Calculating a two byte header in message payload

Can you post your full iRule so we can understand exactly what you're asking? thanks

James

I would start by collecting only 2 bytes. Convert those from hex to decimal and then collect that number of bytes before you release.

when CLIENT_ACCEPTED {
   TCP::collect 2
   set header_collected "false"
}

when CLIENT_DATA {

   if { not ($header_collected) } {
       Comment out one of the two binary scan lines below.
       use this form if lower order byte is last (big endian order)
      binary scan [TCP::payload] S message_length
       use this form if lower order byte is first (little endian order)
      binary scan [TCP::payload] s message_length

      if { $message_length > 0 } {
         set header_collected "true"
         log local0. "Collecting message with length $message_length"
         TCP::collect $message_length
       }
    } else {
       if we are here the actual message is collected.
      set actual_message_text [TCP::payload]
      TCP::release
    }
 }

Feel free to post what you have and we take a look.

Examples of binary scan:

% binary scan \x02\x00 s var1
1
% puts $var1
2
% binary scan \x00\x03 S var1
1
% puts $var1
3
%

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

John

I had to enhance your code slightly as the payload messages are quite small and therefore client_data event was not getting triggered again as the LTM has already buffered the rest of the data. I have therefore now added a check to see if we already have the data or not and if we do TCP::release. I cannot see a more affiant way of doing this, what do you think?

when CLIENT_ACCEPTED {
    TCP::collect 2
    set header_collected "false"
    }
}
when CLIENT_DATA {

    if { not ($header_collected) } {
     Comment out one of the two binary scan lines below.
     use this form if lower order byte is last (big endian order)
    binary scan [TCP::payload] S message_length
     use this form if lower order byte is first (little endian order)
     binary scan [TCP::payload] s message_length

     as the message length collected does not include itself add 2 more onto the result
    set message_length [expr { $message_length + 2 }]

    if { $message_length > 0 } {
        set header_collected "true"
         collect data with the required length
        TCP::collect $message_length
         check if we already have the required data in the buffer if so 
         capture the payload in vars and release it
        if {[TCP::payload length] == $message_length } {
             set vars with payload info for HSL logging later
            set my_req_msg_payload [TCP::payload]
            set my_req_msg_length [TCP::payload length]
             release the data already collected
            TCP::release
        }
       }
    } else {
       if we are here the actual message is collected.
        set my_req_msg_payload [TCP::payload]
        set my_req_msg_length [TCP::payload length]
        TCP::release
    }
}

Good catch.

Your modification look great. Only a couple suggestions:

Here is what it would look like:

when CLIENT_ACCEPTED {
    TCP::collect 2
    set header_collected "false"
    }
}
when CLIENT_DATA {

    if { not ($header_collected) } {
     Comment out one of the two binary scan lines below.
     use this form if lower order byte is last (big endian order)
    binary scan [TCP::payload] S message_length
     use this form if lower order byte is first (little endian order)
     binary scan [TCP::payload] s message_length

     as the message length collected does not include itself add 2 more onto the result
    

    if { $message_length > 0 } {
        set header_collected "true"

         check if we already have the required data in the buffer if so 
         capture the payload in vars and release it
        if {[TCP::payload length] == [expr { $message_length + 2 }] } {
             set vars with payload info for HSL logging later
            set my_req_msg_payload [TCP::payload]
            set my_req_msg_length [TCP::payload length]
             release the data already collected
            TCP::release
        } else {
             collect data with the required length
            TCP::collect $message_length            
        }
       }
    } else {
       if we are here the actual message is collected.
        set my_req_msg_payload [TCP::payload]
        set my_req_msg_length [TCP::payload length]
        TCP::release
    }
}

if you are on 11.4 or above, here is a slight variation in order to demonstrate iRule procedures "proc".

proc save_n_let_it_go args {
         the args variable is ignored here 
        set my_req_msg_payload [TCP::payload]
        set my_req_msg_length [TCP::payload length]
         release the data already collected to be forwarded to destination.
        TCP::release
} 

when CLIENT_ACCEPTED {
    TCP::collect 2
    set header_collected "false"
    }
}
when CLIENT_DATA {

    if { not ($header_collected) } {
     Comment out one of the two binary scan lines below.
     use this form if lower order byte is last (big endian order)
    binary scan [TCP::payload] S message_length
     use this form if lower order byte is first (little endian order)
     binary scan [TCP::payload] s message_length

     as the message length collected does not include itself add 2 more onto the result
    

    if { $message_length > 0 } {
        set header_collected "true"

         check if we already have the required data in the buffer if so 
         capture the payload in vars and release it
        if {[TCP::payload length] == [expr { $message_length + 2 }] } {
             set vars with payload info for HSL logging later
            call save_n_let_it_go
        } else {
             collect data with the required length
            TCP::collect $message_length            
        }
       }
    } else {
       if we are here the actual message is collected.
      call save_n_let_it_go
    }
}