.


ZMQ_NORM_PUSH: Retrieve NORM push mode
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Gets status of NORM stream push mode, which alters the behavior of the sender
when enqueueing new data. By default, NORM will stop accepting new messages
while waiting for old data to be transmitted and/or repaired. Enabling push mode
discards the oldest data (which may be pending repair or may never have been
transmitted) in favor of accepting new data. This may be useful in cases where
it is more important to quickly deliver new data instead of reliably delivering
older data.

NOTE: in DRAFT state, not yet available in stable releases.

[horizontal]
Option value type:: int
Option value unit:: boolean
Default value:: 0 (false)
Applicable socket types:: All, when using NORM transport.


RETURN VALUE
------------
The _zmq_getsockopt()_ 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, or the size of the buffer pointed to by
_option_value_, as specified by _option_len_, is insufficient for storing the
option value.
*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
-------
.Retrieving the high water mark for outgoing messages
----
/* Retrieve high water mark into sndhwm */
int sndhwm;
size_t sndhwm_size = sizeof (sndhwm);
rc = zmq_getsockopt (socket, ZMQ_SNDHWM, &sndhwm, &sndhwm_size);
assert (rc == 0);
----


SEE ALSO
--------
linkzmq:zmq_setsockopt[3]
linkzmq:zmq_socket[3]
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>.