code: func NewPktlineWriter(w io.Writer, c int) *PktlineWriter {
  	if pw, ok := w.(*PktlineWriter); ok {
  		return pw
  	}
  
  	return &PktlineWriter{
  		buf: make([]byte, 0, c),
  		pl:  newPktline(nil, w),
  	}
  }
docs: // NewPktlineWriter returns a new *PktlineWriter, which will write to the
  // underlying data stream "w". The internal buffer is initialized with the given
  // capacity, "c".
  //
  // If "w" is already a `*PktlineWriter`, it will be returned as-is.