117 lines
4.3 KiB
JavaScript
117 lines
4.3 KiB
JavaScript
(function (exports) {
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'use strict';
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// Put some documentation here in these comments.
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// See examples of documentation in parser/type.a.js
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// and parser/type.mx.js
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// If the data type you're wanting to unpack contains labels
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// (meaning text that will be represented as a period-separated
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// domain name, i.e. www.google.com) then you will need to use
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// `unpackLabels`, which has compression pointer support
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var unpackLabels = exports.DNS_UNPACK_LABELS || require('../dns.unpack-labels.js').DNS_UNPACK_LABELS;
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// The parser receives exactly 3 parameters as follows:
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//
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// ab - an ArrayBuffer containing the whole of the packet as binary
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// you will use Uint8Array (for which endianness doesn't matter)
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// and DataView (with wich you MUST always specify 'false' for
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// Big Endian, which is "network byte order")
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//
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// packet - a plain javascript value object (i.e. to/from JSON) that
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// has all of the currently parsed fields (generally not used),
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// containing meta data in `header`, and arrays of potentially
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// parsed (or not yet parsed) records in `question`, `answer`,
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// `authority`, `additional`
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//
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// record - an element of an array in packet (meaning one of `question`,
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// `answer`, `authority`, `additional`) which has potentially
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// helpful data about the record such as `rdstart` and `rdlength`,
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// signifying the type at which the binary segment for this record
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// begins and its length
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//
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exports.DNS_PARSER_TYPE_MX = function (ab, packet, record) {
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//
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// Slicing RData
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//
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// For various reasons it may be easier to work with a slice of the
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// ArrayBuffer container the binary packet that just represents the
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// RData you want to work with starting at 0 and ending at the end of
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// the Resource Record (aka RData) rather than always adding `rdstart`
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// to some offset and checking that you don't read past the record's
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// end (`rdstart + rdlength`)
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var rdataAb = ab.slice(record.rdstart, record.rdstart + record.rdlength);
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//
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// Using Uint8Array
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//
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// it's very likely that you'll want to process individual bytes,
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// for which you would use Uint8Array - for example, if some significant
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// portion of the record is to be read as a non-label string
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var ui8 = new Uint8Array(rdataAb);
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// Example: reading a string whose length is defined by the first byte
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var len = ui8[0];
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var i;
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record.value = '';
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for (i = 0; i < len; i += 1) {
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record.value += String.fromCharCode(ui8[i]);
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}
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// Example: reading a string whose length is terminated with 0
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var i;
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record.value = '';
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for (i = 0; i < len; i += 1) {
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if (0 === ui8[i]) {
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break;
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}
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record.value += String.fromCharCode(ui8[i]);
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}
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//
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// Using DataView
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//
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// it's also very likely that you'll want to interpret some variable
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// byte-width data, such as an id or type number, something of that nature
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var dv = new DataView(rdataAb);
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// Example: reading a single-octet type, a sexdectet id, and quad-octet date
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record.rtype = dv.getUint8(0, false); // start at 0
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record.rid = dv.getUint16(1, false); // next is at 1
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record.date = new Date(dv.getUint32(3, false) * 1000); // advance 2 more bytes to 3
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// the next read, if any, would be at 7
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//
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// Unpacking Labels
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//
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// if your data type contains labels (i.e. www.google.com would be represented
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// as 3 labels and would have the byte sequence 0x03"www"0x06"google"0x03"com),
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// they may contain compression pointers (represented as 0xc0, meaning 192 in
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// decimal - outside the ascii range) and they may be terminated either by 0x00
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// or by the end of the record, so you should use unpackLabels and provide an
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// ArrayBuffer that is sliced to the end of your record (otherwise record-length
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// terminated strings would be misinterpretted overflow)
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// Example: assuming some label started at the 7th byte
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var truncatedAb = new Uint8Array(ab.slice(0, record.rdstart + record.rdlength));
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var labelData = unpackLabels(truncatedAb, record.rdstart+7, { byteLength: 0, cpcount: 0, labels: [], name: '' });
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record.deviceName = labelData.name;
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// finally, return the record
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return record;
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};
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}('undefined' !== typeof window ? window : exports));
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