Question

Server is linux. I am having inexplicable problems when I send POST data to the script.

For example, I send the following POST data: choice=update

Here is the script:

#!/usr/bin/perl -w

print "Content-type: text/html\n\n";


  if ( $ENV{'REQUEST_METHOD'} eq "GET" ) {
    $in = $ENV{'QUERY_STRING'};
  } elsif ($ENV{'REQUEST_METHOD'} eq "POST") {
    read(STDIN,$in,$ENV{'CONTENT_LENGTH'});
  }
  @in = split(/&/,$in);

  foreach $i (0 .. $#in) {
    # Convert plus's to spaces
    $in[$i] =~ s/\+/ /g;

    # Split into key and value.
    ($key, $val) = split(/=/,$in[$i],2); # splits on the first =.

    # Convert %XX from hex numbers to alphanumeric
    $key =~ s/%(..)/pack("c",hex($1))/ge;
    $val =~ s/%(..)/pack("c",hex($1))/ge;

    # Associate key and value
    $in{$key} .= "\0" if (defined($in{$key})); # \0 is the multiple separator
    $in{$key} .= $val;
  }

print $in{'choice'};

The first time I access the script, it prints update
The second time I access it, it prints updateupdate
The third time, it prints updateupdateupdate
…and so on.

What on earth could be causing it to keep appending the string to itself between requests? I am sending exactly the same POST data every time by simply refreshing with my browser. Cookies are not being used. There is nothing else in the file that is not commented out.

Edit: Also, when I print <STDIN> it says choice=update every time. The other updates don’t appear to be added to STDIN

Answer 1

My guess is that the script is kept running between requests. As %in is a global variable it is never cleared, so that $in{$key} .= $value ends up making the string longer and longer. You can probably evade the problem by using lexical variables.

This means you’ll need to find out how the script is being run by the web server.

You’ll also want to look at using modules to do all this parsing work for you, and learn about ways to write perl code avoid the problem you’ve encountered. I’d suggest taking a look at Modern Perl and working from there.