Homework SourseImplement a simple web browser that retrieves a web page usi
Implement a simple web browser that retrieves a web page using HTTP protocol. If the number of arguments is incorrect, then show usage and exit. Establish a TCP connection through socket to the specified port of the host. Compose a string consisting of the HTTP request. Send the request through the socket. Read and display the returned webpage. Usage: Web_browser host_name file_path port_number. All of this should be done in C and uses Linux.
Solution
#include <stdio.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#include <stdlib.h>
#include <netdb.h>
#include <string.h>
int create_tcp_socket();
char *get_ip(char *host);
char *build_get_query(char *host, char *page);
void usage();
#define HOST \"coding.debuntu.org\"
#define PAGE \"/\"
#define PORT 80
#define USERAGENT \"HTMLGET 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;
if(argc == 1){
usage();
exit(2);
}
host = argv[1];
if(argc > 2){
page = argv[2];
}else{
page = PAGE;
}
sock = create_tcp_socket();
ip = get_ip(host);
fprintf(stderr, \"IP is %s\ \", 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\ \", 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);
fprintf(stderr, \"Query is:\ <<START>>\ %s<<END>>\ \", 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 \ \ \ \ part is splitted into two messages
* it will fail to detect the beginning of HTML content
*/
htmlcontent = strstr(buf, \"\ \ \ \ \");
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]\ \\
\\thost: the website hostname. ex: coding.debuntu.org\ \\
\\tpage: the page to retrieve. ex: index.html, default: /\ \");
}
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 *query; char *getpage = page;
char *tpl = \"GET /%s HTTP/1.0\ \ Host: %s\ \ User-Agent: %s\ \ \ \ \";
if(getpage[0] == \'/\'){
getpage = getpage + 1;
fprintf(stderr,\"Removing leading \\\"/\\\", converting %s to %s\ \", 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);
return query;
}
