Add cloud datastore implementation.

service/datastore/raw_interface.go

 // 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 datastore
 
 import (
         "fmt"
 
         "golang.org/x/net/context"
@@ skipping 120 matching lines @@
         //   - query is not nil
         //   - cb is not nil
         Run(q *FinalizedQuery, cb RawRunCB) error
 
         // Count executes the given query and returns the number of entries which
         // match it.
         Count(q *FinalizedQuery) (int64, error)
 
         // GetMulti retrieves items from the datastore.
         //
-        // Callback execues once per key, in the order of keys. Callback may not
-        // execute at all if there's a server error. If callback is nil, this
-        // method does nothing.
+        // If there was a server error, it will be returned directly. Otherwise,
+        // callback will execute once per key/value pair, returning either the
+        // operation result or individual error for each position. If the callback
+        // receives an error, it will immediately forward that error and stop
+        // subsequent callbacks.
         //
         // meta is used to propagate metadata from higher levels.
         //
         // NOTE: Implementations and filters are guaranteed that:
         //   - len(keys) > 0
         //   - all keys are Valid, !Incomplete, and in the current namespace
         //   - cb is not nil
         GetMulti(keys []*Key, meta MultiMetaGetter, cb GetMultiCB) error
 
         // PutMulti writes items to the datastore.
         //
-        // Callback execues once per key/value pair, in the passed-in order. Callback
-        // may not execute at all if there was a server error.
+        // If there was a server error, it will be returned directly. Otherwise,
+        // callback will execute once per key/value pair, returning either the
+        // operation result or individual error for each position. If the callback
+        // receives an error, it will immediately forward that error and stop
+        // subsequent callbacks.
         //
         // NOTE: Implementations and filters are guaranteed that:
         //   - len(keys) > 0
         //   - len(keys) == len(vals)
         //   - all keys are Valid and in the current namespace
         //   - cb is not nil
         PutMulti(keys []*Key, vals []PropertyMap, cb PutMultiCB) error
 
         // DeleteMulti removes items from the datastore.
         //
-        // Callback execues once per key, in the order of keys. Callback may not
-        // execute at all if there's a server error.
+        // If there was a server error, it will be returned directly. Otherwise,
+        // callback will execute once per key/value pair, returning either the
+        // operation result or individual error for each position. If the callback
+        // receives an error, it will immediately forward that error and stop
+        // subsequent callbacks.
         //
         // NOTE: Implementations and filters are guaranteed that
         //   - len(keys) > 0
         //   - all keys are Valid, !Incomplete, and in the current namespace
         //   - none keys of the keys are 'special' (use a kind prefixed with '__')
         //   - cb is not nil
         DeleteMulti(keys []*Key, cb DeleteMultiCB) error
 
         // Testable returns the Testable interface for the implementation, or nil if
         // there is none.
         Testable() Testable
 }