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7.3.12 Helper functions for TCP connections

Those helper function abstract away TCP connection handling from the other examples. It is required to build some examples.

/* This example code is placed in the public domain. */

#include <config.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <unistd.h>

/* tcp.c */
int tcp_connect(void);
void tcp_close(int sd);

/* Connects to the peer and returns a socket
 * descriptor.
extern int tcp_connect(void)
	const char *PORT = "5556";
	const char *SERVER = "";
	int err, sd;
	struct sockaddr_in sa;

	/* connects to server
	sd = socket(AF_INET, SOCK_STREAM, 0);

	memset(&sa, '\0', sizeof(sa));
	sa.sin_family = AF_INET;
	sa.sin_port = htons(atoi(PORT));
	inet_pton(AF_INET, SERVER, &sa.sin_addr);

	err = connect(sd, (struct sockaddr *)&sa, sizeof(sa));
	if (err < 0) {
		fprintf(stderr, "Connect error\n");

	return sd;

/* closes the given socket descriptor.
extern void tcp_close(int sd)
	shutdown(sd, SHUT_RDWR); /* no more receptions */