ResponseWriterWrapper and HTTPInterfaces (#1644)

Signed-off-by: Tw <tw19881113@gmail.com>

caddyhttp/httpserver/responsewriterwrapper.go

@@ -0,0 +1,65 @@
+package httpserver
+
+import (
+	"bufio"
+	"net"
+	"net/http"
+)
+
+// ResponseWriterWrapper wrappers underlying ResponseWriter
+// and inherits its Hijacker/Pusher/CloseNotifier/Flusher as well.
+type ResponseWriterWrapper struct {
+	http.ResponseWriter
+}
+
+// Hijack implements http.Hijacker. It simply wraps the underlying
+// ResponseWriter's Hijack method if there is one, or returns an error.
+func (rww *ResponseWriterWrapper) Hijack() (net.Conn, *bufio.ReadWriter, error) {
+	if hj, ok := rww.ResponseWriter.(http.Hijacker); ok {
+		return hj.Hijack()
+	}
+	return nil, nil, NonHijackerError{Underlying: rww.ResponseWriter}
+}
+
+// Flush implements http.Flusher. It simply wraps the underlying
+// ResponseWriter's Flush method if there is one, or panics.
+func (rww *ResponseWriterWrapper) Flush() {
+	if f, ok := rww.ResponseWriter.(http.Flusher); ok {
+		f.Flush()
+	} else {
+		panic(NonFlusherError{Underlying: rww.ResponseWriter})
+	}
+}
+
+// CloseNotify implements http.CloseNotifier.
+// It just inherits the underlying ResponseWriter's CloseNotify method.
+// It panics if the underlying ResponseWriter is not a CloseNotifier.
+func (rww *ResponseWriterWrapper) CloseNotify() <-chan bool {
+	if cn, ok := rww.ResponseWriter.(http.CloseNotifier); ok {
+		return cn.CloseNotify()
+	}
+	panic(NonCloseNotifierError{Underlying: rww.ResponseWriter})
+}
+
+// Push implements http.Pusher.
+// It just inherits the underlying ResponseWriter's Push method.
+// It panics if the underlying ResponseWriter is not a Pusher.
+func (rww *ResponseWriterWrapper) Push(target string, opts *http.PushOptions) error {
+	if pusher, hasPusher := rww.ResponseWriter.(http.Pusher); hasPusher {
+		return pusher.Push(target, opts)
+	}
+
+	return NonPusherError{Underlying: rww.ResponseWriter}
+}
+
+// HTTPInterfaces mix all the interfaces that middleware ResponseWriters need to support.
+type HTTPInterfaces interface {
+	http.ResponseWriter
+	http.Pusher
+	http.Flusher
+	http.CloseNotifier
+	http.Hijacker
+}
+
+// Interface guards
+var _ HTTPInterfaces = (*ResponseWriterWrapper)(nil)