zmsg(3)
CZMQ Manual - CZMQ/3.0.1
Name
zmsg - working with multipart messages
Synopsis
// Create a new empty message object
CZMQ_EXPORT zmsg_t *
zmsg_new (void);
// Destroy a message object and all frames it contains
CZMQ_EXPORT void
zmsg_destroy (zmsg_t **self_p);
// Receive message from socket, returns zmsg_t object or NULL if the recv
// was interrupted. Does a blocking recv. If you want to not block then use
// the zloop class or zmsg_recv_nowait or zmq_poll to check for socket input
// before receiving.
CZMQ_EXPORT zmsg_t *
zmsg_recv (void *source);
// Send message to destination socket, and destroy the message after sending
// it successfully. If the message has no frames, sends nothing but destroys
// the message anyhow. Nullifies the caller's reference to the message (as
// it is a destructor).
CZMQ_EXPORT int
zmsg_send (zmsg_t **self_p, void *dest);
// Return size of message, i.e. number of frames (0 or more).
CZMQ_EXPORT size_t
zmsg_size (zmsg_t *self);
// Return total size of all frames in message.
CZMQ_EXPORT size_t
zmsg_content_size (zmsg_t *self);
// Push frame to the front of the message, i.e. before all other frames.
// Message takes ownership of frame, will destroy it when message is sent.
// Returns 0 on success, -1 on error. Deprecates zmsg_push, which did not
// nullify the caller's frame reference.
CZMQ_EXPORT int
zmsg_prepend (zmsg_t *self, zframe_t **frame_p);
// Add frame to the end of the message, i.e. after all other frames.
// Message takes ownership of frame, will destroy it when message is sent.
// Returns 0 on success. Deprecates zmsg_add, which did not nullify the
// caller's frame reference.
CZMQ_EXPORT int
zmsg_append (zmsg_t *self, zframe_t **frame_p);
// Remove first frame from message, if any. Returns frame, or NULL. Caller
// now owns frame and must destroy it when finished with it.
CZMQ_EXPORT zframe_t *
zmsg_pop (zmsg_t *self);
// Push block of memory to front of message, as a new frame.
// Returns 0 on success, -1 on error.
CZMQ_EXPORT int
zmsg_pushmem (zmsg_t *self, const void *src, size_t size);
// Add block of memory to the end of the message, as a new frame.
// Returns 0 on success, -1 on error.
CZMQ_EXPORT int
zmsg_addmem (zmsg_t *self, const void *src, size_t size);
// Push string as new frame to front of message.
// Returns 0 on success, -1 on error.
CZMQ_EXPORT int
zmsg_pushstr (zmsg_t *self, const char *string);
// Push string as new frame to end of message.
// Returns 0 on success, -1 on error.
CZMQ_EXPORT int
zmsg_addstr (zmsg_t *self, const char *string);
// Push formatted string as new frame to front of message.
// Returns 0 on success, -1 on error.
CZMQ_EXPORT int
zmsg_pushstrf (zmsg_t *self, const char *format, ...);
// Push formatted string as new frame to end of message.
// Returns 0 on success, -1 on error.
CZMQ_EXPORT int
zmsg_addstrf (zmsg_t *self, const char *format, ...);
// Pop frame off front of message, return as fresh string. If there were
// no more frames in the message, returns NULL.
CZMQ_EXPORT char *
zmsg_popstr (zmsg_t *self);
// Push encoded message as a new frame. Message takes ownership of
// submessage, so the original is destroyed in this call. Returns 0 on
// success, -1 on error.
CZMQ_EXPORT int
zmsg_addmsg (zmsg_t *self, zmsg_t **msg_p);
// Remove first submessage from message, if any. Returns zmsg_t, or NULL if
// decoding was not succesfull. Caller now owns message and must destroy it
// when finished with it.
CZMQ_EXPORT zmsg_t *
zmsg_popmsg (zmsg_t *self);
// Remove specified frame from list, if present. Does not destroy frame.
CZMQ_EXPORT void
zmsg_remove (zmsg_t *self, zframe_t *frame);
// Set cursor to first frame in message. Returns frame, or NULL, if the
// message is empty. Use this to navigate the frames as a list.
CZMQ_EXPORT zframe_t *
zmsg_first (zmsg_t *self);
// Return the next frame. If there are no more frames, returns NULL. To move
// to the first frame call zmsg_first(). Advances the cursor.
CZMQ_EXPORT zframe_t *
zmsg_next (zmsg_t *self);
// Return the last frame. If there are no frames, returns NULL.
CZMQ_EXPORT zframe_t *
zmsg_last (zmsg_t *self);
// Save message to an open file, return 0 if OK, else -1. The message is
// saved as a series of frames, each with length and data. Note that the
// file is NOT guaranteed to be portable between operating systems, not
// versions of CZMQ. The file format is at present undocumented and liable
// to arbitrary change.
CZMQ_EXPORT int
zmsg_save (zmsg_t *self, FILE *file);
// Load/append an open file into message, create new message if
// null message provided. Returns NULL if the message could not
// be loaded.
CZMQ_EXPORT zmsg_t *
zmsg_load (zmsg_t *self, FILE *file);
// Serialize multipart message to a single buffer. Use this method to send
// structured messages across transports that do not support multipart data.
// Allocates and returns a new buffer containing the serialized message.
// To decode a serialized message buffer, use zmsg_decode ().
CZMQ_EXPORT size_t
zmsg_encode (zmsg_t *self, byte **buffer);
// Decodes a serialized message buffer created by zmsg_encode () and returns
// a new zmsg_t object. Returns NULL if the buffer was badly formatted or
// there was insufficient memory to work.
CZMQ_EXPORT zmsg_t *
zmsg_decode (byte *buffer, size_t buffer_size);
// Create copy of message, as new message object. Returns a fresh zmsg_t
// object. If message is null, or memory was exhausted, returns null.
CZMQ_EXPORT zmsg_t *
zmsg_dup (zmsg_t *self);
// Send message to zsys log sink (may be stdout, or system facility as
// configured by zsys_set_logstream).
CZMQ_EXPORT void
zmsg_print (zmsg_t *self);
// Probe the supplied object, and report if it looks like a zmsg_t.
CZMQ_EXPORT bool
zmsg_is (void *self);
// Self test of this class
CZMQ_EXPORT void
zmsg_test (bool verbose);
Description
The zmsg class provides methods to send and receive multipart messages across ØMQ sockets. This class provides a list-like container interface, with methods to work with the overall container. zmsg_t messages are composed of zero or more zframe_t frames.
Example
From zmsg_test method
// Create two PAIR sockets and connect over inproc
zsock_t *output = zsock_new_pair ("@inproc://zmsg.test");
assert (output);
zsock_t *input = zsock_new_pair (">inproc://zmsg.test");
assert (input);
// Test send and receive of single-frame message
zmsg_t *msg = zmsg_new ();
assert (msg);
zframe_t *frame = zframe_new ("Hello", 5);
assert (frame);
zmsg_prepend (msg, &frame);
assert (zmsg_size (msg) == 1);
assert (zmsg_content_size (msg) == 5);
rc = zmsg_send (&msg, output);
assert (msg == NULL);
assert (rc == 0);
msg = zmsg_recv (input);
assert (msg);
assert (zmsg_size (msg) == 1);
assert (zmsg_content_size (msg) == 5);
zmsg_destroy (&msg);
// Test send and receive of multi-frame message
msg = zmsg_new ();
assert (msg);
rc = zmsg_addmem (msg, "Frame0", 6);
assert (rc == 0);
rc = zmsg_addmem (msg, "Frame1", 6);
assert (rc == 0);
rc = zmsg_addmem (msg, "Frame2", 6);
assert (rc == 0);
rc = zmsg_addmem (msg, "Frame3", 6);
assert (rc == 0);
rc = zmsg_addmem (msg, "Frame4", 6);
assert (rc == 0);
rc = zmsg_addmem (msg, "Frame5", 6);
assert (rc == 0);
rc = zmsg_addmem (msg, "Frame6", 6);
assert (rc == 0);
rc = zmsg_addmem (msg, "Frame7", 6);
assert (rc == 0);
rc = zmsg_addmem (msg, "Frame8", 6);
assert (rc == 0);
rc = zmsg_addmem (msg, "Frame9", 6);
assert (rc == 0);
zmsg_t *copy = zmsg_dup (msg);
assert (copy);
rc = zmsg_send (©, output);
assert (rc == 0);
rc = zmsg_send (&msg, output);
assert (rc == 0);
copy = zmsg_recv (input);
assert (copy);
assert (zmsg_size (copy) == 10);
assert (zmsg_content_size (copy) == 60);
zmsg_destroy (©);
msg = zmsg_recv (input);
assert (msg);
assert (zmsg_size (msg) == 10);
assert (zmsg_content_size (msg) == 60);
// create empty file for null test
FILE *file = fopen ("zmsg.test", "w");
assert (file);
fclose (file);
file = fopen ("zmsg.test", "r");
zmsg_t *null_msg = zmsg_load (NULL, file);
assert (null_msg == NULL);
fclose (file);
remove ("zmsg.test");
// Save to a file, read back
file = fopen ("zmsg.test", "w");
assert (file);
rc = zmsg_save (msg, file);
assert (rc == 0);
fclose (file);
file = fopen ("zmsg.test", "r");
rc = zmsg_save (msg, file);
assert (rc == -1);
fclose (file);
zmsg_destroy (&msg);
file = fopen ("zmsg.test", "r");
msg = zmsg_load (NULL, file);
assert (msg);
fclose (file);
remove ("zmsg.test");
assert (zmsg_size (msg) == 10);
assert (zmsg_content_size (msg) == 60);
// Remove all frames except first and last
int frame_nbr;
for (frame_nbr = 0; frame_nbr < 8; frame_nbr++) {
zmsg_first (msg);
frame = zmsg_next (msg);
zmsg_remove (msg, frame);
zframe_destroy (&frame);
}
// Test message frame manipulation
assert (zmsg_size (msg) == 2);
frame = zmsg_last (msg);
assert (zframe_streq (frame, "Frame9"));
assert (zmsg_content_size (msg) == 12);
frame = zframe_new ("Address", 7);
assert (frame);
zmsg_prepend (msg, &frame);
assert (zmsg_size (msg) == 3);
rc = zmsg_addstr (msg, "Body");
assert (rc == 0);
assert (zmsg_size (msg) == 4);
frame = zmsg_pop (msg);
zframe_destroy (&frame);
assert (zmsg_size (msg) == 3);
char *body = zmsg_popstr (msg);
assert (streq (body, "Frame0"));
free (body);
zmsg_destroy (&msg);
// Test encoding/decoding
msg = zmsg_new ();
assert (msg);
byte *blank = (byte *) zmalloc (100000);
assert (blank);
rc = zmsg_addmem (msg, blank, 0);
assert (rc == 0);
rc = zmsg_addmem (msg, blank, 1);
assert (rc == 0);
rc = zmsg_addmem (msg, blank, 253);
assert (rc == 0);
rc = zmsg_addmem (msg, blank, 254);
assert (rc == 0);
rc = zmsg_addmem (msg, blank, 255);
assert (rc == 0);
rc = zmsg_addmem (msg, blank, 256);
assert (rc == 0);
rc = zmsg_addmem (msg, blank, 65535);
assert (rc == 0);
rc = zmsg_addmem (msg, blank, 65536);
assert (rc == 0);
rc = zmsg_addmem (msg, blank, 65537);
assert (rc == 0);
free (blank);
assert (zmsg_size (msg) == 9);
byte *buffer;
size_t buffer_size = zmsg_encode (msg, &buffer);
zmsg_destroy (&msg);
msg = zmsg_decode (buffer, buffer_size);
assert (msg);
free (buffer);
zmsg_destroy (&msg);
// Test submessages
msg = zmsg_new ();
assert (msg);
zmsg_t *submsg = zmsg_new ();
zmsg_pushstr (msg, "matr");
zmsg_pushstr (submsg, "joska");
rc = zmsg_addmsg (msg, &submsg);
assert (rc == 0);
assert (submsg == NULL);
submsg = zmsg_popmsg (msg);
assert (submsg == NULL); // string "matr" is not encoded zmsg_t, so was discarded
submsg = zmsg_popmsg (msg);
assert (submsg);
body = zmsg_popstr (submsg);
assert (streq (body, "joska"));
free (body);
zmsg_destroy (&submsg);
frame = zmsg_pop (msg);
assert (frame == NULL);
zmsg_destroy (&msg);
// Now try methods on an empty message
msg = zmsg_new ();
assert (msg);
assert (zmsg_size (msg) == 0);
assert (zmsg_unwrap (msg) == NULL);
assert (zmsg_first (msg) == NULL);
assert (zmsg_last (msg) == NULL);
assert (zmsg_next (msg) == NULL);
assert (zmsg_pop (msg) == NULL);
// Sending an empty message is valid and destroys the message
assert (zmsg_send (&msg, output) == 0);
assert (!msg);
zsock_destroy (&input); zsock_destroy (&output);
See also
Authors
The CZMQ manual was written by Pieter Hintjens<moc.xitami|hp#moc.xitami|hp>.
Resources
Main web site: http://czmq.zeromq.org/
Report bugs to the ØMQ development mailing list: <gro.qmorez.stsil|ved-qmorez#gro.qmorez.stsil|ved-qmorez>
Copyright
Copyright (c) the Contributors as noted in the AUTHORS file. This file is part of CZMQ, the high-level C binding for ØMQ: http://czmq.zeromq.org. This Source Code Form is subject to the terms of the Mozilla Public License, v. 2.0. If a copy of the MPL was not distributed with this file, You can obtain one at http://mozilla.org/MPL/2.0/.