fs.readFile 只读 2 个前符号

我尝试像这样使用sdk fs：

  var fs = require('sdk/io/fs');
  fs.readFile(filepath, 'utf-8', function (error, data) {
    if (components.isSuccessCode(error)) {
      var lines = data.toString().split(/['r'n]+/);
      for (var i = 0; i < lines.length; i++) {
        listener.process(lines[i]);
      }
    }
    else {
      callback({error: error});
    }
  }

但我只得到 2 个文件的第一个符号（2 MB）。为什么我会有这么奇怪的行为？

来自 sdk 的读取文件声明：

function readFile(path, encoding, callback) {
    if (isFunction(encoding)) {
      callback = encoding
      encoding = null
    }
    let buffer = null;
    try {
      let readStream = new ReadStream(path);
      readStream.on("data", function(data) {
        if (!buffer){
          buffer = data;
        }
        else{
          buffer = Buffer.concat([buffer, data], 2);
        }
      });
      readStream.on("error", function onError(error) {
        callback(error);
      });
      readStream.on("end", function onEnd() {
        // Note: Need to destroy before invoking a callback
        // so that file descriptor is released.
        readStream.destroy();
        callback(null, buffer);
      });
    }
    catch (error) {
      setTimeout(callback, 0, error);
    }
  };