fs/cache: fix parent not getting pinned when remote is a file

Before this change, when cache.GetFn was called on a file rather than a
directory, two cache entries would be added (the file + its parent) but only one
of them would get pinned if the caller then called Pin(f). This left the other
one exposed to expiration if the ci.FsCacheExpireDuration was reached. This was
problematic because both entries point to the same Fs, and if one entry expires
while the other is pinned, the Shutdown method gets erroneously called on an Fs
that is still in use.

An example of the problem showed up in the Hasher backend, which uses the
Shutdown method to stop the bolt db used to store hashes. If a command was run
on a Hasher file (ex. `rclone md5sum --download hasher:somelargefile.zip`) and
hashing the file took longer than the --fs-cache-expire-duration (5m by default), the
bolt db was stopped before the hashing operation completed, resulting in an
error.

This change fixes the issue by ensuring that:
1. only one entry is added to the cache (the file's parent, not the file).
2. future lookups correctly find the entry regardless of whether they are called
	with the parent name or one of its children.
3. fs.ErrorIsFile is returned when (and only when) fsString points to a file
	(preserving the fix from 8d5bc7f28b).

Note that f.Root() should always point to the parent dir as of c69eb84573

fs/cache/cache_test.go

@@ -24,7 +24,7 @@ func mockNewFs(t *testing.T) func(ctx context.Context, path string) (fs.Fs, erro
 		switch path {
 		case "mock:/":
 			return mockfs.NewFs(ctx, "mock", "/", nil)
-		case "mock:/file.txt", "mock:file.txt":
+		case "mock:/file.txt", "mock:file.txt", "mock:/file2.txt", "mock:file2.txt":
 			fMock, err := mockfs.NewFs(ctx, "mock", "/", nil)
 			require.NoError(t, err)
 			return fMock, fs.ErrorIsFile
@@ -55,6 +55,7 @@ func TestGet(t *testing.T) {
 }
 
 func TestGetFile(t *testing.T) {
+	defer ClearMappings()
 	create := mockNewFs(t)
 
 	assert.Equal(t, 0, Entries())
@@ -63,7 +64,7 @@ func TestGetFile(t *testing.T) {
 	require.Equal(t, fs.ErrorIsFile, err)
 	require.NotNil(t, f)
 
-	assert.Equal(t, 2, Entries())
+	assert.Equal(t, 1, Entries())
 
 	f2, err := GetFn(context.Background(), "mock:/file.txt", create)
 	require.Equal(t, fs.ErrorIsFile, err)
@@ -71,7 +72,7 @@ func TestGetFile(t *testing.T) {
 
 	assert.Equal(t, f, f2)
 
-	// check parent is there too
+	// check it is also found when referred to by parent name
 	f2, err = GetFn(context.Background(), "mock:/", create)
 	require.Nil(t, err)
 	require.NotNil(t, f2)
@@ -80,6 +81,7 @@ func TestGetFile(t *testing.T) {
 }
 
 func TestGetFile2(t *testing.T) {
+	defer ClearMappings()
 	create := mockNewFs(t)
 
 	assert.Equal(t, 0, Entries())
@@ -88,7 +90,7 @@ func TestGetFile2(t *testing.T) {
 	require.Equal(t, fs.ErrorIsFile, err)
 	require.NotNil(t, f)
 
-	assert.Equal(t, 2, Entries())
+	assert.Equal(t, 1, Entries())
 
 	f2, err := GetFn(context.Background(), "mock:file.txt", create)
 	require.Equal(t, fs.ErrorIsFile, err)
@@ -96,7 +98,7 @@ func TestGetFile2(t *testing.T) {
 
 	assert.Equal(t, f, f2)
 
-	// check parent is there too
+	// check it is also found when referred to by parent name
 	f2, err = GetFn(context.Background(), "mock:/", create)
 	require.Nil(t, err)
 	require.NotNil(t, f2)
@@ -124,22 +126,22 @@ func TestPutErr(t *testing.T) {
 
 	assert.Equal(t, 0, Entries())
 
-	PutErr("mock:file.txt", f, fs.ErrorIsFile)
+	PutErr("mock:/", f, fs.ErrorNotFoundInConfigFile)
 
 	assert.Equal(t, 1, Entries())
 
-	fNew, err := GetFn(context.Background(), "mock:file.txt", create)
-	require.Equal(t, fs.ErrorIsFile, err)
+	fNew, err := GetFn(context.Background(), "mock:/", create)
+	require.Equal(t, fs.ErrorNotFoundInConfigFile, err)
 	require.Equal(t, f, fNew)
 
 	assert.Equal(t, 1, Entries())
 
 	// Check canonicalisation
 
-	PutErr("mock:/file.txt", f, fs.ErrorIsFile)
+	PutErr("mock:/file.txt", f, fs.ErrorNotFoundInConfigFile)
 
 	fNew, err = GetFn(context.Background(), "mock:/file.txt", create)
-	require.Equal(t, fs.ErrorIsFile, err)
+	require.Equal(t, fs.ErrorNotFoundInConfigFile, err)
 	require.Equal(t, f, fNew)
 
 	assert.Equal(t, 1, Entries())
@@ -190,6 +192,75 @@ func TestPin(t *testing.T) {
 	Unpin(f2)
 }
 
+func TestPinFile(t *testing.T) {
+	defer ClearMappings()
+	create := mockNewFs(t)
+
+	// Test pinning and unpinning nonexistent
+	f, err := mockfs.NewFs(context.Background(), "mock", "/file.txt", nil)
+	require.NoError(t, err)
+	Pin(f)
+	Unpin(f)
+
+	// Now test pinning an existing
+	f2, err := GetFn(context.Background(), "mock:/file.txt", create)
+	require.Equal(t, fs.ErrorIsFile, err)
+	assert.Equal(t, 1, len(childParentMap))
+
+	Pin(f2)
+	assert.Equal(t, 1, Entries())
+	pinned, unpinned := EntriesWithPinCount()
+	assert.Equal(t, 1, pinned)
+	assert.Equal(t, 0, unpinned)
+
+	Unpin(f2)
+	assert.Equal(t, 1, Entries())
+	pinned, unpinned = EntriesWithPinCount()
+	assert.Equal(t, 0, pinned)
+	assert.Equal(t, 1, unpinned)
+
+	// try a different child of the same parent, and parent
+	// should not add additional cache items
+	called = 0 // this one does create() because we haven't seen it before and don't yet know it's a file
+	f3, err := GetFn(context.Background(), "mock:/file2.txt", create)
+	assert.Equal(t, fs.ErrorIsFile, err)
+	assert.Equal(t, 1, Entries())
+	assert.Equal(t, 2, len(childParentMap))
+
+	parent, err := GetFn(context.Background(), "mock:/", create)
+	assert.NoError(t, err)
+	assert.Equal(t, 1, Entries())
+	assert.Equal(t, 2, len(childParentMap))
+
+	Pin(f3)
+	assert.Equal(t, 1, Entries())
+	pinned, unpinned = EntriesWithPinCount()
+	assert.Equal(t, 1, pinned)
+	assert.Equal(t, 0, unpinned)
+
+	Unpin(f3)
+	assert.Equal(t, 1, Entries())
+	pinned, unpinned = EntriesWithPinCount()
+	assert.Equal(t, 0, pinned)
+	assert.Equal(t, 1, unpinned)
+
+	Pin(parent)
+	assert.Equal(t, 1, Entries())
+	pinned, unpinned = EntriesWithPinCount()
+	assert.Equal(t, 1, pinned)
+	assert.Equal(t, 0, unpinned)
+
+	Unpin(parent)
+	assert.Equal(t, 1, Entries())
+	pinned, unpinned = EntriesWithPinCount()
+	assert.Equal(t, 0, pinned)
+	assert.Equal(t, 1, unpinned)
+
+	// all 3 should have equal configstrings
+	assert.Equal(t, fs.ConfigString(f2), fs.ConfigString(f3))
+	assert.Equal(t, fs.ConfigString(f2), fs.ConfigString(parent))
+}
+
 func TestClearConfig(t *testing.T) {
 	create := mockNewFs(t)
 
@@ -198,9 +269,9 @@ func TestClearConfig(t *testing.T) {
 	_, err := GetFn(context.Background(), "mock:/file.txt", create)
 	require.Equal(t, fs.ErrorIsFile, err)
 
-	assert.Equal(t, 2, Entries()) // file + parent
+	assert.Equal(t, 1, Entries())
 
-	assert.Equal(t, 2, ClearConfig("mock"))
+	assert.Equal(t, 1, ClearConfig("mock"))
 
 	assert.Equal(t, 0, Entries())
 }