code: function readChunk(path, start, end, callback) {
    if (end < 0) {
      return readLastChunk(path, start, end, callback);
    }
    var stream = nodeFs.createReadStream(path, {
      start: start,
      end: end - 1
    });
    var chunks = [];
    stream.on("readable", function () {
      var chunk = stream.read();
      if (chunk === null) return callback(null, Buffer.concat(chunks));
      return chunks.push(chunk);
    });
    stream.on("error", function (err) {
      if (err.code === "ENOENT") return callback();
      return callback(err);
    });
  }
docs: Reads bytes from inclusive [start, end) exclusive for given path. => binary => undefined if file does not exist