HTTP::payload

Here's the TCL documentation for the binary scan format:

http://tmml.sourceforge.net/doc/tcl/binary.html

I am no binary scan expert, so you may have to tinker with the formatString (the H10 on the binary scan command line). Give this a try. It loaded with no errors, but it has not been tested:

when HTTP_REQUEST {
    if { [HTTP::payload length] > 10 } {
    binary scan [HTTP::payload] H10 my_variable
    if { $my_variable contains "8100" } {
      use pool left
    } elseif { $my_variable contains "81FF" } {
        use pool right
    }
  }
}