There are several TrafficScript functions that will help you to manage binary data. Here are some points that may help:

• Strings in TrafficScript can contain binary data as well as ascii text. They are not null terminated, or limited in size.

• You can use request.get( n ) to retrieve the first n bytes of the request data. Trafficscript Request rules are executed when ZXTM receives the first request data; if ZXTM has not received all n bytes, the request.get() function will block until the data is collected from the client.

  request.getline( (regex) ) can be used instead; it will happily parse binary data, so if you can identify the end of your request with a regular expression, this may be suitable.

• You can then use string.substring() to extract substrings from binary data.

• The following functions may help to parse binary strings:

  • lang.ord( str ) returns the value of the first byte in str
  • lang.chr( i ) returns a 1-byte string with the value 'i'
  • string.intToBytes() and string.bytesToInt() convert between network-order byte strings and integers; you can specify the width of the byte string.
  • string.BERToInt() and string.intToBER() converts variable length BER-encoded integers in byte strings to integers, and vice versa.

• You can assemble a binary string using:

  • string.replaceBytes() does an in-place replacement
  • string.insertBytes() does an insertion

• You can encode non-printable bytes in a string literal using octal
  escapes:

  $str = "\123\047\110\077";
  

There are also a range of functions that convert between different ASCII encodings of strings, such as hex, base64 and %-encoding, which may also be useful.

Example

Suppose that you have a protocol in which the request looks like the
following:

<2-byte msg length><msg>

You wish to add a header to the msg and update the length in a request rule:

<2 byte msg length2><header><msg>

The following TrafficScript rule will suffice:

# 1. calculate the length of the entire message:
$len_str = request.get( 2 );             # read the 2-byte length
$len = string.bytesToInt( $len_str, 2 ); # parse it

# 2. read the entire message
$msg = request.get( 2 + $len );

# 3. Insert the header just after the length
$msg = string.insertBytes( $msg, $header, 2 );

# 4. Update the length
$len = $len + string.len( $header );
$len_str = string.intToBytes( $len );
$msg = string.replaceBytes( $msg, $len_str, 0 );

# 5. Change the request data
request.set( $msg );

The various TrafficScript functions are documented in detail in the TrafficScript manual. You can download the most recent version of this manual from the Documentation part of this site.

Owen Garrett [Zeus Dev Team] 08 December 2005