examples/privacy: adminonly application example (#840)

examples/privacyadmin/viewer/viewer.go

@@ -0,0 +1,46 @@
+// Copyright 2019-present Facebook Inc. All rights reserved.
+// This source code is licensed under the Apache 2.0 license found
+// in the LICENSE file in the root directory of this source tree.
+
+package viewer
+
+import (
+	"context"
+)
+
+// Role for viewer actions.
+type Role int
+
+// List of roles.
+const (
+	_ Role = 1 << iota
+	Admin
+	View
+)
+
+// Viewer describes the query/mutation viewer-context.
+type Viewer interface {
+	Admin() bool // If viewer is admin.
+}
+
+// UserViewer describes a user-viewer.
+type UserViewer struct {
+	Role Role // Attached roles.
+}
+
+func (v UserViewer) Admin() bool {
+	return v.Role&Admin != 0
+}
+
+type ctxKey struct{}
+
+// FromContext returns the Viewer stored in a context.
+func FromContext(ctx context.Context) Viewer {
+	v, _ := ctx.Value(ctxKey{}).(Viewer)
+	return v
+}
+
+// NewContext returns a copy of parent context with the given Viewer attached with it.
+func NewContext(parent context.Context, v Viewer) context.Context {
+	return context.WithValue(parent, ctxKey{}, v)
+}