vfsutil: add CopyRecursive

Author: tbg

pkg/util/vfsutil/BUILD.bazel

@@ -0,0 +1,19 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library", "go_test")
+
+go_library(
+    name = "vfsutil",
+    srcs = ["copy.go"],
+    importpath = "github.com/cockroachdb/cockroach/pkg/util/vfsutil",
+    visibility = ["//visibility:public"],
+    deps = ["@com_github_cockroachdb_pebble//vfs"],
+)
+
+go_test(
+    name = "vfsutil_test",
+    srcs = ["copy_test.go"],
+    deps = [
+        ":vfsutil",
+        "@com_github_cockroachdb_pebble//vfs",
+        "@com_github_stretchr_testify//require",
+    ],
+)

pkg/util/vfsutil/copy.go

@@ -0,0 +1,70 @@
+// Copyright 2025 The Cockroach Authors.
+//
+// Use of this software is governed by the CockroachDB Software License
+// included in the /LICENSE file.
+
+package vfsutil
+
+import (
+	"io"
+
+	"github.com/cockroachdb/pebble/vfs"
+)
+
+// CopyRecursive recursively copies all files and directories from srcPath on
+// srcFS to dstPath on dstFS. If the destination path does not exist, it is
+// created.
+// Files that already exist in the destination path will be replaced.
+func CopyRecursive(srcFS, dstFS vfs.FS, srcPath, dstPath string) error {
+	srcInfo, err := srcFS.Stat(srcPath)
+	if err != nil {
+		return err
+	}
+
+	if srcInfo.IsDir() {
+		if err := dstFS.MkdirAll(dstPath, srcInfo.Mode()); err != nil {
+			return err
+		}
+
+		entries, err := srcFS.List(srcPath)
+		if err != nil {
+			return err
+		}
+
+		for _, entry := range entries {
+			srcEntryPath := srcFS.PathJoin(srcPath, entry)
+			dstEntryPath := dstFS.PathJoin(dstPath, entry)
+			if err := CopyRecursive(srcFS, dstFS, srcEntryPath, dstEntryPath); err != nil {
+				return err
+			}
+		}
+		return nil
+	}
+
+	// Copy regular file
+	return copyFile(srcFS, dstFS, srcPath, dstPath)
+}
+
+func copyFile(srcFS, dstFS vfs.FS, srcPath, dstPath string) error {
+	// Open source file
+	src, err := srcFS.Open(srcPath)
+	if err != nil {
+		return err
+	}
+	defer src.Close()
+
+	// Create destination file
+	dst, err := dstFS.Create(dstPath, vfs.WriteCategoryUnspecified)
+	if err != nil {
+		return err
+	}
+	defer dst.Close()
+
+	// Copy file contents
+	if _, err := io.Copy(dst, src); err != nil {
+		return err
+	}
+
+	// Sync to ensure data is written
+	return dst.Sync()
+}

pkg/util/vfsutil/copy_test.go

@@ -0,0 +1,57 @@
+// Copyright 2025 The Cockroach Authors.
+//
+// Use of this software is governed by the CockroachDB Software License
+// included in the /LICENSE file.
+
+package vfsutil_test
+
+import (
+	"testing"
+
+	"github.com/cockroachdb/cockroach/pkg/util/vfsutil"
+	"github.com/cockroachdb/pebble/vfs"
+	"github.com/stretchr/testify/require"
+)
+
+func TestCopyRecursive(t *testing.T) {
+	// Create source memFS with test data
+	srcFS := vfs.NewMem()
+
+	// Create a directory structure
+	require.NoError(t, srcFS.MkdirAll("testdir/subdir", 0755))
+
+	// Create some test files
+	f1, err := srcFS.Create("testdir/file1.txt", vfs.WriteCategoryUnspecified)
+	require.NoError(t, err)
+	_, err = f1.Write([]byte("hello world"))
+	require.NoError(t, err)
+	require.NoError(t, f1.Close())
+
+	f2, err := srcFS.Create("testdir/subdir/file2.txt", vfs.WriteCategoryUnspecified)
+	require.NoError(t, err)
+	_, err = f2.Write([]byte("nested file"))
+	require.NoError(t, err)
+	require.NoError(t, f2.Close())
+
+	// Create destination FS (real filesystem for this example)
+	dstFS := vfs.Default
+
+	// Copy from memFS to real filesystem in a temp directory
+	tempDir := t.TempDir()
+	require.NoError(t, vfsutil.CopyRecursive(srcFS, dstFS, "testdir", dstFS.PathJoin(tempDir, "copied")))
+
+	// Verify the copy worked
+	files, err := dstFS.List(dstFS.PathJoin(tempDir, "copied"))
+	require.NoError(t, err)
+	require.Contains(t, files, "file1.txt")
+	require.Contains(t, files, "subdir")
+
+	// Verify nested file
+	content, err := dstFS.Open(dstFS.PathJoin(tempDir, "copied", "subdir", "file2.txt"))
+	require.NoError(t, err)
+	defer content.Close()
+	buf := make([]byte, 100)
+	n, err := content.Read(buf)
+	require.NoError(t, err)
+	require.Equal(t, "nested file", string(buf[:n]))
+}