Split off serialization and key functions to their own packages.

service/datastore/dskey/generic_key.go

Index: service/datastore/dskey/generic_key.go
diff --git a/service/datastore/dskey/generic_key.go b/service/datastore/dskey/generic_key.go
new file mode 100644
index 0000000000000000000000000000000000000000..64e5b659ebbae0419db4f1933737f1f966663aae
--- /dev/null
+++ b/service/datastore/dskey/generic_key.go
@@ -0,0 +1,122 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+package dskey
+
+import (
+	"encoding/json"
+
+	ds "github.com/luci/gae/service/datastore"
+)
+
+// Generic is an implementation of Key which doesn't rely on the
+// SDK's implementation. It differs slightly in that it's not recursive (and
+// thus cannot express some of the invalid Key's that the SDK implementation
+// can). In particular, it's not possible to have a Generic in a namespace
+// whose Parent() is in a different namespace.
+//
+// Generic also implements json.Marshaler and json.Unmarshaler so it's
+// suitable for use in structs which need to serialize both to json and to
+// datastore.
+type Generic struct {
+	appID     string
+	namespace string
+	toks      []ds.KeyTok
+}
+
+var _ interface {
+	ds.Key
+	json.Marshaler
+	json.Unmarshaler
+} = (*Generic)(nil)
+
+// NewToks creates a new Generic. It is the Key implementation
+// returned from the various PropertyMap serialization routines, as well as
+// the native key implementation for the in-memory implementation of gae.
+func NewToks(appID, ns string, toks []ds.KeyTok) *Generic {
+	newToks := make([]ds.KeyTok, len(toks))
+	copy(newToks, toks)
+	return &Generic{appID, ns, newToks}
+}
+
+// New is a wrapper around NewToks which has an interface similar
+// to NewKey in the SDK.
+func New(appID, ns, kind, stringID string, intID int64, parent ds.Key) *Generic {
+	_, _, toks := Split(parent)
+	newToks := make([]ds.KeyTok, len(toks))
+	copy(newToks, toks)
+	newToks = append(newToks, ds.KeyTok{Kind: kind, StringID: stringID, IntID: intID})
+	return &Generic{appID, ns, newToks}
+}
+
+// NewFromEncoded decodes and returns a *Generic
+func NewFromEncoded(encoded string) (ret *Generic, err error) {
+	ret = &Generic{}
+	ret.appID, ret.namespace, ret.toks, err = ToksDecode(encoded)
+	return
+}
+
+func (k *Generic) lastTok() ds.KeyTok {
+	if len(k.toks) > 0 {
+		return k.toks[len(k.toks)-1]
+	}
+	return ds.KeyTok{}
+}
+
+// AppID returns the application ID that this Key is for.
+func (k *Generic) AppID() string { return k.appID }
+
+// Namespace returns the namespace that this Key is for.
+func (k *Generic) Namespace() string { return k.namespace }
+
+// Kind returns the datastore kind of the entity.
+func (k *Generic) Kind() string { return k.lastTok().Kind }
+
+// StringID returns the string ID of the entity (if defined, otherwise "").
+func (k *Generic) StringID() string { return k.lastTok().StringID }
+
+// IntID returns the int64 ID of the entity (if defined, otherwise 0).
+func (k *Generic) IntID() int64 { return k.lastTok().IntID }
+
+// String returns a human-readable version of this Key.
+func (k *Generic) String() string { return String(k) }
+
+// Incomplete returns true iff k doesn't have an id yet
+func (k *Generic) Incomplete() bool { return Incomplete(k) }
+
+// Valid returns true if this key is complete and suitable for use with the
+// datastore. See the package-level Valid function for more information.
+func (k *Generic) Valid(allowSpecial bool, aid, ns string) bool {
+	return Valid(k, allowSpecial, aid, ns)
+}
+
+// PartialValid returns true if this key is suitable for use with a Put
+// operation. See the package-level PartialValid function for more information.
+func (k *Generic) PartialValid(aid, ns string) bool {
+	return PartialValid(k, aid, ns)
+}
+
+// Parent returns the parent Key of this *Generic, or nil. The parent
+// will always have the concrete type of *Generic.
+func (k *Generic) Parent() ds.Key {
+	if len(k.toks) <= 1 {
+		return nil
+	}
+	return &Generic{k.appID, k.namespace, k.toks[:len(k.toks)-1]}
+}
+
+// MarshalJSON allows this key to be automatically marshaled by encoding/json.
+func (k *Generic) MarshalJSON() ([]byte, error) {
+	return MarshalJSON(k)
+}
+
+// UnmarshalJSON allows this key to be automatically unmarshaled by encoding/json.
+func (k *Generic) UnmarshalJSON(buf []byte) error {
+	appID, namespace, toks, err := UnmarshalJSON(buf)
+	if err != nil {
+		return err
+	}
+	*k = *NewToks(appID, namespace, toks)
+	return nil
+}