Simple Linux DynDNS update client

dyndnsclient.c

// Based on http://coding.debuntu.org/c-linux-socket-programming-tcp-simple-http-client

#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <netdb.h>
#include <string.h>
#include <sys/types.h>
#include <netinet/in.h>
#include <netinet/tcp.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/select.h>
#include <sys/time.h>
#include <sys/un.h>


int create_tcp_socket();
char *get_ip(char *host);
char *build_get_query(char *host, char *page, char *auth);
void usage();

#define HOST ""
#define PAGE "/"
#define PORT 80
#define USERAGENT "Company - Device - 1.0"

int main(int argc, char **argv)
{
	struct sockaddr_in *remote;
	int sock;
	int tmpres;
	char *ip;
	char *get;
	char buf[BUFSIZ + 1];
	char *host;
	char *page;
	char *auth;

	if (argc == 1) {
		usage();
		exit(2);
	}
	host = argv[1];

	if (argc > 2) {
		page = argv[2];
	}
	else {
		page = PAGE;
	}

	if (argc > 3) {
		auth = argv[3];
	}

	sock = create_tcp_socket();
	ip = get_ip(host);
	fprintf(stderr, "IP is %s\n", ip);
	remote = (struct sockaddr_in *)malloc(sizeof(struct sockaddr_in *));
	remote->sin_family = AF_INET;
	tmpres = inet_pton(AF_INET, ip, (void *)(&(remote->sin_addr.s_addr)));
	if (tmpres < 0)
	{
		perror("Can't set remote->sin_addr.s_addr");
		exit(1);
	}
	else if (tmpres == 0)
	{
		fprintf(stderr, "%s is not a valid IP address\n", ip);
		exit(1);
	}
	remote->sin_port = htons(PORT);

	if (connect(sock, (struct sockaddr *)remote, sizeof(struct sockaddr)) < 0) {
		perror("Could not connect");
		exit(1);
	}
	get = build_get_query(host, page, auth);
	fprintf(stderr, "Query is:\n<<START>>\n%s<<END>>\n", get);

	//Send the query to the server
	int sent = 0;
	while (sent < strlen(get))
	{
		tmpres = send(sock, get + sent, strlen(get) - sent, 0);
		if (tmpres == -1) {
			perror("Can't send query");
			exit(1);
		}
		sent += tmpres;
	}
	//now it is time to receive the page
	memset(buf, 0, sizeof(buf));
	int htmlstart = 0;
	char * htmlcontent;
	while ((tmpres = recv(sock, buf, BUFSIZ, 0)) > 0) {
		if (htmlstart == 0)
		{
			/* Under certain conditions this will not work.
			* If the \r\n\r\n part is splitted into two messages
			* it will fail to detect the beginning of HTML content
			*/
			htmlcontent = strstr(buf, "\r\n\r\n");
			if (htmlcontent != NULL) {
				htmlstart = 1;
				htmlcontent += 4;
			}
		}
		else {
			htmlcontent = buf;
		}
		if (htmlstart) {
			fprintf(stdout, htmlcontent);
		}

		memset(buf, 0, tmpres);
	}
	if (tmpres < 0)
	{
		perror("Error receiving data");
	}
	free(get);
	free(remote);
	free(ip);
	close(sock);
	return 0;
}

void usage()
{
	fprintf(stderr, "USAGE: htmlget host [page]\n\
\thost: the website hostname. ex: coding.debuntu.org\n\
\tpage: the page to retrieve. ex: index.html, default: /\n");
}


int create_tcp_socket()
{
	int sock;
	if ((sock = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP)) < 0) {
		perror("Can't create TCP socket");
		exit(1);
	}
	return sock;
}


char *get_ip(char *host)
{
	struct hostent *hent;
	int iplen = 15; //XXX.XXX.XXX.XXX
	char *ip = (char *)malloc(iplen + 1);
	memset(ip, 0, iplen + 1);
	if ((hent = gethostbyname(host)) == NULL)
	{
		herror("Can't get IP");
		exit(1);
	}
	if (inet_ntop(AF_INET, (void *)hent->h_addr_list[0], ip, iplen) == NULL)
	{
		perror("Can't resolve host");
		exit(1);
	}
	return ip;
}

char *build_get_query(char *host, char *page, char *auth)
{
	char *query;
	char *getpage = page;
	char *tpl = "GET /%s HTTP/1.0\r\nHost: %s\r\nUser-Agent: %s\r\nAuthorization: Basic %s\r\n\r\n";
	if (getpage[0] == '/') {
		getpage = getpage + 1;
		fprintf(stderr, "Removing leading \"/\", converting %s to %s\n", page, getpage);
	}
	// -5 is to consider the %s %s %s in tpl and the ending \0
	query = (char *)malloc(strlen(host) + strlen(getpage) + strlen(USERAGENT) + strlen(tpl) - 5);
	sprintf(query, tpl, getpage, host, USERAGENT, auth);
	return query;
}

USAGE: htmlget host page auth
host: the website hostname. ex: members.dyndns.org
page: the page to retrieve. ex: nic/update?hostname=myhost.dyndns.org
auth: base64 encode of username:password