libnanomsg pattern guide

bus communication topology

Bus (Routing)

The bus protocol is useful for routing applications, or for building fully interconnected mesh networks. In this pattern, messages are sent to every directly connected peer.

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

#include <nanomsg/nn.h>
#include <nanomsg/bus.h>

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

int
node(const int argc, const char **argv)
{
        int sock;

        if ((sock = nn_socket (AF_SP, NN_BUS)) < 0) {
                fatal("nn_socket");
        }
          if (nn_bind(sock, argv[2]) < 0) {
                fatal("nn_bind");
        }

        sleep(1); // wait for peers to bind
        if (argc >= 3) {
                for (int x = 3; x < argc; x++) {
                        if (nn_connect(sock, argv[x]) < 0) {
                                fatal("nn_connect");
                        }
                }
        }
        sleep(1); // wait for connections
        int to = 100;
        if (nn_setsockopt(sock, NN_SOL_SOCKET, NN_RCVTIMEO, &to,
            sizeof (to)) < 0) {
                fatal("nn_setsockopt");
        }

        // SEND
        int sz_n = strlen(argv[1]) + 1; // '\0' too
        printf("%s: SENDING '%s' ONTO BUS\n", argv[1], argv[1]);
        if (nn_send(sock, argv[1], sz_n, 0) < 0) {
                fatal("nn_send");
        }

        // RECV
        for (;;) {
                char *buf = NULL;
                int recv = nn_recv(sock, &buf, NN_MSG, 0);
                if (recv >= 0) {
                        printf("%s: RECEIVED '%s' FROM BUS\n", argv[1], buf); (1)
                        nn_freemsg(buf);
                }
        }
        return (nn_shutdown(sock, 0));
}

int
main(int argc, const char **argv)
{
        if (argc >= 3) {
                return (node(argc, argv));
        }
        fprintf(stderr, "Usage: bus <NODE_NAME> <URL> <URL> ...\n");
        return 1;
}
1 Blithely assumes message is ASCIIZ string. Real code should check it.
Compilation
gcc bus.c -lnanomsg -o bus
Execution
./bus node0 ipc:///tmp/node0.ipc ipc:///tmp/node1.ipc ipc:///tmp/node2.ipc & node0=$!
./bus node1 ipc:///tmp/node1.ipc ipc:///tmp/node2.ipc ipc:///tmp/node3.ipc & node1=$!
./bus node2 ipc:///tmp/node2.ipc ipc:///tmp/node3.ipc & node2=$!
./bus node3 ipc:///tmp/node3.ipc ipc:///tmp/node0.ipc & node3=$!
sleep 5
kill $node0 $node1 $node2 $node3
Output
node0: SENDING 'node0' ONTO BUS
node1: SENDING 'node1' ONTO BUS
node2: SENDING 'node2' ONTO BUS
node3: SENDING 'node3' ONTO BUS
node0: RECEIVED 'node1' FROM BUS
node0: RECEIVED 'node2' FROM BUS
node0: RECEIVED 'node3' FROM BUS
node1: RECEIVED 'node0' FROM BUS
node1: RECEIVED 'node2' FROM BUS
node1: RECEIVED 'node3' FROM BUS
node2: RECEIVED 'node0' FROM BUS
node2: RECEIVED 'node1' FROM BUS
node2: RECEIVED 'node3' FROM BUS
node3: RECEIVED 'node0' FROM BUS
node3: RECEIVED 'node1' FROM BUS
node3: RECEIVED 'node2' FROM BUS