NAME

zmq_socket - create 0MQ socket

SYNOPSIS

void *zmq_socket (void '*context', int 'type');

DESCRIPTION

The 'zmq_socket()' function shall create a 0MQ socket within the specified 'context' and return an opaque handle to the newly created socket. The 'type' argument specifies the socket type, which determines the semantics of communication over the socket.

The newly created socket is initially unbound, and not associated with any endpoints. In order to establish a message flow a socket must first be connected to at least one endpoint with zmq_connect, or at least one endpoint must be created for accepting incoming connections with zmq_bind

Key differences to conventional sockets

Generally speaking, conventional sockets present a synchronous interface to either connection-oriented reliable byte streams (SOCK_STREAM), or connection-less unreliable datagrams (SOCK_DGRAM). In comparison, 0MQ sockets present an abstraction of an asynchronous message queue, with the exact queueing semantics depending on the socket type in use. Where conventional sockets transfer streams of bytes or discrete datagrams, 0MQ sockets transfer discrete messages.

0MQ sockets being asynchronous means that the timings of the physical connection setup and tear down, reconnect and effective delivery are transparent to the user and organized by 0MQ itself. Further, messages may be queued in the event that a peer is unavailable to receive them.

Conventional sockets allow only strict one-to-one (two peers), many-to-one (many clients, one server), or in some cases one-to-many (multicast) relationships. With the exception of 'ZMQ_PAIR' and 'ZMQ_CHANNEL', 0MQ sockets may be connected to multiple endpoints using zmq_connect(), while simultaneously accepting incoming connections from multiple endpoints bound to the socket using zmq_bind(), thus allowing many-to-many relationships.

Thread safety

0MQ has both thread safe socket type and not thread safe socket types. Applications MUST NOT use a not thread safe socket from multiple threads under any circumstances. Doing so results in undefined behaviour.

Following are the thread safe sockets: * ZMQ_CLIENT * ZMQ_SERVER * ZMQ_DISH * ZMQ_RADIO * ZMQ_SCATTER * ZMQ_GATHER * ZMQ_PEER * ZMQ_CHANNEL

Socket types

The following sections present the socket types defined by 0MQ, grouped by the general messaging pattern which is built from related socket types.

Client-server pattern

The client-server pattern is used to allow a single 'ZMQ_SERVER' server talk to one or more 'ZMQ_CLIENT' clients. The client always starts the conversation, after which either peer can send messages asynchronously, to the other.

The client-server pattern is formally defined by http://rfc.zeromq.org/spec:41.

Note
Server-client is still in draft phase.

ZMQ_CLIENT

A 'ZMQ_CLIENT' socket talks to a 'ZMQ_SERVER' socket. Either peer can connect, though the usual and recommended model is to bind the 'ZMQ_SERVER' and connect the 'ZMQ_CLIENT'.

If the 'ZMQ_CLIENT' socket has established a connection, zmq_send will accept messages, queue them, and send them as rapidly as the network allows. The outgoing buffer limit is defined by the high water mark for the socket. If the outgoing buffer is full, or, for connection-oriented transports, if the ZMQ_IMMEDIATE option is set and there is no connected peer, zmq_send will block. The 'ZMQ_CLIENT' socket will not drop messages.

When a 'ZMQ_CLIENT' socket is connected to multiple 'ZMQ_SERVER' sockets, outgoing messages are distributed between connected peers on a round-robin basis. Likewise, the 'ZMQ_CLIENT' socket receives messages fairly from each connected peer. This usage is sensible only for stateless protocols.

'ZMQ_CLIENT' sockets are threadsafe and can be used from multiple threads at the same time. Note that replies from a 'ZMQ_SERVER' socket will go to the first client thread that calls zmq_msg_recv If you need to get replies back to the originating thread, use one 'ZMQ_CLIENT' socket per thread.

Note
'ZMQ_CLIENT' sockets are threadsafe. They do not accept the ZMQ_SNDMORE option on sends not ZMQ_RCVMORE on receives. This limits them to single part data. The intention is to extend the API to allow scatter/gather of multi-part data.
Summary of ZMQ_CLIENT characteristics
Compatible peer sockets

'ZMQ_SERVER'

Direction

Bidirectional

Send/receive pattern

Unrestricted

Outgoing routing strategy

Round-robin

Incoming routing strategy

Fair-queued

Action in mute state

Block

ZMQ_SERVER

A 'ZMQ_SERVER' socket talks to a set of 'ZMQ_CLIENT' sockets. A 'ZMQ_SERVER' socket can only reply to an incoming message: the 'ZMQ_CLIENT' peer must always initiate a conversation.

Each received message has a 'routing_id' that is a 32-bit unsigned integer. The application can fetch this with zmq_msg_routing_id To send a message to a given 'ZMQ_CLIENT' peer the application must set the peer’s 'routing_id' on the message, using zmq_msg_set_routing_id

If the 'routing_id' is not specified, or does not refer to a connected client peer, the send call will fail with EHOSTUNREACH. If the outgoing buffer for the client peer is full, the send call shall block, unless ZMQ_DONTWAIT is used in the send, in which case it shall fail with EAGAIN. The 'ZMQ_SERVER' socket shall not drop messages in any case.

Note
'ZMQ_SERVER' sockets are threadsafe. They do not accept the ZMQ_SNDMORE option on sends not ZMQ_RCVMORE on receives. This limits them to single part data. The intention is to extend the API to allow scatter/gather of multi-part data.
Summary of ZMQ_SERVER characteristics
Compatible peer sockets

'ZMQ_CLIENT'

Direction

Bidirectional

Send/receive pattern

Unrestricted

Outgoing routing strategy

See text

Incoming routing strategy

Fair-queued

Action in mute state

Return EAGAIN

Radio-dish pattern

The radio-dish pattern is used for one-to-many distribution of data from a single publisher to multiple subscribers in a fan out fashion.

Radio-dish is using groups (vs Pub-sub topics), Dish sockets can join a group and each message sent by Radio sockets belong to a group.

Groups are null terminated strings limited to 16 chars length (including null). The intention is to increase the length to 40 chars (including null). The encoding of groups shall be UTF8.

Groups are matched using exact matching (vs prefix matching of PubSub).

Note
Radio-dish is still in draft phase.

ZMQ_RADIO ^^^ A socket of type 'ZMQ_RADIO' is used by a publisher to distribute data. Each message belong to a group, a group is specified with zmq_msg_set_group Messages are distributed to all members of a group. The zmq_recv function is not implemented for this socket type.

When a 'ZMQ_RADIO' socket enters the 'mute' state due to having reached the high water mark for a subscriber, then any messages that would be sent to the subscriber in question shall instead be dropped until the mute state ends. The zmq_send() function shall never block for this socket type.

Note
'ZMQ_RADIO' sockets are threadsafe. They do not accept the ZMQ_SNDMORE option on sends. This limits them to single part data.
Summary of ZMQ_RADIO characteristics
Compatible peer sockets

'ZMQ_DISH'

Direction

Unidirectional

Send/receive pattern

Send only

Incoming routing strategy

N/A

Outgoing routing strategy

Fan out

Action in mute state

Drop

ZMQ_DISH

A socket of type 'ZMQ_DISH' is used by a subscriber to subscribe to groups distributed by a radio. Initially a 'ZMQ_DISH' socket is not subscribed to any groups, use zmq_join to join a group. To get the group the message belong to call zmq_msg_group The zmq_send() function is not implemented for this socket type.

Note
'ZMQ_DISH' sockets are threadsafe. They do not accept ZMQ_RCVMORE on receives. This limits them to single part data.
Summary of ZMQ_DISH characteristics
Compatible peer sockets

'ZMQ_RADIO'

Direction

Unidirectional

Send/receive pattern

Receive only

Incoming routing strategy

Fair-queued

Outgoing routing strategy

N/A

Publish-subscribe pattern

The publish-subscribe pattern is used for one-to-many distribution of data from a single publisher to multiple subscribers in a fan out fashion.

The publish-subscribe pattern is formally defined by http://rfc.zeromq.org/spec:29.

ZMQ_PUB

A socket of type 'ZMQ_PUB' is used by a publisher to distribute data. Messages sent are distributed in a fan out fashion to all connected peers. The zmq_recv function is not implemented for this socket type.

When a 'ZMQ_PUB' socket enters the 'mute' state due to having reached the high water mark for a subscriber, then any messages that would be sent to the subscriber in question shall instead be dropped until the mute state ends. The zmq_send() function shall never block for this socket type.

Summary of ZMQ_PUB characteristics
Compatible peer sockets

'ZMQ_SUB', 'ZMQ_XSUB'

Direction

Unidirectional

Send/receive pattern

Send only

Incoming routing strategy

N/A

Outgoing routing strategy

Fan out

Action in mute state

Drop

ZMQ_SUB

A socket of type 'ZMQ_SUB' is used by a subscriber to subscribe to data distributed by a publisher. Initially a 'ZMQ_SUB' socket is not subscribed to any messages, use the 'ZMQ_SUBSCRIBE' option of zmq_setsockopt to specify which messages to subscribe to. The zmq_send() function is not implemented for this socket type.

Summary of ZMQ_SUB characteristics
Compatible peer sockets

'ZMQ_PUB', 'ZMQ_XPUB'

Direction

Unidirectional

Send/receive pattern

Receive only

Incoming routing strategy

Fair-queued

Outgoing routing strategy

N/A

ZMQ_XPUB

Same as ZMQ_PUB except that you can receive subscriptions from the peers in form of incoming messages. Subscription message is a byte 1 (for subscriptions) or byte 0 (for unsubscriptions) followed by the subscription body. Messages without a sub/unsub prefix are also received, but have no effect on subscription status.

Summary of ZMQ_XPUB characteristics
Compatible peer sockets

'ZMQ_SUB', 'ZMQ_XSUB'

Direction

Unidirectional

Send/receive pattern

Send messages, receive subscriptions

Incoming routing strategy

N/A

Outgoing routing strategy

Fan out

Action in mute state

Drop

ZMQ_XSUB

Same as ZMQ_SUB except that you subscribe by sending subscription messages to the socket. Subscription message is a byte 1 (for subscriptions) or byte 0 (for unsubscriptions) followed by the subscription body. Messages without a sub/unsub prefix may also be sent, but have no effect on subscription status.

Summary of ZMQ_XSUB characteristics
Compatible peer sockets

'ZMQ_PUB', 'ZMQ_XPUB'

Direction

Unidirectional

Send/receive pattern

Receive messages, send subscriptions

Incoming routing strategy

Fair-queued

Outgoing routing strategy

N/A

Action in mute state

Drop

Pipeline pattern

The pipeline pattern is used for distributing data to nodes arranged in a pipeline. Data always flows down the pipeline, and each stage of the pipeline is connected to at least one node. When a pipeline stage is connected to multiple nodes data is round-robined among all connected nodes.

The pipeline pattern is formally defined by http://rfc.zeromq.org/spec:30.

ZMQ_PUSH

A socket of type 'ZMQ_PUSH' is used by a pipeline node to send messages to downstream pipeline nodes. Messages are round-robined to all connected downstream nodes. The zmq_recv() function is not implemented for this socket type.

When a 'ZMQ_PUSH' socket enters the 'mute' state due to having reached the high water mark for all downstream nodes, or, for connection-oriented transports, if the ZMQ_IMMEDIATE option is set and there are no downstream nodes at all, then any zmq_send operations on the socket shall block until the mute state ends or at least one downstream node becomes available for sending; messages are not discarded.

Summary of ZMQ_PUSH characteristics
Compatible peer sockets

'ZMQ_PULL'

Direction

Unidirectional

Send/receive pattern

Send only

Incoming routing strategy

N/A

Outgoing routing strategy

Round-robin

Action in mute state

Block

ZMQ_PULL

A socket of type 'ZMQ_PULL' is used by a pipeline node to receive messages from upstream pipeline nodes. Messages are fair-queued from among all connected upstream nodes. The zmq_send() function is not implemented for this socket type.

Summary of ZMQ_PULL characteristics
Compatible peer sockets

'ZMQ_PUSH'

Direction

Unidirectional

Send/receive pattern

Receive only

Incoming routing strategy

Fair-queued

Outgoing routing strategy

N/A

Action in mute state

Block

Scatter-gather pattern ~~~~~~ The scatter-gather pattern is the thread-safe version of the pipeline pattern. The scatter-gather pattern is used for distributing data to nodes arranged in a pipeline. Data always flows down the pipeline, and each stage of the pipeline is connected to at least one node. When a pipeline stage is connected to multiple nodes data is round-robined among all connected nodes.

ZMQ_SCATTER ^^^^ A socket of type 'ZMQ_SCATTER' is used by a scatter-gather node to send messages to downstream scatter-gather nodes. Messages are round-robined to all connected downstream nodes. The zmq_recv() function is not implemented for this socket type.

When a 'ZMQ_SCATTER' socket enters the 'mute' state due to having reached the high water mark for all downstream nodes, or, for connection-oriented transports, if the ZMQ_IMMEDIATE option is set and there are no downstream nodes at all, then any zmq_send operations on the socket shall block until the mute state ends or at least one downstream node becomes available for sending; messages are not discarded.

Note
'ZMQ_SCATTER' sockets are threadsafe. They do not accept ZMQ_RCVMORE on receives. This limits them to single part data.
Summary of ZMQ_SCATTER characteristics
Compatible peer sockets

'ZMQ_SCATTER'

Direction

Unidirectional

Send/receive pattern

Send only

Incoming routing strategy

N/A

Outgoing routing strategy

Round-robin

Action in mute state

Block

ZMQ_GATHER ^^^^ A socket of type 'ZMQ_GATHER' is used by a scatter-gather node to receive messages from upstream scatter-gather nodes. Messages are fair-queued from among all connected upstream nodes. The zmq_send() function is not implemented for this socket type.

Note
'ZMQ_GATHER' sockets are threadsafe. They do not accept ZMQ_RCVMORE on receives. This limits them to single part data.
Summary of ZMQ_GATHER characteristics
Compatible peer sockets

'ZMQ_GATHER'

Direction

Unidirectional

Send/receive pattern

Receive only

Incoming routing strategy

Fair-queued

Outgoing routing strategy

N/A

Action in mute state

Block

Exclusive pair pattern

The exclusive pair pattern is used to connect a peer to precisely one other peer. This pattern is used for inter-thread communication across the inproc transport.

The exclusive pair pattern is formally defined by http://rfc.zeromq.org/spec:31.

ZMQ_PAIR

A socket of type 'ZMQ_PAIR' can only be connected to a single peer at any one time. No message routing or filtering is performed on messages sent over a 'ZMQ_PAIR' socket.

When a 'ZMQ_PAIR' socket enters the 'mute' state due to having reached the high water mark for the connected peer, or, for connection-oriented transports, if the ZMQ_IMMEDIATE option is set and there is no connected peer, then any zmq_send operations on the socket shall block until the peer becomes available for sending; messages are not discarded.

While 'ZMQ_PAIR' sockets can be used over transports other than zmq_inproc, their inability to auto-reconnect coupled with the fact new incoming connections will be terminated while any previous connections (including ones in a closing state) exist makes them unsuitable for TCP in most cases.

Note
'ZMQ_PAIR' sockets are designed for inter-thread communication across the zmq_inproc transport and do not implement functionality such as auto-reconnection.
Summary of ZMQ_PAIR characteristics
Compatible peer sockets

'ZMQ_PAIR'

Direction

Bidirectional

Send/receive pattern

Unrestricted

Incoming routing strategy

N/A

Outgoing routing strategy

N/A

Action in mute state

Block

Peer-to-peer pattern ~~~~~~~~

The peer-to-peer pattern is used to connect a peer to multiple peers. Peer can both connect and bind and mix both of them with the same socket. The peer-to-peer pattern is useful to build peer-to-peer networks (e.g zyre, bitcoin, torrent) where a peer can both accept connections from other peers or connect to them.

Note
Peer-to-peer is still in draft phase.

ZMQ_PEER

A 'ZMQ_PEER' socket talks to a set of 'ZMQ_PEER' sockets.

To connect and fetch the 'routing_id' of the peer use zmq_connect_peer

Each received message has a 'routing_id' that is a 32-bit unsigned integer. The application can fetch this with zmq_msg_routing_id

To send a message to a given 'ZMQ_PEER' peer the application must set the peer’s 'routing_id' on the message, using zmq_msg_set_routing_id

If the 'routing_id' is not specified, or does not refer to a connected client peer, the send call will fail with EHOSTUNREACH. If the outgoing buffer for the peer is full, the send call shall block, unless ZMQ_DONTWAIT is used in the send, in which case it shall fail with EAGAIN. The 'ZMQ_PEER' socket shall not drop messages in any case.

Note
'ZMQ_PEER' sockets are threadsafe. They do not accept the ZMQ_SNDMORE option on sends not ZMQ_RCVMORE on receives. This limits them to single part data.
Summary of ZMQ_PEER characteristics
Compatible peer sockets

'ZMQ_PEER'

Direction

Bidirectional

Send/receive pattern

Unrestricted

Outgoing routing strategy

See text

Incoming routing strategy

Fair-queued

Action in mute state

Return EAGAIN

Channel pattern ~~~~~~~~ The channel pattern is the thread-safe version of the exclusive pair pattern. The channel pattern is used to connect a peer to precisely one other peer. This pattern is used for inter-thread communication across the inproc transport.

Note
Channel is still in draft phase.

ZMQ_CHANNEL ^^^^ A socket of type 'ZMQ_CHANNEL' can only be connected to a single peer at any one time. No message routing or filtering is performed on messages sent over a 'ZMQ_CHANNEL' socket.

When a 'ZMQ_CHANNEL' socket enters the 'mute' state due to having reached the high water mark for the connected peer, or, for connection-oriented transports, if the ZMQ_IMMEDIATE option is set and there is no connected peer, then any zmq_send operations on the socket shall block until the peer becomes available for sending; messages are not discarded.

While 'ZMQ_CHANNEL' sockets can be used over transports other than zmq_inproc, their inability to auto-reconnect coupled with the fact new incoming connections will be terminated while any previous connections (including ones in a closing state) exist makes them unsuitable for TCP in most cases.

Note
'ZMQ_CHANNEL' sockets are designed for inter-thread communication across the zmq_inproc transport and do not implement functionality such as auto-reconnection.
Note
'ZMQ_CHANNEL' sockets are threadsafe. They do not accept ZMQ_RCVMORE on receives. This limits them to single part data.
Summary of ZMQ_CHANNEL characteristics
Compatible peer sockets

'ZMQ_CHANNEL'

Direction

Bidirectional

Send/receive pattern

Unrestricted

Incoming routing strategy

N/A

Outgoing routing strategy

N/A

Action in mute state

Block

Native Pattern

The native pattern is used for communicating with TCP peers and allows asynchronous requests and replies in either direction.

ZMQ_STREAM

A socket of type 'ZMQ_STREAM' is used to send and receive TCP data from a non-0MQ peer, when using the tcp:// transport. A 'ZMQ_STREAM' socket can act as client and/or server, sending and/or receiving TCP data asynchronously.

When receiving TCP data, a 'ZMQ_STREAM' socket shall prepend a message part containing the routing id of the originating peer to the message before passing it to the application. Messages received are fair-queued from among all connected peers.

When sending TCP data, a 'ZMQ_STREAM' socket shall remove the first part of the message and use it to determine the routing id of the peer the message shall be routed to, and unroutable messages shall cause an EHOSTUNREACH or EAGAIN error.

To open a connection to a server, use the zmq_connect call, and then fetch the socket routing id using the zmq_getsockopt call with the ZMQ_ROUTING_ID option.

To close a specific connection, send the routing id frame followed by a zero-length message (see EXAMPLE section).

When a connection is made, a zero-length message will be received by the application. Similarly, when the peer disconnects (or the connection is lost), a zero-length message will be received by the application.

You must send one routing id frame followed by one data frame. The ZMQ_SNDMORE flag is required for routing id frames but is ignored on data frames.

Summary of ZMQ_STREAM characteristics
Compatible peer sockets

none.

Direction

Bidirectional

Send/receive pattern

Unrestricted

Outgoing routing strategy

See text

Incoming routing strategy

Fair-queued

Action in mute state

EAGAIN

Request-reply pattern

The request-reply pattern is used for sending requests from a ZMQ_REQ client to one or more ZMQ_REP services, and receiving subsequent replies to each request sent.

The request-reply pattern is formally defined by http://rfc.zeromq.org/spec:28.

ZMQ_REQ

A socket of type 'ZMQ_REQ' is used by a client to send requests to and receive replies from a service. This socket type allows only an alternating sequence of zmq_send(request) and subsequent zmq_recv(reply) calls. Each request sent is round-robined among all services, and each reply received is matched with the last issued request.

For connection-oriented transports, If the ZMQ_IMMEDIATE option is set and there is no service available, then any send operation on the socket shall block until at least one service becomes available. The REQ socket shall not discard messages.

Summary of ZMQ_REQ characteristics
Compatible peer sockets

'ZMQ_REP', 'ZMQ_ROUTER'

Direction

Bidirectional

Send/receive pattern

Send, Receive, Send, Receive, …​

Outgoing routing strategy

Round-robin

Incoming routing strategy

Last peer

Action in mute state

Block

ZMQ_REP

A socket of type 'ZMQ_REP' is used by a service to receive requests from and send replies to a client. This socket type allows only an alternating sequence of zmq_recv(request) and subsequent zmq_send(reply) calls. Each request received is fair-queued from among all clients, and each reply sent is routed to the client that issued the last request. If the original requester does not exist any more the reply is silently discarded.

Summary of ZMQ_REP characteristics
Compatible peer sockets

'ZMQ_REQ', 'ZMQ_DEALER'

Direction

Bidirectional

Send/receive pattern

Receive, Send, Receive, Send, …​

Incoming routing strategy

Fair-queued

Outgoing routing strategy

Last peer

ZMQ_DEALER

A socket of type 'ZMQ_DEALER' is an advanced pattern used for extending request/reply sockets. Each message sent is round-robined among all connected peers, and each message received is fair-queued from all connected peers.

When a 'ZMQ_DEALER' socket enters the 'mute' state due to having reached the high water mark for all peers, or, for connection-oriented transports, if the ZMQ_IMMEDIATE option is set and there are no peers at all, then any zmq_send operations on the socket shall block until the mute state ends or at least one peer becomes available for sending; messages are not discarded.

When a 'ZMQ_DEALER' socket is connected to a 'ZMQ_REP' socket each message sent must consist of an empty message part, the delimiter, followed by one or more body parts.

Summary of ZMQ_DEALER characteristics
Compatible peer sockets

'ZMQ_ROUTER', 'ZMQ_REP', 'ZMQ_DEALER'

Direction

Bidirectional

Send/receive pattern

Unrestricted

Outgoing routing strategy

Round-robin

Incoming routing strategy

Fair-queued

Action in mute state

Block

ZMQ_ROUTER

A socket of type 'ZMQ_ROUTER' is an advanced socket type used for extending request/reply sockets. When receiving messages a 'ZMQ_ROUTER' socket shall prepend a message part containing the routing id of the originating peer to the message before passing it to the application. Messages received are fair-queued from among all connected peers. When sending messages a 'ZMQ_ROUTER' socket shall remove the first part of the message and use it to determine the _routing id _ of the peer the message shall be routed to. If the peer does not exist anymore, or has never existed, the message shall be silently discarded. However, if 'ZMQ_ROUTER_MANDATORY' socket option is set to '1', the socket shall fail with EHOSTUNREACH in both cases.

When a 'ZMQ_ROUTER' socket enters the 'mute' state due to having reached the high water mark for all peers, then any messages sent to the socket shall be dropped until the mute state ends. Likewise, any messages routed to a peer for which the individual high water mark has been reached shall also be dropped. If, 'ZMQ_ROUTER_MANDATORY' is set to '1', the socket shall block or return EAGAIN in both cases.

When a 'ZMQ_ROUTER' socket has 'ZMQ_ROUTER_MANDATORY' flag set to '1', the socket shall generate 'ZMQ_POLLIN' events upon reception of messages from one or more peers. Likewise, the socket shall generate 'ZMQ_POLLOUT' events when at least one message can be sent to one or more peers.

When a 'ZMQ_REQ' socket is connected to a 'ZMQ_ROUTER' socket, in addition to the routing id of the originating peer each message received shall contain an empty delimiter message part. Hence, the entire structure of each received message as seen by the application becomes: one or more routing id parts, delimiter part, one or more body parts. When sending replies to a 'ZMQ_REQ' socket the application must include the delimiter part.

Summary of ZMQ_ROUTER characteristics
Compatible peer sockets

'ZMQ_DEALER', 'ZMQ_REQ', 'ZMQ_ROUTER'

Direction

Bidirectional

Send/receive pattern

Unrestricted

Outgoing routing strategy

See text

Incoming routing strategy

Fair-queued

Action in mute state

Drop (see text)

RETURN VALUE

The zmq_socket() function shall return an opaque handle to the newly created socket if successful. Otherwise, it shall return NULL and set 'errno' to one of the values defined below.

ERRORS

EINVAL

The requested socket 'type' is invalid.

EFAULT

The provided 'context' is invalid.

EMFILE

The limit on the total number of open 0MQ sockets has been reached.

ETERM

The context specified was shutdown or terminated.

EXAMPLE

Creating a simple HTTP server using ZMQ_STREAM
void *ctx = zmq_ctx_new ();
assert (ctx);
/* Create ZMQ_STREAM socket */
void *socket = zmq_socket (ctx, ZMQ_STREAM);
assert (socket);
int rc = zmq_bind (socket, "tcp://*:8080");
assert (rc == 0);
/* Data structure to hold the ZMQ_STREAM routing id */
uint8_t routing_id [256];
size_t routing_id_size = 256;
/* Data structure to hold the ZMQ_STREAM received data */
uint8_t raw [256];
size_t raw_size = 256;
while (1) {
	/*  Get HTTP request; routing id frame and then request */
	routing_id_size = zmq_recv (socket, routing_id, 256, 0);
	assert (routing_id_size > 0);
	do {
		raw_size = zmq_recv (socket, raw, 256, 0);
		assert (raw_size >= 0);
	} while (raw_size == 256);
	/* Prepares the response */
	char http_response [] =
		"HTTP/1.0 200 OK\r\n"
		"Content-Type: text/plain\r\n"
		"\r\n"
		"Hello, World!";
	/* Sends the routing id frame followed by the response */
	zmq_send (socket, routing_id, routing_id_size, ZMQ_SNDMORE);
	zmq_send (socket, http_response, strlen (http_response), 0);
	/* Closes the connection by sending the routing id frame followed by a zero response */
	zmq_send (socket, routing_id, routing_id_size, ZMQ_SNDMORE);
	zmq_send (socket, 0, 0, 0);
}
zmq_close (socket);
zmq_ctx_destroy (ctx);

SEE ALSO

AUTHORS

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