Fix fs.Sub problems on Windows

Author: aldas

context_fs_go1.16.go

@@ -28,7 +28,7 @@ func fsFile(c Context, file string, filesystem fs.FS) error {
 
 	fi, _ := f.Stat()
 	if fi.IsDir() {
-		file = filepath.Join(file, indexPage)
+		file = filepath.ToSlash(filepath.Join(file, indexPage))
 		f, err = filesystem.Open(file)
 		if err != nil {
 			return ErrNotFound

echo_fs_go1.16.go

@@ -62,7 +62,7 @@ func StaticDirectoryHandler(fileSystem fs.FS, disablePathUnescaping bool) Handle
 		}
 
 		// fs.FS.Open() already assumes that file names are relative to FS root path and considers name with prefix `/` as invalid
-		name := filepath.Clean(strings.TrimPrefix(p, "/"))
+		name := filepath.ToSlash(filepath.Clean(strings.TrimPrefix(p, "/")))
 		fi, err := fs.Stat(fileSystem, name)
 		if err != nil {
 			return ErrNotFound
@@ -113,6 +113,7 @@ func (fs defaultFS) Open(name string) (fs.File, error) {
 }
 
 func subFS(currentFs fs.FS, root string) (fs.FS, error) {
+	root = filepath.ToSlash(filepath.Clean(root)) // note: fs.FS operates only with slashes. `ToSlash` is necessary for Windows
 	if dFS, ok := currentFs.(*defaultFS); ok {
 		// we need to make exception for `defaultFS` instances as it interprets root prefix differently from fs.FS to
 		// allow cases when root is given as `../somepath` which is not valid for fs.FS
@@ -122,5 +123,5 @@ func subFS(currentFs fs.FS, root string) (fs.FS, error) {
 			fs:     os.DirFS(root),
 		}, nil
 	}
-	return fs.Sub(currentFs, filepath.Clean(root))
+	return fs.Sub(currentFs, root)
 }

echo_fs_go1.16_test.go

@@ -244,7 +244,7 @@ func TestEcho_StaticPanic(t *testing.T) {
 			e.Filesystem = os.DirFS("./")
 
 			assert.PanicsWithError(t, tc.expectError, func() {
-				e.Static("/assets", tc.givenRoot)
+				e.Static("../assets", tc.givenRoot)
 			})
 		})
 	}