Implement a server-side config service interface.

luci_config/server/cfgclient/backend/get_all.go

Index: luci_config/server/cfgclient/backend/get_all.go
diff --git a/luci_config/server/cfgclient/backend/get_all.go b/luci_config/server/cfgclient/backend/get_all.go
new file mode 100644
index 0000000000000000000000000000000000000000..a789e85dc3b785cf9fad6d92eaaa657562126622
--- /dev/null
+++ b/luci_config/server/cfgclient/backend/get_all.go
@@ -0,0 +1,54 @@
+// Copyright 2016 The LUCI Authors. All rights reserved.
+// Use of this source code is governed under the Apache License, Version 2.0
+// that can be found in the LICENSE file.
+
+package backend
+
+import (
+	"bytes"
+
+	"github.com/luci/luci-go/common/errors"
+)
+
+// GetAllTarget is the type of configuration to retrieve with GetAll.
+//
+// GetAllTarget marshals/unmarshals to/from a compact JSON representation. This is
+// used by the caching layer.
+type GetAllTarget string
+
+const (
+	// GetAllProject indicates that project configus should be retrieved.
+	GetAllProject = GetAllTarget("Project")
+	// GetAllRef indicates that ref configs should be retrieved.
+	GetAllRef = GetAllTarget("Ref")
+)
+
+var (
+	projectJSON = []byte(`"P"`)
+	refJSON     = []byte(`"R"`)
+)
+
+// MarshalJSON implements json.Marshaler.
+func (gat GetAllTarget) MarshalJSON() ([]byte, error) {
+	switch gat {
+	case GetAllProject:
+		return projectJSON, nil
+	case GetAllRef:
+		return refJSON, nil
+	default:
+		return nil, errors.Reason("unknown GetAllTarget: %(value)v").D("value", gat).Err()
+	}
+}
+
+// UnmarshalJSON implements json.Unmarshaler.
+func (gat *GetAllTarget) UnmarshalJSON(d []byte) error {
+	switch {
+	case bytes.Equal(d, projectJSON):
+		*gat = GetAllProject
+	case bytes.Equal(d, refJSON):
+		*gat = GetAllRef
+	default:
+		return errors.Reason("unknown GetAllTarget: %(value)q").D("value", d).Err()
+	}
+	return nil
+}