Simple echo server: Refactor #1: Move the socket setup code into its own function.

echo-server-1.c

/**
 * Simple echo server
 *
 * This program listens for connections on the
 * loopback interface, on port 9999. Upon connecting,
 * The first line we read, of up to BUF_LEN bytes, is
 * then sent back to the sender, and the connection
 * is closed.
 *
 * Refactor #1 - Move socket creation code into its own
 * function.
 *
 */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>

#define BUF_LEN 25
static char buf[BUF_LEN + 1];

/**
 * Create a socket which will be listening for connections
 * on localhost:9999.
 */
int setup_socket()
{
	int fd, i=1;
	struct sockaddr_in sa;

	/* Open a TCP socket */
	if ((fd = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
		perror("socket");
		return -1;
	}

	/* Let's ensure we can reuse our address */
	setsockopt(fd, SOL_SOCKET, SO_REUSEADDR, &i, sizeof(int));

	/* This will bind to localhost:9999 */
	memset(&sa, 0, sizeof(sa));
	sa.sin_family      = AF_INET;
	sa.sin_port        = htons(9999);
	sa.sin_addr.s_addr = htonl(INADDR_LOOPBACK);

	if (bind(fd, (struct sockaddr *)&sa, sizeof(sa)) < 0) {
		perror("bind");
		close(fd);
		return -1;
	}

	/* Listen for one connection at a time */
	if (listen(fd, 1) < 0) {
		perror("listen");
		close(fd);
		return -1;
	}

	return fd;
}

int main(int argc, char *argv[])
{
	int fd, c_fd = 0, i;
	unsigned int bytes_read = 0;

	if ((fd = setup_socket()) < 0)
		return EXIT_FAILURE;

	while (1) {
		/* Initialize our state variables and wait for connections */
		c_fd = 0;
		bytes_read = 0;
		memset(buf, 0, BUF_LEN+1);

		if ((c_fd = accept(fd, NULL, NULL)) < 0) {
			perror("accept");
			break;
		}

		/* We've got a live one. */
		printf("Got connection\n");

		/**
		 * Read data until the buffer is full, we get an EOF, or
		 * we've read a '\n'.
		 */
		while (bytes_read < BUF_LEN) {
			i = recv(c_fd, buf + bytes_read, BUF_LEN - bytes_read, 0);
			if (!i) break;

			if (i < 0) {
				if (errno == EINTR)
					continue;
				perror("recv");
				close(c_fd);
				break;
			}

			bytes_read += i;
			if (strchr(buf, '\n')) break;
		}

		/* Echo data if we got it */
		if (bytes_read) {
			buf[bytes_read + 1] = 0;
			printf("Read: %s\n", buf);

			if (send(c_fd, buf, bytes_read, 0) < 0)
				perror("send");
		}

		/* Kill this one, and wait for the next victim... */
		close(c_fd);
	}

	if (c_fd) close(c_fd);
	close(fd);
	return EXIT_SUCCESS;
}