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Getting a file from another host in C

Posted on 1997-08-10
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Last Modified: 2013-12-23
I want that my C program reads a file located in another host,  passing it  the URL location as parameter.
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Question by:gambito042797
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6 Comments
 
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Expert Comment

by:pxh
ID: 1582231
What server function does the other host have?
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Author Comment

by:gambito042797
ID: 1582232
I need the necesary instructions to make my program behaves as does a browser. For example, if you type in a browser http://www.host.xxx/path/filename.gif, then you get in the browser that file, wathever SO and functions the server you adressed has, well, that server must have a Web Server serving those files. I think this must be done by doing that my program send a CGI request such as

GET /docX.html HTTP/1.0
Accept: www/source
Accept: text/html
Accept: image/gif
User-Agent:  Lynx/2.2  libwww/2.14
From:  myname@myhost.xxx
     * blank line *

and then the program must receive an answer from the server similar to this one:

HTTP/1.0 200 OK
Date: Monday, 02-Feb-96 23:04:12 GMT
Server: NCSA/1.1
MIME-version: 1.0
Last-modified: Monday, 15-May-96 23:33:16 GMT
Content-type: text/html
Content-length: 2345
     * blank line *
<HTML><HEAD><TITLE> . . . the HTML page


I do know how to implement the server CGI part, but what I want is to implement the client behavior in my program (not a full browser, only be able to get a file from another server), that is, how does my program has to send the request and how does it has to wait for the answer.


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LVL 5

Expert Comment

by:julio011597
ID: 1582233
This just involves a bit of socket programming - it's like a client which telnets to port 80 of a server machine.

But, are you aware that, when a web server sends, say, an image, it usually sends it encoded?

-julio
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Author Comment

by:gambito042797
ID: 1582234
Yes, I've put above the encoding. The difference in image files is the line Content-type that will be:

Content-type: image/gif

and after the blank line will come the binary data of the file instead of the code for an html page. But thanks.
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Accepted Solution

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julio011597 earned 800 total points
ID: 1582235
Ok, i'll give you the code.

It should be easy to customize, but feel free to add comments if you need any clarifications.


-//--
/* url_get: get an url from a web server (port 80) */
/* Please, check the include files on your platform */

#include <stdlib.h>
#include <stdio.h>
#include <string.h>     /* bzero() and bcopy() */
#include <netdb.h>      /* gethostbyname() */
#include <sys/socket.h> /* socket() and connect() */
#include <arpa/inet.h>  /* htons() */
#include <sys/errno.h>  /* errno */

int main(void)
{
  /* this are the parameters */
  /* in case you need to make this a function */
  FILE *answer = stdout;
  char host[] = "www.experts-exchange.com";
  char url[] = "/";
  char err_str[80];

  int sock;
  struct hostent *hep;
  struct sockaddr_in sai;
  FILE *infile, *outfile;
  char buff[BUFSIZ];

  if(!(hep = gethostbyname(host))) {
    strcpy(err_str, "gethostbyname error");
    return errno;
  }
  if((sock = socket(AF_INET, SOCK_STREAM, 0)) == -1) {
    strcpy(err_str, "socket error");
    return errno;
  }

  bzero((char *)&sai, sizeof(struct sockaddr_in));
  sai.sin_family = AF_INET;
  sai.sin_port = htons((unsigned short)80);
  bcopy(hep->h_addr, (char *)&(sai.sin_addr.s_addr), hep->h_length); /* note: could just be 'sai.sin_addr' */

  if(connect(sock, (struct sockaddr *)&sai, sizeof(sai)) == -1) {
    strcpy(err_str, "connect error");
    return errno;
  }

  if(!(infile = fdopen(sock, "r"))) {
    strcpy(err_str, "fdopen(in) error");
    return errno;
  }
  if(!(outfile = fdopen(sock, "w"))) {
    strcpy(err_str, "fdopen(out) error");
    return errno;
  }

  fprintf(outfile, "GET %s HTTP1.0\n\n", url);
  fflush(outfile);

  while(fgets(buff, BUFSIZ, infile)) fputs(buff, answer);
  fflush(answer);

  fclose(infile); fclose(outfile);
  close(sock);

  return EXIT_SUCCESS;
}
--//--

As you may see, this is a self standing program, so that you may check it from the command line.

Just, remember to compile it first ;)

Cheers, julio
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Author Comment

by:gambito042797
ID: 1582236
It worked!!!  I changed  the host and the path and worked fine.
Thanks a lot Julio.
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