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       //  Long messages are truncated.
180       CZMQ_EXPORT void
181           zmsg_print (zmsg_t *self);
182
183       //  Return true if the two messages have the same number of frames and each
184       //  frame in the first message is identical to the corresponding frame in the
185       //  other message. As with zframe_eq, return false if either message is NULL.
186       CZMQ_EXPORT bool
187           zmsg_eq (zmsg_t *self, zmsg_t *other);
188
189       //  Return signal value, 0 or greater, if message is a signal, -1 if not.
190       CZMQ_EXPORT int
191           zmsg_signal (zmsg_t *self);
192
193       //  Probe the supplied object, and report if it looks like a zmsg_t.
194       CZMQ_EXPORT bool
195           zmsg_is (void *self);
196
197       //  Self test of this class.
198       CZMQ_EXPORT void
199           zmsg_test (bool verbose);
200
201       #ifdef CZMQ_BUILD_DRAFT_API
202       //  *** Draft method, for development use, may change without warning ***
203       //  Return message routing ID, if the message came from a ZMQ_SERVER socket.
204       //  Else returns zero.
205       CZMQ_EXPORT uint32_t
206           zmsg_routing_id (zmsg_t *self);
207
208       //  *** Draft method, for development use, may change without warning ***
209       //  Set routing ID on message. This is used if/when the message is sent to a
210       //  ZMQ_SERVER socket.
211       CZMQ_EXPORT void
212           zmsg_set_routing_id (zmsg_t *self, uint32_t routing_id);
213
214       //  *** Draft method, for development use, may change without warning ***
215       //  Send message to zsys log sink (may be stdout, or system facility as
216       //  configured by zsys_set_logstream).
217       //  Message length is specified; no truncation unless length is zero.
218       //  Backwards compatible with zframe_print when length is zero.
219       CZMQ_EXPORT void
220           zmsg_print_n (zmsg_t *self, size_t size);
221
222       #endif // CZMQ_BUILD_DRAFT_API
223       Please add '@interface' section in './../src/zmsg.c'.
224

DESCRIPTION

226       The zmsg class provides methods to send and receive multipart messages
227       across 0MQ sockets. This class provides a list-like container
228       interface, with methods to work with the overall container. zmsg_t
229       messages are composed of zero or more zframe_t frames.
230
231       Please add @discuss section in ./../src/zmsg.c.
232

EXAMPLE

234       From zmsg_test method.
235
236           //  Create two PAIR sockets and connect over inproc
237           zsock_t *output = zsock_new_pair ("@inproc://zmsg.test");
238           assert (output);
239           zsock_t *input = zsock_new_pair (">inproc://zmsg.test");
240           assert (input);
241
242           //  Test send and receive of single-frame message
243           zmsg_t *msg = zmsg_new ();
244           assert (msg);
245           zframe_t *frame = zframe_new ("Hello", 5);
246           assert (frame);
247           zmsg_prepend (msg, &frame);
248           assert (zmsg_size (msg) == 1);
249           assert (zmsg_content_size (msg) == 5);
250           rc = zmsg_send (&msg, output);
251           assert (msg == NULL);
252           assert (rc == 0);
253
254           msg = zmsg_recv (input);
255           assert (msg);
256           assert (zmsg_size (msg) == 1);
257           assert (zmsg_content_size (msg) == 5);
258           zmsg_destroy (&msg);
259
260           //  Test send and receive of multi-frame message
261           msg = zmsg_new ();
262           assert (msg);
263           rc = zmsg_addmem (msg, "Frame0", 6);
264           assert (rc == 0);
265           rc = zmsg_addmem (msg, "Frame1", 6);
266           assert (rc == 0);
267           rc = zmsg_addmem (msg, "Frame2", 6);
268           assert (rc == 0);
269           rc = zmsg_addmem (msg, "Frame3", 6);
270           assert (rc == 0);
271           rc = zmsg_addmem (msg, "Frame4", 6);
272           assert (rc == 0);
273           rc = zmsg_addmem (msg, "Frame5", 6);
274           assert (rc == 0);
275           rc = zmsg_addmem (msg, "Frame6", 6);
276           assert (rc == 0);
277           rc = zmsg_addmem (msg, "Frame7", 6);
278           assert (rc == 0);
279           rc = zmsg_addmem (msg, "Frame8", 6);
280           assert (rc == 0);
281           rc = zmsg_addmem (msg, "Frame9", 6);
282           assert (rc == 0);
283           zmsg_t *copy = zmsg_dup (msg);
284           assert (copy);
285           rc = zmsg_send (&copy, output);
286           assert (rc == 0);
287           rc = zmsg_send (&msg, output);
288           assert (rc == 0);
289
290           copy = zmsg_recv (input);
291           assert (copy);
292           assert (zmsg_size (copy) == 10);
293           assert (zmsg_content_size (copy) == 60);
294           zmsg_destroy (&copy);
295
296           msg = zmsg_recv (input);
297           assert (msg);
298           assert (zmsg_size (msg) == 10);
299           assert (zmsg_content_size (msg) == 60);
300
301           //  Save to a file, read back
302           FILE *file = fopen ("zmsg.test", "w");
303           assert (file);
304           rc = zmsg_save (msg, file);
305           assert (rc == 0);
306           fclose (file);
307
308           file = fopen ("zmsg.test", "r");
309           rc = zmsg_save (msg, file);
310           assert (rc == -1);
311           fclose (file);
312           zmsg_destroy (&msg);
313
314           file = fopen ("zmsg.test", "r");
315           msg = zmsg_load (file);
316           assert (msg);
317           fclose (file);
318           remove ("zmsg.test");
319           assert (zmsg_size (msg) == 10);
320           assert (zmsg_content_size (msg) == 60);
321
322           //  Remove all frames except first and last
323           int frame_nbr;
324           for (frame_nbr = 0; frame_nbr < 8; frame_nbr++) {
325               zmsg_first (msg);
326               frame = zmsg_next (msg);
327               zmsg_remove (msg, frame);
328               zframe_destroy (&frame);
329           }
330           //  Test message frame manipulation
331           assert (zmsg_size (msg) == 2);
332           frame = zmsg_last (msg);
333           assert (zframe_streq (frame, "Frame9"));
334           assert (zmsg_content_size (msg) == 12);
335           frame = zframe_new ("Address", 7);
336           assert (frame);
337           zmsg_prepend (msg, &frame);
338           assert (zmsg_size (msg) == 3);
339           rc = zmsg_addstr (msg, "Body");
340           assert (rc == 0);
341           assert (zmsg_size (msg) == 4);
342           frame = zmsg_pop (msg);
343           zframe_destroy (&frame);
344           assert (zmsg_size (msg) == 3);
345           char *body = zmsg_popstr (msg);
346           assert (streq (body, "Frame0"));
347           freen (body);
348           zmsg_destroy (&msg);
349
350           //  Test encoding/decoding
351           msg = zmsg_new ();
352           assert (msg);
353           byte *blank = (byte *) zmalloc (100000);
354           assert (blank);
355           rc = zmsg_addmem (msg, blank, 0);
356           assert (rc == 0);
357           rc = zmsg_addmem (msg, blank, 1);
358           assert (rc == 0);
359           rc = zmsg_addmem (msg, blank, 253);
360           assert (rc == 0);
361           rc = zmsg_addmem (msg, blank, 254);
362           assert (rc == 0);
363           rc = zmsg_addmem (msg, blank, 255);
364           assert (rc == 0);
365           rc = zmsg_addmem (msg, blank, 256);
366           assert (rc == 0);
367           rc = zmsg_addmem (msg, blank, 65535);
368           assert (rc == 0);
369           rc = zmsg_addmem (msg, blank, 65536);
370           assert (rc == 0);
371           rc = zmsg_addmem (msg, blank, 65537);
372           assert (rc == 0);
373           freen (blank);
374           assert (zmsg_size (msg) == 9);
375           frame = zmsg_encode (msg);
376           zmsg_destroy (&msg);
377           msg = zmsg_decode (frame);
378           assert (msg);
379           zmsg_destroy (&msg);
380           zframe_destroy (&frame);
381
382           //  Test submessages
383           msg = zmsg_new ();
384           assert (msg);
385           zmsg_t *submsg = zmsg_new ();
386           zmsg_pushstr (msg, "matr");
387           zmsg_pushstr (submsg, "joska");
388           rc = zmsg_addmsg (msg, &submsg);
389           assert (rc == 0);
390           assert (submsg == NULL);
391           submsg = zmsg_popmsg (msg);
392           assert (submsg == NULL);   // string "matr" is not encoded zmsg_t, so was discarded
393           submsg = zmsg_popmsg (msg);
394           assert (submsg);
395           body = zmsg_popstr (submsg);
396           assert (streq (body, "joska"));
397           freen (body);
398           zmsg_destroy (&submsg);
399           frame = zmsg_pop (msg);
400           assert (frame == NULL);
401           zmsg_destroy (&msg);
402
403           //  Test comparison of two messages
404           msg = zmsg_new ();
405           zmsg_addstr (msg, "One");
406           zmsg_addstr (msg, "Two");
407           zmsg_addstr (msg, "Three");
408           zmsg_t *msg_other = zmsg_new ();
409           zmsg_addstr (msg_other, "One");
410           zmsg_addstr (msg_other, "Two");
411           zmsg_addstr (msg_other, "One-Hundred");
412           zmsg_t *msg_dup = zmsg_dup (msg);
413           zmsg_t *empty_msg = zmsg_new ();
414           zmsg_t *empty_msg_2 = zmsg_new ();
415           assert (zmsg_eq (msg, msg_dup));
416           assert (!zmsg_eq (msg, msg_other));
417           assert (zmsg_eq (empty_msg, empty_msg_2));
418           assert (!zmsg_eq (msg, NULL));
419           assert (!zmsg_eq (NULL, empty_msg));
420           assert (!zmsg_eq (NULL, NULL));
421           zmsg_destroy (&msg);
422           zmsg_destroy (&msg_other);
423           zmsg_destroy (&msg_dup);
424           zmsg_destroy (&empty_msg);
425           zmsg_destroy (&empty_msg_2);
426
427           //  Test signal messages
428           msg = zmsg_new_signal (0);
429           assert (zmsg_signal (msg) == 0);
430           zmsg_destroy (&msg);
431           msg = zmsg_new_signal (-1);
432           assert (zmsg_signal (msg) == 255);
433           zmsg_destroy (&msg);
434
435           //  Now try methods on an empty message
436           msg = zmsg_new ();
437           assert (msg);
438           assert (zmsg_size (msg) == 0);
439           assert (zmsg_unwrap (msg) == NULL);
440           assert (zmsg_first (msg) == NULL);
441           assert (zmsg_last (msg) == NULL);
442           assert (zmsg_next (msg) == NULL);
443           assert (zmsg_pop (msg) == NULL);
444           //  Sending an empty message is valid and destroys the message
445           assert (zmsg_send (&msg, output) == 0);
446           assert (!msg);
447
448           zsock_destroy (&input);
449           zsock_destroy (&output);
450
451           #if defined (ZMQ_SERVER)
452           //  Create server and client sockets and connect over inproc
453           zsock_t *server = zsock_new_server ("inproc://zmsg-test-routing");
454           assert (server);
455           zsock_t *client = zsock_new_client ("inproc://zmsg-test-routing");
456           assert (client);
457
458           //  Send request from client to server
459           zmsg_t *request = zmsg_new ();
460           assert (request);
461           zmsg_addstr (request, "Hello");
462           rc = zmsg_send (&request, client);
463           assert (rc == 0);
464           assert (!request);
465
466           //  Read request and send reply
467           request = zmsg_recv (server);
468           assert (request);
469           char *string = zmsg_popstr (request);
470           assert (streq (string, "Hello"));
471           assert (zmsg_routing_id (request));
472           zstr_free (&string);
473
474           zmsg_t *reply = zmsg_new ();
475           assert (reply);
476           zmsg_addstr (reply, "World");
477           zmsg_set_routing_id (reply, zmsg_routing_id (request));
478           rc = zmsg_send (&reply, server);
479           assert (rc == 0);
480           zmsg_destroy (&request);
481
482           //  Read reply
483           reply = zmsg_recv (client);
484           string = zmsg_popstr (reply);
485           assert (streq (string, "World"));
486           assert (zmsg_routing_id (reply) == 0);
487           zmsg_destroy (&reply);
488           zstr_free (&string);
489
490           //  Client and server disallow multipart
491           msg = zmsg_new ();
492           zmsg_addstr (msg, "One");
493           zmsg_addstr (msg, "Two");
494           rc = zmsg_send (&msg, client);
495           assert (rc == -1);
496           assert (zmsg_size (msg) == 2);
497           rc = zmsg_send (&msg, server);
498           assert (rc == -1);
499           assert (zmsg_size (msg) == 2);
500           zmsg_destroy (&msg);
501
502           zsock_destroy (&client);
503           zsock_destroy (&server);
504           #endif
505
506           //  Test message length calculation after removal
507           msg = zmsg_new ();
508           zmsg_addstr (msg, "One");
509           zmsg_addstr (msg, "Two");
510           size_t size_before = zmsg_content_size (msg);
511           frame = zframe_new ("Three", strlen ("Three"));
512           assert (frame);
513           zmsg_remove (msg, frame);
514           size_t size_after = zmsg_content_size (msg);
515           assert (size_before == size_after);
516           zframe_destroy (&frame);
517           zmsg_destroy (&msg);
518
519           #if defined (__WINDOWS__)
520           zsys_shutdown();
521           #endif
522
523

AUTHORS

525       The czmq manual was written by the authors in the AUTHORS file.
526

RESOURCES

528       Main web site:
529
530       Report bugs to the email <zeromq-dev@lists.zeromq.org[1]>
531
533       Copyright (c) the Contributors as noted in the AUTHORS file. This file
534       is part of CZMQ, the high-level C binding for 0MQ:
535       http://czmq.zeromq.org. This Source Code Form is subject to the terms
536       of the Mozilla Public License, v. 2.0. If a copy of the MPL was not
537       distributed with this file, You can obtain one at
538       http://mozilla.org/MPL/2.0/. LICENSE included with the czmq
539       distribution.
540

NOTES

542        1. zeromq-dev@lists.zeromq.org
543           mailto:zeromq-dev@lists.zeromq.org
544
545
546
547CZMQ 4.2.1                        07/19/2023                           ZMSG(3)
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