Getting Started with 'nng'

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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'.

Pair (Two Way Radio)

The pair pattern is used when there a one-to-one peer relationship. Only one peer may be connected to another peer at a time, but both may speak freely.

pair.c

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

#include <nng/nng.h>
#include <nng/protocol/pair0/pair.h>

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

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

int
send_name(nng_socket sock, char *name)
{
        int rv;
        printf("%s: SENDING \"%s\"\n", name, name);
        if ((rv = nng_send(sock, name, strlen(name) + 1, 0)) != 0) {
                fatal("nng_send", rv);
        }
        return (rv);
}

int
recv_name(nng_socket sock, char *name)
{
        char *buf = NULL;
        int rv;
        size_t sz;
        if ((rv = nng_recv(sock, &buf, &sz, NNG_FLAG_ALLOC)) == 0) {
                printf("%s: RECEIVED \"%s\"\n", name, buf); (1)
                nng_free(buf, sz);
        }
        return (rv);
}

int
send_recv(nng_socket sock, char *name)
{
        int rv;
        if ((rv = nng_setopt_ms(sock, NNG_OPT_RECVTIMEO, 100)) != 0) {
                fatal("nng_setopt_ms", rv);
        }
        for (;;) {
                recv_name(sock, name);
                sleep(1);
                send_name(sock, name);
        }
}

int
node0(const char *url)
{
        nng_socket sock;
        int rv;
        if ((rv = nng_pair0_open(&sock)) != 0) {
                fatal("nng_pair0_open", rv);
        }
         if ((rv = nng_listen(sock, url, NULL, 0)) !=0) {
                fatal("nng_listen", rv);
        }
        return (send_recv(sock, NODE0));
}

int
node1(const char *url)
{
        nng_socket sock;
        int rv;
        sleep(1);
        if ((rv = nng_pair0_open(&sock)) != 0) {
                fatal("nng_pair0_open", rv);
        }
        if ((rv = nng_dial(sock, url, NULL, 0)) != 0) {
                fatal("nng_dial", rv);
        }
        return (send_recv(sock, NODE1));
}

int
main(int argc, 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: pair %s|%s <URL> <ARG> ...\n", NODE0, NODE1);
        return 1;
}

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

Compilation

gcc pair.c -lnng -o pair

Execution

./pair node0 ipc:///tmp/pair.ipc & node0=$!
./pair node1 ipc:///tmp/pair.ipc & node1=$!
sleep 3
kill $node0 $node1

Output

node0: SENDING "node0"
node1: RECEIVED "node0"
node1: SENDING "node1"
node0: SENDING "node0"
node0: RECEIVED "node1"
node1: RECEIVED "node0"

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