old school

cgilib.pl

sub cgiReadInput {
    if ($ENV{'REQUEST_METHOD'} eq 'POST') {
        read(STDIN, $query_string, $ENV{'CONTENT_LENGTH'});
    }

    if ($ENV{'REQUEST_METHOD'} eq 'GET') {
        $query_string = $ENV{'QUERY_STRING'};
    }

    @pairs = split(/&/, $query_string);

    foreach $field(@pairs) {
        ($name, $value) = split(/=/, $field);
        $name = &strURLDecode($name);
        $value = &strURLDecode($value);
        $FORM{$name} = $value;
    }

    $cookie_string = $ENV{'HTTP_COOKIE'};
    @pairs = split(/; /, $cookie_string);

    foreach $field(@pairs) {
        ($name, $value) = split(/=/, $field);
        $name = &strURLDecode($name);
        $value = &strURLDecode($value);
        $COOKIE{$name} = $value;
    }
}

sub strURLEncode {
    $str = '';

    for ($i = 0; $i < length($_[0]); $i++) {
        $tok = substr($_[0], $i, 1);

        if ($tok =~ /[ 0-9A-Za-z@.]/) {
            if ($tok =~ / /) { 
                $str .= "+"; 
            } else { 
                $str .= $tok; 
            }
        } else {
            $str .= "%";
            $str .= sprintf("%02X", ord($tok));
        }
    }

    $str;
}

sub strURLDecode {
    $str = $_[0];
    $str =~ tr/+/ /;	 
    $str =~ s/%([A-F0-9][A-F0-9])/pack("C", hex($1))/egi;
    $str;
}

sub cgiSetCookie {
    $name = $_[0];
    $value = $_[1];
    $name = &strURLEncode($name);
    $value = &strURLEncode($value); 
    print "Set-Cookie: $name=$value;\n";

}

return 1;

compile.sh

$ gcc write.c cgic.c -o write.cgi

parse_arguments.cgi

sub parse_arguments {
  local($pair, $name, $value, $content_type, $content_length, $buffer, $dump, $boundary, $line, $array_value, $i);
  local(@pairs, @column);

  if ($ENV{'QUERY_STRING'}) {
    @pairs = split(/&/, $ENV{'QUERY_STRING'});

    foreach $pair (@pairs) {
      ($name, $value) = split(/=/, $pair);

      $value =~ tr/+/ /;
      $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",hex($1))/eg;

      if ($name eq 'head' || $name eq 'foot') {
        $value =~ s/\n/\\n/g ;
        $value =~ s/\n/\\n/g ;
      } elsif ($name ne 'profile') {
        $value =~ s/\n//g ;
      }

      $FORM{$name} = $value;
    }
  } else {
    $content_type = $ENV{'CONTENT_TYPE'};
    $content_length = $ENV{'CONTENT_LENGTH'};

    binmode STDIN;
    read(STDIN,$buffer,$content_length);

    if ((!$content_type) || ($content_type eq 'application/x-www-form-urlencoded')) {
      @pairs = split(/&/, $buffer);

      foreach $pair (@pairs)  {
        ($name, $value) = split(/=/,$pair);

        $value =~ tr/+/ /;
        $value =~ s/%([a-fA-F0-9][a-fA-F0-9])/pack("C",hex($1))/eg;
        $value =~ s/\n//g unless ($name eq 'body');

        $FORM{$name} = $value;
      }
    } elsif ($content_type =~ m#^multipart/form-data#) {
      ($boundary = $content_type) =~ s/^.*boundary=(.*)$/\1/;
      @pairs = split(/--$boundary/, $buffer);
      @pairs = splice(@pairs,1,$#pairs-1);

      $i = 0;
      for $pair (@pairs)  {
        ($dump,$line,$value) = split(/\r\n/,$pair,3);
        if ($line =~ /filename/) {
          $gRealFile[$i++] = $line;
        }

        next if $line =~ /filename=\"\"/;

        $line =~ s/^Content-Disposition: form-data; //;
        (@column) = split(/;\s+/, $line);
        ($name = $column[0]) =~ s/^name="([^"]+)"$/\1/g;

        if ($#column > 0) {
          if($value =~ /^Content-Type:/)  {
            ($dump,$dump,$value) = split(/\r\n/,$value,3);
          } else {
            ($dump,$value) = split(/\r\n/,$value,2);
          }
        } else {
          ($dump,$value) = split(/\r\n/,$value,2);
          if (grep(/^$name$/, keys(%CGI))) {
            if (@{$FORM{$name}} > 0) {
              push(@{$FORM{$name}}, $value);
            } else {
              $array_value = $FORM{$name};
              undef $FORM{$name};
              $FORM{$name}[0] = $array_value;
              push(@{$FORM{$name}}, $value);
            }
          } else {
            next if $value =~ /^\s*$/;

            $FORM{$name} = $value;
            chop($FORM{$name});
            chop($FORM{$name});
          }
          next;
        }
                
        $FORM{$name} = $value;
      }
    } else {
      print "Invalid content type!\n";
      exit(1);
    }
  }
}

write.c

#include "cgic.h"

#define MAX_LEN 255

int str_check(char *str) {
    if (str === NULL) {
        return 0;
    }

    if (strlen(str) === 0) {
        return 0;
    }

    return 1;
}

void cgi_error_message(char *msg) {
    cgiHeaderContentType("text/plain");
    printf("%s", msg);
    exit(1);
}

int cgi_main(void) {
    char name[MAX_LEN], title[MAX_LEN], doc[MAX_LEN], email[MAX_LEN], homepage[MAX_LEN];

    cgiFormString("writer", name, MAX_LEN);
    cgiFormString("title", title, MAX_LEN);
    cgiFormString("doc", doc, MAX_LEN);
    cgiFormString("email", email, MAX_LEN);
    cgiFormString("homepage", homepage, MAX_LEN);

    if (! str_check(name)) {
        cgi_error_message("Please provide you name");
    }

    if (! str_check(title)) {
        cgi_error_message("Please provide a title");
    }

    if (! str_check(doc)) {
        cgi_error_message("Please provide post contents");
    }

    cgiHeaderContentType("text/html");

    printf("<html>\n");
    printf("<head><title>GuestBook</title></head>\n");
    printf("<body>\n");
    printf("<h2>GuestBook</h2>\n");
    printf("<hr>\n");

    printf("<p>\n");
    if (str_check(email)) {
        printf("<a href=\"mailto:%s\">%s</a>\n", email, name);
    } else {
        printf("%s\n", name);
    }

    if (str_check(homepage)) {
        printf("<small><a href=\"%s\">%s</small>\n", homepage, homepage);
    }
    printf("</p>\n");

    printf("<p>What you wrote is:</p>\n")

    printf("<table border=\"1\">\n");
    printf("<tr>\n");
    printf("<td><b>Title</b> : %s</td>\n", title);
    printf("</tr>\n");
    printf("<tr>\n");
    printf("<td>%s</td>\n", doc);
    printf("</tr>\n");
    printf("</table>\n");

    printf("<p>Your post has been saved !</p>\n");

    printf("</body>\n");
    printf("</html>");
}