fix!: reverse proxy to sub-directory (#3483)

from this commit, if you want reverse proxy to sub-directory like `alist` with `nginx`, you need config:

```nginx
location /alist/ {
    proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
    proxy_set_header X-Forwarded-Proto $scheme;
    proxy_set_header Host $http_host;
    proxy_set_header X-Real-IP $remote_addr;
    proxy_set_header Range $http_range;
    proxy_set_header If-Range $http_if_range;
    proxy_redirect off;
    proxy_pass http://127.0.0.1:5244/alist/;
    # the max size of file to upload
    client_max_body_size 20000m;
}
```

server/router.go

@@ -4,6 +4,7 @@ import (
 	"github.com/alist-org/alist/v3/cmd/flags"
 	"github.com/alist-org/alist/v3/internal/conf"
 	"github.com/alist-org/alist/v3/internal/message"
+	"github.com/alist-org/alist/v3/pkg/utils"
 	"github.com/alist-org/alist/v3/server/common"
 	"github.com/alist-org/alist/v3/server/handles"
 	"github.com/alist-org/alist/v3/server/middlewares"
@@ -12,21 +13,27 @@ import (
 	"github.com/gin-gonic/gin"
 )
 
-func Init(r *gin.Engine) {
-	common.SecretKey = []byte(conf.Conf.JwtSecret)
-	Cors(r)
-	r.Use(middlewares.StoragesLoaded)
-	if conf.Conf.MaxConnections > 0 {
-		r.Use(middlewares.MaxAllowed(conf.Conf.MaxConnections))
+func Init(e *gin.Engine) {
+	if !utils.SliceContains([]string{"", "/"}, conf.URL.Path) {
+		e.GET("/", func(c *gin.Context) {
+			c.Redirect(302, conf.URL.Path)
+		})
 	}
-	WebDav(r.Group("/dav"))
+	g := e.Group(conf.URL.Path)
+	common.SecretKey = []byte(conf.Conf.JwtSecret)
+	Cors(g)
+	g.Use(middlewares.StoragesLoaded)
+	if conf.Conf.MaxConnections > 0 {
+		g.Use(middlewares.MaxAllowed(conf.Conf.MaxConnections))
+	}
+	WebDav(g.Group("/dav"))
 
-	r.GET("/favicon.ico", handles.Favicon)
-	r.GET("/i/:link_name", handles.Plist)
-	r.GET("/d/*path", middlewares.Down, handles.Down)
-	r.GET("/p/*path", middlewares.Down, handles.Proxy)
+	g.GET("/favicon.ico", handles.Favicon)
+	g.GET("/i/:link_name", handles.Plist)
+	g.GET("/d/*path", middlewares.Down, handles.Down)
+	g.GET("/p/*path", middlewares.Down, handles.Proxy)
 
-	api := r.Group("/api")
+	api := g.Group("/api")
 	auth := api.Group("", middlewares.Auth)
 
 	api.POST("/auth/login", handles.Login)
@@ -46,9 +53,11 @@ func Init(r *gin.Engine) {
 	_fs(auth.Group("/fs"))
 	admin(auth.Group("/admin", middlewares.AuthAdmin))
 	if flags.Dev {
-		dev(r.Group("/dev"))
+		dev(g.Group("/dev"))
 	}
-	static.Static(r)
+	static.Static(g, func(handlers ...gin.HandlerFunc) {
+		e.NoRoute(handlers...)
+	})
 }
 
 func admin(g *gin.RouterGroup) {
@@ -124,10 +133,9 @@ func _fs(g *gin.RouterGroup) {
 	g.POST("/add_qbit", handles.AddQbittorrent)
 }
 
-func Cors(r *gin.Engine) {
+func Cors(r *gin.RouterGroup) {
 	config := cors.DefaultConfig()
 	config.AllowAllOrigins = true
-	//config.AllowHeaders = append(config.AllowHeaders, "Authorization", "range", "File-Path", "As-Task", "Password")
 	config.AllowHeaders = []string{"*"}
 	config.AllowMethods = []string{"*"}
 	r.Use(cors.New(config))

server/static/config.go

@@ -1,7 +1,6 @@
 package static
 
 import (
-	"net/url"
 	"strings"
 
 	"github.com/alist-org/alist/v3/internal/conf"
@@ -15,20 +14,16 @@ type SiteConfig struct {
 }
 
 func getSiteConfig() SiteConfig {
-	u, err := url.Parse(conf.Conf.SiteURL)
-	if err != nil {
-		utils.Log.Fatalf("can't parse site_url: %+v", err)
-	}
 	siteConfig := SiteConfig{
 		ApiURL:   conf.Conf.SiteURL,
-		BasePath: u.Path,
+		BasePath: conf.URL.Path,
 		Cdn:      strings.ReplaceAll(strings.TrimSuffix(conf.Conf.Cdn, "/"), "$version", conf.WebVersion),
 	}
 	if siteConfig.BasePath != "" {
 		siteConfig.BasePath = utils.FixAndCleanPath(siteConfig.BasePath)
 	}
 	if siteConfig.Cdn == "" {
-		siteConfig.Cdn = siteConfig.BasePath
+		siteConfig.Cdn = strings.TrimSuffix(siteConfig.BasePath, "/")
 	}
 	return siteConfig
 }

server/static/static.go

@@ -62,7 +62,7 @@ func UpdateIndex() {
 	}
 }
 
-func Static(r *gin.Engine) {
+func Static(r *gin.RouterGroup, noRoute func(handlers ...gin.HandlerFunc)) {
 	InitIndex()
 	folders := []string{"assets", "images", "streamer", "static"}
 	r.Use(func(c *gin.Context) {
@@ -81,7 +81,7 @@ func Static(r *gin.Engine) {
 		r.StaticFS(fmt.Sprintf("/%s/", folders[i]), http.FS(sub))
 	}
 
-	r.NoRoute(func(c *gin.Context) {
+	noRoute(func(c *gin.Context) {
 		c.Header("Content-Type", "text/html")
 		c.Status(200)
 		if strings.HasPrefix(c.Request.URL.Path, "/@manage") {

server/webdav.go

@@ -3,7 +3,9 @@ package server
 import (
 	"context"
 	"net/http"
+	"path"
 
+	"github.com/alist-org/alist/v3/internal/conf"
 	"github.com/alist-org/alist/v3/internal/model"
 	"github.com/alist-org/alist/v3/internal/op"
 	"github.com/alist-org/alist/v3/pkg/utils"
@@ -14,17 +16,14 @@ import (
 
 var handler *webdav.Handler
 
-func init() {
+func WebDav(dav *gin.RouterGroup) {
 	handler = &webdav.Handler{
-		Prefix:     "/dav",
+		Prefix:     path.Join(conf.URL.Path, "/dav"),
 		LockSystem: webdav.NewMemLS(),
 		Logger: func(request *http.Request, err error) {
 			log.Errorf("%s %s %+v", request.Method, request.URL.Path, err)
 		},
 	}
-}
-
-func WebDav(dav *gin.RouterGroup) {
 	dav.Use(WebDAVAuth)
 	dav.Any("/*path", ServeWebDAV)
 	dav.Any("", ServeWebDAV)