Getting Started with 'nanomsg'

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This document is derived from an original post by Tim Dysinger. That post is no longer available, but we have modified and restructured it, as well as making enhancments and corrections. Tim’s original code is on github, but we recommend using the examples here as they have a number of corrections.

If you want to use the experimental nng library instead, see the document Getting Started with 'nng'.

Request/Reply (I ask, you answer)

Request/Reply is used for synchronous communications where each question is responded with a single answer, for example remote procedure calls (RPCs). Like Pipeline, it also can perform load-balancing. This is the only reliaable messaging pattern in the suite, as it automatically will retry if a request is not matched with a response.

reqprep.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <nanomsg/nn.h>
#include <nanomsg/reqrep.h>

#define NODE0 "node0"
#define NODE1 "node1"
#define DATE "DATE"

void
fatal(const char *func)
{
        fprintf(stderr, "%s: %s\n", func, nn_strerror(nn_errno()));
        exit(1);
}

char *
date(void)
{
        time_t now = time(&now);
        struct tm *info = localtime(&now);
        char *text = asctime(info);
        text[strlen(text)-1] = '\0'; // remove '\n'
        return (text);
}

int
node0(const char *url)
{
        int sz_date = strlen(DATE) + 1; // '\0' too
        int sock;
        int rv;

        if ((sock = nn_socket(AF_SP, NN_REP)) < 0) {
                fatal("nn_socket");
        }
          if ((rv = nn_bind(sock, url)) < 0) {
                fatal("nn_bind");
        }
        for (;;) {
                char *buf = NULL;
                int bytes;
                if ((bytes = nn_recv(sock, &buf, NN_MSG, 0)) < 0) {
                        fatal("nn_recv");
                }
                if ((bytes == (strlen(DATE) + 1)) && (strcmp(DATE, buf) == 0)) {
                        printf("NODE0: RECEIVED DATE REQUEST\n");
                        char *d = date();
                        int sz_d = strlen(d) + 1; // '\0' too
                        printf("NODE0: SENDING DATE %s\n", d);
                        if ((bytes = nn_send(sock, d, sz_d, 0)) < 0) {
                                fatal("nn_send");
                        }
                }
                nn_freemsg(buf);
        }
}

int
node1(const char *url)
{
        int sz_date = strlen(DATE) + 1; // '\0' too
        char *buf = NULL;
        int bytes = -1;
        int sock;
        int rv;

        if ((sock = nn_socket(AF_SP, NN_REQ)) < 0) {
                fatal("nn_socket");
        }
        if ((rv = nn_connect (sock, url)) < 0) {
                fatal("nn_connect");
        }
        printf("NODE1: SENDING DATE REQUEST %s\n", DATE);
        if ((bytes = nn_send(sock, DATE, sz_date, 0)) < 0) {
                fatal("nn_send");
        }
        if ((bytes = nn_recv(sock, &buf, NN_MSG, 0)) < 0) {
                fatal("nn_recv");
        }
        printf("NODE1: RECEIVED DATE %s\n", buf);  (1)
        nn_freemsg(buf);
        return (nn_shutdown(sock, 0));
}

int
main(const int argc, const char **argv)
{
        if ((argc > 1) && (strcmp(NODE0, argv[1]) == 0))
                return (node0(argv[2]));

        if ((argc > 1) && (strcmp(NODE1, argv[1]) == 0))
                return (node1(argv[2]));

      fprintf(stderr, "Usage: reqrep %s|%s <URL> ...\n", NODE0, NODE1);
      return (1);
}

1	Blithely assumes message is ASCIIZ string. Real code should check it.

Compilation

gcc reqrep.c -lnanomsg -o reqrep

Execution

./reqrep node0 ipc:///tmp/reqrep.ipc & node0=$! && sleep 1
./reqrep node1 ipc:///tmp/reqrep.ipc
kill $node0

Output

NODE1: SENDING DATE REQUEST DATE
NODE0: RECEIVED DATE REQUEST
NODE0: SENDING DATE Sat Sep  7 17:39:01 2013
NODE1: RECEIVED DATE Sat Sep  7 17:39:01 2013

"nanomsg" is a trademark of Garrett D'Amore.