dns-suite.js/parser/type.TEMPLATE.js

// (function (exports) {
'use strict';

// Put some documentation here in these comments.
// See examples of documentation in parser/type.a.js
// and parser/type.mx.js

// If the data type you're wanting to unpack contains labels
// (meaning text that will be represented as a period-separated
// domain name, i.e. www.google.com) then you will need to use
// `unpackLabels`, which has compression pointer support
var unpackLabels = exports.DNS_UNPACK_LABELS || require('../dns.unpack-labels.js').DNS_UNPACK_LABELS;

// The parser receives exactly 3 parameters as follows:
//
// ab     - an ArrayBuffer containing the whole of the packet as binary
//          you will use Uint8Array (for which endianness doesn't matter)
//          and DataView (with wich you MUST always specify 'false' for
//          Big Endian, which is "network byte order")
//
// packet - a plain javascript value object (i.e. to/from JSON) that
//          has all of the currently parsed fields (generally not used),
//          containing meta data in `header`, and arrays of potentially
//          parsed (or not yet parsed) records in `question`, `answer`,
//          `authority`, `additional`
//
// record - an element of an array in packet (meaning one of `question`,
//          `answer`, `authority`, `additional`) which has potentially
//          helpful data about the record such as `rdstart` and `rdlength`,
//          signifying the type at which the binary segment for this record
//          begins and its length
//
exports.DNS_PARSER_TYPE_MX = function (ab, packet, record) {
  //
  // Slicing RData
  //

  // For various reasons it may be easier to work with a slice of the
  // ArrayBuffer container the binary packet that just represents the
  // RData you want to work with starting at 0 and ending at the end of
  // the Resource Record (aka RData) rather than always adding `rdstart`
  // to some offset and checking that you don't read past the record's
  // end (`rdstart + rdlength`)
  var rdataAb = ab.slice(record.rdstart, record.rdstart + record.rdlength);



  //
  // Using Uint8Array
  //

  // it's very likely that you'll want to process individual bytes,
  // for which you would use Uint8Array - for example, if some significant
  // portion of the record is to be read as a non-label string
  var ui8 = new Uint8Array(rdataAb);

  // Example: reading a string whose length is defined by the first byte
  var len = ui8[0];
  var i;
  record.value = '';
  for (i = 0; i < len; i += 1) {
    record.value += String.fromCharCode(ui8[i]);
  }

  // Example: reading a string whose length is terminated with 0
  var i;
  record.value = '';
  for (i = 0; i < len; i += 1) {
    if (0 === ui8[i]) {
      break;
    }
    record.value += String.fromCharCode(ui8[i]);
  }



  //
  // Using DataView
  //

  // it's also very likely that you'll want to interpret some variable
  // byte-width data, such as an id or type number, something of that nature
  var dv = new DataView(rdataAb);

  // Example: reading a single-octet type, a sexdectet id, and quad-octet date
  record.rtype  = dv.getUint8(0, false);                    // start at 0
  record.rid    = dv.getUint16(1, false);                   // next is at 1
  record.date   = new Date(dv.getUint32(3, false) * 1000);  // advance 2 more bytes to 3
                                                        // the next read, if any, would be at 7



  //
  // Unpacking Labels
  //

  // if your data type contains labels (i.e. www.google.com would be represented
  // as 3 labels and would have the byte sequence 0x03"www"0x06"google"0x03"com),
  // they may contain compression pointers (represented as 0xc0, meaning 192 in
  // decimal - outside the ascii range) and they may be terminated either by 0x00
  // or by the end of the record, so you should use unpackLabels and provide an
  // ArrayBuffer that is sliced to the end of your record (otherwise record-length
  // terminated strings would be misinterpretted overflow)

  // Example: assuming some label started at the 7th byte
  var truncatedAb = new Uint8Array(ab.slice(0, record.rdstart + record.rdlength));
  var labelData = unpackLabels(truncatedAb, record.rdstart+7, { byteLength: 0, cpcount: 0, labels: [], name: '' });
  record.deviceName = labelData.name;



  // finally, return the record
  return record;
};

// }('undefined' !== typeof window ? window : exports));