Make ROOT_URL support using request Host header (#32564)

Resolve #32554

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/httplib/url.go

@@ -70,11 +70,16 @@ func GuessCurrentHostURL(ctx context.Context) string {
 	// 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.
-	// 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.
+	// Without more information, 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/" behind a "https" reverse proxy, which is not accessible by end users.
+	// So we introduced "UseHostHeader" option, it could be enabled by setting "ROOT_URL" to empty
 	reqScheme := getRequestScheme(req)
 	if reqScheme == "" {
+		// if no reverse proxy header, try to use "Host" header for absolute URL
+		if setting.UseHostHeader && req.Host != "" {
+			return util.Iif(req.TLS == nil, "http://", "https://") + req.Host
+		}
+		// fall back to default AppURL
 		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 +40,25 @@ func TestIsRelativeURL(t *testing.T) {
 	}
 }
 
+func TestGuessCurrentHostURL(t *testing.T) {
+	defer test.MockVariableValue(&setting.AppURL, "http://cfg-host/sub/")()
+	defer test.MockVariableValue(&setting.AppSubURL, "/sub")()
+	defer test.MockVariableValue(&setting.UseHostHeader, false)()
+
+	ctx := t.Context()
+	assert.Equal(t, "http://cfg-host", GuessCurrentHostURL(ctx))
+
+	ctx = context.WithValue(ctx, RequestContextKey, &http.Request{Host: "localhost:3000"})
+	assert.Equal(t, "http://cfg-host", GuessCurrentHostURL(ctx))
+
+	defer test.MockVariableValue(&setting.UseHostHeader, true)()
+	ctx = context.WithValue(ctx, RequestContextKey, &http.Request{Host: "http-host:3000"})
+	assert.Equal(t, "http://http-host:3000", GuessCurrentHostURL(ctx))
+
+	ctx = context.WithValue(ctx, RequestContextKey, &http.Request{Host: "http-host", TLS: &tls.ConnectionState{}})
+	assert.Equal(t, "https://http-host", GuessCurrentHostURL(ctx))
+}
+
 func TestMakeAbsoluteURL(t *testing.T) {
 	defer test.MockVariableValue(&setting.Protocol, "http")()
 	defer test.MockVariableValue(&setting.AppURL, "http://cfg-host/sub/")()

modules/setting/server.go

@@ -46,25 +46,37 @@ var (
 	// AppURL is the Application ROOT_URL. It always has a '/' suffix
 	// It maps to ini:"ROOT_URL"
 	AppURL string
-	// AppSubURL represents the sub-url mounting point for gitea. It is either "" or starts with '/' and ends without '/', such as '/{subpath}'.
+
+	// AppSubURL represents the sub-url mounting point for gitea, parsed from "ROOT_URL"
+	// It is either "" or starts with '/' and ends without '/', such as '/{sub-path}'.
 	// This value is empty if site does not have sub-url.
 	AppSubURL string
-	// UseSubURLPath makes Gitea handle requests with sub-path like "/sub-path/owner/repo/...", to make it easier to debug sub-path related problems without a reverse proxy.
+
+	// UseSubURLPath makes Gitea handle requests with sub-path like "/sub-path/owner/repo/...",
+	// to make it easier to debug sub-path related problems without a reverse proxy.
 	UseSubURLPath bool
+
+	// UseHostHeader makes Gitea prefer to use the "Host" request header for construction of absolute URLs.
+	UseHostHeader bool
+
 	// AppDataPath is the default path for storing data.
 	// It maps to ini:"APP_DATA_PATH" in [server] and defaults to AppWorkPath + "/data"
 	AppDataPath string
+
 	// LocalURL is the url for locally running applications to contact Gitea. It always has a '/' suffix
 	// It maps to ini:"LOCAL_ROOT_URL" in [server]
 	LocalURL string
-	// AssetVersion holds a opaque value that is used for cache-busting assets
+
+	// AssetVersion holds an opaque value that is used for cache-busting assets
 	AssetVersion string
 
-	appTempPathInternal string // the temporary path for the app, it is only an internal variable, do not use it, always use AppDataTempDir
+	// appTempPathInternal is the temporary path for the app, it is only an internal variable
+	// DO NOT use it directly, always use AppDataTempDir
+	appTempPathInternal string
 
 	Protocol                   Scheme
-	UseProxyProtocol           bool // `ini:"USE_PROXY_PROTOCOL"`
-	ProxyProtocolTLSBridging   bool //`ini:"PROXY_PROTOCOL_TLS_BRIDGING"`
+	UseProxyProtocol           bool
+	ProxyProtocolTLSBridging   bool
 	ProxyProtocolHeaderTimeout time.Duration
 	ProxyProtocolAcceptUnknown bool
 	Domain                     string
@@ -181,13 +193,14 @@ func loadServerFrom(rootCfg ConfigProvider) {
 		EnableAcme = sec.Key("ENABLE_LETSENCRYPT").MustBool(false)
 	}
 
-	Protocol = HTTP
 	protocolCfg := sec.Key("PROTOCOL").String()
 	if protocolCfg != "https" && EnableAcme {
 		log.Fatal("ACME could only be used with HTTPS protocol")
 	}
 
 	switch protocolCfg {
+	case "", "http":
+		Protocol = HTTP
 	case "https":
 		Protocol = HTTPS
 		if EnableAcme {
@@ -243,7 +256,7 @@ func loadServerFrom(rootCfg ConfigProvider) {
 		case "unix":
 			log.Warn("unix PROTOCOL value is deprecated, please use http+unix")
 			fallthrough
-		case "http+unix":
+		default: // "http+unix"
 			Protocol = HTTPUnix
 		}
 		UnixSocketPermissionRaw := sec.Key("UNIX_SOCKET_PERMISSION").MustString("666")
@@ -256,6 +269,8 @@ func loadServerFrom(rootCfg ConfigProvider) {
 		if !filepath.IsAbs(HTTPAddr) {
 			HTTPAddr = filepath.Join(AppWorkPath, HTTPAddr)
 		}
+	default:
+		log.Fatal("Invalid PROTOCOL %q", Protocol)
 	}
 	UseProxyProtocol = sec.Key("USE_PROXY_PROTOCOL").MustBool(false)
 	ProxyProtocolTLSBridging = sec.Key("PROXY_PROTOCOL_TLS_BRIDGING").MustBool(false)
@@ -268,12 +283,16 @@ func loadServerFrom(rootCfg ConfigProvider) {
 	PerWritePerKbTimeout = sec.Key("PER_WRITE_PER_KB_TIMEOUT").MustDuration(PerWritePerKbTimeout)
 
 	defaultAppURL := string(Protocol) + "://" + Domain + ":" + HTTPPort
-	AppURL = sec.Key("ROOT_URL").MustString(defaultAppURL)
+	AppURL = sec.Key("ROOT_URL").String()
+	if AppURL == "" {
+		UseHostHeader = true
+		AppURL = defaultAppURL
+	}
 
 	// Check validity of AppURL
 	appURL, err := url.Parse(AppURL)
 	if err != nil {
-		log.Fatal("Invalid ROOT_URL '%s': %s", AppURL, err)
+		log.Fatal("Invalid ROOT_URL %q: %s", AppURL, err)
 	}
 	// Remove default ports from AppURL.
 	// (scheme-based URL normalization, RFC 3986 section 6.2.3)
@@ -309,13 +328,15 @@ func loadServerFrom(rootCfg ConfigProvider) {
 		defaultLocalURL = AppURL
 	case FCGIUnix:
 		defaultLocalURL = AppURL
-	default:
+	case HTTP, HTTPS:
 		defaultLocalURL = string(Protocol) + "://"
 		if HTTPAddr == "0.0.0.0" {
 			defaultLocalURL += net.JoinHostPort("localhost", HTTPPort) + "/"
 		} else {
 			defaultLocalURL += net.JoinHostPort(HTTPAddr, HTTPPort) + "/"
 		}
+	default:
+		log.Fatal("Invalid PROTOCOL %q", Protocol)
 	}
 	LocalURL = sec.Key("LOCAL_ROOT_URL").MustString(defaultLocalURL)
 	LocalURL = strings.TrimRight(LocalURL, "/") + "/"