Simple echo server: Refactor #5: Reduce the depth of nesting in main().

echo-server-5.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.
 */
#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];

int main(int argc, char *argv[])
{
	int fd, c_fd = 0, i = 1;
	unsigned int bytes_read = 0;
	struct sockaddr_in sa;

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

	/* 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");
		goto done;
	}

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

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

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

	/* 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'.
	 */
readit:
	if ((i = recv(c_fd, buf + bytes_read, BUF_LEN - bytes_read, 0)) > 0) {
		bytes_read += i;
		if (bytes_read < BUF_LEN && !strchr(buf, '\n'))
			goto readit;
	}

	if (i < 0) {
		if (errno == EINTR)
			goto readit;
		perror("recv");
		goto next;
	}

	/* 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... */
next:
	close(c_fd);
	goto loop;

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