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dnsserver.js
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dnsserver.js
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// Copyright (c) 2010 Tom Hughes-Croucher
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
//
var sys = require('sys'),
Buffer = require('buffer').Buffer,
dgram = require('dgram');
host = 'localhost';
port = 9999;
// slices a single byte into bits
// assuming only single bytes
var sliceBits = function(b, off, len) {
var s = 7 - (off + len - 1);
b = b >>> s;
return b & ~(0xff << len);
};
var server = dgram.createSocket('udp4');
server.on('message', function (msg, rinfo) {
//split up the message into the dns request header info and the query
var q = processRequest(msg);
buf = createResponse(q);
server.send(buf, 0, buf.length, rinfo.port, rinfo.address, function (err, sent) {
});
});
//takes a buffer as a request
var processRequest = function(req) {
//see rfc1035 for more details
//http://tools.ietf.org/html/rfc1035#section-4.1.1
var query = {};
query.header = {};
//TODO write code to break questions up into an array
query.question = {};
var tmpSlice;
var tmpByte;
//transaction id
// 2 bytes
query.header.id = req.slice(0,2);
//slice out a byte for the next section to dice into binary.
tmpSlice = req.slice(2,3);
//convert the binary buf into a string and then pull the char code
//for the byte
tmpByte = tmpSlice.toString('binary', 0, 1).charCodeAt(0);
//qr
// 1 bit
query.header.qr = sliceBits(tmpByte, 0,1);
//opcode
// 0 = standard, 1 = inverse, 2 = server status, 3-15 reserved
// 4 bits
query.header.opcode = sliceBits(tmpByte, 1,4);
//authorative answer
// 1 bit
query.header.aa = sliceBits(tmpByte, 5,1);
//truncated
// 1 bit
query.header.tc = sliceBits(tmpByte, 6,1);
//recursion desired
// 1 bit
query.header.rd = sliceBits(tmpByte, 7,1);
//slice out a byte to dice into binary
tmpSlice = req.slice(3,4);
//convert the binary buf into a string and then pull the char code
//for the byte
tmpByte = tmpSlice.toString('binary', 0, 1).charCodeAt(0);
//recursion available
// 1 bit
query.header.ra = sliceBits(tmpByte, 0,1);
//reserved 3 bits
// rfc says always 0
query.header.z = sliceBits(tmpByte, 1,3);
//response code
// 0 = no error, 1 = format error, 2 = server failure
// 3 = name error, 4 = not implemented, 5 = refused
// 6-15 reserved
// 4 bits
query.header.rcode = sliceBits(tmpByte, 4,4);
//question count
// 2 bytes
query.header.qdcount = req.slice(4,6);
//answer count
// 2 bytes
query.header.ancount = req.slice(6,8);
//ns count
// 2 bytes
query.header.nscount = req.slice(8,10);
//addition resources count
// 2 bytes
query.header.arcount = req.slice(10, 12);
//assuming one question
//qname is the sequence of domain labels
//qname length is not fixed however it is 4
//octets from the end of the buffer
query.question.qname = req.slice(12, req.length - 4);
//qtype
query.question.qtype = req.slice(req.length - 4, req.length - 2);
//qclass
query.question.qclass = req.slice(req.length - 2, req.length);
return query;
};
var createResponse = function(query) {
/*
* Step 1: find record associated with query
*/
var results = findRecords(query.question.qname, 1);
/*
* Step 2: construct response object
*/
var response = {};
response.header = {};
//1 byte
response.header.id = query.header.id; //same as query id
//combined 1 byte
response.header.qr = 1; //this is a response
response.header.opcode = 0; //standard for now TODO: add other types 4-bit!
response.header.aa = 0; //authority... TODO this should be modal
response.header.tc = 0; //truncation
response.header.rd = 1; //recursion asked for
//combined 1 byte
response.header.ra = 0; //no rescursion here TODO
response.header.z = 0; // spec says this MUST always be 0. 3bit
response.header.rcode = 0; //TODO add error codes 4 bit.
//1 byte
response.header.qdcount = 1; //1 question
//1 byte
response.header.ancount = results.length; //number of rrs returned from query
//1 byte
response.header.nscount = 0;
//1 byte
response.header.arcount = 0;
response.question = {};
response.question.qname = query.question.qname;
response.question.qtype = query.question.qtype;
response.question.qclass = query.question.qclass;
response.rr = results;
/*
* Step 3 render response into output buffer
*/
var buf = buildResponseBuffer(response);
/*
* Step 4 return buffer
*/
return buf;
};
var domainToQname = function(domain) {
var tokens = domain.split(".");
len = domain.length + 2;
var qname = new Buffer(len);
var offset = 0;
for(var i=0; i<tokens.length;i++) {
qname[offset]=tokens[i].length;
offset++;
for(var j=0;j<tokens[i].length;j++) {
qname[offset] = tokens[i].charCodeAt(j);
offset++;
}
}
qname[offset] = 0;
return qname;
};
var getZeroBuf = function(len) {
buf = new Buffer(len);
for(var i=0;i<buf.length;i++) { buf[i]=0;}
return buf;
};
var buildResponseBuffer = function(response) {
//calculate len in octets
//NB not calculating rr this is done later
//headers(12) + qname(qname + 2 + 2)
//e.g. 16 + 2 * qname;
//qnames are Buffers so length is already in octs
var qnameLen = response.question.qname.length;
var len = 16 + qnameLen;
var buf = getZeroBuf(len);
response.header.id.copy(buf, 0, 0, 2);
buf[2] = 0x00 | response.header.qr << 7 | response.header.opcode << 3 | response.header.aa << 2 | response.header.tc << 1 | response.header.rd;
buf[3] = 0x00 | response.header.ra << 7 | response.header.z << 4 | response.header.rcode;
numToBuffer(buf, 4, response.header.qdcount, 2);
numToBuffer(buf, 6, response.header.ancount, 2);
numToBuffer(buf, 8, response.header.nscount, 2);
numToBuffer(buf, 10, response.header.arcount, 2);
//end header
response.question.qname.copy(buf, 12, 0, qnameLen);
response.question.qtype.copy(buf, 12+qnameLen, 0, 2);
response.question.qclass.copy(buf, 12+qnameLen+2, 0, 2);
var rrStart = 12+qnameLen+4;
for (var i=0;i<response.rr.length;i++) {
//TODO figure out if this is actually cheaper than just iterating
//over the rr section up front and counting before creating buf
//
//create a new buffer to hold the request plus the rr
//len of each response is 14 bytes of stuff + qname len
var tmpBuf = getZeroBuf(buf.length + response.rr[i].qname.length + 14);
buf.copy(tmpBuf, 0, 0, buf.length);
response.rr[i].qname.copy(tmpBuf, rrStart, 0, response.rr[i].qname.length);
numToBuffer(tmpBuf, rrStart+response.rr[i].qname.length, response.rr[i].qtype, 2);
numToBuffer(tmpBuf, rrStart+response.rr[i].qname.length+2, response.rr[i].qclass, 2);
numToBuffer(tmpBuf, rrStart+response.rr[i].qname.length+4, response.rr[i].ttl, 4);
numToBuffer(tmpBuf, rrStart+response.rr[i].qname.length+8, response.rr[i].rdlength, 2);
numToBuffer(tmpBuf, rrStart+response.rr[i].qname.length+10, response.rr[i].rdata, response.rr[i].rdlength); // rdlength indicates rdata length
rrStart = rrStart + response.rr[i].qname.length + 14;
buf = tmpBuf;
}
//TODO compression
return buf;
};
//take a number and make sure it's written to the buffer as
//the correct length of bytes with leading 0 padding where necessary
// takes buffer, offset, number, length in bytes to insert
var numToBuffer = function(buf, offset, num, len, debug) {
if (typeof num != 'number') {
throw new Error('Num must be a number');
}
for (var i=offset;i<offset+len;i++) {
var shift = 8*((len - 1) - (i - offset));
var insert = (num >> shift) & 255;
buf[i] = insert;
}
return buf;
};
var findRecords = function(qname, qtype, qclass) {
//assuming we are always going to get internet
//request but adding basic qclass support
//for completeness
//TODO replace throws with error responses
if (qclass === undefined || qclass === 1) {
qclass = 'in';
} else {
throw new Error('Only internet class records supported');
}
switch(qtype) {
case 1:
qtype = 'a'; //a host address
break;
case 2:
qtype = 'ns'; //an authoritative name server
break;
case 3:
qtype = 'md'; //a mail destination (Obsolete - use MX)
break;
case 4:
qtype = 'mf'; //a mail forwarder (Obsolete - use MX)
break;
case 5:
qtype = 'cname'; //the canonical name for an alias
break;
case 6:
qtype = 'soa'; //marks the start of a zone of authority
break;
case 7:
qtype = 'mb'; //a mailbox domain name (EXPERIMENTAL)
break;
case 8:
qtype = 'mg'; //a mail group member (EXPERIMENTAL)
break;
case 9:
qtype = 'mr'; //a mail rename domain name (EXPERIMENTAL)
break;
case 10:
qtype = 'null'; //a null RR (EXPERIMENTAL)
break;
case 11:
qtype = 'wks'; //a well known service description
break;
case 12:
qtype = 'ptr'; //a domain name pointer
break;
case 13:
qtype = 'hinfo'; //host information
break;
case 14:
qtype = 'minfo'; //mailbox or mail list information
break;
case 15:
qtype = 'mx'; //mail exchange
break;
case 16:
qtype = 'txt'; //text strings
break;
case 255:
qtype = '*'; //select all types
break;
default:
throw new Error('No valid type specified');
break;
}
var domain = qnameToDomain(qname);
//TODO add support for wildcard
if (qtype === '*') {
throw new Error('Wildcard not support');
} else {
var rr = records[domain][qclass][qtype];
}
return rr;
};
var qnameToDomain = function(qname) {
var domain= '';
for(var i=0;i<qname.length;i++) {
if (qname[i] == 0) {
//last char chop trailing .
domain = domain.substring(0, domain.length - 1);
break;
}
var tmpBuf = qname.slice(i+1, i+qname[i]+1);
domain += tmpBuf.toString('binary', 0, tmpBuf.length);
domain += '.';
i = i + qname[i];
}
return domain;
};
server.addListener('error', function (e) {
throw e;
});
//
//TODO create records database
records = {};
records['tomhughescroucher.com'] = {};
records['tomhughescroucher.com']['in'] = {};
records['tomhughescroucher.com']['in']['a'] = [];
var r = {};
r.qname = domainToQname('tomhughescroucher.com');
r.qtype = 1;
r.qclass = 1;
r.ttl = 1;
r.rdlength = 4;
r.rdata = 0xBC8A0009;
records['tomhughescroucher.com']['in']['a'].push(r);
r = {};
r.qname = domainToQname('tomhughescroucher.com');
r.qtype = 1;
r.qclass = 1;
r.ttl = 1;
r.rdlength = 4;
r.rdata = 0x7F000001;
records['tomhughescroucher.com']['in']['a'].push(r);
server.bind(port, host);
console.log('Started server on ' + host + ':' + port);