add path prefix to ObjectStorage.Iterator (#23332)

Support to iterator subdirectory in ObjectStorage for
ObjectStorage.Iterator method.

It's required for https://github.com/go-gitea/gitea/pull/22738 to make
artifact files cleanable.

---------

Co-authored-by: Jason Song <i@wolfogre.com>
Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

modules/storage/local_test.go

@@ -4,6 +4,10 @@
 package storage
 
 import (
+	"bytes"
+	"context"
+	"os"
+	"path/filepath"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -50,3 +54,41 @@ func TestBuildLocalPath(t *testing.T) {
 		})
 	}
 }
+
+func TestLocalStorageIterator(t *testing.T) {
+	dir := filepath.Join(os.TempDir(), "TestLocalStorageIteratorTestDir")
+	l, err := NewLocalStorage(context.Background(), LocalStorageConfig{Path: dir})
+	assert.NoError(t, err)
+
+	testFiles := [][]string{
+		{"a/1.txt", "a1"},
+		{"/a/1.txt", "aa1"}, // same as above, but with leading slash that will be trim
+		{"b/1.txt", "b1"},
+		{"b/2.txt", "b2"},
+		{"b/3.txt", "b3"},
+		{"b/x 4.txt", "bx4"},
+	}
+	for _, f := range testFiles {
+		_, err = l.Save(f[0], bytes.NewBufferString(f[1]), -1)
+		assert.NoError(t, err)
+	}
+
+	expectedList := map[string][]string{
+		"a":           {"a/1.txt"},
+		"b":           {"b/1.txt", "b/2.txt", "b/3.txt", "b/x 4.txt"},
+		"":            {"a/1.txt", "b/1.txt", "b/2.txt", "b/3.txt", "b/x 4.txt"},
+		"/":           {"a/1.txt", "b/1.txt", "b/2.txt", "b/3.txt", "b/x 4.txt"},
+		"a/b/../../a": {"a/1.txt"},
+	}
+	for dir, expected := range expectedList {
+		count := 0
+		err = l.IterateObjects(dir, func(path string, f Object) error {
+			defer f.Close()
+			assert.Contains(t, expected, path)
+			count++
+			return nil
+		})
+		assert.NoError(t, err)
+		assert.Equal(t, count, len(expected))
+	}
+}