code: func HandleBytes(f func(b []byte, ctx *ProxyCtx) []byte) RespHandler {
  	return FuncRespHandler(func(resp *http.Response, ctx *ProxyCtx) *http.Response {
  		b, err := ioutil.ReadAll(resp.Body)
  		if err != nil {
  			ctx.Warnf("Cannot read response %s", err)
  			return resp
  		}
  		resp.Body.Close()
  
  		resp.Body = ioutil.NopCloser(bytes.NewBuffer(f(b, ctx)))
  		return resp
  	})
  }
docs: // HandleBytes will return a RespHandler that read the entire body of the request
  // to a byte array in memory, would run the user supplied f function on the byte arra,
  // and will replace the body of the original response with the resulting byte array.