ZSTR

NAME

zstr - Class for 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 ***
// 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'.

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);

#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

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.

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