Provided by: libzmq3-dev_4.0.4+dfsg-2ubuntu0.1_amd64 
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_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.
Option value type int
Option value unit N/A
Default value N/A
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 zmq_send(3) and zmq_recv(3) for a detailed description of multi-part messages.
Option value type int
Option value unit boolean
Default value N/A
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 zmq_socket(3) for details on the
exact action taken for each socket type.
Option value type int
Option value unit messages
Default value 1000
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 zmq_socket(3) for details on the
exact action taken for each socket type.
Option value type int
Option value unit messages
Default value 1000
Applicable socket types all
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 zmq_init(3) for details on allocating the number of I/O threads for a specific
context.
Option value type uint64_t
Option value unit N/A (bitmap)
Default value 0
Applicable socket types N/A
ZMQ_IDENTITY: Retrieve socket identity
The ZMQ_IDENTITY option shall retrieve 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.
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_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.
Option value type int
Option value unit kilobits per second
Default value 100
Applicable socket types all, when using multicast
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.
Option value type int
Option value unit milliseconds
Default value 10000
Applicable socket types all, when using multicast
transports
ZMQ_SNDBUF: Retrieve kernel transmit buffer size
The ZMQ_SNDBUF option shall retrieve the underlying kernel transmit buffer size for the
specified socket. A value of zero means that the OS default is in effect. For details
refer to your operating system documentation for the SO_SNDBUF socket option.
Option value type int
Option value unit bytes
Default value 0
Applicable socket types all
ZMQ_RCVBUF: Retrieve kernel receive buffer size
The ZMQ_RCVBUF option shall retrieve the underlying kernel receive buffer size for the
specified socket. A value of zero means that the OS default is in effect. For details
refer to your operating system documentation for the SO_RCVBUF socket option.
Option value type int
Option value unit bytes
Default value 0
Applicable socket types all
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 zmq_close(3), and further affects the
termination of the socket’s context with 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.
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.
Option value type int
Option value unit milliseconds
Default value 100
Applicable socket types all, only for
connection-oriented transports
ZMQ_RECONNECT_IVL_MAX: Retrieve maximum reconnection interval
The ZMQ_RECONNECT_IVL_MAX option shall retrieve 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.
Option value type int
Option value unit milliseconds
Default value 0 (only use ZMQ_RECONNECT_IVL)
Applicable socket types all, only for
connection-oriented transport
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.
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
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.
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
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.
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 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.
Option value type int
Option value unit milliseconds
Default value -1 (infinite)
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.
Option value type int
Option value unit milliseconds
Default value -1 (infinite)
Applicable socket types all
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.
Option value type int
Option value unit boolean
Default value 0 (false)
Applicable socket types all, when using TCP transports.
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.
Option value type int
Option value unit boolean
Default value 1 (true)
Applicable socket types all, when using TCP transports.
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.
Option value type int
Option value unit boolean
Default value 0 (false)
Applicable socket types all, primarily when using
TCP/IPC transports.
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.
Option value type int on POSIX systems, SOCKET on
Windows
Option value unit N/A
Default value N/A
Applicable socket types all
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.
Option value type int
Option value unit N/A (flags)
Default value N/A
Applicable socket types all
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).
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_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.
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.
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.
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.
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_MECHANISM: Retrieve current security mechanism
The ZMQ_MECHANISM option shall retrieve the current security mechanism for the socket.
Option value type int
Option value unit ZMQ_NULL, ZMQ_PLAIN, or
ZMQ_CURVE
Default value ZMQ_NULL
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.
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.
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_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.
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_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.
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.
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 40 byte buffer, to retrieve the key in a
printable Z85 format.
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_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. The returned size SHALL
include the terminating null byte.
Option value type character string
Option value unit N/A
Default value not set
Applicable socket types all, when using TCP 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
zmq_setsockopt(3) zmq_socket(3) zmq(7)
AUTHORS
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