Allow LocalURL to be passed in the Host header

Fix go-gitea#32554

modules/httplib/url.go

@@ -68,12 +68,19 @@ func GuessCurrentHostURL(ctx context.Context) string {
 	// There are some cases:
 	// 1. The reverse proxy is configured correctly, it passes "X-Forwarded-Proto/Host" headers. Perfect, Gitea can handle it correctly.
 	// 2. The reverse proxy is not configured correctly, doesn't pass "X-Forwarded-Proto/Host" headers, eg: only one "proxy_pass http://gitea:3000" in Nginx.
-	// 3. There is no reverse proxy.
+	// 3. There is no reverse proxy. In this case, we allow the configured LocalURL to be passed in the Host header.
 	// Without an extra config option, Gitea is impossible to distinguish between case 2 and case 3,
 	// then case 2 would result in wrong guess like guessed AppURL becomes "http://gitea:3000/", which is not accessible by end users.
 	// So in the future maybe it should introduce a new config option, to let site admin decide how to guess the AppURL.
 	reqScheme := getRequestScheme(req)
 	if reqScheme == "" {
+		localURL, err := url.Parse(setting.LocalURL)
+		if err == nil &&
+			strings.EqualFold(req.Host, localURL.Host) &&
+			(req.TLS != nil) == (localURL.Scheme == "https") {
+			return strings.TrimSuffix(setting.LocalURL, setting.AppSubURL+"/")
+		}
+
 		return strings.TrimSuffix(setting.AppURL, setting.AppSubURL+"/")
 	}
 	// X-Forwarded-Host has many problems: non-standard, not well-defined (X-Forwarded-Port or not), conflicts with Host header.

modules/httplib/url_test.go

@@ -5,6 +5,7 @@ package httplib
 
 import (
 	"context"
+	"crypto/tls"
 	"net/http"
 	"testing"
 
@@ -39,6 +40,33 @@ func TestIsRelativeURL(t *testing.T) {
 	}
 }
 
+func TestGuessCurrentHostURL(t *testing.T) {
+	defer test.MockVariableValue(&setting.AppURL, "http://cfg-host/sub/")()
+	defer test.MockVariableValue(&setting.LocalURL, "http://localhost:3000/sub/")()
+	defer test.MockVariableValue(&setting.AppSubURL, "/sub")()
+
+	ctx := context.Background()
+	assert.Equal(t, "http://cfg-host", GuessCurrentHostURL(ctx))
+
+	ctx = context.WithValue(ctx, RequestContextKey, &http.Request{
+		Host: "localhost:3000",
+	})
+	assert.Equal(t, "http://localhost:3000", GuessCurrentHostURL(ctx))
+
+	ctx = context.WithValue(ctx, RequestContextKey, &http.Request{
+		Host: "localhost:3000",
+		TLS:  &tls.ConnectionState{},
+	})
+	assert.Equal(t, "http://cfg-host", GuessCurrentHostURL(ctx))
+
+	defer test.MockVariableValue(&setting.LocalURL, "https://localhost/sub/")()
+	ctx = context.WithValue(ctx, RequestContextKey, &http.Request{
+		Host: "localhost",
+		TLS:  &tls.ConnectionState{},
+	})
+	assert.Equal(t, "https://localhost", GuessCurrentHostURL(ctx))
+}
+
 func TestMakeAbsoluteURL(t *testing.T) {
 	defer test.MockVariableValue(&setting.Protocol, "http")()
 	defer test.MockVariableValue(&setting.AppURL, "http://cfg-host/sub/")()