TCP::payload

Description

Returns the accumulated TCP data content, or replaces collected payload with the specified data.

Syntax

TCP::payload [<size>]
TCP::payload replace <offset> <length> <data>
TCP::payload length

TCP::payload [<size>]

  • Returns the accumulated TCP data content. If <size> is specified, and more than <size> bytes are available, only the first <size> bytes of collected data are returned.

TCP::payload replace <offset> <length> <data>

  • Replaces <length> bytes of the collected payload data starting at <offset> with the given <data>.

TCP::payload length

  • Returns the amount of accumulated TCP data content in bytes.

Note: Currently, iRules usually treats binary data in TCL variables as UTF-8 strings. Therefore, care must be taken when processing binary TCP payloads. In particular, do not assign the result of TCP::payload to a variable if non-text data should be processed literally. See the third example below for a way to do a binary search-and-replace in a TCP::payload. TCL variables explicitly created as binary data (e.g. via the binary format command) are not treated as UTF-8 strings. There is an outstanding enhancement request (tracked as CR47762 / BZ273220) to treat TCL variables as binary data (rather than UTF-8 strings) as appropriate.

Examples

when CLIENT_ACCEPTED {
  TCP::collect 15
}
when CLIENT_DATA {
  if { [TCP::payload 15] contains "XYZ" } {
     pool xyz_servers
  } else {
     pool web_servers
 }
 TCP::release
}


when CLIENT_ACCEPTED {
  TCP::collect
}
when CLIENT_DATA {
  # empty payload entirely so there is no packet to send to the server
  TCP::payload replace 0 [TCP::payload length] ""

  # craft a string to hold our  packet data, 0x01 0x00 0x00 0x00 0x02 0x00 0x00 0x00 0x03 0x00 0x00 0x00
  set packetdata [binary format i1i1i1 1 2 3 ]

  # then fill payload with our own data from arbitrary length string called packetdata to send to the server
  # this actually inserts it at the start of the packet, but because we emptied the packet above it becomes the new packet
  TCP::payload replace 0 0 $packetdata

  # release the payload to the server
  TCP::release

  # set up to grab the next packet
  TCP::collect
}


when CLIENT_ACCEPTED {
  TCP::collect
}
when CLIENT_DATA {
  #
  # Do a regex search and replace of binary TCP data
  #
  if { [regexp -indices "\x61\x62\x63\x64\x65\x66" [TCP::payload] firstmatch] } {
    set matchlen [expr [lindex $firstmatch 1] - [lindex $firstmatch 0] + 1]
    set replacement [binary format c* {97 98 99 0 100 101 102}]
    TCP::payload replace [lindex $firstmatch 0] $matchlen $replacement
    TCP::release
  }
}