index.js

'use strict';

var b2a = typeof btoa === 'undefined' ? require('./b.js').btoa : btoa;
var a2b = typeof atob === 'undefined' ? require('./b.js').atob : atob;

exports.reduce = function(desc) {
  var sdp = desc.sdp;
  var lines = sdp.split('\r\n');
  lines = lines.filter(function (line) {
    return ((line.indexOf('a=candidate:') === 0) && line.indexOf('typ relay') !== -1 && line.charAt(14) === '1') || 
      line.indexOf('a=ice-ufrag:') === 0 ||
      line.indexOf('a=ice-pwd:') === 0 ||
      line.indexOf('a=fingerprint:') === 0;
  });
  lines = lines.sort().reverse();
  // why is chrome reporting more than one candidate?
  // pick last candidate
  //lines = lines.slice(0, 3).concat(lines[4]);

  var firstcand = true;
  var comp = lines.map(function (line) {
    switch(line.split(':')[0]) {
      case 'a=fingerprint':
        var hex = line.substr(22).split(':').map(function (h) {
          return parseInt(h, 16);
        });
        // b64 is slightly more concise than colon-hex
        return b2a(String.fromCharCode.apply(String, hex));
      case 'a=ice-pwd':
        return line.substr(10); // already b64
      case 'a=ice-ufrag':
        return line.substr(12); // already b64
      case 'a=candidate':
        var parts = line.substr(12).split(' ');        
        var ip = parts[4].split('.').reduce(function (prev, cur) { return (prev << 8) + parseInt(cur, 10); });
        // take ip/port from candidate, encode
        // foundation and priority are not required
        // can I have sprintf("%4c%4c%4c%2c") please? pike rocks
        // since chrome (for whatever reason) generates two candidates with the same foundation, ip and different port
        // (possibly the reason for this is multiple local interfaces but still...)
        if (firstcand) {
          firstcand = false;
          return [ip, parseInt(parts[5])].map(function (a) { return a.toString(32); }).join(',');
        } else {
          return [parseInt(parts[5])].map(function (a) { return a.toString(32); }).join(',');
        }
    }
  });
  return [desc.type === 'offer' ? 'O' : 'A'].concat(comp).join(',');
};

exports.expand = function(str) {
  var comp = str.split(',');
  var sdp = ['v=0',
    'o=- 5498186869896684180 2 IN IP4 127.0.0.1',
    's=-', 't=0 0', 'a=msid-semantic: WMS',
    'm=application 9 DTLS/SCTP 5000',
    'c=IN IP4 0.0.0.0',
    'a=mid:data',
    'a=sctpmap:5000 webrtc-datachannel 1024'
  ];
  if (comp[0] === 'A') {
    sdp.push('a=setup:active');
  } else {
    sdp.push('a=setup:actpass');
  }
  sdp.push('a=ice-ufrag:' + comp[1]);
  sdp.push('a=ice-pwd:' + comp[2]);
  sdp.push('a=fingerprint:sha-256 ' + a2b(comp[3]).split('').map(function (c) { var d = c.charCodeAt(0); var e = c.charCodeAt(0).toString(16).toUpperCase(); if (d < 16) e = '0' + e; return e; }).join(':'));
  var candparts;
  candparts = comp.splice(4, 2).map(function (c) { return parseInt(c, 32); });
  var ip = [(candparts[0] >> 24) & 0xff, (candparts[0] >> 16) & 0xff, (candparts[0] >> 8) & 0xff, candparts[0] & 0xff].join('.');
  var cand = ['a=candidate:0', // foundation 0
     '1', 'udp',
     '1', // priority 1
     ip,
     candparts[1],
     'typ host' // well, not a host cand but...
  ];
  sdp.push(cand.join(' '));
  // parse subsequent candidates
  var prio = 2;
  for (var i = 4; i < comp.length; i++) {
    cand = ['a=candidate:0',
       '1', 'udp',
       prio++, // increase priority
       ip, // ip stays the same
       parseInt(comp[i], 32), // port changes 
       'typ host' // well, not a host cand but...
    ];
    sdp.push(cand.join(' '));
  }
  return {type: comp[0] === 'O' ? 'offer' : 'answer', sdp: sdp.join('\r\n') + '\r\n'};
};