Tries to reconnect to server

hwserver.c

//
//  Hello World server
//  Binds REP socket to tcp://*:5555
//  Expects "Hello" from client, replies with "World"
//
//  Changes for 2.1:
//  - added socket close before terminating
//
#include <zmq.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>

int main () {
    void *context = zmq_init (1);

    //  Socket to talk to clients
    void *responder = zmq_socket (context, ZMQ_REP);
    zmq_bind (responder, "tcp://*:5555");

    while (1) {
        //  Wait for next request from client
        zmq_msg_t request;
        zmq_msg_init (&request);
        zmq_recv (responder, &request, 0);
        printf ("Received Hello\n");
        zmq_msg_close (&request);

        //  Do some 'work'
        sleep (1);

        //  Send reply back to client
        zmq_msg_t reply;
        zmq_msg_init_data (&reply, "World", 5, NULL, NULL);
        zmq_send (responder, &reply, 0);
        zmq_msg_close (&reply);
    }
    //  We never get here but if we did, this would be how we end
    zmq_close (responder);
    zmq_term (context);
    return 0;
}

piclient.c

//
//  Client-side pirate
//  Use zmq_poll to do a safe request-reply
//  To run, start hwserver and then randomly kill/restart it
//
#include "zhelpers.h"

#define REQUEST_TIMEOUT     2500    //  msecs
#define REQUEST_RETRIES     3       //  Before we abandon

int main () {
    void *context = zmq_init (1);
    void *client = zmq_socket (context, ZMQ_REQ);
    int rc = zmq_connect (client, "tcp://localhost:5555");
    assert (rc == 0);

    //  Socket to talk to server
    printf ("Connecting to hello world server...\n");

    int retries_left = REQUEST_RETRIES;
    while (1) {
        rc = s_send (client, "HELLO");
        printf ("Trying to contact server, %s\n", rc == 0? "OK": "FAILED");

        zmq_pollitem_t items [] = { { client, 0, ZMQ_POLLIN, 0 } };
        zmq_poll (items, 1, REQUEST_TIMEOUT * 1000);

        if (items [0].revents & ZMQ_POLLIN) {
            //  We got a reply from the server
            char *reply = s_recv (client);
            free (reply);
            printf ("Server replied\n");
            retries_left = REQUEST_RETRIES;
        }
        else {
            //  No response from server
            if (--retries_left == 0) {
                printf ("E: server seems to be offline, abandoning\n");
                break;
            }
            else
                printf ("W: no response from server, retrying...\n");
        }
    }
    //  Discard any outgoing requests
    int linger = 0;
    zmq_setsockopt (client, ZMQ_LINGER, &linger, sizeof (linger));
    
    zmq_close (client);
    zmq_term (context);
    return 0;
}

zhelpers.h

/*  =========================================================================
    zhelpers.h

    Helper header file for example applications.

    -------------------------------------------------------------------------
    Copyright (c) 1991-2010 iMatix Corporation <www.imatix.com>
    Copyright other contributors as noted in the AUTHORS file.

    This file is part of the ZeroMQ Guide: http://zguide.zeromq.org

    This is free software; you can redistribute it and/or modify it under the
    terms of the GNU Lesser General Public License as published by the Free
    Software Foundation; either version 3 of the License, or (at your option)
    any later version.

    This software is distributed in the hope that it will be useful, but
    WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABIL-
    ITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General
    Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program. If not, see <http://www.gnu.org/licenses/>.
    =========================================================================
*/

#ifndef __ZHELPERS_H_INCLUDED__
#define __ZHELPERS_H_INCLUDED__

//  Include a bunch of headers that we will need in the examples

#include <zmq.h>

#include <pthread.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <string.h>
#include <sys/time.h>
#include <time.h>
#include <unistd.h>
#include <assert.h>
#include <inttypes.h>

//  Bring Windows MSVC up to C99 scratch
#if (defined (__WINDOWS__))
    typedef unsigned long ulong;
    typedef unsigned int  uint;
    typedef __int64 int64_t;
#endif

//  Provide random number from 0..(num-1)
#define randof(num)   (int) ((float) (num) * random () / (RAND_MAX + 1.0))

//  Receive 0MQ string from socket and convert into C string
//  Caller must free returned string. Returns NULL if the context
//  is being terminated.
static char *
s_recv (void *socket) {
    zmq_msg_t message;
    zmq_msg_init (&message);
    if (zmq_recv (socket, &message, 0))
        return (NULL);
    int size = zmq_msg_size (&message);
    char *string = malloc (size + 1);
    memcpy (string, zmq_msg_data (&message), size);
    zmq_msg_close (&message);
    string [size] = 0;
    return (string);
}

//  Convert C string to 0MQ string and send to socket
static int
s_send (void *socket, char *string) {
    int rc;
    zmq_msg_t message;
    zmq_msg_init_size (&message, strlen (string));
    memcpy (zmq_msg_data (&message), string, strlen (string));
    rc = zmq_send (socket, &message, 0);
    zmq_msg_close (&message);
    return (rc);
}

//  Sends string as 0MQ string, as multipart non-terminal
static int
s_sendmore (void *socket, char *string) {
    int rc;
    zmq_msg_t message;
    zmq_msg_init_size (&message, strlen (string));
    memcpy (zmq_msg_data (&message), string, strlen (string));
    rc = zmq_send (socket, &message, ZMQ_SNDMORE);
    zmq_msg_close (&message);
    return (rc);
}

//  Receives all message parts from socket, prints neatly
//
static void
s_dump (void *socket)
{
    puts ("----------------------------------------");
    while (1) {
        //  Process all parts of the message
        zmq_msg_t message;
        zmq_msg_init (&message);
        zmq_recv (socket, &message, 0);

        //  Dump the message as text or binary
        char *data = zmq_msg_data (&message);
        int size = zmq_msg_size (&message);
        int is_text = 1;
        int char_nbr;
        for (char_nbr = 0; char_nbr < size; char_nbr++)
            if ((unsigned char) data [char_nbr] < 32
            ||  (unsigned char) data [char_nbr] > 127)
                is_text = 0;

        printf ("[%03d] ", size);
        for (char_nbr = 0; char_nbr < size; char_nbr++) {
            if (is_text)
                printf ("%c", data [char_nbr]);
            else
                printf ("%02X", (unsigned char) data [char_nbr]);
        }
        printf ("\n");

        int64_t more;           //  Multipart detection
        size_t more_size = sizeof (more);
        zmq_getsockopt (socket, ZMQ_RCVMORE, &more, &more_size);
        zmq_msg_close (&message);
        if (!more)
            break;      //  Last message part
    }
}

//  Set simple random printable identity on socket
//
static void
s_set_id (void *socket)
{
    char identity [10];
    sprintf (identity, "%04X-%04X", randof (0x10000), randof (0x10000));
    zmq_setsockopt (socket, ZMQ_IDENTITY, identity, strlen (identity));
}


//  Report 0MQ version number
//
static void
s_version (void)
{
    int major, minor, patch;
    zmq_version (&major, &minor, &patch);
    printf ("Current 0MQ version is %d.%d.%d\n", major, minor, patch);
}

//  Require at least some specified version
static void
s_version_assert (int want_major, int want_minor)
{
    int major, minor, patch;
    zmq_version (&major, &minor, &patch);
    if (major < want_major
    || (major == want_major && minor < want_minor)) {
        printf ("Current 0MQ version is %d.%d\n", major, minor);
        printf ("Application needs at least %d.%d - cannot continue\n", 
            want_major, want_minor);
        exit (EXIT_FAILURE);
    }
}

//  Sleep for a number of milliseconds
static void
s_sleep (int msecs) 
{
#if (defined (__WINDOWS__))
    Sleep (msecs);
#else
    struct timespec t;
    t.tv_sec  =  msecs / 1000;
    t.tv_nsec = (msecs % 1000) * 1000000;
    int rc = nanosleep (&t, NULL);
    assert (rc == 0);
#endif
}

//  Return current system clock as milliseconds
static int64_t
s_clock (void)
{
#if (defined (__WINDOWS__))
    SYSTEMTIME st;
    GetSystemTime (&st);
    return (int64_t) st.wSecond * 1000 + st.wMilliseconds;
#else
    struct timeval tv;
    int rc = gettimeofday (&tv, NULL);
    assert (rc == 0);
    return (int64_t) (tv.tv_sec * 1000 + tv.tv_usec / 1000);
#endif
}


#endif  //  __ZHELPERS_H_INCLUDED__