@homebridge/dbus-native/lib/dbus-buffer.js

D-bus protocol implementation in native javascript

const Long = require('long');
const parseSignature = require('./signature');

// Buffer + position + global start position ( used in alignment )
function DBusBuffer(buffer, startPos, options) {
  if (typeof options !== 'object') {
    options = { ayBuffer: true, ReturnLongjs: false };
  } else if (options.ayBuffer === undefined) {
    // default settings object
    options.ayBuffer = true; // enforce truthy default props
  }
  this.options = options;
  this.buffer = buffer;
  (this.startPos = startPos ? startPos : 0), (this.pos = 0);
}

DBusBuffer.prototype.align = function (power) {
  var allbits = (1 << power) - 1;
  var paddedOffset = ((this.pos + this.startPos + allbits) >> power) << power;
  this.pos = paddedOffset - this.startPos;
};

DBusBuffer.prototype.readInt8 = function () {
  this.pos++;
  return this.buffer[this.pos - 1];
};

DBusBuffer.prototype.readSInt16 = function () {
  this.align(1);
  var res = this.buffer.readInt16LE(this.pos);
  this.pos += 2;
  return res;
};

DBusBuffer.prototype.readInt16 = function () {
  this.align(1);
  var res = this.buffer.readUInt16LE(this.pos);
  this.pos += 2;
  return res;
};

DBusBuffer.prototype.readSInt32 = function () {
  this.align(2);
  var res = this.buffer.readInt32LE(this.pos);
  this.pos += 4;
  return res;
};

DBusBuffer.prototype.readInt32 = function () {
  this.align(2);
  var res = this.buffer.readUInt32LE(this.pos);
  this.pos += 4;
  return res;
};

DBusBuffer.prototype.readDouble = function () {
  this.align(3);
  var res = this.buffer.readDoubleLE(this.pos);
  this.pos += 8;
  return res;
};

DBusBuffer.prototype.readString = function (len) {
  if (len === 0) {
    this.pos++;
    return '';
  }
  var res = this.buffer.toString('utf8', this.pos, this.pos + len);
  this.pos += len + 1; // dbus strings are always zero-terminated ('s' and 'g' types)
  return res;
};

DBusBuffer.prototype.readTree = function readTree(tree) {
  switch (tree.type) {
    case '(':
    case '{':
    case 'r':
      this.align(3);
      return this.readStruct(tree.child);
    case 'a':
      if (!tree.child || tree.child.length !== 1)
        throw new Error('Incorrect array element signature');
      var arrayBlobLength = this.readInt32();
      return this.readArray(tree.child[0], arrayBlobLength);
    case 'v':
      return this.readVariant();
    default:
      return this.readSimpleType(tree.type);
  }
};

DBusBuffer.prototype.read = function read(signature) {
  var tree = parseSignature(signature);
  return this.readStruct(tree);
};

DBusBuffer.prototype.readVariant = function readVariant() {
  var signature = this.readSimpleType('g');
  var tree = parseSignature(signature);
  return [tree, this.readStruct(tree)];
};

DBusBuffer.prototype.readStruct = function readStruct(struct) {
  var result = [];
  for (var i = 0; i < struct.length; ++i) {
    result.push(this.readTree(struct[i]));
  }
  return result;
};

DBusBuffer.prototype.readArray = function readArray(eleType, arrayBlobSize) {
  var result;
  var start = this.pos;

  // special case: treat ay as Buffer
  if (eleType.type === 'y' && this.options.ayBuffer) {
    this.pos += arrayBlobSize;
    return this.buffer.slice(start, this.pos);
  }

  // end of array is start of first element + array size
  // we need to add 4 bytes if not on 8-byte boundary
  // and array element needs 8 byte alignment
  if (['x', 't', 'd', '{', '(', 'r'].indexOf(eleType.type) !== -1)
    this.align(3);
  var end = this.pos + arrayBlobSize;
  result = [];
  while (this.pos < end) result.push(this.readTree(eleType));
  return result;
};

DBusBuffer.prototype.readSimpleType = function readSimpleType(t) {
  var data, len, word0, word1;
  switch (t) {
    case 'y':
      return this.readInt8();
    case 'b':
      // TODO: spec says that true is strictly 1 and false is strictly 0
      // shold we error (or warn?) when non 01 values?
      return this.readInt32() ? true : false;
    case 'n':
      return this.readSInt16();
    case 'q':
      return this.readInt16();
    case 'u':
      return this.readInt32();
    case 'i':
      return this.readSInt32();
    case 'g':
      len = this.readInt8();
      return this.readString(len);
    case 's':
    case 'o':
      len = this.readInt32();
      return this.readString(len);
    // TODO: validate object path here
    //if (t === 'o' && !isValidObjectPath(str))
    //  throw new Error('string is not a valid object path'));
    case 'x':
      //signed
      this.align(3);
      word0 = this.readInt32();
      word1 = this.readInt32();
      data = Long.fromBits(word0, word1, false);
      if (this.options.ReturnLongjs) return data;
      return data.toNumber(); // convert to number (good up to 53 bits)
    case 't':
      //unsigned
      this.align(3);
      word0 = this.readInt32();
      word1 = this.readInt32();
      data = Long.fromBits(word0, word1, true);
      if (this.options.ReturnLongjs) return data;
      return data.toNumber(); // convert to number (good up to 53 bits)
    case 'd':
      return this.readDouble();
    default:
      throw new Error(`Unsupported type: ${t}`);
  }
};

module.exports = DBusBuffer;