fix(webdav): optimize `HEAD` request (close #5182)

server/webdav.go

@@ -51,6 +51,7 @@ func WebDAVAuth(c *gin.Context) {
 	username, password, ok := c.Request.BasicAuth()
 	if !ok {
 		bt := c.GetHeader("Authorization")
+		log.Debugf("[webdav auth] token: %s", bt)
 		if strings.HasPrefix(bt, "Bearer") {
 			bt = strings.TrimPrefix(bt, "Bearer ")
 			token := setting.GetStr(conf.Token)

server/webdav/prop.go

@@ -460,7 +460,7 @@ type ETager interface {
 func findETag(ctx context.Context, ls LockSystem, name string, fi model.Obj) (string, error) {
 	if do, ok := fi.(ETager); ok {
 		etag, err := do.ETag(ctx)
-		if err != ErrNotImplemented {
+		if !errors.Is(err, ErrNotImplemented) {
 			return etag, err
 		}
 	}

server/webdav/webdav.go

@@ -8,7 +8,6 @@ package webdav // import "golang.org/x/net/webdav"
 import (
 	"errors"
 	"fmt"
-	"github.com/alist-org/alist/v3/internal/stream"
 	"net/http"
 	"net/url"
 	"os"
@@ -16,6 +15,8 @@ import (
 	"strings"
 	"time"
 
+	"github.com/alist-org/alist/v3/internal/stream"
+
 	"github.com/alist-org/alist/v3/internal/errs"
 	"github.com/alist-org/alist/v3/internal/fs"
 	"github.com/alist-org/alist/v3/internal/model"
@@ -219,20 +220,24 @@ func (h *Handler) handleGetHeadPost(w http.ResponseWriter, r *http.Request) (sta
 	user := ctx.Value("user").(*model.User)
 	reqPath, err = user.JoinPath(reqPath)
 	if err != nil {
-		return 403, err
+		return http.StatusForbidden, err
 	}
 	fi, err := fs.Get(ctx, reqPath, &fs.GetArgs{})
 	if err != nil {
 		return http.StatusNotFound, err
 	}
-	if fi.IsDir() {
-		return http.StatusMethodNotAllowed, nil
-	}
 	etag, err := findETag(ctx, h.LockSystem, reqPath, fi)
 	if err != nil {
 		return http.StatusInternalServerError, err
 	}
 	w.Header().Set("ETag", etag)
+	if r.Method == http.MethodHead {
+		w.Header().Set("Content-Length", fmt.Sprintf("%d", fi.GetSize()))
+		return http.StatusOK, nil
+	}
+	if fi.IsDir() {
+		return http.StatusMethodNotAllowed, nil
+	}
 	// Let ServeContent determine the Content-Type header.
 	storage, _ := fs.GetStorage(reqPath, &fs.GetStoragesArgs{})
 	downProxyUrl := storage.GetStorage().DownProxyUrl