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'.

Survey (Everybody Votes)

The surveyor pattern is used to send a timed survey out, responses are individually returned until the survey has expired. This pattern is useful for service discovery and voting algorithms.

survey.c

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

#include <nng/nng.h>
#include <nng/protocol/survey0/survey.h>
#include <nng/protocol/survey0/respond.h>

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

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

        if ((rv = nng_surveyor0_open(&sock)) != 0) {
                fatal("nng_surveyor0_open", rv);
        }
        if ((rv = nng_listen(sock, url, NULL, 0)) != 0) {
                fatal("nng_listen", rv);
        }
        for (;;) {
                printf("SERVER: SENDING DATE SURVEY REQUEST\n");
                if ((rv = nng_send(sock, DATE, strlen(DATE) + 1, 0)) != 0) {
                        fatal("nng_send", rv);
                }

                for (;;) {
                        char *buf = NULL;
                        size_t sz;
                        rv = nng_recv(sock, &buf, &sz, NNG_FLAG_ALLOC);
                        if (rv == NNG_ETIMEDOUT) {
                                break;
                        }
                        if (rv != 0) {
                                fatal("nng_recv", rv);
                        }
                        printf("SERVER: RECEIVED \"%s\" SURVEY RESPONSE\n",
                            buf); (1)
                        nng_free(buf, sz);
                }

                printf("SERVER: SURVEY COMPLETE\n");
        }
}

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

        if ((rv = nng_respondent0_open(&sock)) != 0) {
                fatal("nng_respondent0_open", rv);
        }
        if ((rv = nng_dial(sock, url, NULL, NNG_FLAG_NONBLOCK)) != 0) {
                fatal("nng_dial", rv);
        }
        for (;;) {
                char *buf = NULL;
                size_t sz;
                if ((rv = nng_recv(sock, &buf, &sz, NNG_FLAG_ALLOC)) == 0) {
                        printf("CLIENT (%s): RECEIVED \"%s\" SURVEY REQUEST\n",
                            name, buf); (1)
                        nng_free(buf, sz);
                        char *d = date();
                        printf("CLIENT (%s): SENDING DATE SURVEY RESPONSE\n",
                           name);
                        if ((rv = nng_send(sock, d, strlen(d) + 1, 0)) != 0) {
                                fatal("nng_send", rv);
                        }
                }
        }
}

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: survey %s|%s <URL> <ARG> ...\n",
            SERVER, CLIENT);
        return 1;
}

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

Compilation

gcc survey.c -lnng -o survey

Execution

./survey server ipc:///tmp/survey.ipc & server=$!
./survey client ipc:///tmp/survey.ipc client0 & client0=$!
./survey client ipc:///tmp/survey.ipc client1 & client1=$!
./survey client ipc:///tmp/survey.ipc client2 & client2=$!
sleep 3 (1)
kill $server $client0 $client1 $client2

1	The first survey times out with no responses because the clients aren’t connected yet.

Output

SERVER: SENDING DATE SURVEY REQUEST
SERVER: SURVEY COMPLETE
SERVER: SENDING DATE SURVEY REQUEST
CLIENT (client2): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client0): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client1): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client2): SENDING DATE SURVEY RESPONSE
CLIENT (client1): SENDING DATE SURVEY RESPONSE
CLIENT (client0): SENDING DATE SURVEY RESPONSE
SERVER: RECEIVED "Tue Jan  9 11:33:40 2018" SURVEY RESPONSE
SERVER: RECEIVED "Tue Jan  9 11:33:40 2018" SURVEY RESPONSE
SERVER: RECEIVED "Tue Jan  9 11:33:40 2018" SURVEY RESPONSE
SERVER: SURVEY COMPLETE
SERVER: SENDING DATE SURVEY REQUEST
CLIENT (client2): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client2): SENDING DATE SURVEY RESPONSE
CLIENT (client0): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client0): SENDING DATE SURVEY RESPONSE
CLIENT (client1): RECEIVED "DATE" SURVEY REQUEST
CLIENT (client1): SENDING DATE SURVEY RESPONSE
SERVER: RECEIVED "Tue Jan  9 11:33:41 2018" SURVEY RESPONSE
SERVER: RECEIVED "Tue Jan  9 11:33:41 2018" SURVEY RESPONSE
SERVER: RECEIVED "Tue Jan  9 11:33:41 2018" SURVEY RESPONSE

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