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Retrieving remote file information

Posted on 1997-07-07
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Last Modified: 2013-12-25
Is it possible to use PERL and/or CGI to query a remote server to retrieve file information?  Basically, I am looking to get the date created or last modified date of files on different servers.  If it is possible to do this, how is it done (please provide code if possible).  What information can you retrieve about remote files on servers you access anonymously?  Thanks for your assistance.  
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Question by:mtob
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julio011597 earned 400 total points
ID: 1828904
Sure, i'll give a ready routine to get file informations through use of the web server's HEAD method.

You can embedd this routine anywhere you need; just pass it the right parameters - this means you could put it into a program to invoke from the shell, or into a CGI.

Please check function return types and include files on your OS, since there may be slight differences.

--//--
#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 <errno.h>      /* errno */

#define PORT 80

/* get_url()
 * answer: file to write to (must be already open for writing - it may be stdin)
 * host: e.g. "www.experts-exchange.com"
 * url : e.g. "/topics/comp/lang/c"
 * err_str: to eventually store an error message
 *
 * returns 0 if succesful, errno otherwise
 */

int get_url(FILE *answer, const char *host, const char *url, char err_str[])
{
  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)PORT);
  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;
  }

  /* fine: now we are connected */
  /* let's work with stdio */
  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;
  }

  /* now, the query: i'll leave error checking now on! */
  fprintf(outfile, "HEAD %s HTTP1.0\n", url);
  fflush(outfile); /* this is mandatory: outfile would buffer */

  while(fgets(buff, BUFSIZ, infile)) fputs(buff, answer);
  fflush(answer); /* this is not mandatory:) */

  /* cleanup */
  /* note: the two fclose's are also mandatory: */
  /* the file tables are not automagically deallocated */
  /* if you just close the socket (at least on my system), */
  /* and you could go out of resources if you loop */
  /* to connect to more than one site */
  fclose(infile); fclose(outfile);
  close(sock);

  return 0;
}
--//--

Cheers, julio

P.S. maybe this is worth more than 100 points...
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Author Comment

by:mtob
ID: 1828905
You're right, it was worth more.  Thank you very much.  If you could help though, is there a PERL way of doing it.  I can do it through C if I have to but would much rather through PERL.
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