Clean up callback interfaces.

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"
 )
 
 // Cursor wraps datastore.Cursor.
 type Cursor interface {
         fmt.Stringer
 }
 
 // CursorCB is used to obtain a Cursor while Run'ing a query on either
 // Interface or RawInterface.
 //
 // it can be invoked to obtain the current cursor.
 type CursorCB func() (Cursor, error)
 
 // RawRunCB is the callback signature provided to RawInterface.Run
 //
 //   - key is the Key of the entity
 //   - val is the data of the entity (or nil, if the query was keys-only)
 //
-// Return true to continue iterating through the query results, or false to stop.
-type RawRunCB func(key *Key, val PropertyMap, getCursor CursorCB) bool
+// Return nil to continue iterating through the query results, or an error to
+// stop. If you return the error `Stop`, then Run will stop the query and
+// return nil.
+type RawRunCB func(key *Key, val PropertyMap, getCursor CursorCB) error
 
 // GetMultiCB is the callback signature provided to RawInterface.GetMulti
 //
 //   - val is the data of the entity
 //     * It may be nil if some of the keys to the GetMulti were bad, since all
 //       keys are validated before the RPC occurs!
 //   - err is an error associated with this entity (e.g. ErrNoSuchEntity).
-type GetMultiCB func(val PropertyMap, err error)
+type GetMultiCB func(val PropertyMap, err error) error
 
 // PutMultiCB is the callback signature provided to RawInterface.PutMulti
 //
 //   - key is the new key for the entity (if the original was incomplete)
 //     * It may be nil if some of the keys/vals to the PutMulti were bad, since
 //       all keys are validated before the RPC occurs!
 //   - err is an error associated with putting this entity.
-type PutMultiCB func(key *Key, err error)
+type PutMultiCB func(key *Key, err error) error
 
 // DeleteMultiCB is the callback signature provided to RawInterface.DeleteMulti
 //
 //   - err is an error associated with deleting this entity.
-type DeleteMultiCB func(err error)
+type DeleteMultiCB func(err error) error
 
 type nullMetaGetterType struct{}
 
 func (nullMetaGetterType) GetMeta(string) (interface{}, bool) { return nil, false }
 
 var nullMetaGetter MetaGetter = nullMetaGetterType{}
 
 // MultiMetaGetter is a carrier for metadata, used with RawInterface.GetMulti
 //
 // It's OK to default-construct this. GetMeta will just return
@@ skipping 98 matching lines @@
         //   - 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
 }