zmq_socket.txt 23.2 KB
Newer Older
1 2 3 4 5 6
zmq_socket(3)
=============


NAME
----
Martin Lucina's avatar
Martin Lucina committed
7
zmq_socket - create 0MQ socket
8 9 10 11


SYNOPSIS
--------
Martin Lucina's avatar
Martin Lucina committed
12
*void *zmq_socket (void '*context', int 'type');*
13 14 15 16


DESCRIPTION
-----------
Martin Lucina's avatar
Martin Lucina committed
17 18
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'
Martin Lucina's avatar
Martin Lucina committed
19
argument specifies the socket type, which determines the semantics of
Martin Lucina's avatar
Martin Lucina committed
20 21
communication over the socket.

22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37
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 linkzmq:zmq_connect[3], or at least one
endpoint must be created for accepting incoming connections with
linkzmq:zmq_bind[3].

.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
38
connection setup and tear down, reconnect and effective delivery are transparent
39 40 41 42 43 44 45 46 47 48
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', 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.

49
.Thread safety
50 51
0MQ has both thread safe socket type and _not_ thread safe socket types.
Applications MUST NOT use a _not_ thread safe socket
52
from multiple threads except after migrating a socket from one thread to
53
another with a "full fence" memory barrier.
54

55 56 57 58 59 60 61 62
Following are the thread safe sockets:
* ZMQ_CLIENT
* ZMQ_SERVER
* ZMQ_DISH
* ZMQ_RADIO
* ZMQ_SCATTER
* ZMQ_GATHER

63
.Socket types
64 65
The following sections present the socket types defined by 0MQ, grouped by the
general _messaging pattern_ which is built from related socket types.
66 67


68 69 70 71 72 73 74 75 76
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.

77 78
NOTE: Server-client is still in draft phase.

79 80 81 82 83 84 85 86 87
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, linkzmq:zmq_send[3]
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
88 89 90 91
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,
linkzmq:zmq_send[3] will block.
The 'ZMQ_CLIENT' socket will not drop messages.
92 93 94 95

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
96
connected peer. This usage is sensible only for stateless protocols.
97 98 99

'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
100
the first client thread that calls linkzmq:zmq_msg_recv[3]. If you need to get
101 102 103
replies back to the originating thread, use one 'ZMQ_CLIENT' socket per
thread.

104 105 106 107 108
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.

109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131
[horizontal]
.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 linkzmq:zmq_msg_routing_id[3]. To send
a message to a given 'ZMQ_CLIENT' peer the application must set the peer's
'routing_id' on the message, using linkzmq:zmq_msg_set_routing_id[3].

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
132
the client peer is full, the send call shall block, unless ZMQ_DONTWAIT is
133 134
used in the send, in which case it shall fail with EAGAIN. The 'ZMQ_SERVER'
socket shall not drop messages in any case.
135

136 137 138 139 140
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.

141 142 143 144 145 146 147 148 149 150
[horizontal]
.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


151
Radio-dish pattern
152 153
~~~~~~~~~~~~~~~~~~

154 155 156 157 158 159 160 161
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).
162
The encoding of groups shall be UTF8.
163 164 165 166 167 168 169 170

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.
171
Each message belong to a group, a group is specified with linkzmq:zmq_msg_set_group[3].
172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193
Messages are distributed to all members of a group.
The linkzmq:zmq_recv[3] 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.

[horizontal]
.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
194
^^^^^^^^
195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213
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 linkzmq:zmq_join[3] to
join a group.
To get the group the message belong to call linkzmq:zmq_msg_group[3].
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.

[horizontal]
.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


Martin Lucina's avatar
Martin Lucina committed
214 215 216
Publish-subscribe pattern
~~~~~~~~~~~~~~~~~~~~~~~~~
The publish-subscribe pattern is used for one-to-many distribution of data from
217
a single _publisher_ to multiple _subscribers_ in a fan out fashion.
Martin Lucina's avatar
Martin Lucina committed
218

219
The publish-subscribe pattern is formally defined by http://rfc.zeromq.org/spec:29.
Martin Lucina's avatar
Martin Lucina committed
220

221 222
ZMQ_PUB
^^^^^^^
Martin Lucina's avatar
Martin Lucina committed
223
A socket of type 'ZMQ_PUB' is used by a _publisher_ to distribute data.
224
Messages sent are distributed in a fan out fashion to all connected peers.
225
The linkzmq:zmq_recv[3] function is not implemented for this socket type.
Martin Lucina's avatar
Martin Lucina committed
226

Pieter Hintjens's avatar
Pieter Hintjens committed
227
When a 'ZMQ_PUB' socket enters the 'mute' state due to having reached the
228
high water mark for a _subscriber_, then any messages that would be sent to the
Pieter Hintjens's avatar
Pieter Hintjens committed
229
_subscriber_ in question shall instead be dropped until the mute state
230
ends. The _zmq_send()_ function shall never block for this socket type.
Martin Lucina's avatar
Martin Lucina committed
231

232 233
[horizontal]
.Summary of ZMQ_PUB characteristics
234
Compatible peer sockets:: 'ZMQ_SUB', 'ZMQ_XSUB'
235
Direction:: Unidirectional
236 237
Send/receive pattern:: Send only
Incoming routing strategy:: N/A
238
Outgoing routing strategy:: Fan out
Pieter Hintjens's avatar
Pieter Hintjens committed
239
Action in mute state:: Drop
240 241 242 243


ZMQ_SUB
^^^^^^^
Martin Lucina's avatar
Martin Lucina committed
244 245
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
246 247 248 249 250 251
any messages, use the 'ZMQ_SUBSCRIBE' option of linkzmq:zmq_setsockopt[3] to
specify which messages to subscribe to. The _zmq_send()_ function is not
implemented for this socket type.

[horizontal]
.Summary of ZMQ_SUB characteristics
252
Compatible peer sockets:: 'ZMQ_PUB', 'ZMQ_XPUB'
253
Direction:: Unidirectional
254 255 256
Send/receive pattern:: Receive only
Incoming routing strategy:: Fair-queued
Outgoing routing strategy:: N/A
Martin Lucina's avatar
Martin Lucina committed
257 258


259 260 261 262 263
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
264 265
body. Messages without a sub/unsub prefix are also received, but have no
effect on subscription status.
266 267 268 269

[horizontal]
.Summary of ZMQ_XPUB characteristics
Compatible peer sockets:: 'ZMQ_SUB', 'ZMQ_XSUB'
270
Direction:: Unidirectional
271 272 273
Send/receive pattern:: Send messages, receive subscriptions
Incoming routing strategy:: N/A
Outgoing routing strategy:: Fan out
Pieter Hintjens's avatar
Pieter Hintjens committed
274
Action in mute state:: Drop
275 276


277 278
ZMQ_XSUB
^^^^^^^^
279 280
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
281 282
(for unsubscriptions) followed by the subscription body. Messages without a
sub/unsub prefix may also be sent, but have no effect on subscription status.
283 284 285 286

[horizontal]
.Summary of ZMQ_XSUB characteristics
Compatible peer sockets:: 'ZMQ_PUB', 'ZMQ_XPUB'
287
Direction:: Unidirectional
288 289 290
Send/receive pattern:: Receive messages, send subscriptions
Incoming routing strategy:: Fair-queued
Outgoing routing strategy:: N/A
Pieter Hintjens's avatar
Pieter Hintjens committed
291
Action in mute state:: Drop
292 293


294 295 296
Pipeline pattern
~~~~~~~~~~~~~~~~
The pipeline pattern is used for distributing data to _nodes_ arranged in
Martin Lucina's avatar
Martin Lucina committed
297 298
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
299
multiple _nodes_ data is round-robined among all connected _nodes_.
Martin Lucina's avatar
Martin Lucina committed
300

301
The pipeline pattern is formally defined by http://rfc.zeromq.org/spec:30.
Martin Lucina's avatar
Martin Lucina committed
302

303 304 305
ZMQ_PUSH
^^^^^^^^
A socket of type 'ZMQ_PUSH' is used by a pipeline _node_ to send messages
306
to downstream pipeline _nodes_. Messages are round-robined to all connected
307 308
downstream _nodes_. The _zmq_recv()_ function is not implemented for this
socket type.
Martin Lucina's avatar
Martin Lucina committed
309

Pieter Hintjens's avatar
Pieter Hintjens committed
310
When a 'ZMQ_PUSH' socket enters the 'mute' state due to having reached the
311 312 313 314 315
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 linkzmq:zmq_send[3] 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.
316

317
[horizontal]
318 319
.Summary of ZMQ_PUSH characteristics
Compatible peer sockets:: 'ZMQ_PULL'
320 321 322
Direction:: Unidirectional
Send/receive pattern:: Send only
Incoming routing strategy:: N/A
323
Outgoing routing strategy:: Round-robin
Pieter Hintjens's avatar
Pieter Hintjens committed
324
Action in mute state:: Block
325

Martin Lucina's avatar
Martin Lucina committed
326

327 328 329 330 331 332 333
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.

334
[horizontal]
335 336
.Summary of ZMQ_PULL characteristics
Compatible peer sockets:: 'ZMQ_PUSH'
337 338 339 340
Direction:: Unidirectional
Send/receive pattern:: Receive only
Incoming routing strategy:: Fair-queued
Outgoing routing strategy:: N/A
Pieter Hintjens's avatar
Pieter Hintjens committed
341
Action in mute state:: Block
342

Martin Lucina's avatar
Martin Lucina committed
343

344 345
Exclusive pair pattern
~~~~~~~~~~~~~~~~~~~~~~
346 347 348
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.
Martin Lucina's avatar
Martin Lucina committed
349

350
The exclusive pair pattern is formally defined by http://rfc.zeromq.org/spec:31.
Martin Lucina's avatar
Martin Lucina committed
351

352 353
ZMQ_PAIR
^^^^^^^^
354 355 356
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.
Martin Lucina's avatar
Martin Lucina committed
357

Pieter Hintjens's avatar
Pieter Hintjens committed
358
When a 'ZMQ_PAIR' socket enters the 'mute' state due to having reached the
359 360
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
361 362 363
any linkzmq:zmq_send[3] operations on the socket shall block until the peer
becomes available for sending; messages are not discarded.

364 365 366 367 368
While 'ZMQ_PAIR' sockets can be used over transports other than linkzmq:zmq_inproc[7],
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.

369 370
NOTE: 'ZMQ_PAIR' sockets are designed for inter-thread communication across
the linkzmq:zmq_inproc[7] transport and do not implement functionality such
371
as auto-reconnection.
372

373 374 375 376 377 378 379
[horizontal]
.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
Pieter Hintjens's avatar
Pieter Hintjens committed
380
Action in mute state:: Block
381

382

383 384
Native Pattern
~~~~~~~~~~~~~~
385
The native pattern is used for communicating with TCP peers and allows
386 387 388 389 390
asynchronous requests and replies in either direction.


ZMQ_STREAM
^^^^^^^^^^
391 392
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
393 394 395
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
396
containing the _routing id_ of the originating peer to the message before passing
397 398
it to the application. Messages received are fair-queued from among all
connected peers.
399

400
When sending TCP data, a 'ZMQ_STREAM' socket shall remove the first part of the
401
message and use it to determine the _routing id_ of the peer the message shall be
402 403
routed to, and unroutable messages shall cause an EHOSTUNREACH or EAGAIN error.

404
To open a connection to a server, use the zmq_connect call, and then fetch the
405
socket routing id using the zmq_getsockopt call with the ZMQ_ROUTING_ID option.
406

407
To close a specific connection, send the routing id frame followed by a
408 409 410 411 412
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.
413

414 415
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.
416

417 418 419 420 421 422 423 424 425 426
[horizontal]
.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


427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442
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.

443 444 445
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.
446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481

[horizontal]
.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.

[horizontal]
.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
482 483 484 485
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
linkzmq:zmq_send[3] operations on the socket shall block until the mute state
ends or at least one peer becomes available for sending; messages are not discarded.
486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504

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_.

[horizontal]
.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
505
prepend a message part containing the _routing id_ of the originating peer to the
506 507
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
508
remove the first part of the message and use it to determine the _routing id _ of
509 510 511 512
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.
513 514 515 516

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
517 518 519 520 521 522 523 524
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.
525 526

When a 'ZMQ_REQ' socket is connected to a 'ZMQ_ROUTER' socket, in addition to the
527
_routing id_ of the originating peer each message received shall contain an empty
528
_delimiter_ message part. Hence, the entire structure of each received message
529
as seen by the application becomes: one or more _routing id_ parts, _delimiter_
530 531 532 533 534 535 536 537 538 539
part, one or more _body parts_. When sending replies to a 'ZMQ_REQ' socket the
application must include the _delimiter_ part.

[horizontal]
.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
540
Action in mute state:: Drop (see text)
541 542


543 544
RETURN VALUE
------------
Martin Lucina's avatar
Martin Lucina committed
545 546 547
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.
548 549 550 551 552


ERRORS
------
*EINVAL*::
Martin Lucina's avatar
Martin Lucina committed
553
The requested socket 'type' is invalid.
554
*EFAULT*::
555
The provided 'context' is invalid.
556 557
*EMFILE*::
The limit on the total number of open 0MQ sockets has been reached.
558 559
*ETERM*::
The context specified was terminated.
560

561 562 563 564 565 566 567 568 569 570 571
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);
572 573 574
/* Data structure to hold the ZMQ_STREAM routing id */
uint8_t routing_id [256];
size_t routing_id_size = 256;
575 576 577
/* Data structure to hold the ZMQ_STREAM received data */
uint8_t raw [256];
size_t raw_size = 256;
578
while (1) {
579 580 581
	/*  Get HTTP request; routing id frame and then request */
	routing_id_size = zmq_recv (socket, routing_id, 256, 0);
	assert (routing_id_size > 0);
582 583 584 585
	do {
		raw_size = zmq_recv (socket, raw, 256, 0);
		assert (raw_size >= 0);
	} while (raw_size == 256);
586 587 588 589 590 591
	/* Prepares the response */
	char http_response [] =
		"HTTP/1.0 200 OK\r\n"
		"Content-Type: text/plain\r\n"
		"\r\n"
		"Hello, World!";
592 593
	/* Sends the routing id frame followed by the response */
	zmq_send (socket, routing_id, routing_id_size, ZMQ_SNDMORE);
594
	zmq_send (socket, http_response, strlen (http_response), 0);
595 596
	/* Closes the connection by sending the routing id frame followed by a zero response */
	zmq_send (socket, routing_id, routing_id_size, ZMQ_SNDMORE);
597
	zmq_send (socket, 0, 0, 0);
598 599 600 601 602 603
}
zmq_close (socket);
zmq_ctx_destroy (ctx);
----


604 605 606 607 608 609 610 611
SEE ALSO
--------
linkzmq:zmq_init[3]
linkzmq:zmq_setsockopt[3]
linkzmq:zmq_bind[3]
linkzmq:zmq_connect[3]
linkzmq:zmq_send[3]
linkzmq:zmq_recv[3]
612
linkzmq:zmq_inproc[7]
613
linkzmq:zmq[7]
614

615 616 617

AUTHORS
-------
618 619
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>.