zmsg man page

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

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]>

Notes

1.

zeromq-dev@lists.zeromq.org

mailto:zeromq-dev@lists.zeromq.org

Referenced By

czmq(7).

11/11/2016 CZMQ 4.0.1 CZMQ Manual