Comment 1 by runner.mei:

Sorry, the above code was wrong.
  var buffer bytes.Buffer
  ch := make(chan io.Reader)
  // .....
  for _, reader := range ch {
    buffer.Reset()    // buffer is reused, redue gc
    ioutil.Copy(buffer, reader)
    dec := json.NewDecoderWithBytes(buffer.Bytes()) // This line of code above was wrong.
    dec.UseNumber()
    dec.Decode(&m) 
  }

Comment 2:

You can use bytes.NewReader with json.NewDecoder.

Status changed to WorkingAsIntended.

Comment 3 by runner.mei:

use json.NewDecoder with bytes.NewReader, should copy all bytes to Decoder, it is what I
want to avoid。I want to reuse buffer and zero copy, Reducing the number of GC