C Program To Download File From Http Server

#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\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);

  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 = NULL;

  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, "%s", htmlcontent);

    }

    memset(buf, 0X0, 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 *query;

  char *getpage = page;

  char *tpl = "GET /%s HTTP/1.0\r\nHost: %s\r\nUser-Agent: %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);

  return query;

}