func (rww *ResponseWriterWrapper) Push(target string, opts *http.PushOptions) error {
	if pusher, ok := rww.ResponseWriter.(http.Pusher); ok {
		return pusher.Push(target, opts)
	}
	return ErrNotImplemented
}
Push implements http.Pusher. It simply calls the underlying
ResponseWriter's Push method if there is one, or returns
ErrNotImplemented otherwise.
package caddyhttp
import (
	"bufio"
	"bytes"
	"fmt"
	"io"
	"net"
	"net/http"
)
type ResponseWriterWrapper struct {
	http.ResponseWriter
}
func (rww *ResponseWriterWrapper) Hijack() (net.Conn, *bufio.ReadWriter, error) {
	if hj, ok := rww.ResponseWriter.(http.Hijacker); ok {
		return hj.Hijack()
	}
	return nil, nil, ErrNotImplemented
}
func (rww *ResponseWriterWrapper) Flush() {
	if f, ok := rww.ResponseWriter.(http.Flusher); ok {
		f.Flush()
	}
}