1ZMSG(3)                           CZMQ Manual                          ZMSG(3)
2
3
4

NAME

6       zmsg - Class for working with multipart messages
7

SYNOPSIS

9       //  This is a stable class, and may not change except for emergencies. It
10       //  is provided in stable builds.
11       //  This class has draft methods, which may change over time. They are not
12       //  in stable releases, by default. Use --enable-drafts to enable.
13       //  Create a new empty message object
14       CZMQ_EXPORT zmsg_t *
15           zmsg_new (void);
16
17       //  Receive message from socket, returns zmsg_t object or NULL if the recv
18       //  was interrupted. Does a blocking recv. If you want to not block then use
19       //  the zloop class or zmsg_recv_nowait or zmq_poll to check for socket input
20       //  before receiving.
21       CZMQ_EXPORT zmsg_t *
22           zmsg_recv (void *source);
23
24       //  Load/append an open file into new message, return the message.
25       //  Returns NULL if the message could not be loaded.
26       CZMQ_EXPORT zmsg_t *
27           zmsg_load (FILE *file);
28
29       //  Decodes a serialized message frame created by zmsg_encode () and returns
30       //  a new zmsg_t object. Returns NULL if the frame was badly formatted or
31       //  there was insufficient memory to work.
32       CZMQ_EXPORT zmsg_t *
33           zmsg_decode (zframe_t *frame);
34
35       //  Generate a signal message encoding the given status. A signal is a short
36       //  message carrying a 1-byte success/failure code (by convention, 0 means
37       //  OK). Signals are encoded to be distinguishable from "normal" messages.
38       CZMQ_EXPORT zmsg_t *
39           zmsg_new_signal (byte status);
40
41       //  Destroy a message object and all frames it contains
42       CZMQ_EXPORT void
43           zmsg_destroy (zmsg_t **self_p);
44
45       //  Send message to destination socket, and destroy the message after sending
46       //  it successfully. If the message has no frames, sends nothing but destroys
47       //  the message anyhow. Nullifies the caller's reference to the message (as
48       //  it is a destructor).
49       CZMQ_EXPORT int
50           zmsg_send (zmsg_t **self_p, void *dest);
51
52       //  Send message to destination socket as part of a multipart sequence, and
53       //  destroy the message after sending it successfully. Note that after a
54       //  zmsg_sendm, you must call zmsg_send or another method that sends a final
55       //  message part. If the message has no frames, sends nothing but destroys
56       //  the message anyhow. Nullifies the caller's reference to the message (as
57       //  it is a destructor).
58       CZMQ_EXPORT int
59           zmsg_sendm (zmsg_t **self_p, void *dest);
60
61       //  Return size of message, i.e. number of frames (0 or more).
62       CZMQ_EXPORT size_t
63           zmsg_size (zmsg_t *self);
64
65       //  Return total size of all frames in message.
66       CZMQ_EXPORT size_t
67           zmsg_content_size (zmsg_t *self);
68
69       //  Push frame to the front of the message, i.e. before all other frames.
70       //  Message takes ownership of frame, will destroy it when message is sent.
71       //  Returns 0 on success, -1 on error. Deprecates zmsg_push, which did not
72       //  nullify the caller's frame reference.
73       CZMQ_EXPORT int
74           zmsg_prepend (zmsg_t *self, zframe_t **frame_p);
75
76       //  Add frame to the end of the message, i.e. after all other frames.
77       //  Message takes ownership of frame, will destroy it when message is sent.
78       //  Returns 0 on success. Deprecates zmsg_add, which did not nullify the
79       //  caller's frame reference.
80       CZMQ_EXPORT int
81           zmsg_append (zmsg_t *self, zframe_t **frame_p);
82
83       //  Remove first frame from message, if any. Returns frame, or NULL.
84       //  Caller owns return value and must destroy it when done.
85       CZMQ_EXPORT zframe_t *
86           zmsg_pop (zmsg_t *self);
87
88       //  Push block of memory to front of message, as a new frame.
89       //  Returns 0 on success, -1 on error.
90       CZMQ_EXPORT int
91           zmsg_pushmem (zmsg_t *self, const void *data, size_t size);
92
93       //  Add block of memory to the end of the message, as a new frame.
94       //  Returns 0 on success, -1 on error.
95       CZMQ_EXPORT int
96           zmsg_addmem (zmsg_t *self, const void *data, size_t size);
97
98       //  Push string as new frame to front of message.
99       //  Returns 0 on success, -1 on error.
100       CZMQ_EXPORT int
101           zmsg_pushstr (zmsg_t *self, const char *string);
102
103       //  Push string as new frame to end of message.
104       //  Returns 0 on success, -1 on error.
105       CZMQ_EXPORT int
106           zmsg_addstr (zmsg_t *self, const char *string);
107
108       //  Push formatted string as new frame to front of message.
109       //  Returns 0 on success, -1 on error.
110       CZMQ_EXPORT int
111           zmsg_pushstrf (zmsg_t *self, const char *format, ...) CHECK_PRINTF (2);
112
113       //  Push formatted string as new frame to end of message.
114       //  Returns 0 on success, -1 on error.
115       CZMQ_EXPORT int
116           zmsg_addstrf (zmsg_t *self, const char *format, ...) CHECK_PRINTF (2);
117
118       //  Pop frame off front of message, return as fresh string. If there were
119       //  no more frames in the message, returns NULL.
120       //  Caller owns return value and must destroy it when done.
121       CZMQ_EXPORT char *
122           zmsg_popstr (zmsg_t *self);
123
124       //  Push encoded message as a new frame. Message takes ownership of
125       //  submessage, so the original is destroyed in this call. Returns 0 on
126       //  success, -1 on error.
127       CZMQ_EXPORT int
128           zmsg_addmsg (zmsg_t *self, zmsg_t **msg_p);
129
130       //  Remove first submessage from message, if any. Returns zmsg_t, or NULL if
131       //  decoding was not successful.
132       //  Caller owns return value and must destroy it when done.
133       CZMQ_EXPORT zmsg_t *
134           zmsg_popmsg (zmsg_t *self);
135
136       //  Remove specified frame from list, if present. Does not destroy frame.
137       CZMQ_EXPORT void
138           zmsg_remove (zmsg_t *self, zframe_t *frame);
139
140       //  Set cursor to first frame in message. Returns frame, or NULL, if the
141       //  message is empty. Use this to navigate the frames as a list.
142       CZMQ_EXPORT zframe_t *
143           zmsg_first (zmsg_t *self);
144
145       //  Return the next frame. If there are no more frames, returns NULL. To move
146       //  to the first frame call zmsg_first(). Advances the cursor.
147       CZMQ_EXPORT zframe_t *
148           zmsg_next (zmsg_t *self);
149
150       //  Return the last frame. If there are no frames, returns NULL.
151       CZMQ_EXPORT zframe_t *
152           zmsg_last (zmsg_t *self);
153
154       //  Save message to an open file, return 0 if OK, else -1. The message is
155       //  saved as a series of frames, each with length and data. Note that the
156       //  file is NOT guaranteed to be portable between operating systems, not
157       //  versions of CZMQ. The file format is at present undocumented and liable
158       //  to arbitrary change.
159       CZMQ_EXPORT int
160           zmsg_save (zmsg_t *self, FILE *file);
161
162       //  Serialize multipart message to a single message frame. Use this method
163       //  to send structured messages across transports that do not support
164       //  multipart data. Allocates and returns a new frame containing the
165       //  serialized message. To decode a serialized message frame, use
166       //  zmsg_decode ().
167       //  Caller owns return value and must destroy it when done.
168       CZMQ_EXPORT zframe_t *
169           zmsg_encode (zmsg_t *self);
170
171       //  Create copy of message, as new message object. Returns a fresh zmsg_t
172       //  object. If message is null, or memory was exhausted, returns null.
173       //  Caller owns return value and must destroy it when done.
174       CZMQ_EXPORT zmsg_t *
175           zmsg_dup (zmsg_t *self);
176
177       //  Send message to zsys log sink (may be stdout, or system facility as
178       //  configured by zsys_set_logstream).
179       CZMQ_EXPORT void
180           zmsg_print (zmsg_t *self);
181
182       //  Return true if the two messages have the same number of frames and each
183       //  frame in the first message is identical to the corresponding frame in the
184       //  other message. As with zframe_eq, return false if either message is NULL.
185       CZMQ_EXPORT bool
186           zmsg_eq (zmsg_t *self, zmsg_t *other);
187
188       //  Return signal value, 0 or greater, if message is a signal, -1 if not.
189       CZMQ_EXPORT int
190           zmsg_signal (zmsg_t *self);
191
192       //  Probe the supplied object, and report if it looks like a zmsg_t.
193       CZMQ_EXPORT bool
194           zmsg_is (void *self);
195
196       //  Self test of this class.
197       CZMQ_EXPORT void
198           zmsg_test (bool verbose);
199
200       #ifdef CZMQ_BUILD_DRAFT_API
201       //  *** Draft method, for development use, may change without warning ***
202       //  Return message routing ID, if the message came from a ZMQ_SERVER socket.
203       //  Else returns zero.
204       CZMQ_EXPORT uint32_t
205           zmsg_routing_id (zmsg_t *self);
206
207       //  *** Draft method, for development use, may change without warning ***
208       //  Set routing ID on message. This is used if/when the message is sent to a
209       //  ZMQ_SERVER socket.
210       CZMQ_EXPORT void
211           zmsg_set_routing_id (zmsg_t *self, uint32_t routing_id);
212
213       #endif // CZMQ_BUILD_DRAFT_API
214       Please add '@interface' section in './../src/zmsg.c'.
215

DESCRIPTION

217       The zmsg class provides methods to send and receive multipart messages
218       across 0MQ sockets. This class provides a list-like container
219       interface, with methods to work with the overall container. zmsg_t
220       messages are composed of zero or more zframe_t frames.
221
222       Please add @discuss section in ./../src/zmsg.c.
223

EXAMPLE

225       From zmsg_test method.
226
227           //  Create two PAIR sockets and connect over inproc
228           zsock_t *output = zsock_new_pair ("@inproc://zmsg.test");
229           assert (output);
230           zsock_t *input = zsock_new_pair (">inproc://zmsg.test");
231           assert (input);
232
233           //  Test send and receive of single-frame message
234           zmsg_t *msg = zmsg_new ();
235           assert (msg);
236           zframe_t *frame = zframe_new ("Hello", 5);
237           assert (frame);
238           zmsg_prepend (msg, &frame);
239           assert (zmsg_size (msg) == 1);
240           assert (zmsg_content_size (msg) == 5);
241           rc = zmsg_send (&msg, output);
242           assert (msg == NULL);
243           assert (rc == 0);
244
245           msg = zmsg_recv (input);
246           assert (msg);
247           assert (zmsg_size (msg) == 1);
248           assert (zmsg_content_size (msg) == 5);
249           zmsg_destroy (&msg);
250
251           //  Test send and receive of multi-frame message
252           msg = zmsg_new ();
253           assert (msg);
254           rc = zmsg_addmem (msg, "Frame0", 6);
255           assert (rc == 0);
256           rc = zmsg_addmem (msg, "Frame1", 6);
257           assert (rc == 0);
258           rc = zmsg_addmem (msg, "Frame2", 6);
259           assert (rc == 0);
260           rc = zmsg_addmem (msg, "Frame3", 6);
261           assert (rc == 0);
262           rc = zmsg_addmem (msg, "Frame4", 6);
263           assert (rc == 0);
264           rc = zmsg_addmem (msg, "Frame5", 6);
265           assert (rc == 0);
266           rc = zmsg_addmem (msg, "Frame6", 6);
267           assert (rc == 0);
268           rc = zmsg_addmem (msg, "Frame7", 6);
269           assert (rc == 0);
270           rc = zmsg_addmem (msg, "Frame8", 6);
271           assert (rc == 0);
272           rc = zmsg_addmem (msg, "Frame9", 6);
273           assert (rc == 0);
274           zmsg_t *copy = zmsg_dup (msg);
275           assert (copy);
276           rc = zmsg_send (&copy, output);
277           assert (rc == 0);
278           rc = zmsg_send (&msg, output);
279           assert (rc == 0);
280
281           copy = zmsg_recv (input);
282           assert (copy);
283           assert (zmsg_size (copy) == 10);
284           assert (zmsg_content_size (copy) == 60);
285           zmsg_destroy (&copy);
286
287           msg = zmsg_recv (input);
288           assert (msg);
289           assert (zmsg_size (msg) == 10);
290           assert (zmsg_content_size (msg) == 60);
291
292           //  Save to a file, read back
293           FILE *file = fopen ("zmsg.test", "w");
294           assert (file);
295           rc = zmsg_save (msg, file);
296           assert (rc == 0);
297           fclose (file);
298
299           file = fopen ("zmsg.test", "r");
300           rc = zmsg_save (msg, file);
301           assert (rc == -1);
302           fclose (file);
303           zmsg_destroy (&msg);
304
305           file = fopen ("zmsg.test", "r");
306           msg = zmsg_load (file);
307           assert (msg);
308           fclose (file);
309           remove ("zmsg.test");
310           assert (zmsg_size (msg) == 10);
311           assert (zmsg_content_size (msg) == 60);
312
313           //  Remove all frames except first and last
314           int frame_nbr;
315           for (frame_nbr = 0; frame_nbr < 8; frame_nbr++) {
316               zmsg_first (msg);
317               frame = zmsg_next (msg);
318               zmsg_remove (msg, frame);
319               zframe_destroy (&frame);
320           }
321           //  Test message frame manipulation
322           assert (zmsg_size (msg) == 2);
323           frame = zmsg_last (msg);
324           assert (zframe_streq (frame, "Frame9"));
325           assert (zmsg_content_size (msg) == 12);
326           frame = zframe_new ("Address", 7);
327           assert (frame);
328           zmsg_prepend (msg, &frame);
329           assert (zmsg_size (msg) == 3);
330           rc = zmsg_addstr (msg, "Body");
331           assert (rc == 0);
332           assert (zmsg_size (msg) == 4);
333           frame = zmsg_pop (msg);
334           zframe_destroy (&frame);
335           assert (zmsg_size (msg) == 3);
336           char *body = zmsg_popstr (msg);
337           assert (streq (body, "Frame0"));
338           freen (body);
339           zmsg_destroy (&msg);
340
341           //  Test encoding/decoding
342           msg = zmsg_new ();
343           assert (msg);
344           byte *blank = (byte *) zmalloc (100000);
345           assert (blank);
346           rc = zmsg_addmem (msg, blank, 0);
347           assert (rc == 0);
348           rc = zmsg_addmem (msg, blank, 1);
349           assert (rc == 0);
350           rc = zmsg_addmem (msg, blank, 253);
351           assert (rc == 0);
352           rc = zmsg_addmem (msg, blank, 254);
353           assert (rc == 0);
354           rc = zmsg_addmem (msg, blank, 255);
355           assert (rc == 0);
356           rc = zmsg_addmem (msg, blank, 256);
357           assert (rc == 0);
358           rc = zmsg_addmem (msg, blank, 65535);
359           assert (rc == 0);
360           rc = zmsg_addmem (msg, blank, 65536);
361           assert (rc == 0);
362           rc = zmsg_addmem (msg, blank, 65537);
363           assert (rc == 0);
364           freen (blank);
365           assert (zmsg_size (msg) == 9);
366           frame = zmsg_encode (msg);
367           zmsg_destroy (&msg);
368           msg = zmsg_decode (frame);
369           assert (msg);
370           zmsg_destroy (&msg);
371           zframe_destroy (&frame);
372
373           //  Test submessages
374           msg = zmsg_new ();
375           assert (msg);
376           zmsg_t *submsg = zmsg_new ();
377           zmsg_pushstr (msg, "matr");
378           zmsg_pushstr (submsg, "joska");
379           rc = zmsg_addmsg (msg, &submsg);
380           assert (rc == 0);
381           assert (submsg == NULL);
382           submsg = zmsg_popmsg (msg);
383           assert (submsg == NULL);   // string "matr" is not encoded zmsg_t, so was discarded
384           submsg = zmsg_popmsg (msg);
385           assert (submsg);
386           body = zmsg_popstr (submsg);
387           assert (streq (body, "joska"));
388           freen (body);
389           zmsg_destroy (&submsg);
390           frame = zmsg_pop (msg);
391           assert (frame == NULL);
392           zmsg_destroy (&msg);
393
394           //  Test comparison of two messages
395           msg = zmsg_new ();
396           zmsg_addstr (msg, "One");
397           zmsg_addstr (msg, "Two");
398           zmsg_addstr (msg, "Three");
399           zmsg_t *msg_other = zmsg_new ();
400           zmsg_addstr (msg_other, "One");
401           zmsg_addstr (msg_other, "Two");
402           zmsg_addstr (msg_other, "One-Hundred");
403           zmsg_t *msg_dup = zmsg_dup (msg);
404           zmsg_t *empty_msg = zmsg_new ();
405           zmsg_t *empty_msg_2 = zmsg_new ();
406           assert (zmsg_eq (msg, msg_dup));
407           assert (!zmsg_eq (msg, msg_other));
408           assert (zmsg_eq (empty_msg, empty_msg_2));
409           assert (!zmsg_eq (msg, NULL));
410           assert (!zmsg_eq (NULL, empty_msg));
411           assert (!zmsg_eq (NULL, NULL));
412           zmsg_destroy (&msg);
413           zmsg_destroy (&msg_other);
414           zmsg_destroy (&msg_dup);
415           zmsg_destroy (&empty_msg);
416           zmsg_destroy (&empty_msg_2);
417
418           //  Test signal messages
419           msg = zmsg_new_signal (0);
420           assert (zmsg_signal (msg) == 0);
421           zmsg_destroy (&msg);
422           msg = zmsg_new_signal (-1);
423           assert (zmsg_signal (msg) == 255);
424           zmsg_destroy (&msg);
425
426           //  Now try methods on an empty message
427           msg = zmsg_new ();
428           assert (msg);
429           assert (zmsg_size (msg) == 0);
430           assert (zmsg_unwrap (msg) == NULL);
431           assert (zmsg_first (msg) == NULL);
432           assert (zmsg_last (msg) == NULL);
433           assert (zmsg_next (msg) == NULL);
434           assert (zmsg_pop (msg) == NULL);
435           //  Sending an empty message is valid and destroys the message
436           assert (zmsg_send (&msg, output) == 0);
437           assert (!msg);
438
439           zsock_destroy (&input);
440           zsock_destroy (&output);
441
442           #if defined (ZMQ_SERVER)
443           //  Create server and client sockets and connect over inproc
444           zsock_t *server = zsock_new_server ("inproc://zmsg-test-routing");
445           assert (server);
446           zsock_t *client = zsock_new_client ("inproc://zmsg-test-routing");
447           assert (client);
448
449           //  Send request from client to server
450           zmsg_t *request = zmsg_new ();
451           assert (request);
452           zmsg_addstr (request, "Hello");
453           rc = zmsg_send (&request, client);
454           assert (rc == 0);
455           assert (!request);
456
457           //  Read request and send reply
458           request = zmsg_recv (server);
459           assert (request);
460           char *string = zmsg_popstr (request);
461           assert (streq (string, "Hello"));
462           assert (zmsg_routing_id (request));
463           zstr_free (&string);
464
465           zmsg_t *reply = zmsg_new ();
466           assert (reply);
467           zmsg_addstr (reply, "World");
468           zmsg_set_routing_id (reply, zmsg_routing_id (request));
469           rc = zmsg_send (&reply, server);
470           assert (rc == 0);
471           zmsg_destroy (&request);
472
473           //  Read reply
474           reply = zmsg_recv (client);
475           string = zmsg_popstr (reply);
476           assert (streq (string, "World"));
477           assert (zmsg_routing_id (reply) == 0);
478           zmsg_destroy (&reply);
479           zstr_free (&string);
480
481           //  Client and server disallow multipart
482           msg = zmsg_new ();
483           zmsg_addstr (msg, "One");
484           zmsg_addstr (msg, "Two");
485           rc = zmsg_send (&msg, client);
486           assert (rc == -1);
487           assert (zmsg_size (msg) == 2);
488           rc = zmsg_send (&msg, server);
489           assert (rc == -1);
490           assert (zmsg_size (msg) == 2);
491           zmsg_destroy (&msg);
492
493           zsock_destroy (&client);
494           zsock_destroy (&server);
495           #endif
496
497           //  Test message length calculation after removal
498           msg = zmsg_new ();
499           zmsg_addstr (msg, "One");
500           zmsg_addstr (msg, "Two");
501           size_t size_before = zmsg_content_size (msg);
502           frame = zframe_new ("Three", strlen ("Three"));
503           assert (frame);
504           zmsg_remove (msg, frame);
505           size_t size_after = zmsg_content_size (msg);
506           assert (size_before == size_after);
507           zframe_destroy (&frame);
508           zmsg_destroy (&msg);
509
510           #if defined (__WINDOWS__)
511           zsys_shutdown();
512           #endif
513
514

AUTHORS

516       The czmq manual was written by the authors in the AUTHORS file.
517

RESOURCES

519       Main web site:
520
521       Report bugs to the email <zeromq-dev@lists.zeromq.org[1]>
522
524       Copyright (c) the Contributors as noted in the AUTHORS file. This file
525       is part of CZMQ, the high-level C binding for 0MQ:
526       http://czmq.zeromq.org. This Source Code Form is subject to the terms
527       of the Mozilla Public License, v. 2.0. If a copy of the MPL was not
528       distributed with this file, You can obtain one at
529       http://mozilla.org/MPL/2.0/. LICENSE included with the czmq
530       distribution.
531

NOTES

533        1. zeromq-dev@lists.zeromq.org
534           mailto:zeromq-dev@lists.zeromq.org
535
536
537
538CZMQ 4.1.1                        01/31/2019                           ZMSG(3)
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