unix datagram client

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <sys/epoll.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <unistd.h>

#define SOCK_PATH "test_socket"
#define MAX_EVENTS 10

/* make gcc -std=c99 -g3 -Wall -o client client.c */
int
main(void)
{
	int sockfd, epollfd;
	struct sockaddr_un server;
	struct epoll_event ev;
	char buf[1024];

	sockfd = socket(AF_UNIX, SOCK_DGRAM, 0);
	if (sockfd == -1) {
		printf("SOCKET ERROR = %d\n", errno);
		exit(1);
	}

	epollfd = epoll_create(1024);
	if (epollfd < 0) {
		printf("epoll failed %d: %s", errno, strerror(errno));
		exit(1);
	}

	// notify on EPOLLOUT events (ie: fd becomes writable) with edge-triggered behavior
	ev.events = EPOLLOUT | EPOLLHUP | EPOLLERR | EPOLLET;
	ev.data.fd = sockfd;
	if (epoll_ctl(epollfd, EPOLL_CTL_ADD, sockfd, &ev) == -1) {
		perror("epoll_ctl: sockfd");
		exit(EXIT_FAILURE);
	}

	// combine edge-triggered epolling with non-blocking sockets
	if (fcntl(sockfd, F_SETFL, O_NONBLOCK) < 0) {
		printf("fcntl F_SETFL failed.%s", strerror(errno));
		exit(1);
	}

	memset(&server, 0, sizeof(struct sockaddr_un));
	server.sun_family = AF_UNIX;
	strcpy(server.sun_path, SOCK_PATH);

	for (unsigned i = 0; ; i++) {
		struct epoll_event events[MAX_EVENTS];
		int nfds = epoll_wait(epollfd, events, MAX_EVENTS, -1);
		if (nfds == -1) {
			perror("epoll_wait");
			exit(EXIT_FAILURE);
		}

		for (unsigned n = 0; n < nfds; n++) {
			if (events[n].data.fd != sockfd) {
				continue;
			}
			if (events[n].events & EPOLLHUP) {
				printf("EPOLLUP! events is %u\n", events[n].events);
				exit(1);
			}
			if (events[n].events & EPOLLERR) {
				printf("EPOLLERR! events is %u\n", events[n].events);
				exit(1);
			}
			if (!(events[n].events & EPOLLOUT)) {
				exit(1);
			}

			strcpy(buf, "this is a message in a buffer over unix datagrams\n");
			if (i % 10000  == 0) {
				printf("Sent %u packets\n", i);
				printf("events is %u\n", (unsigned)(events[n].events));
			}

			while (1) {
				int r = sendto(sockfd, buf, strlen(buf), 0, (struct sockaddr *) &server, sizeof(server));
				int err = errno;
				if (r == -1 && err == EAGAIN) {
					// eagain means we should break and wait
					break;
				} else if (r == -1 && err == ECONNREFUSED) {
					// connrefused is ok
					continue;
				} else if (r == -1 && err == ENOENT) {
					// enoent is ok
					continue;
				} else if (r == -1) {
					printf("sendto failed with %d: %s\n", err, strerror(errno));
					exit(1);
				}
			}
		}
	}

	return 0;
}