ZMSG(3)

NAME
zmsg - working with multipart messages

SYNOPSIS

//  This is a stable class, and may not change except for emergencies. It
//  is provided in stable builds.
//  This class has draft methods, which may change over time. They are not
//  in stable releases, by default. Use --enable-drafts to enable.
//  Create a new empty message object
CZMQ_EXPORT zmsg_t *
    zmsg_new (void);
//  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);
//  Load/append an open file into new message, return the message.
//  Returns NULL if the message could not be loaded.
CZMQ_EXPORT zmsg_t *
    zmsg_load (FILE *file);
//  Decodes a serialized message frame created by zmsg_encode () and returns
//  a new zmsg_t object. Returns NULL if the frame was badly formatted or
//  there was insufficient memory to work.
CZMQ_EXPORT zmsg_t *
    zmsg_decode (zframe_t *frame);
//  Generate a signal message encoding the given status. A signal is a short
//  message carrying a 1-byte success/failure code (by convention, 0 means
//  OK). Signals are encoded to be distinguishable from "normal" messages.
CZMQ_EXPORT zmsg_t *
    zmsg_new_signal (byte status);
//  Destroy a message object and all frames it contains
CZMQ_EXPORT void
    zmsg_destroy (zmsg_t **self_p);
//  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);
//  Send message to destination socket as part of a multipart sequence, and
//  destroy the message after sending it successfully. Note that after a
//  zmsg_sendm, you must call zmsg_send or another method that sends a final
//  message part. 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_sendm (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 owns return value and must destroy it when done.
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 *data, 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 *data, 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, ...) CHECK_PRINTF (2);
//  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, ...) CHECK_PRINTF (2);
//  Pop frame off front of message, return as fresh string. If there were
//  no more frames in the message, returns NULL.
//  Caller owns return value and must destroy it when done.
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 successful.
//  Caller owns return value and must destroy it when done.
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);
//  Serialize multipart message to a single message frame. Use this method
//  to send structured messages across transports that do not support
//  multipart data. Allocates and returns a new frame containing the
//  serialized message. To decode a serialized message frame, use
//  zmsg_decode ().
//  Caller owns return value and must destroy it when done.
CZMQ_EXPORT zframe_t *
    zmsg_encode (zmsg_t *self);
//  Create copy of message, as new message object. Returns a fresh zmsg_t
//  object. If message is null, or memory was exhausted, returns null.
//  Caller owns return value and must destroy it when done.
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);
//  Return true if the two messages have the same number of frames and each
//  frame in the first message is identical to the corresponding frame in the
//  other message. As with zframe_eq, return false if either message is NULL.
CZMQ_EXPORT bool
    zmsg_eq (zmsg_t *self, zmsg_t *other);
//  Return signal value, 0 or greater, if message is a signal, -1 if not.
CZMQ_EXPORT int
    zmsg_signal (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);
#ifdef CZMQ_BUILD_DRAFT_API
//  *** Draft method, for development use, may change without warning ***
//  Return message routing ID, if the message came from a ZMQ_SERVER socket.
//  Else returns zero.
CZMQ_EXPORT uint32_t
    zmsg_routing_id (zmsg_t *self);
//  *** Draft method, for development use, may change without warning ***
//  Set routing ID on message. This is used if/when the message is sent to a
//  ZMQ_SERVER socket.
CZMQ_EXPORT void
    zmsg_set_routing_id (zmsg_t *self, uint32_t routing_id);
#endif // CZMQ_BUILD_DRAFT_API
Please add '@interface' section in './../src/zmsg.c'.

DESCRIPTION

The zmsg class provides methods to send and receive multipart messages across 0MQ 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.

Please add @discuss section in ./../src/zmsg.c.

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 (&copy, 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 (&copy);
    msg = zmsg_recv (input);
    assert (msg);
    assert (zmsg_size (msg) == 10);
    assert (zmsg_content_size (msg) == 60);
    //  Save to a file, read back
    FILE *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 (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);
    frame = zmsg_encode (msg);
    zmsg_destroy (&msg);
    msg = zmsg_decode (frame);
    assert (msg);
    zmsg_destroy (&msg);
    zframe_destroy (&frame);
    //  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);
    //  Test comparison of two messages
    msg = zmsg_new ();
    zmsg_addstr (msg, "One");
    zmsg_addstr (msg, "Two");
    zmsg_addstr (msg, "Three");
    zmsg_t *msg_other = zmsg_new ();
    zmsg_addstr (msg_other, "One");
    zmsg_addstr (msg_other, "Two");
    zmsg_addstr (msg_other, "One-Hundred");
    zmsg_t *msg_dup = zmsg_dup (msg);
    zmsg_t *empty_msg = zmsg_new ();
    zmsg_t *empty_msg_2 = zmsg_new ();
    assert (zmsg_eq (msg, msg_dup));
    assert (!zmsg_eq (msg, msg_other));
    assert (zmsg_eq (empty_msg, empty_msg_2));
    assert (!zmsg_eq (msg, NULL));
    assert (!zmsg_eq (NULL, empty_msg));
    assert (!zmsg_eq (NULL, NULL));
    zmsg_destroy (&msg);
    zmsg_destroy (&msg_other);
    zmsg_destroy (&msg_dup);
    zmsg_destroy (&empty_msg);
    zmsg_destroy (&empty_msg_2);
    //  Test signal messages
    msg = zmsg_new_signal (0);
    assert (zmsg_signal (msg) == 0);
    zmsg_destroy (&msg);
    msg = zmsg_new_signal (-1);
    assert (zmsg_signal (msg) == 255);
    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);
    #if defined (ZMQ_SERVER)
    //  Create server and client sockets and connect over inproc
    zsock_t *server = zsock_new_server ("inproc://zmsg-test-routing");
    assert (server);
    zsock_t *client = zsock_new_client ("inproc://zmsg-test-routing");
    assert (client);
    //  Send request from client to server
    zmsg_t *request = zmsg_new ();
    assert (request);
    zmsg_addstr (request, "Hello");
    rc = zmsg_send (&request, client);
    assert (rc == 0);
    assert (!request);
    //  Read request and send reply
    request = zmsg_recv (server);
    assert (request);
    char *string = zmsg_popstr (request);
    assert (streq (string, "Hello"));
    assert (zmsg_routing_id (request));
    zstr_free (&string);
    zmsg_t *reply = zmsg_new ();
    assert (reply);
    zmsg_addstr (reply, "World");
    zmsg_set_routing_id (reply, zmsg_routing_id (request));
    rc = zmsg_send (&reply, server);
    assert (rc == 0);
    zmsg_destroy (&request);
    //  Read reply
    reply = zmsg_recv (client);
    string = zmsg_popstr (reply);
    assert (streq (string, "World"));
    assert (zmsg_routing_id (reply) == 0);
    zmsg_destroy (&reply);
    zstr_free (&string);
    //  Client and server disallow multipart
    msg = zmsg_new ();
    zmsg_addstr (msg, "One");
    zmsg_addstr (msg, "Two");
    rc = zmsg_send (&msg, client);
    assert (rc == -1);
    assert (zmsg_size (msg) == 2);
    rc = zmsg_send (&msg, server);
    assert (rc == -1);
    assert (zmsg_size (msg) == 2);
    zmsg_destroy (&msg);
    zsock_destroy (&client);
    zsock_destroy (&server);
    #endif

AUTHORS

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

RESOURCES

Main web site:

Report bugs to the email <zeromq-dev@lists.zeromq.org[1]>

COPYRIGHT

Copyright (c) the Contributors as noted in the AUTHORS file. This file is part of CZMQ, the high-level C binding for 0MQ: 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/. LICENSE included with the czmq distribution.

NOTES

1.  zeromq-dev@lists.zeromq.org
    mailto:zeromq-dev@lists.zeromq.org