rtc-sdp/index.js

rtc.io utility module for patching (munging) SDP

/* jshint node: true */
'use strict';

var nub = require('whisk/nub');
var pluck = require('whisk/pluck');
var flatten = require('whisk/flatten');
var reLineBreak = /\r?\n/;
var reTrailingNewlines = /\r?\n$/;

// list sdp line types that are not "significant"
var nonHeaderLines = [ 'a', 'c', 'b', 'k' ];
var parsers = require('./parsers');

/**
  # rtc-sdp

  This is a utility module for intepreting and patching sdp.

  ## Usage

  The `rtc-sdp` main module exposes a single function that is capable of
  parsing lines of SDP, and providing an object allowing you to perform
  operations on those parsed lines:

  ```js
  var sdp = require('rtc-sdp')(lines);
  ```

  The currently supported operations are listed below:

**/
module.exports = function(sdp) {
  var ops = {};
  var parsed = [];
  var activeCollector;

  // initialise the lines
  var lines = sdp.split(reLineBreak).filter(Boolean).map(function(line) {
    return line.split('=');
  });

  var inputOrder = nub(lines.filter(function(line) {
    return line[0] && nonHeaderLines.indexOf(line[0]) < 0;
  }).map(pluck(0)));

  var findLine = ops.findLine = function(type, index) {
    var lineData = parsed.filter(function(line) {
      return line[0] === type;
    })[index || 0];

    return lineData && lineData[1];
  };

  // push into parsed sections
  lines.forEach(function(line) {
    var customParser = parsers[line[0]];

    if (customParser) {
      activeCollector = customParser(parsed, line);
    }
    else if (activeCollector) {
      activeCollector = activeCollector(line);
    }
    else {
      parsed.push(line);
    }
  });

  /**
    ### `sdp.addIceCandidate(data)`

    Modify the sdp to include candidates as denoted by the data.

**/
  ops.addIceCandidate = function(data) {
    var lineIndex = (data || {}).lineIndex || (data || {}).sdpMLineIndex;
    var mLine = typeof lineIndex != 'undefined' && findLine('m', lineIndex);
    var candidate = (data || {}).candidate;

    // if we have the mLine add the new candidate
    if (mLine && candidate) {
      mLine.childlines.push(candidate.replace(reTrailingNewlines, '').split('='));
    }
  };

  /**
    ### `sdp.getMediaTypes() => []`

    Retrieve the list of media types that have been defined in the sdp via
    `m=` lines.
  **/
  ops.getMediaTypes = function() {
    function getMediaType(data) {
      return data[1].def.split(/\s/)[0];
    }

    return parsed.filter(function(parts) {
      return parts[0] === 'm' && parts[1] && parts[1].def;
    }).map(getMediaType);
  };

  /**
    ### `sdp.getMediaIDs() => []`

    Returns the list of unique media line IDs that have been defined in the sdp
    via `a=mid:` lines.
   **/
  ops.getMediaIDs = function() {
    return parsed.filter(function(parts) {
      return parts[0] === 'm' && parts[1] && parts[1].childlines && parts[1].childlines.length > 0;
    }).map(function(mediaLine) {
      var lines = mediaLine[1].childlines;
      // Default ID to the media type
      var mediaId = mediaLine[1].def.split(/\s/)[0];

      // Look for the media ID
      for (var i = 0; i < lines.length; i++) {
        var tokens = lines[i][1].split(':');
        if (tokens.length > 0 && tokens[0] === 'mid') {
          mediaId = tokens[1];
          break;
        }
      }
      return mediaId;
    });
  };

  /**
    ### `sdp.toString()`

    Convert the SDP structure that is currently retained in memory, into a string
    that can be provided to a `setLocalDescription` (or `setRemoteDescription`)
    WebRTC call.

  **/
  ops.toString = function() {
    return parsed.map(function(line) {
      return typeof line[1].toArray == 'function' ? line[1].toArray() : [ line ];
    }).reduce(flatten).map(function(line) {
      return line.join('=');
    }).join('\r\n') + '\r\n';
  };

  /**
    ## SDP Filtering / Munging Functions

    There are additional functions included in the module to assign with
    performing "single-shot" SDP filtering (or munging) operations:

  **/

  return ops;
};