enable h2c for vhost server (#4582)

pkg/util/vhost/http.go

@@ -29,6 +29,8 @@ import (
 
 	libio "github.com/fatedier/golib/io"
 	"github.com/fatedier/golib/pool"
+	"golang.org/x/net/http2"
+	"golang.org/x/net/http2/h2c"
 
 	httppkg "github.com/fatedier/frp/pkg/util/http"
 	"github.com/fatedier/frp/pkg/util/log"
@@ -41,7 +43,7 @@ type HTTPReverseProxyOptions struct {
 }
 
 type HTTPReverseProxy struct {
-	proxy       *httputil.ReverseProxy
+	proxy       http.Handler
 	vhostRouter *Routers
 
 	responseHeaderTimeout time.Duration
@@ -138,7 +140,7 @@ func NewHTTPReverseProxy(option HTTPReverseProxyOptions, vhostRouter *Routers) *
 			_, _ = rw.Write(getNotFoundPageContent())
 		},
 	}
-	rp.proxy = proxy
+	rp.proxy = h2c.NewHandler(proxy, &http2.Server{})
 	return rp
 }