ZMQ_GETSOCKOPT(3)

📦
version 4.3.5 · 11 versions
, in epel 10, fedora 43, fedora 44, opensuse-leap 16.0

ZMQ_GETSOCKOPT 💅✨

okay bestie, welcome to the 0MQ manual — yes that's the section name, don't @ me — and today we're learning how to peek at all the lil settings on your 0MQ socket. no cap, this one's a banger. 🔥

🌸 NAME 🌸

zmq_getsockopt — get 0MQ socket options

like, literally, it goes and fetches your socket's option values for you. that's the whole vibe.

🎀 SYNOPSIS 🎀

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

💖 DESCRIPTION 💖

so the way that zmq_getsockopt() works is: it goes and retrieves the value for whatever option you named in the option_name argument, on the 0MQ socket that socket is pointing at, and it drops that value into the buffer that option_value points to. 📥

and option_len? that's the size in bytes of the buffer option_value points at. and here's the cute part — once it's done successfully, zmq_getsockopt() modifies option_len to tell you the actual size of the option value it just stored in your buffer. so it updates itself. main character energy fr fr. 💅

the following options can be retrieved with the zmq_getsockopt() function:

ZMQ_AFFINITY: Retrieve I/O thread affinity 🧵

the ZMQ_AFFINITY option retrieves the I/O thread affinity for newly created connections on the socket you specified.

affinity decides which threads, from the 0MQ I/O thread pool that belongs to the socket's context, are gonna handle newly created connections. a value of zero = no affinity, meaning the work gets distributed fairly among all the 0MQ I/O threads in the pool. for non-zero values: the lowest bit maps to thread 1, the second lowest bit maps to thread 2, and so on down the line. for example, a value of 3 means subsequent connections on that socket get handled exclusively by I/O threads 1 and 2. iconic bit math, honestly. ✨

also see zmq_init(3) for the deets 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_BACKLOG: Retrieve maximum length of the queue of outstanding connections 📚

the ZMQ_BACKLOG option retrieves the maximum length of the queue of outstanding peer connections for the socket you specified — and heads up, this only applies to connection-oriented transports. for the details, go read your operating system's documentation for the listen function. iykyk. 🫶

  • 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, e.g. an interface or VRF. if a socket is bound to an interface, only packets received from that interface get processed by the socket. and if the device is a VRF device, then subsequent binds/connects to that socket use addresses in the VRF routing table. lowkey fancy. 🌈

  • 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 timeout error — setting this option lets the library time out the call at an earlier interval. so you don't gotta sit there waiting like 😭

  • 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 hand it 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 hand it 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_SERVERKEY: Retrieve current CURVE server key 🖥️

retrieves the current server key for the client socket. you can hand it 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_EVENTS: Retrieve socket event state 🎉

the ZMQ_EVENTS option retrieves the event state for the socket you specified. the returned value is a bit mask constructed by OR'ing a combination of these 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.

and listen — 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. it's giving "false alarm, we move." 🚨

  • 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 retrieves the file descriptor associated with the socket you specified. the returned file descriptor can be used to integrate the socket into an existing event loop; the 0MQ library signals 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. do not do it bestie, i'm so serious. 🙈
  • 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 communications will be plaintext. a value of 0 means communications will be encrypted.

  • 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 retrieves the principal name set for the GSSAPI security mechanism. the returned value is 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_GSSAPI_SERVER: Retrieve current GSSAPI server role 👑

returns the ZMQ_GSSAPI_SERVER option, if any, previously set on the socket.

  • 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 retrieves the principal name of the GSSAPI server to which a GSSAPI client socket intends to connect. the returned value is 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_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's interpreted as a local user name. a value of ZMQ_GSSAPI_NT_KRB5_PRINCIPAL (2) means it's interpreted as an unparsed principal name string (valid only with the krb5 GSSAPI mechanism). three whole vibes, pick your fighter. ✨

  • 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

and that's a wrap on part 1 bestie... but we're so not done yet, there's more coming 💖

🦋 ZMQ_GSSAPI_PRINCIPAL_NAMETYPE: Retrieve nametype for service principal

Hands back the ZMQ_GSSAPI_PRINCIPAL_NAMETYPE option, if there's one you set on the socket before. So like, what kind of name are we dealing with here:

  • ZMQ_GSSAPI_NT_HOSTBASED (0) → the name you gave with ZMQ_GSSAPI_PRINCIPAL gets read as a host based name, periodt.
  • ZMQ_GSSAPI_NT_USER_NAME (1) → it gets read as a local user name.
  • ZMQ_GSSAPI_NT_KRB5_PRINCIPAL (2) → it gets read as an unparsed principal name string, and heads up, this one is valid only with the krb5 GSSAPI mechanism.
  • 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

Grabs the max handshake interval for the socket you asked about. And what even is a handshake? Bestie it's the exchange of socket configuration info — socket type, routing id, security — that happens the very first time a connection opens up, and only for connection-oriented transports. If the handshake doesn't wrap up inside the time you configured, the connection gets closed, no cap. And a value of 0 means literally no handshake time limit at all, live your truth.

  • 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, babe. Use ZMQ_ROUTING_ID instead. ZMQ_IDENTITY remains as an alias for now.

🎀 ZMQ_IMMEDIATE: Retrieve attach-on-connect value

Retrieves the state of the attach on connect value. If it's set to 1, it delays attaching a pipe on connect until the underlying connection has fully completed. Which means the socket will block if there are no other connections — lowkey a vibe killer but — it also prevents queues from filling up on pipes that are still waiting to connect. Tradeoffs, iykyk.

  • 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 is using inverted prefix matching. Chaotic? A little. Iconic? Also yes.

On PUB and XPUB sockets, this makes messages get sent to all connected sockets except the ones subscribed to a prefix that matches the message. On SUB sockets, it flips the other way: only incoming messages that don't match any of the socket's subscriptions actually make it through to the user.

Okay this part matters: 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. If they don't, the SUB sockets will reject literally everything the PUB socket sends them. 😭 XSUB sockets don't need to do this though, because they don't filter incoming messages in the first place.
  • 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

Retrieves the IPv4-only option for the socket.

Heads up bestie, this option is deprecated. Please use the ZMQ_IPV6 option instead. 💅
  • 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

Retrieves the IPv6 option for the socket. 1 means IPv6 is enabled on the socket, while 0 means the socket will use only IPv4. And the cute part: when IPv6 is enabled, the socket will connect to, or accept connections from, both IPv4 and IPv6 hosts. Best of both worlds fr fr.

  • 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

This one retrieves the last endpoint bound for TCP and IPC transports. What comes back is a string in the form of a ZMQ DSN. Now real talk: if the TCP host is INADDR_ANY, which shows up as a *, then the returned address will be 0.0.0.0 (for IPv4). And — Note: not supported on GNU/Hurd with IPC due to non-working getsockname(). 🙈

  • 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

Retrieves the linger period for the socket. The linger period decides how long pending messages that haven't been sent to a peer yet shall linger in memory after the socket gets closed with zmq_close(3) — and it further affects how the socket's context terminates with zmq_ctx_term(3). Here's the whole rundown, no skipping:

  • 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.
  • Option value type — int
  • Option value unit — milliseconds
  • Default value — -1 (infinite)
  • Applicable socket types — all

👑 ZMQ_MAXMSGSIZE: Maximum acceptable inbound message size

Retrieves the limit for inbound messages. If a peer sends a message bigger than ZMQ_MAXMSGSIZE, it gets disconnected. Simple as that. And a value of -1 means no limit — go wild.

  • Option value type — int64_t
  • Option value unit — bytes
  • Default value — -1
  • Applicable socket types — all

🔥 ZMQ_MECHANISM: Retrieve current security mechanism

Retrieves the current security mechanism for the socket. Just, like, what are we running here.

  • 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

Retrieves the time-to-live used for outbound multicast packets. The default of 1 means the multicast packets don't leave the local network — they stay home, cozy, in their lane. 🏠

  • 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

Retrieves 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. Respect the MTU bestie, it's not optional.

  • 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

Retrieves 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. Yes, the null byte counts. It always counts.

  • 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.

  • Option value type — int
  • Option value unit — 0, 1
  • Default value — int
  • Applicable socket types — all, when using TCP or IPC transports
Not me noticing the manpage literally lists the default value as int here 😭 i'm not touching it, that's what it says, fr fr.

💜 ZMQ_PLAIN_USERNAME: Retrieve current PLAIN username

Retrieves 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_USE_FD: Retrieve the pre-allocated socket file descriptor

Retrieves the pre-allocated file descriptor that has been assigned to a ZMQ socket, if any. And -1 shall be returned if a pre-allocated file descriptor was not set for the socket. No fd, no problem.

  • 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.

  • 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

Retrieves the maximum send or receive data rate for multicast transports using the specified socket. Throttle it, diva.

  • 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

Retrieves the underlying kernel receive buffer size for the specified socket. For details, go refer to your operating system documentation for the SO_RCVBUF socket option — that's where the real lore lives.

  • Option value type — int
  • Option value unit — bytes
  • Default value — 8192
  • Applicable socket types — all

ZMQ_RCVHWM: Retrieve high water mark for inbound messages 🫶

Okay bestie, this one hands you 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_RCVMORE: More message data parts to follow 💖

This 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_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_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 max reconnection interval 📈

The ZMQ_RECONNECT_IVL_MAX option shall retrieve the max reconnection interval for the specified socket. 0MQ shall wait at most the configured interval between reconnection attempts. The interval grows exponentionally (i.e.: it is doubled) with each attempt until it reaches ZMQ_RECONNECT_IVL_MAX. Default value means that the reconnect interval is based exclusively on ZMQ_RECONNECT_IVL and no exponential backoff is performed.

Note 🚨 Value has to be greater or equal than ZMQ_RECONNECT_IVL, or else it will be ignored.
  • Option value type — int
  • Option value unit — milliseconds
  • Default value — 0 (ZMQ_RECONNECT_IVL will be used)
  • Applicable socket types — all, only for connection-oriented transport

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.

  • 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.

  • 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.

  • 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.

  • 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 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_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_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.

  • 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.

  • 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.

  • 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.

  • 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_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.

  • 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 zmq_socket(3) for which sockets are thread-safe.

  • 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.

  • 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.

  • Option value type — int
  • Option value unit — N/A
  • Default value — N/A
  • Applicable socket types — all

ZMQ_ZAP_DOMAIN 🌸 — grab the RFC 27 authentication domain

okay so ZMQ_ZAP_DOMAIN hands you back the last ZAP domain that got set on this socket. The value you get is a NULL-terminated string and it MAY be empty — and bestie, an empty string means ZAP authentication is disabled, so don't sleep on that. The returned size SHALL include that terminating null byte. periodt.

  • 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 ✨ — grab the ZAP domain handling mode

This one fetches the flag that decides whether a ZAP domain is strictly required or not. that's it, that's the vibe check 🦋

  • Option value type — int
  • Option value unit — 0, 1
  • Default value — 0
  • Applicable socket types — all, when using ZAP

ZMQ_VMCI_BUFFER_SIZE 💅 — grab the buffer size of the VMCI socket

Gets you the size of the underlying buffer for the socket. lowkey important: it's used during negotiation before the connection is established. 🤝

  • 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 🎀 — grab the min buffer size of the VMCI socket

The min size of the underlying buffer, bestie. Also used during negotiation before the connection goes live.

  • 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 🫶 — grab the max buffer size of the VMCI socket

And this one's the max size of the underlying buffer. Same deal: negotiation-time only, before the connection exists.

  • Option value type — uint64_t
  • Option value unit — bytes
  • Default value — 262144
  • Applicable socket types — all, when using VMCI transport

ZMQ_VMCI_CONNECT_TIMEOUT ⏳ — grab the connection timeout of the VMCI socket

Fetches the connection timeout for the socket. no drama, it's giving exactly what it says. 😌

  • Option value type — int
  • Option value unit — milliseconds
  • Default value — -1
  • Applicable socket types — all, when using VMCI transport

ZMQ_MULTICAST_LOOP 🌈 — grab the multicast local loopback config

Retrieves the current multicast loopback configuration. A value of 1 means the multicast packets sent on this socket get looped back to the local listening interface. it's giving echo but make it networking 🔁

  • 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 🔔 — grab router socket notification settings

Gets the current notification settings of a router socket. What comes back is a bitmask made of the ZMQ_NOTIFY_CONNECT and ZMQ_NOTIFY_DISCONNECT flags — those turn on connect and disconnect notifications respectively. A value of 0 means notifications are off, plain and simple. 💀

Note ✋ in DRAFT state, not yet available in stable releases.
  • 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. and fr fr, it cannot be zero. 🙅‍♀️

Note ✋ in DRAFT state, not yet available in stable releases.
  • 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. same rule, bestie: cannot be zero.

Note ✋ in DRAFT state, not yet available in stable releases.
  • 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.
  • 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 🚦 — grab the NORM Sender Mode

Gets the NORM sender mode, which controls how the NORM transport operates. NORM supports a whole menu of modes:

  • 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
  • ECN-only congestion control — 4=ZMQ_NORM_CCE_ECNONLY

The default is TCP-friendly congestion control mode. Fixed rate mode (using the datarate set by ZMQ_RATE) offers better performance, but care must be taken to prevent data loss — so like, be responsible with that one. ⚠️

Note ✋ in DRAFT state, not yet available in stable releases.
  • 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 🎯 — grab the NORM Unicast NACK mode

Retrieves the status of the NORM unicast NACK mode setting for multicast receivers. If it's set, the NORM receiver sends Negative ACKnowledgements (NACKs) back to the sender using unicast instead of multicast. And heads up: NORM transport endpoints that specify a unicast address use unicast NACKs by default — no need to set ZMQ_NORM_UNICAST_NACK yourself. 🫡

Note ✋ in DRAFT state, not yet available in stable releases.
  • Option value type — int
  • Option value unit — boolean
  • Default value — 0 (false)
  • Applicable socket types — All, when using NORM transport.

ZMQ_NORM_BUFFER_SIZE 🧺 — grab the NORM buffer size

Gets the NORM buffer size for the NORM transport sender, receiver, and stream. one size fits all three, iconic. 👑

Note ✋ in DRAFT state, not yet available in stable releases.
  • Option value type — int
  • Option value unit — kilobytes
  • Default value — 2048
  • Applicable socket types — All, when using NORM transport.

ZMQ_NORM_SEGMENT_SIZE ✂️ — grab the NORM segment size

Gets the NORM sender segment size — that's the maximum message payload size of individual NORM messages (and yes, ZMQ messages may get split over multiple NORM messages, no biggie). Ideally this value should fit within the system/network maximum transmission unit (MTU) after accounting for additional NORM message headers (up to 48 bytes). math is math, bestie. 📐

Note ✋ in DRAFT state, not yet available in stable releases.
  • Option value type — int
  • Option value unit — bytes
  • Default value — 1400
  • Applicable socket types — All, when using NORM transport.

ZMQ_NORM_BLOCK_SIZE 🧱 — grab the NORM block size

Gets the 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). The effective value may be different based on the settings of ZMQ_NORM_NUM_PARITY and ZMQ_NORM_NUM_AUTOPARITY if invalid settings are provided. so like, don't try to be clever. 🙈

Note ✋ in DRAFT state, not yet available in stable releases.
  • Option value type — int
  • Option value unit — >0, ⟨255
  • Default value — 16
  • Applicable socket types — All, when using NORM transport.

ZMQ_NORM_NUM_PARITY 🛠️ — grab the 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 it's further limited to a value of (255 - ZMQ_NORM_BLOCK_SIZE). Minimum value is ZMQ_NORM_NUM_AUTOPARITY. The 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.
  • Option value type — int
  • Option value unit — >0, <255
  • Default value — 4
  • Applicable socket types — All, when using NORM transport.

ZMQ_NORM_NUM_AUTOPARITY 🍓 — grab the 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 are sent at all — instead, parity segments only go out in response to repair requests (NACKs). Maximum value is 255, but it's further limited to a maximum value of ZMQ_NORM_NUM_PARITY. not me double-checking my limits 😭

Note ✋ in DRAFT state, not yet available in stable releases.
  • Option value type — int
  • Option value unit — >=0, <255
  • Default value — 0
  • Applicable socket types — All, when using NORM transport.

ZMQ_NORM_PUSH 🚀 — grab the NORM push mode

Gets the status of NORM stream push mode, which alters the behavior of the sender when enqueueing new data. By default, NORM stops accepting new messages while it's 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's more important to quickly deliver new data instead of reliably delivering older data. it's giving main character energy for the freshest packet 💅

Note ✋ in DRAFT state, not yet available in stable releases.
  • Option value type — int
  • Option value unit — boolean
  • Default value — 0 (false)
  • Applicable socket types — All, when using NORM transport.

💖 RETURN VALUE 💖

Okay bestie, here's the tea: zmq_getsockopt() hands you back zero when it ate and left no crumbs. That's the slay outcome. 🎀

But if it's not that? It returns -1 and sets errno to one of the little gremlins listed right below. Check errno, always. No cap. 👑

😭 ERRORS 😭

  • EINVAL — the requested option option_name is unknown, or the option_len or option_value you passed is invalid, or the buffer pointed to by option_value — sized by option_len — is too small to actually store the option value. It's giving "your container cannot hold this much aura". 💀
  • ETERM — the 0MQ context that was associated with the specified socket got terminated. RIP to that context, fr fr. 🪦
  • ENOTSOCK — the socket you handed over was invalid. Not a socket. Just vibes. 🙈
  • EINTR — the operation got interrupted because a signal showed up uninvited. Not me getting jumpscared mid-call. 😭

✨ EXAMPLE ✨

Retrieving the high water mark for outgoing messages. Lowkey iconic of you to want to know. 🦋

/* 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);

Periodt. That's the whole move. 💅

🌈 SEE ALSO 🌈

Go read those too, bestie, they're literally right there. 📚

👑 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.

Community-written, community-loved — that's the vibe. If you wanna pitch in, read the policy first, okay? 🫶

And that's a wrap on ZMQ_GETSOCKOPT(3), babes!! 💖 This lil masterpiece is from 0MQ 4.3.5, dated 10/09/2023, and it lives at the very bottom of the page like a little signature. Thanks for reading all five parts, you're genuinely the main character. Mwah. 😘✨

📦 where this page comes from