leases: support resource management

Add three methods for lease service so that the client can use it to
manage the resource by lease, not just gc.root label. With the following
methods, it is easy for client to maintain their own cache system.

```
 - AddResource(context.Context, Lease, Resource) error
 - RemoveResource(context.Context, Lease, Resource) error
 - ListResources(context.Context, Lease) ([]Resource, error)
```

And the resource is to be

```golang
type Resource {
  ID   string
  Type string
}
```

For the snapshots, the Type field will be formatted by
snapshots/%{type}, like snapshots/overlayfs.

fix: #3295

Signed-off-by: Wei Fu <fuweid89@gmail.com>

metadata/leases_test.go

@@ -264,3 +264,181 @@ func TestLeasesList(t *testing.T) {
 		}
 	}
 }
+
+func TestLeaseResource(t *testing.T) {
+	ctx, db, cancel := testEnv(t)
+	defer cancel()
+
+	var (
+		leaseID = "l1"
+
+		lease = leases.Lease{
+			ID: leaseID,
+		}
+
+		snapshotterKey = "RstMI3X8vguKoPFkmIStZ5fQFI7F1L0o"
+	)
+
+	// prepare lease
+	if err := db.Update(func(tx *bolt.Tx) error {
+		_, err0 := NewLeaseManager(tx).Create(ctx, leases.WithID(leaseID))
+		return err0
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	testCases := []struct {
+		lease    leases.Lease
+		resource leases.Resource
+		err      error
+	}{
+		{
+			lease: lease,
+			resource: leases.Resource{
+				ID:   "sha256:29f5d56d12684887bdfa50dcd29fc31eea4aaf4ad3bec43daf19026a7ce69912",
+				Type: "content",
+			},
+		},
+		{
+			lease: lease,
+			resource: leases.Resource{
+				ID:   "d2UdcINOwrBTQG9kS8rySAM3eMNBSojH",
+				Type: "ingests",
+			},
+		},
+		{
+			// allow to add resource which exists
+			lease: lease,
+			resource: leases.Resource{
+				ID:   "d2UdcINOwrBTQG9kS8rySAM3eMNBSojH",
+				Type: "ingests",
+			},
+		},
+		{
+			// not allow to reference to lease
+			lease: lease,
+			resource: leases.Resource{
+				ID:   "xCAV3F6PddlXitbtby0Vo23Qof6RTWpG",
+				Type: "leases",
+			},
+			err: errdefs.ErrNotImplemented,
+		},
+		{
+			// not allow to reference to container
+			lease: lease,
+			resource: leases.Resource{
+				ID:   "05O9ljptPu5Qq9kZGOacEfymBwQFM8ZH",
+				Type: "containers",
+			},
+			err: errdefs.ErrNotImplemented,
+		},
+		{
+			// not allow to reference to image
+			lease: lease,
+			resource: leases.Resource{
+				ID:   "qBUHpWBn03YaCt9cL3PPGKWoxBqTlLfu",
+				Type: "image",
+			},
+			err: errdefs.ErrNotImplemented,
+		},
+		{
+			lease: lease,
+			resource: leases.Resource{
+				ID:   "HMemOhlygombYhkhHhAZj5aRbDy2a3z2",
+				Type: "snapshots",
+			},
+			err: errdefs.ErrInvalidArgument,
+		},
+		{
+			lease: lease,
+			resource: leases.Resource{
+				ID:   snapshotterKey,
+				Type: "snapshots/overlayfs",
+			},
+		},
+		{
+			lease: lease,
+			resource: leases.Resource{
+				ID:   "HMemOhlygombYhkhHhAZj5aRbDy2a3z2",
+				Type: "snapshots/overlayfs/type1",
+			},
+			err: errdefs.ErrInvalidArgument,
+		},
+		{
+			lease: leases.Lease{
+				ID: "non-found",
+			},
+			resource: leases.Resource{
+				ID:   "HMemOhlygombYhkhHhAZj5aRbDy2a3z2",
+				Type: "snapshots/overlayfs",
+			},
+			err: errdefs.ErrNotFound,
+		},
+	}
+
+	idxList := make(map[leases.Resource]bool)
+	for i, tc := range testCases {
+		if err := db.Update(func(tx *bolt.Tx) error {
+			err0 := NewLeaseManager(tx).AddResource(ctx, tc.lease, tc.resource)
+			if got := errors.Cause(err0); got != tc.err {
+				return errors.Errorf("expect error (%v), but got (%v)", tc.err, err0)
+			}
+
+			if err0 == nil {
+				// not visited yet
+				idxList[tc.resource] = false
+			}
+			return nil
+		}); err != nil {
+			t.Fatalf("failed to run case %d with resource: %v", i, err)
+		}
+	}
+
+	// check list function
+	var gotList []leases.Resource
+	if err := db.View(func(tx *bolt.Tx) error {
+		var err error
+		gotList, err = NewLeaseManager(tx).ListResources(ctx, lease)
+		return err
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	if len(gotList) != len(idxList) {
+		t.Fatalf("expected (%d) resources, but got (%d)", len(idxList), len(gotList))
+	}
+
+	for _, r := range gotList {
+		visited, ok := idxList[r]
+		if !ok {
+			t.Fatalf("unexpected resource(%v)", r)
+		}
+		if visited {
+			t.Fatalf("duplicate resource(%v)", r)
+		}
+		idxList[r] = true
+	}
+
+	// remove snapshots
+	if err := db.Update(func(tx *bolt.Tx) error {
+		return NewLeaseManager(tx).DeleteResource(ctx, lease, leases.Resource{
+			ID:   snapshotterKey,
+			Type: "snapshots/overlayfs",
+		})
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	// check list number
+	if err := db.View(func(tx *bolt.Tx) error {
+		var err error
+		gotList, err = NewLeaseManager(tx).ListResources(ctx, lease)
+		return err
+	}); err != nil {
+		t.Fatal(err)
+	}
+
+	if len(gotList)+1 != len(idxList) {
+		t.Fatalf("expected (%d) resources, but got (%d)", len(idxList)-1, len(gotList))
+	}
+}