/****************************************************************************
 * netutils/thttpd/cgi-src/redirect.c
 * Simple redirection CGI program
 *
 *   Copyright (C) 2009 Gregory Nutt. All rights reserved.
 *   Author: Gregory Nutt <spudmonkey@racsa.co.cr>
 *
 * Derived from the file of the same name in the original THTTPD package:
 *
 *   Copyright © 1995 by Jef Poskanzer <jef@mail.acme.com>.
 *   All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 *
 ****************************************************************************/

/* Three steps to set up a redirection:
 *
 *  1. Make sure your web server is set up to allow CGI programs.
 *  2. Make a symbolic link from the file you want to redirect,
 *     pointing at this program in the CGI bin directory.
 *  3. Add an entry to the file ".redirects" in the directory where your
 *     http server runs CGI programs.  For most servers, this is the
 *     directory where the given CGI program lives.  The format of the
 *     file is a bunch of lines with a filename, whitespace, and the new
 *     URL.  For example:
 *
 *     /test/oldfile.html    http://www.acme.com/test/newfile.html
 *
 *     The easiest way to figure out precisely what filename to put into
 *     .redirects is to set up the symlink and then click on it.  You'll get
 *     back a "404 Not Found" page which includes the filename as received by
 *     the redirect program, and that's what you want to use.
 *
 * Note: this is designed for thttpd (http://www.acme.com/software/thttpd/)
 * and using it with other web servers may require some hacking.  A possible
 * gotcha is with the symbolic link from the old file pointing at this
 * script - servers other than thttpd may not allow that link to be run
 * as a CGI program, because they don't check the link to see that it
 * points into the allowed CGI directory.
 *
 * Note two: It would be really cool to have this program look for
 * the .redirects file in the same directory as the file being redirected,
 * instead of in the binaries directory.  Unfortunately, this appears
 * to be impossible with the information CGI gives, plus the non-standardized
 * but widespread practice of running CGI programs in the directory where
 * the binary lives.  Perhaps CGI 1.2 will address this.
 */

/****************************************************************************
 * Public Functions
 ****************************************************************************/

#include <sys/types.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>

#include "config.h"

/****************************************************************************
 * Pre-Processor Definitions
 ****************************************************************************/

#define LINE_SIZE 80

/****************************************************************************
 * Private Data
 ****************************************************************************/

static char g_iobuffer[LINE_SIZE];
static char g_file[LINE_SIZE];
static char g_url[LINE_SIZE];

/****************************************************************************
 * Private Functions
 ****************************************************************************/

static void internal_error(FILE *outstream, char *reason)
{
  char *title = "500 Internal Error";

  (void)fprintf(outstream,
"\
Status: %s\n\
Content-type: text/html\n\
\n\
<HTML><HEAD><TITLE>%s</TITLE></HEAD>\n\
<BODY><H2>%s</H2>\n\
Something unusual went wrong during a redirection request:\n\
<BLOCKQUOTE>\n\
%s\n\
</BLOCKQUOTE>\n\
</BODY></HTML>\n", title, title, title, reason);
}

static void not_found(FILE *outstream, char *script_name)
{
  char *title = "404 Not Found";

  (void)fprintf(outstream,
"\
Status: %s\n\
Content-type: text/html\n\
\n\
<HTML><HEAD><TITLE>%s</TITLE></HEAD>\n\
<BODY><H2>%s</H2>\n\
The requested filename, %s, is set up to be redirected to another URL;\n\
however, the new URL has not yet been specified.\n\
</BODY></HTML>\n", title, title, title, script_name);
}

static void moved(FILE *outstream, char *script_name, char *url)
{
  char *title = "Moved";

  (void)fprintf(outstream,
"\
Location: %s\n\
Content-type: text/html\n\
\n\
<HTML><HEAD><TITLE>%s</TITLE></HEAD>\n\
<BODY><H2>%s</H2>\n\
The requested filename, %s, has moved to a new URL:\n\
<A HREF=\"%s\">%s</A>.\n\
</BODY></HTML>\n", url, title, title, script_name, url, url);
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

int main(int argc, char **argv)
{
  FILE *outstream;
  char *script_name;
  char *path_info;
  char *cp = 0;
  FILE *fp;
  char *star;
  int  err = 0;

  outstream = fdopen(CONFIG_THTTPD_CGI_OUTFD, "w");
  if (!outstream)
    {
      fprintf(stderr, "fdopen failed: %d\n", errno);
      err = 1;
      goto errout;
    }

  /* Get the name that we were run as, which is the filename being **
   * redirected.
   */

  script_name = getenv("SCRIPT_NAME");
  if (!script_name)
    {
      internal_error(outstream, "Couldn't get SCRIPT_NAME environment variable.");
      err = 2;
      goto errout_with_outstream;
    }

  /* Append the PATH_INFO, if any.  This allows redirection of whole **
   * directories.
   */

  path_info = getenv("PATH_INFO");
  if (path_info)
    {
      cp = (char *)malloc(strlen(script_name) + strlen(path_info) + 1);
      if (!cp)
        {
          internal_error(outstream, "Out of memory.");
          err = 3;
          goto errout_with_outstream;
        }

      (void)sprintf(cp, "%s%s", script_name, path_info);
      script_name = cp;
    }

  /* Open the redirects file. */

  fp = fopen(".redirects", "r");
  if (fp == (FILE *) 0)
    {
      internal_error(outstream, "Couldn't open .redirects file.");
      err = 4;
      goto errout_with_cp;
    }

  /* Search the file for a matching entry. */

  while (fgets(g_iobuffer, LINE_SIZE, fp) != NULL)
    {
      /* Remove comments. */

      cp = strchr(g_iobuffer, '#');
      if (cp)
        {
          *cp = '\0';
        }

      /* Skip leading whitespace. */

      cp = g_iobuffer;
      cp += strspn(cp, " \t");

      /* Check for blank line. */

      if (*cp != '\0')
        {
          /* Parse line. */

          if (sscanf(cp, "%[^ \t\n] %[^ \t\n]", g_file, g_url) == 2)
            {
              /* Check for wildcard match. */

              star = strchr(g_file, '*');
              if (star != (char *)0)
                {
                  /* Check for leading match. */

                  if (strncmp(g_file, script_name, star - g_file) == 0)
                    {
                      /* Got it; put together the full name. */

                      strcat(g_url, script_name + (star - g_file));

                      /* XXX Whack the script_name, too? */

                      moved(outstream, script_name, g_url);
                      goto success_out;
                    }
                }

              /* Check for exact match. */

              if (strcmp(g_file, script_name) == 0)
                {
                  /* Got it. */

                  moved(outstream, script_name, g_url);
                  goto success_out;
                }
            }
        }
    }

  /* No match found. */

  not_found(outstream, script_name);
  err = 5;

success_out:
  fclose(fp);
errout_with_cp:
  if (cp)
    {
      free(cp);
    }
errout_with_outstream:
  fclose(outstream);
errout:
  return err;
}