fix handling for h2c

modules/caddyhttp/app.go

@@ -552,6 +552,7 @@ func (app *App) Start() error {
 					// check if the connection is h2c
 					ln = &http2Listener{
 						useTLS:   useTLS,
+						useH2C:   h2cok,
 						Listener: ln,
 						logger:   app.logger,
 					}

modules/caddyhttp/http2listener.go

@@ -23,6 +23,7 @@ type connectionStater interface {
 // wrapper authors will hopefully implement it.
 type http2Listener struct {
 	useTLS bool
+	useH2C bool
 	net.Listener
 	logger *zap.Logger
 }
@@ -52,6 +53,13 @@ func (h *http2Listener) Accept() (net.Conn, error) {
 		}, nil
 	}
 
+	if h.useH2C {
+		return &http2Conn{
+			idx:  len(http2.ClientPreface),
+			Conn: conn,
+		}, nil
+	}
+
 	return &http2Conn{
 		Conn: conn,
 	}, nil