Socket non blocking and socket size

socket_nonblocking.c

/* Author: Hugo Guiroux: http://hugoguiroux.blogspot.fr/ */
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <fcntl.h>
#include <string.h>
#include <errno.h>

int main()
{
	/*
	 * 1. Open socket
	 * 2. Set non clocking
	 * 3. do n write up to filling socket
	 * 4. do 10 read
	 * 5. fill up to 10 to check it works
	 * 6. close socket
	 */

	// 1
	int fds[2];

	if (socketpair(AF_UNIX, SOCK_STREAM, 0, fds) != 0) {
		perror("socketpair() failed");
		return -1;
	}
	// 2
	if (fcntl(fds[0], F_SETFL, O_NONBLOCK) != 0) {
		perror("fnctl() failed");
		return -1;
	}
	// 3
	ssize_t size;
	char c = 0;
	ssize_t ret;

	for (size = 0;; size++) {
		ret = write(fds[0], &c, 1);

		if (ret != 1) {
			printf
			    ("[expected]: write returning %zd, error = %s(%d)\n",
			     ret, strerror(errno), errno);
			break;
		}
	}

	printf("Found max size of socket is %zd\n", size);

	// 4
	for (int i = 0; i < 10; i++) {
		if (read(fds[1], &c, 1) != 1) {
			perror("read() error");
			return -1;
		}
	}

	// 5
	for (int i = 0; i < 10; i++) {
		if (write(fds[0], &c, 1) != 1) {
			perror("write() error");
			return -1;
		}
	}

	ret = write(fds[0], &c, 1);
	if (ret == 1) {
		printf
		    ("error while filling up again the socket, no error was raised !\n");
		return -1;
	}
	// 6
	close(fds[0]);
	close(fds[1]);

	return 0;
}