Getting Started with 'nng'

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nanomsg^™

This document is derived from an original post by Tim Dysinger. However, the examples here are for nng instead of nanomsg. For the legacy nanomsg version of this, see Getting Started with 'nanomsg'.

Pub/Sub (Topics & Broadcast)

This pattern is used to allow a single broadcaster to publish messages to many subscribers, which may choose to limit which messages they receive.

pubsub.c

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <time.h>
#include <unistd.h>

#include <nng/nng.h>
#include <nng/protocol/pubsub0/pub.h>
#include <nng/protocol/pubsub0/sub.h>

#define SERVER "server"
#define CLIENT "client"

void
fatal(const char *func, int rv)
{
        fprintf(stderr, "%s: %s\n", func, nng_strerror(rv));
}

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
server(const char *url)
{
        nng_socket sock;
        int rv;

        if ((rv = nng_pub0_open(&sock)) != 0) {
                fatal("nng_pub0_open", rv);
        }
        if ((rv = nng_listen(sock, url, NULL, 0)) < 0) {
                fatal("nng_listen", rv);
        }
        for (;;) {
                char *d = date();
                printf("SERVER: PUBLISHING DATE %s\n", d);
                if ((rv = nng_send(sock, d, strlen(d) + 1, 0)) != 0) {
                        fatal("nng_send", rv);
                }
                sleep(1);
        }
}

int
client(const char *url, const char *name)
{
        nng_socket sock;
        int rv;

        if ((rv = nng_sub0_open(&sock)) != 0) {
                fatal("nng_sub0_open", rv);
        }

        // subscribe to everything (empty means all topics)
        if ((rv = nng_setopt(sock, NNG_OPT_SUB_SUBSCRIBE, "", 0)) != 0) {
                fatal("nng_setopt", rv);
        }
        if ((rv = nng_dial(sock, url, NULL, 0)) != 0) {
                fatal("nng_dial", rv);
        }
        for (;;) {
                char *buf = NULL;
                size_t sz;
                if ((rv = nng_recv(sock, &buf, &sz, NNG_FLAG_ALLOC)) != 0) {
                        fatal("nng_recv", rv);
                }
                printf("CLIENT (%s): RECEIVED %s\n", name, buf); (1)
                nng_free(buf, sz);
        }
}

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

          if ((argc >= 3) && (strcmp(CLIENT, argv[1]) == 0))
                return (client (argv[2], argv[3]));

        fprintf(stderr, "Usage: pubsub %s|%s <URL> <ARG> ...\n",
            SERVER, CLIENT);
        return 1;
}

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

Compilation

gcc pubsub.c -lnng -o pubsub

Execution

./pubsub server ipc:///tmp/pubsub.ipc & server=$! && sleep 1
./pubsub client ipc:///tmp/pubsub.ipc client0 & client0=$!
./pubsub client ipc:///tmp/pubsub.ipc client1 & client1=$!
./pubsub client ipc:///tmp/pubsub.ipc client2 & client2=$!
sleep 5
kill $server $client0 $client1 $client2

Output

SERVER: PUBLISHING DATE Tue Jan  9 08:21:31 2018
SERVER: PUBLISHING DATE Tue Jan  9 08:21:32 2018
CLIENT (client2): RECEIVED Tue Jan  9 08:21:32 2018
CLIENT (client1): RECEIVED Tue Jan  9 08:21:32 2018
CLIENT (client0): RECEIVED Tue Jan  9 08:21:32 2018
SERVER: PUBLISHING DATE Tue Jan  9 08:21:33 2018
CLIENT (client0): RECEIVED Tue Jan  9 08:21:33 2018
CLIENT (client2): RECEIVED Tue Jan  9 08:21:33 2018
CLIENT (client1): RECEIVED Tue Jan  9 08:21:33 2018
SERVER: PUBLISHING DATE Tue Jan  9 08:21:34 2018
CLIENT (client2): RECEIVED Tue Jan  9 08:21:34 2018
CLIENT (client0): RECEIVED Tue Jan  9 08:21:34 2018
CLIENT (client1): RECEIVED Tue Jan  9 08:21:34 2018
SERVER: PUBLISHING DATE Tue Jan  9 08:21:35 2018
CLIENT (client0): RECEIVED Tue Jan  9 08:21:35 2018
CLIENT (client1): RECEIVED Tue Jan  9 08:21:35 2018
CLIENT (client2): RECEIVED Tue Jan  9 08:21:35 2018
SERVER: PUBLISHING DATE Tue Jan  9 08:21:36 2018
CLIENT (client0): RECEIVED Tue Jan  9 08:21:36 2018
CLIENT (client1): RECEIVED Tue Jan  9 08:21:36 2018
CLIENT (client2): RECEIVED Tue Jan  9 08:21:36 2018

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