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Man Pages
ZSTR(3) CZMQ Manual ZSTR(3)

zstr - Class for sending and receiving strings

//  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 *** // De-compress and receive C string from socket, received as a message // with two frames: size of the uncompressed string, and the string itself. // 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_compress (void *source);
// *** Draft method, for development use, may change without warning *** // Compress and send a C string to a socket, as a message with two frames: // size of the uncompressed string, and the string itself. The string is // sent without trailing null byte; to read this you can use // zstr_recv_compress, or a similar method that de-compresses and adds a // null terminator on the received string. CZMQ_EXPORT int zstr_send_compress (void *dest, const char *string);
// *** Draft method, for development use, may change without warning *** // Compress and send a C string to a socket, as zstr_send_compress(), // with a MORE flag, so that you can send further strings in the same // multi-part message. CZMQ_EXPORT int zstr_sendm_compress (void *dest, const char *string);
// *** 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'.

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 |
       +---+-------------+          +-------------+---+

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);
#ifdef HAVE_LIBLZ4 int ret = zstr_send_compress (output, "loooong"); assert (ret == 0); char *string = zstr_recv_compress (input); assert (string); assert (streq (string, "loooong")); zstr_free (&string);
zstr_send_compress (output, "loooong"); assert (ret == 0); zmsg_t *msg = zmsg_recv (input); assert (msg); assert (*((size_t *)zframe_data (zmsg_first (msg))) == strlen ("loooong")); zmsg_destroy (&msg); #endif
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)); freen (request);
rc = zstr_send (server, "World"); assert (rc == 0); char *reply = zstr_recv (client); assert (streq (reply, "World")); freen (reply);
rc = zstr_sendf (server, "%s", "World"); assert (rc == 0); reply = zstr_recv (client); assert (streq (reply, "World")); freen (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")); freen (request);
rc = zstr_sendx (server, "World", NULL); assert (rc == 0); rc = zstr_recvx (client, &reply, NULL); assert (rc >= 0); assert (streq (reply, "World")); freen (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
#if defined (__WINDOWS__) zsys_shutdown(); #endif

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

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

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.

1.
zeromq-dev@lists.zeromq.org
mailto:zeromq-dev@lists.zeromq.org
01/02/2019 CZMQ 4.1.1

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