ZSTR(3)

NAME
zstr - sending and receiving strings

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.
//  Receive C string from socket. Caller must free returned string using
//  zstr_free(). Returns NULL if the context is being terminated or the
//  process was interrupted.
//  Caller owns return value and must destroy it when done.
CZMQ_EXPORT char *
    zstr_recv (void *source);
//  Receive a series of strings (until NULL) from multipart data.
//  Each string is allocated and filled with string data; if there
//  are not enough frames, unallocated strings are set to NULL.
//  Returns -1 if the message could not be read, else returns the
//  number of strings filled, zero or more. Free each returned string
//  using zstr_free(). If not enough strings are provided, remaining
//  multipart frames in the message are dropped.
CZMQ_EXPORT int
    zstr_recvx (void *source, char **string_p, ...);
//  Send a C string to a socket, as a frame. The string is sent without
//  trailing null byte; to read this you can use zstr_recv, or a similar
//  method that adds a null terminator on the received string. String
//  may be NULL, which is sent as "".
CZMQ_EXPORT int
    zstr_send (void *dest, const char *string);
//  Send a C string to a socket, as zstr_send(), with a MORE flag, so that
//  you can send further strings in the same multi-part message.
CZMQ_EXPORT int
    zstr_sendm (void *dest, const char *string);
//  Send a formatted string to a socket. Note that you should NOT use
//  user-supplied strings in the format (they may contain '%' which
//  will create security holes).
CZMQ_EXPORT int
    zstr_sendf (void *dest, const char *format, ...) CHECK_PRINTF (2);
//  Send a formatted string to a socket, as for zstr_sendf(), with a
//  MORE flag, so that you can send further strings in the same multi-part
//  message.
CZMQ_EXPORT int
    zstr_sendfm (void *dest, const char *format, ...) CHECK_PRINTF (2);
//  Send a series of strings (until NULL) as multipart data
//  Returns 0 if the strings could be sent OK, or -1 on error.
CZMQ_EXPORT int
    zstr_sendx (void *dest, const char *string, ...);
//  Free a provided string, and nullify the parent pointer. Safe to call on
//  a null pointer.
CZMQ_EXPORT void
    zstr_free (char **string_p);
//  Self test of this class.
CZMQ_EXPORT void
    zstr_test (bool verbose);
#ifdef CZMQ_BUILD_DRAFT_API
//  *** Draft method, for development use, may change without warning ***
//  Accepts a void pointer and returns a fresh character string. If source
//  is null, returns an empty string.
//  Caller owns return value and must destroy it when done.
CZMQ_EXPORT char *
    zstr_str (void *source);
#endif // CZMQ_BUILD_DRAFT_API
Please add '@interface' section in './../src/zstr.c'.

DESCRIPTION

The zstr class provides utility functions for sending and receiving C strings across 0MQ sockets. It sends strings without a terminating null, and appends a null byte on received strings. This class is for simple message sending.

           Memory                       Wire
           +-------------+---+          +---+-------------+
    Send   | S t r i n g | 0 |  ---->   | 6 | S t r i n g |
           +-------------+---+          +---+-------------+

           Wire                         Heap
           +---+-------------+          +-------------+---+
    Recv   | 6 | S t r i n g |  ---->   | S t r i n g | 0 |
           +---+-------------+          +-------------+---+

EXAMPLE

From zstr_test method.

    //  Create two PAIR sockets and connect over inproc
    zsock_t *output = zsock_new_pair ("@inproc://zstr.test");
    assert (output);
    zsock_t *input = zsock_new_pair (">inproc://zstr.test");
    assert (input);
    //  Send ten strings, five strings with MORE flag and then END
    int string_nbr;
    for (string_nbr = 0; string_nbr < 10; string_nbr++)
        zstr_sendf (output, "this is string %d", string_nbr);
    zstr_sendx (output, "This", "is", "almost", "the", "very", "END", NULL);
    //  Read and count until we receive END
    string_nbr = 0;
    for (string_nbr = 0;; string_nbr++) {
        char *string = zstr_recv (input);
        assert (string);
        if (streq (string, "END")) {
            zstr_free (&string);
            break;
        }
        zstr_free (&string);
    }
    assert (string_nbr == 15);
    zsock_destroy (&input);
    zsock_destroy (&output);
    #if defined (ZMQ_SERVER)
    //  Test SERVER/CLIENT over zstr
    zsock_t *server = zsock_new_server ("inproc://zstr-test-routing");
    zsock_t *client = zsock_new_client ("inproc://zstr-test-routing");;
    assert (server);
    assert (client);
    //  Try normal ping-pong to check reply routing ID
    int rc = zstr_send (client, "Hello");
    assert (rc == 0);
    char *request = zstr_recv (server);
    assert (streq (request, "Hello"));
    assert (zsock_routing_id (server));
    free (request);
    rc = zstr_send (server, "World");
    assert (rc == 0);
    char *reply = zstr_recv (client);
    assert (streq (reply, "World"));
    free (reply);
    rc = zstr_sendf (server, "%s", "World");
    assert (rc == 0);
    reply = zstr_recv (client);
    assert (streq (reply, "World"));
    free (reply);
    //  Try ping-pong using sendx and recx
    rc = zstr_sendx (client, "Hello", NULL);
    assert (rc == 0);
    rc = zstr_recvx (server, &request, NULL);
    assert (rc >= 0);
    assert (streq (request, "Hello"));
    free (request);
    rc = zstr_sendx (server, "World", NULL);
    assert (rc == 0);
    rc = zstr_recvx (client, &reply, NULL);
    assert (rc >= 0);
    assert (streq (reply, "World"));
    free (reply);
    //  Client and server disallow multipart
    rc = zstr_sendm (client, "Hello");
    assert (rc == -1);
    rc = zstr_sendm (server, "World");
    assert (rc == -1);
    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