Unix Socket example, modified to see the behavior of poll() when remote socket is closed before recv() call is made on server.

unix_client.c

/*
* Code borrowed from http://beej.us/guide/bgipc/output/html/multipage/unixsock.html
*/

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

#define SOCK_PATH "/tmp/unix.socket.ex"

int main(void)
{
    int s, t, len;
    struct sockaddr_un remote;
    char str[100];
    char *hello = "hello 123123123";

    if ((s = socket(AF_UNIX, SOCK_SEQPACKET | SOCK_CLOEXEC, 0)) == -1) {
        perror("socket");
        exit(1);
    }

    printf("Trying to connect...\n");

    remote.sun_family = AF_UNIX;
    strcpy(remote.sun_path, SOCK_PATH);
    len = strlen(remote.sun_path) + sizeof(remote.sun_family);
    if (connect(s, (struct sockaddr *)&remote, len) == -1) {
        perror("connect");
        exit(1);
    }

    printf("Connected.\n");
#if 0
    while(printf("> "), fgets(str, 100, stdin), !feof(stdin)) {
        if (send(s, str, strlen(str), 0) == -1) {
            perror("send");
            exit(1);
        }

        if ((t=recv(s, str, 100, 0)) > 0) {
            str[t] = '\0';
            printf("echo> %s", str);
        } else {
            if (t < 0) perror("recv");
            else printf("Server closed connection\n");
            exit(1);
        }
    }
#else
    if (send(s, hello, strlen(hello), 0) < 0)
	    printf("Send failed\n");
    else
	    printf("data sent\n");
#endif
    close(s);

    return 0;
}

unix_server.c

/*
 * Code borrowed from http://beej.us/guide/bgipc/output/html/multipage/unixsock.html
 */

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

#define SOCK_PATH "/tmp/unix.socket.ex"

int main(void)
{
	int s, s2, t, len;
	struct sockaddr_un local, remote;
	char str[100] = {0};
	struct pollfd pfd;

	if ((s = socket(AF_UNIX, SOCK_SEQPACKET | SOCK_CLOEXEC, 0)) == -1) {
		perror("socket");
		exit(1);
	}

	local.sun_family = AF_UNIX;
	strcpy(local.sun_path, SOCK_PATH);
	unlink(local.sun_path);
	len = strlen(local.sun_path) + sizeof(local.sun_family);
	if (bind(s, (struct sockaddr *)&local, len) == -1) {
		perror("bind");
		exit(1);
	}

	if (listen(s, 5) == -1) {
		perror("listen");
		exit(1);
	}

	for(;;) {
		int done, n;
		printf("Waiting for a connection...\n");
		t = sizeof(remote);
		if ((s2 = accept(s, (struct sockaddr *)&remote, &t)) == -1) {
			perror("accept");
			exit(1);
		}

		printf("Connected.\n");

		done = 0;
		do {
			int rc;
			printf("Sleeping for 5 seconds, connect the client and exit from client\n");
			sleep(5);
			pfd.fd = s2;
		        pfd.events = POLLIN;
			rc = poll(&pfd, 1, 15000);
			if (!rc) printf("poll timed out\n");
			if (rc < 0) printf("poll failed\n");
			printf("events: 0x%x\n", pfd.revents);
			if (pfd.revents & POLLIN) {
				n = recv(s2, str, 100, MSG_PEEK);
				printf("There are %d bytes to be read\n", n);
			}

		//	printf("1000 seconds sleep before receive\n");
		//	sleep (1000);
			n = recv(s2, str, 100, 0);
			if (n <= 0) {
				if (n < 0) perror("recv");
				done = 1;
			}
			printf("data recvd: %s\n", str);
			break;

			if (!done)
				if (send(s2, str, n, 0) < 0) {
					perror("send");
					done = 1;
				}
		} while (!done);

		close(s2);
	}

	return 0;
}