使用createReadStream在演示脚本中出错

Question

为什么我在node.js中收到此错误？这个想法是在完全读取一堆之后写一些东西，以避免在读取文件内容之前放入数据。因为他们要求更多细节，所以我在这里放了一些虚拟文本，以满足最小文本的要求。

> pi@raspberrypi:~/nodetest $ sudo node readstream.js
VAR1=2
VAR3=4
Fri Jan 06 2017 12:11:37 GMT+0000 (UTC)
Fri Jan 06 2017 12:33:14 GMT+0000 (UTC)
Fri Jan 06 2017 12:34:12 GMT+0000 (UTC)
appending
appending
appending
appending
appending
appending
appending

Fri Jan 06 2017 12:11:37 GMT+0000 (UTC)
Fri Jan 06 2017 12:33:14 GMT+0000 (UTC)
Fri Jan
Fri Jan 06 2017 12:11:37 GMT+0000 (UTC)
Fri Jan 06 2017 12:33:14 GMT+0000 (UTC)
Fri Jan
end

events.js:72
        throw er; // Unhandled 'error' event
              ^
Error: EBADF, write

我的代码：

fs = require('fs');
path = 'config.txt';
readableStream = fs.createReadStream(path);
readableStream.setEncoding('utf8');
readableStream.once('data', function(data){ console.log(data); }  );

readableStream.once('end', function(){
 fs.open(path, 'a+', function(err, fd){

  readStream = fs.createReadStream(null, {fd: fd, encoding: 'utf8', start: 14, end: 100});
  readStream.once('data', function(data){ console.log(data);} );
  readStream.once('data', console.log); // shorter
  readStream.once('end', function(){
     console.log('end');
     try {
      readStream.removeListener('data', function(data){} );
      writeStream = fs.createWriteStream(null, {fd: fd, encoding: 'utf8', flags: 'a+'});
      writeStream.write('appending\n'); // not working???
     }
     catch(err) {
      console.log('error: [' + err.message + ']');
     };

  } );

 } );
} );