创建一个 node.js 可写流，将数据代理到另一个可写流，但首先添加一些自己的数据

Question

I have a writable stream that I would like to wrap with a stream of my own to prepend some data to whatever goes into the output stream.

I would normally write inputStream.pipe(outputStream) , where inputStream would provide foo bar and outputStream would recieve foo bar .

I would like to be able to write inputStream.pipe(proxyStream('prefix ', outputStream)) , where inputStream would provide foo bar , but outputStream would recieve prefix foo bar .

I've tried the following code, but I get Error: write after end almost immediately after the pipe starts.

class DetectStream extends stream.Writable {
  constructor (prefix, output) {
    super();
    this._output = output;
    this._output.write(prefix, 'utf-8');
  }
  _write (chunk, enc, next) {
    this._output.write(chunk, enc, next);
  }
}

Answer 1

Why don't you just write to the outputStream before piping the inputStream into it?

function proxyStream (prefix, output) {
  output.write(prefix, 'utf-8')
  return output
}

Then use it just like you said:

inputStream.pipe(proxyStream('prefix ', outputStream))