Help with iRule

Okay, so basically it looks like this. Let's assume the incoming URI is /pool1/foo/bar and the virtual server is test_vs.

when HTTP_REQUEST priority 100 {
    set poolId [string range [HTTP::uri] 1 [expr [string first "/" [HTTP::uri] 1]-1]]
     This grabs the first part of the URI ("pool1") and assigns it to a variable. So string range, starting at the second character (/ is 0), and stopping at the first occurrence of "/".

    set poolIdLen [string length $poolId]
     This sets the length of the above string, in this case 5.

    set newUri "[string range [HTTP::uri] [expr $poolIdLen+1] end]"
     This grabs everything after the first section (/foo/bar), which will become the new URI that gets passed to the application. So string range, starting at character 6 (5 + 1), going all the way to the end.

    set uriPoolMapClass "[string range [virtual name] 0 end-2]uri_pool_map_class"
     This creates a string based on the virtual server name (test_vs), minus the last two characters in the name (so "test_"), then appends that to the string "uri_pool_map_class", which should in this case derive the string "test_uri_pool_map_class". Presumably there's a data group named this, and inside the data group is a key-value pair, where the key is the poolId value and the value is the actual pool name.

    set dstPool [class lookup [string tolower $poolId] $uriPoolMapClass]
     This grabs the real pool name from the data group based on the poolId value passed in the URI.

    if {$dstPool ne ""} {
         Hash out next line to disable logging
         log local0.debug "poolId: $poolId | poolIdLen: $poolIdLen | newUri: $newUri | dgl_name: $uriPoolMapClass dstPool: $dstPool"
        HTTP::uri $newUri
        pool $dstPool
         Assuming there's a data group match, change the inbound URI to the server to newURI value (/foo/bar), and pool to the matched pool name.

    } else {
         Hash out next line to disable logging
         log local0.debug "poolId: $poolId | poolIdLen: $poolIdLen | newUri: $newUri | no pool set"
         TODO this needs to be changed to reject if there isn't another iRule which ends in a deny_all
        return
         Otherwise just use the pool that's assigned to the VIP.

    }
}

The whole point of this iRule is to allow an application to dictate which pool to send traffic to by injecting the pool into the URL.