feat(proxy): add HTTP to HTTPS redirection support

pkg/util/vhost/http.go

@@ -39,11 +39,15 @@ var ErrNoRouteFound = errors.New("no route found")
 
 type HTTPReverseProxyOptions struct {
 	ResponseHeaderTimeoutS int64
+	// HTTPSRedirector, if set, redirects requests whose host has no HTTP
+	// route but opted into HTTP to HTTPS redirection.
+	HTTPSRedirector *HTTPSRedirector
 }
 
 type HTTPReverseProxy struct {
-	proxy       http.Handler
-	vhostRouter *Routers
+	proxy           http.Handler
+	vhostRouter     *Routers
+	httpsRedirector *HTTPSRedirector
 
 	responseHeaderTimeout time.Duration
 }
@@ -55,6 +59,7 @@ func NewHTTPReverseProxy(option HTTPReverseProxyOptions, vhostRouter *Routers) *
 	rp := &HTTPReverseProxy{
 		responseHeaderTimeout: time.Duration(option.ResponseHeaderTimeoutS) * time.Second,
 		vhostRouter:           vhostRouter,
+		httpsRedirector:       option.HTTPSRedirector,
 	}
 	proxy := &httputil.ReverseProxy{
 		// Modify incoming requests by route policies.
@@ -281,6 +286,12 @@ func (rp *HTTPReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request)
 		return
 	}
 
+	// Hosts without any real HTTP route may still ask for a redirect to
+	// their HTTPS endpoint; registered HTTP routes always take precedence.
+	if rc == nil && rp.httpsRedirector != nil && rp.httpsRedirector.Redirect(rw, newreq) {
+		return
+	}
+
 	if req.Method == http.MethodConnect {
 		rp.connectHandler(rw, newreq)
 	} else {

pkg/util/vhost/https_redirect.go

@@ -0,0 +1,83 @@
+// Copyright 2026 The frp Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package vhost
+
+import (
+	"net/http"
+	"strconv"
+	"sync"
+
+	httppkg "github.com/fatedier/frp/pkg/util/http"
+)
+
+// HTTPSRedirector tracks domains of HTTPS proxies that opted into automatic
+// HTTP to HTTPS redirection. The HTTP reverse proxy consults it as a fallback
+// for hosts that have no real HTTP route, so registered HTTP proxies on the
+// same domain always take precedence over the redirect.
+type HTTPSRedirector struct {
+	mu      sync.RWMutex
+	domains map[string]int // domain -> number of proxies requesting the redirect
+	port    int            // port used in the redirect Location, as seen by browsers
+}
+
+func NewHTTPSRedirector(port int) *HTTPSRedirector {
+	return &HTTPSRedirector{
+		domains: make(map[string]int),
+		port:    port,
+	}
+}
+
+func (r *HTTPSRedirector) Add(domain string) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	r.domains[domain]++
+}
+
+func (r *HTTPSRedirector) Remove(domain string) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+	if r.domains[domain] <= 1 {
+		delete(r.domains, domain)
+	} else {
+		r.domains[domain]--
+	}
+}
+
+func (r *HTTPSRedirector) match(host string) bool {
+	r.mu.RLock()
+	defer r.mu.RUnlock()
+	return r.domains[host] > 0
+}
+
+// Redirect responds with a redirect to the HTTPS endpoint of the requested
+// host if the host opted into redirection. It reports whether the request
+// was handled.
+func (r *HTTPSRedirector) Redirect(rw http.ResponseWriter, req *http.Request) bool {
+	if req.Method == http.MethodConnect {
+		return false
+	}
+	host, err := httppkg.CanonicalHost(req.Host)
+	if err != nil || !r.match(host) {
+		return false
+	}
+
+	target := "https://" + host
+	if r.port != 443 {
+		target += ":" + strconv.Itoa(r.port)
+	}
+	target += req.URL.RequestURI()
+	http.Redirect(rw, req, target, http.StatusMovedPermanently)
+	return true
+}

pkg/util/vhost/https_redirect_test.go

@@ -0,0 +1,46 @@
+package vhost
+
+import (
+	"net/http/httptest"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestHTTPSRedirectorRedirect(t *testing.T) {
+	r := NewHTTPSRedirector(443)
+	r.Add("a.example.com")
+
+	// registered domain, port stripped from host, path and query preserved
+	req := httptest.NewRequest("GET", "http://a.example.com:8080/foo?x=1", nil)
+	rw := httptest.NewRecorder()
+	require.True(t, r.Redirect(rw, req))
+	require.Equal(t, 301, rw.Code)
+	require.Equal(t, "https://a.example.com/foo?x=1", rw.Header().Get("Location"))
+
+	// unknown domain is not handled
+	req = httptest.NewRequest("GET", "http://b.example.com/", nil)
+	require.False(t, r.Redirect(httptest.NewRecorder(), req))
+}
+
+func TestHTTPSRedirectorNonDefaultPort(t *testing.T) {
+	r := NewHTTPSRedirector(8443)
+	r.Add("a.example.com")
+
+	req := httptest.NewRequest("GET", "http://a.example.com/", nil)
+	rw := httptest.NewRecorder()
+	require.True(t, r.Redirect(rw, req))
+	require.Equal(t, "https://a.example.com:8443/", rw.Header().Get("Location"))
+}
+
+func TestHTTPSRedirectorRefCount(t *testing.T) {
+	r := NewHTTPSRedirector(443)
+	r.Add("a.example.com")
+	r.Add("a.example.com")
+
+	r.Remove("a.example.com")
+	require.True(t, r.match("a.example.com"), "domain removed while another proxy still references it")
+
+	r.Remove("a.example.com")
+	require.False(t, r.match("a.example.com"))
+}