serve nfs: make metadata files have special file handles

Metadata files have the file handle of their source file with
0x00000001 suffixed in big endian so we can look them up directly from
their file handles.

cmd/serve/nfs/cache_test.go

@@ -5,10 +5,13 @@ package nfs
 import (
 	"context"
 	"fmt"
+	"strings"
 	"sync"
 	"testing"
 
 	"github.com/rclone/rclone/fs"
+	"github.com/rclone/rclone/fs/object"
+	"github.com/rclone/rclone/vfs"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -18,6 +21,8 @@ const testSymlinkCache = "go test -c && sudo setcap cap_dac_read_search+ep ./nfs
 
 // Check basic CRUD operations
 func testCacheCRUD(t *testing.T, h *Handler, c Cache, fileName string) {
+	isMetadata := strings.HasSuffix(fileName, ".metadata")
+
 	// Check reading a non existent handle returns an error
 	_, _, err := c.FromHandle([]byte{10})
 	assert.Error(t, err)
@@ -26,6 +31,11 @@ func testCacheCRUD(t *testing.T, h *Handler, c Cache, fileName string) {
 	splitPath := []string{"dir", fileName}
 	fh := c.ToHandle(h.billyFS, splitPath)
 	assert.True(t, len(fh) > 0)
+	if isMetadata {
+		assert.Equal(t, metadataSuffix, fh[len(fh)-len(metadataSuffix):])
+	} else {
+		assert.NotEqual(t, metadataSuffix, fh[len(fh)-len(metadataSuffix):])
+	}
 
 	// Read the handle back
 	newFs, newSplitPath, err := c.FromHandle(fh)
@@ -43,8 +53,13 @@ func testCacheCRUD(t *testing.T, h *Handler, c Cache, fileName string) {
 
 	// Check the handle is gone and returning stale handle error
 	_, _, err = c.FromHandle(fh)
-	require.Error(t, err)
-	assert.Equal(t, errStaleHandle, err)
+	if !isMetadata {
+		require.Error(t, err)
+		assert.Equal(t, errStaleHandle, err)
+	} else {
+		// Can't invalidate metadata handles
+		require.NoError(t, err)
+	}
 }
 
 // Thrash the cache operations in parallel on different files
@@ -113,8 +128,10 @@ func TestCache(t *testing.T) {
 		cacheType := cacheType
 		t.Run(cacheType.String(), func(t *testing.T) {
 			h := &Handler{
+				vfs:     vfs.New(object.MemoryFs, nil),
 				billyFS: billyFS,
 			}
+			h.vfs.Opt.MetadataExtension = ".metadata"
 			h.opt.HandleLimit = 1000
 			h.opt.HandleCache = cacheType
 			h.opt.HandleCacheDir = t.TempDir()
@@ -151,6 +168,10 @@ func TestCache(t *testing.T) {
 				t.Run("ThrashSame", func(t *testing.T) {
 					testCacheThrashSame(t, h, c)
 				})
+				// Metadata file handles only supported on non memory
+				t.Run("CRUDMetadata", func(t *testing.T) {
+					testCacheCRUD(t, h, c, "file.metadata")
+				})
 			}
 		})
 	}