/* DNS protocol library
 * The DNS class Uses events, so the calling script *MUST* set js.do_callbacks
 * Example usage:
 *
 * js.do_callbacks = true;
 * load('dns.js');
 *
 * function handle(resp)
 * {
 * 	log(LOG_ERROR, JSON.stringify(resp));
 * 	exit(0);
 * }
 *
 * dns = new DNS();
 * dns.resolve('example.com', handle);
 *
 * In synchronous mode, DNS does not use events, so callback arguments are optional:
 *
 * load('dns.js');
 * dns = new DNS(true);
 * log(LOG_ERROR, dns.resolve('example.com').toSource());
 *
 */

require('sockdefs.js', 'SOCK_DGRAM');

function DNS(synchronous, servers) {
	var nextid = 0;

	if (synchronous === undefined)
		synchronous = false;

	Object.defineProperty(this, 'synchronous', {get: function() {
		 return synchronous;
	}});
	this.outstanding = {};
	this.sockets = [];

	if (this.synchronous)
		this.query = this.synchronous_query;
	else
		this.query = this.asynchronous_query;

	function handle_response() {
		var resp = this.dnsObject.handle_response(this);

		if (resp)
			resp.q.callback.call(resp.q.thisObj, resp.ret);
	}

	if (servers === undefined)
		servers = system.name_servers;

	servers.forEach(function(server) {
		var sock = new Socket(SOCK_DGRAM, "dns", server.indexOf(':') >= 0);
		sock.bind();
		sock.connect(server, 53);
		if (!this.synchronous) {
			sock.cbID = sock.on('read', handle_response);
			sock.dnsObject = this;
		}
		this.sockets.push(sock);
	}, this);

	if (this.sockets.length < 1)
		throw('Unable to create any sockets');

	this.increment_id = function() {
		var ret = nextid;
		do {
			nextid++;
			if (nextid > 65535)
				nextid = 0;
		} while (this.outstanding[nextid] !== undefined);
		return ret;
	};
}

/*
 * Class properties and methods
 */
DNS.types = {
	'A':1,
	'NS':2,
	'MD':3,
	'MF':4,
	'CNAME':5,
	'SOA':6,
	'MB':7,
	'MG':8,
	'MR':9,
	'NULL':10,
	'WKS':11,
	'PTR':12,
	'HINFO':13,
	'MINFO':14,
	'MX':15,
	'TXT':16,
	'AAAA':28,
	'SRV':33,
	'NAPTR':35,
	'URI':256
};

DNS.classes = {
	'IN':1,
	'CS':2,
	'CH':3,
	'HS':4
};

DNS.prototype.generate_query = function(queries, recursive) {
	var id;
	var namebits = {};
	var query = {};

	function int16_to_string(id) {
		return ascii((id & 0xff00) >> 8) + ascii(id & 0xff);
	}

	queries.forEach(function(query) {
		if (query.str === undefined)
			query.str = 'example.com';
		if (query.type === undefined)
			query.type = 'AAAA';
		if (DNS.types[query.type] !== undefined)
			query.type = DNS.types[query.type];
		query.type = parseInt(query.type, 10);
		if (isNaN(query.type)) {
			throw new Error('Invalid type');
		}
		if (query.class === undefined)
			query.class = 'IN';
		if (DNS.classes[query.class] !== undefined)
			query.class = DNS.classes[query.class];
		query.class = parseInt(query.class, 10);
		if (isNaN(query.class)) {
			throw new Error('Invalid class');
		}
	});

	if (recursive === undefined)
		recursive = true;

	// Header
	query.id = this.increment_id();
	query.buf = int16_to_string(query.id);
	query.buf += ascii(recursive ? 1 : 0);
	query.buf += ascii(0);
	query.buf += int16_to_string(queries.length);	// Questions
	query.buf += int16_to_string(0);	// Answers
	query.buf += int16_to_string(0);	// Name Servers
	query.buf += int16_to_string(0);	// Additional Records

	// Queries
	queries.forEach(function(oneQuery) {
		var thisname = '';
		var fields = oneQuery.query.split(/\./).reverse();
		var matched;

		fields.forEach(function(field) {
			if (field.length > 63)
				throw new Error('invalid field in query "'+field+'" (longer than 63 characters)');
			thisname = ascii(field.length) + field + thisname;
			if (namebits[thisname] !== undefined && namebits[thisname] > 0) {
				matched = {'offset':namebits[thisname], 'length':thisname.length};
			}
			else {
				namebits[thisname] = 0 - thisname.length;
			}
		});

		// Now fix up negative namebits...
		Object.keys(namebits).forEach(function(name) {
			if (namebits[name] < 0) {
				namebits[name] = query.buf.length + thisname.length + namebits[name];
			}
		});

		// And use the match
		if (matched !== undefined) {
			thisname = thisname.substr(0, thisname.length - matched.length);
			thisname = thisname + ascii(0xc0 | ((matched.offset & 0x3f) >> 8)) + ascii(matched.offset & 0xff);
		}
		else
			thisname += ascii(0);
		query.buf += thisname;
		query.buf += int16_to_string(oneQuery.type);
		query.buf += int16_to_string(oneQuery.class);
	});

	this.outstanding[query.id] = {'query':queries, 'recursive':recursive, 'id':query.id, 'obj':this};
	return query;
};

DNS.prototype.handle_response = function(sock) {
	var resp;
	var id;
	var offset = 0;
	var queries;
	var answers;
	var nameservers;
	var arecords;
	var q;
	var i;
	var ret = {'queries':[], 'answers':[], 'nameservers':[], 'additional':[]};
	var rdata;
	var rdlen;
	var tmp;

	function string_to_int16(str) {
		return ((ascii(str[0])<<8) | (ascii(str[1])));
	}

	function string_to_int32(str) {
		return ((ascii(str[0])<<24) | (ascii(str[1]) << 16) | (ascii(str[1]) << 8) | (ascii(str[1])));
	}

	function get_string(resp, offset) {
		var len = ascii(resp[offset]);
		return {'len':len + 1, 'string':resp.substr(offset + 1, len)};
	}

	function get_name(resp, offset) {
		var len;
		var name = '';
		var ret = 0;
		var compressed = false;

		do {
			len = ascii(resp[offset]);
			if (!compressed)
				ret++;
			offset++;
			if (len > 63) {
				offset = ((len & 0x3f) << 8) | ascii(resp[offset]);
				if (!compressed)
					ret++;
				compressed = true;
			}
			else {
				if (!compressed)
					ret += len;
				if (name.length > 0 && len > 0)
					name += '.';
				name += resp.substr(offset, len);
				offset += len;
			}
		} while (len != 0);

		return {'len':ret, 'name':name};
	}

	function parse_rdata(type, resp, offset, len) {
		var tmp;
		var tmp2;
		var tmp3;
		var tmp4;

		switch(type) {
			case 1:	 // A
				return ascii(resp[offset]) + '.' +
				       ascii(resp[offset + 1]) + '.' +
				       ascii(resp[offset + 2]) + '.' +
				       ascii(resp[offset + 3]);
			case 2:   // NS
				return get_name(resp, offset).name;
			case 5:   // CNAME
				return get_name(resp, offset).name;
			case 6:   // SOA
				tmp = {};
				tmp2 = 0;
				tmp3 = get_name(resp, offset + tmp2);
				tmp.mname = tmp3.name;
				tmp2 += tmp3.len;
				tmp3 = get_name(resp, offset + tmp2);
				tmp.rname = tmp3.name;
				tmp2 += tmp3.len;
				tmp.serial = string_to_int32(resp.substr(offset + tmp2, 4));
				tmp2 += 4;
				tmp.refresh = string_to_int32(resp.substr(offset + tmp2, 4));
				tmp2 += 4;
				tmp.retry = string_to_int32(resp.substr(offset + tmp2, 4));
				tmp2 += 4;
				tmp.export = string_to_int32(resp.substr(offset + tmp2, 4));
				tmp2 += 4;
				tmp.minimum = string_to_int32(resp.substr(offset + tmp2, 4));
				tmp2 += 4;
				return tmp;
			case 11:  // WKS
				tmp = {};
				tmp.address = ascii(resp[offset]) + '.' +
				              ascii(resp[offset + 1]) + '.' +
				              ascii(resp[offset + 2]) + '.' +
				              ascii(resp[offset + 3]);
				tmp.protocol = ascii(resp[offset + 4]);
				tmp2 = 5;
				tmp.ports = [];
				while (tmp2 < len) {
					tmp3 = ascii(resp[offset + tmp2]);
					for (tmp4 = 0; tmp4 < 8; tmp4++) {
						if (tmp3 & (1 << tmp4))
							tmp.ports.push(8 * (tmp2 - 5) + tmp3);
					}
				}
				return tmp;
			case 12:  // PTR
				return get_name(resp, offset).name;
			case 13:  // HINFO
				tmp = get_string(resp, offset);
				return {'cpu':tmp.string, 'os':get_string(resp, offset + tmp.len).string};
			case 15:  // MX
				tmp = {};
				tmp.preference = string_to_int16(resp.substr(offset, 2));
				tmp.exchange = get_name(resp, offset + 2).name;
				return tmp;
			case 16:  // TXT
				tmp = [];
				tmp2 = 0;
				do {
					tmp3 = get_string(resp, offset + tmp2);
					tmp.push(tmp3.string);
					tmp2 += tmp3.len;
				} while (tmp2 < len);
				return tmp;
			case 28:  // AAAA
				return format("%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x:%02x%02x",
				               ascii(resp[offset + 0]),  ascii(resp[offset + 1]),
				               ascii(resp[offset + 2]),  ascii(resp[offset + 3]),
				               ascii(resp[offset + 4]),  ascii(resp[offset + 5]),
				               ascii(resp[offset + 6]),  ascii(resp[offset + 7]), 
				               ascii(resp[offset + 8]),  ascii(resp[offset + 9]),
				               ascii(resp[offset + 10]), ascii(resp[offset + 11]),
				               ascii(resp[offset + 12]), ascii(resp[offset + 13]),
				               ascii(resp[offset + 14]), ascii(resp[offset + 15])
				             ).replace(/(0000:)+/, ':').replace(/(^|:)0{1,3}/g, '$1');
			case 33:  // SRV
				tmp = {};
				tmp.priority = string_to_int16(resp.substr(offset, 2));
				offset += 2;
				tmp.weight = string_to_int16(resp.substr(offset, 2));
				offset += 2;
				tmp.port = string_to_int16(resp.substr(offset, 2));
				offset += 2;
				tmp.target = get_name(resp, offset).name;
				return tmp;
			case 35:  // NAPTR
				tmp = {};
				tmp.order = string_to_int16(resp.substr(offset, 2));
				offset += 2;
				tmp.preference = string_to_int16(resp.substr(offset, 2));
				offset += 2;
				tmp2 = get_string(resp, offset);
				tmp.flags = tmp2.string;
				offset += tmp2.len;
				tmp2 = get_string(resp, offset);
				tmp.services = tmp2.string;
				offset += tmp2.len;
				tmp2 = get_string(resp, offset);
				tmp.regexp = tmp2.string;
				offset += tmp2.len;
				tmp.replacement = get_name(resp, offset).name;
				return tmp;
			case 256: // URI
				tmp = {};
				tmp.priority = string_to_int16(resp.substr(offset, 2));
				offset += 2;
				tmp.weight = string_to_int16(resp.substr(offset, 2));
				offset += 2;
				tmp.target = get_string(resp, offset).string;
				tmp.target = tmp.target.replace(/\\"/g, '"');
				tmp.target = tmp.target.replace(/^"(.*)"$/, '$1');
				return tmp;
			case 3:   // MD
			case 4:   // MF
			case 7:   // MB
			case 8:   // MG
			case 9:   // MR
			case 10:  // NULL
			case 14:  // MINFO
				return {'raw':resp.substr(offset, len)};
		}
	}

	resp = sock.recv(10000);
	id = string_to_int16(resp);
	if (this.outstanding[id] === undefined)
		return null;

	q = this.outstanding[id];
	delete this.outstanding[id];

	ret.id = id;
	ret.response = !!(ascii(resp[2]) & 0x80);
	if (!ret.response)
		return null;
	ret.opcode = (ascii(resp[2]) & 0x78) >> 3;
	if (ret.opcode !== 0 && ret.opcode !== 2)
		return null;
	ret.authoritative = !!(ascii(resp[2]) & (1<<2));
	ret.truncation = !!(ascii(resp[2]) & (1<<1));
	ret.recusrion_desired = !!(ascii(resp[2]) & (1));
	ret.recusrion_available = !!(ascii(resp[2]) & (1<<7));
	ret.reserved = (ascii(resp[3]) & 0x70) >> 4;
	ret.rcode = ascii(resp[3]) & 0x0f;

	queries = string_to_int16(resp.substr(4, 2));
	answers = string_to_int16(resp.substr(6, 2));
	nameservers = string_to_int16(resp.substr(8, 2));
	arecords = string_to_int16(resp.substr(10, 2));
	if (q.timeoutid !== undefined)
		js.clearTimeout(q.timeoutid);
	offset = 12;
	for (i = 0; i < queries; i++) {
		rdata = {};
		tmp = get_name(resp, offset);
		rdata.name = tmp.name;
		offset += tmp.len;
		rdata.type = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		rdata.class = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		ret.queries.push(rdata);
	}

	for (i = 0; i < answers; i++) {
		rdata = {};
		tmp = get_name(resp, offset);
		rdata.name = tmp.name;
		offset += tmp.len;
		rdata.type = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		rdata.class = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		rdata.ttl = string_to_int32(resp.substr(offset, 4));
		offset += 4;
		rdlen = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		rdata.rdata = parse_rdata(rdata.type, resp, offset, rdlen);
		offset += rdlen;
		ret.answers.push(rdata);
	}

	for (i = 0; i < nameservers; i++) {
		rdata = {};
		tmp = get_name(resp, offset);
		rdata.name = tmp.name;
		offset += tmp.len;
		rdata.type = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		rdata.class = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		rdata.ttl = string_to_int32(resp.substr(offset, 4));
		offset += 4;
		rdlen = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		rdata.rdata = parse_rdata(rdata.type, resp, offset, rdlen);
		offset += rdlen;
		ret.nameservers.push(rdata);
	}

	for (i = 0; i < arecords; i++) {
		rdata = {};
		tmp = get_name(resp, offset);
		rdata.name = tmp.name;
		offset += tmp.len;
		rdata.type = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		rdata.class = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		rdata.ttl = string_to_int32(resp.substr(offset, 4));
		offset += 4;
		rdlen = string_to_int16(resp.substr(offset, 2));
		offset += 2;
		rdata.rdata = parse_rdata(rdata.type, resp, offset, rdlen);
		offset += rdlen;
		ret.additional.push(rdata);
	}

	return {'q':q, 'ret':ret};
}

DNS.prototype.asynchronous_query = function(queries, /* queryStr, type, class, */callback, thisObj, recursive, timeout, failures, failed) {
	var query;

	if (callback === undefined)
		throw new Error('callback is required');
	if (thisObj === undefined)
		thisObj = this;
	if (recursive === undefined)
		recursive = true;
	if (timeout === undefined)
		timeout = 5000;
	if (failures === undefined)
		failures = 3;
	if (failed === undefined)
		failed = 0;

	function handle_timeout() {
		this.failed++;
		delete this.obj.outstanding[this.id];
		if (this.failed >= this.failures)
			this.callback.call(this);
		else
			this.obj.query(this.query, this.callback, this.thisObj, this.recursive, this.timeout, this.failures,
			    this.failed);
	}

	queries.forEach(function(q) {
		query = this.generate_query([q], recursive);

		if (query) {
			this.outstanding[query.id].callback = callback;
			this.outstanding[query.id].thisObj = thisObj;
			this.outstanding[query.id].timeout = timeout;
			this.outstanding[query.id].failures = failures;
			this.outstanding[query.id].failed = failed;
			this.outstanding[query.id].timeoutid = js.setTimeout(handle_timeout, timeout, this.outstanding[query.id]);

			this.sockets.forEach(function(sock) {
				sock.write(query.buf);
			});
		}
	}, this);
	return undefined;
};

DNS.prototype.synchronous_query = function(queries, callback, thisObj, recursive, timeout, failures, failed) {
	var query;
	var ret;
	var socket_array = [];
	var end;
	var to;
	var resp;
	var ready;
	var done = false;

	if (thisObj === undefined)
		thisObj = this;
	if (recursive === undefined)
		recursive = true;
	if (timeout === undefined)
		timeout = 5000;
	if (failures === undefined)
		failures = 3;
	if (failed === undefined)
		failed = 0;

	queries.forEach(function(q) {
		query = this.generate_query([q], recursive);

		if (query) {
			this.outstanding[query.id].callback = callback;
			this.outstanding[query.id].thisObj = thisObj;
			this.outstanding[query.id].timeout = timeout;
			this.outstanding[query.id].failures = failures;
			this.outstanding[query.id].failed = failed;

			this.sockets.forEach(function(sock) {
				sock.write(query.buf);
			});
		}
	}, this);

	ret = [];

	end = system.timer + timeout / 1000;
	do {
		to = end - system.timer;
		if (to < 0)
			to = 0;
		ready = socket_select(this.sockets, to);
		if (ready === null)
			break;
		ready.forEach(function(sid) {
			resp = this.handle_response(this.sockets[sid]);
			if (resp !== null) {
				ret.push(resp.ret);
				if (callback !== undefined) {
					callback.call(thisObj, resp.ret);
				}
			}
		}, this);
	} while (!done && system.timer < end && ret.length < queries.length);

	if (callback === undefined)
		return ret;
};

DNS.prototype.resolveIPv4 = function(host, callback, thisObj) {
	this.resolveProcess(host, callback, [{query:host, type:'A'}], thisObj);
}

DNS.prototype.resolveIPv6 = function(host, callback, thisObj) {
	this.resolveProcess(host, callback, [{query:host, type:'AAAA'}], thisObj);
}

DNS.prototype.resolve = function(host, callback, thisObj) {
	this.resolveProcess(host, callback, [{query:host, type:'AAAA'},{query:host, type:'A'}], thisObj);
}

DNS.prototype.resolveProcess = function(host, callback, dnstype, thisObj)
{
	var ctx = {A:{}, AAAA:{}, unique_id:'DNS.prototype.resolve'};
	var final;
	var respA;
	var respAAAA;
	var queries;
	var queries_done;

	this.sockets.forEach(function(sock) {
		ctx.unique_id += '.'+sock.local_port;
	});
	ctx.unique_id += this.increment_id().toString();

	if (host === undefined)
		throw new Error('No host specified');

	if (!this.synchronous && callback === undefined)
		throw new Error('No callback specified');
	if (thisObj === undefined)
		thisObj = this;

	ctx.callback = callback;
	ctx.thisObj = thisObj;

	ctx.final_callback = function() {
		this.ret = [];
		if (this.AAAA.addrs !== undefined) {
			this.AAAA.addrs.forEach(function(addr) {
				this.ret.push(addr);
			}, this);
		}
		if (this.A.addrs !== undefined) {
			this.A.addrs.forEach(function(addr) {
				this.ret.push(addr);
			}, this);
		}
		if (this.callback !== undefined) {
			js.removeEventListener(this.final);
			js.removeEventListener(this.respA);
			js.removeEventListener(this.respAAAA);
			this.callback.call(this.thisObj, this.ret);
		}
	};
	if (callback !== undefined)
		ctx.final = js.addEventListener(ctx.unique_id+'.final', ctx.final_callback);

	ctx.respA_callback = function() {
		this.queries_done++;
		if (this.queries_done >= this.queries) {
			if (this.final !== undefined)
				js.dispatchEvent(this.unique_id + '.final', this);
			else
				this.final_callback(this);
		}
	};
	if (callback !== undefined)
		ctx.respA = js.addEventListener(ctx.unique_id+'.respA', ctx.respA_callback);

	ctx.respAAAA_callback = function() {
		this.queries_done++;
		if (this.queries_done >= this.queries) {
			if (this.final !== undefined)
				js.dispatchEvent(this.unique_id + '.final', this);
			else
				this.final_callback(this);
		}
	}
	if (callback !== undefined)
		ctx.respAAAA = js.addEventListener(ctx.unique_id+'.respAAAA', ctx.respAAAA_callback);

	function handle_response(resp) {
		var rectype;

		if (resp !== null && resp !== undefined) {
			switch(resp.queries[0].type) {
				case DNS.types.A:
					rectype = 'A';
					break;
				case DNS.types.AAAA:
					rectype = 'AAAA';
					break;
			};
		}
		if (rectype === undefined) {
			this.callback.call(this.thisObj, null);
			return;
		}

		if (this[rectype].addrs === undefined)
			this[rectype].addrs = [];

		if (resp !== null && resp.answers !== undefined) {
			resp.answers.forEach(function(ans) {
				if (resp.queries[0].type != ans.type || resp.queries[0].class != ans.class)
					return;
				this[rectype].addrs.push(ans.rdata);
			}, this);
		}
		if (this.callback !== undefined)
			js.dispatchEvent(this.unique_id + '.resp'+rectype, this);
		else
			this['resp'+rectype+'_callback']();
	}

	ctx.queries = dnstype.length;
	ctx.queries_done = 0;

	this.query(dnstype, handle_response, ctx);
	return ctx.ret;
};

DNS.prototype.resolveTypeClass = function(host, type, class, callback, thisObj)
{
	var ctx = {};
	var final;
	var respA;
	var respAAAA;
	var ret;

	if (host === undefined)
		throw new Error('No host specified');

	if (type === undefined)
		throw new Error('No type specified');

	if (class === undefined)
		throw new Error('No class specified');

	if (!this.synchronous && callback === undefined)
		throw new Error('No callback specified');
	ctx.callback = callback;

	if (thisObj === undefined)
		thisObj = this;
	ctx.thisObj = thisObj;

	function handle_response(resp) {
		if (this.ret === undefined)
			this.ret = [];
		if (resp !== undefined && resp.answers !== undefined) {
			resp.answers.forEach(function(ans) {
				if (resp.queries[0].type != ans.type || resp.queries[0].class != ans.class)
					return;
				if (resp.rcode !== 0)
					return;
				this.ret.push(ans.rdata);
			}, this);
		}
		if (this.callback !== undefined)
			this.callback.call(this.thisObj, this.ret);
	}

	this.query([{query:host, type:type, class:class}], handle_response, ctx);
	if (callback === undefined)
		return ctx.ret;
};

DNS.prototype.reverse = function(ip, callback, thisObj)
{
	var qstr;
	var m;
	var a;
	var fillpos;

	if (ip === undefined)
		throw new Error('No IP specified');

	if (!this.synchronous && callback === undefined)
		throw new Error('No callback specified');

	if (thisObj === undefined)
		thisObj = this;

	// Sure, this doesn't deal with terrible ipv4-mapped representations.  Suck it.
	m = ip.match(/^(?:::ffff:)?([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})\.([0-9]{1,3})$/i);
	if (m !== null) {
		// IPv4 Address
		if (parseInt(m[1], 10) > 255 || parseInt(m[2], 10) > 255 || parseInt(m[3], 10) > 255 || parseInt(m[4], 10) > 255)
			throw new Error('Malformed IP address '+ip);
		qstr = m[4] + '.' + m[3] + '.' + m[2] + '.' + m[1] + '.in-addr.arpa';
	}
	else {
		a = ip.split(/:/);
		if (a.length < 3 || a.length > 8)
			throw new Error('Malformed IP address '+ip);
		if (ip.search(/^[a-fA-F0-9:]+$/) != 0)
			throw new Error('Malformed IP address '+ip);
		a.forEach(function(piece, idx, arr) {
			if (piece !== '') {
				while (piece.length < 4)
					piece = '0'+piece;
			}
			arr[idx] = piece;
		});
		if (a[0] == '')
			a[0] = '0000';
		if (a[a.length - 1] == '')
			a[a.length] = '0000';
		while (a.length < 8) {
			fillpos = a.indexOf('');
			if (fillpos === -1)
				throw('Unable to expand IPv6 address');
			a.splice(fillpos, 0, '0000');
		}
		fillpos = a.indexOf('');
		if (fillpos != -1)
			a.splice(fillpos, 1, '0000');
		a.reverse();
		qstr = '';
		a.forEach(function(piece) {
			qstr += piece[3] + '.' + piece[2] + '.' + piece[1] + '.' + piece[0] + '.';
		});
		qstr += 'ip6.arpa';
	}

	return this.resolveTypeClass(qstr, 'PTR', 'IN', callback, thisObj);
};

DNS.prototype.resolveMX = function(host, callback, thisObj)
{
	var ctx = {callback:callback};
	var qstr;
	var m;
	var a;
	var fillpos;

	if (host === undefined)
		throw new Error('No host specified');

	if (!this.synchronous && callback === undefined)
		throw new Error('No callback specified');

	if (thisObj === undefined)
		thisObj = this;
	ctx.thisObj = thisObj;

	function handler(resp) {
		var ret = [];
		resp.sort(function(a, b) {
			return a.preference - b.preference;
		});
		resp.forEach(function(r) {
			ret.push(r.exchange);
		});
		if (this.callback === undefined)
			this.ret = ret;
		else
			this.callback.call(this.thisObj, ret);
	}

	this.resolveTypeClass(host, 'MX', 'IN', handler, ctx);
	return ctx.ret;
};
