Add 'user friendly' datastore API.

service/rawdatastore/context.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 rawdatastore
-
-import (
-        "golang.org/x/net/context"
-)
-
-type key int
-
-var (
-        rawDatastoreKey       key
-        rawDatastoreFilterKey key = 1
-)
-
-// Factory is the function signature for factory methods compatible with
-// SetFactory.
-type Factory func(context.Context) Interface
-
-// Filter is the function signature for a filter RDS implementation. It
-// gets the current RDS implementation, and returns a new RDS implementation
-// backed by the one passed in.
-type Filter func(context.Context, Interface) Interface
-
-// getUnfiltered gets gets the Interface implementation from context without
-// any of the filters applied.
-func getUnfiltered(c context.Context) Interface {
-        if f, ok := c.Value(rawDatastoreKey).(Factory); ok && f != nil {
-                return f(c)
-        }
-        return nil
-}
-
-// Get gets the Interface implementation from context.
-func Get(c context.Context) Interface {
-        ret := getUnfiltered(c)
-        if ret == nil {
-                return nil
-        }
-        for _, f := range getCurFilters(c) {
-                ret = f(c, ret)
-        }
-        return applyCheckFilter(c, ret)
-}
-
-// SetFactory sets the function to produce Datastore instances, as returned by
-// the Get method.
-func SetFactory(c context.Context, rdsf Factory) context.Context {
-        return context.WithValue(c, rawDatastoreKey, rdsf)
-}
-
-// Set sets the current Datastore object in the context. Useful for testing with
-// a quick mock. This is just a shorthand SetFactory invocation to set a factory
-// which always returns the same object.
-func Set(c context.Context, rds Interface) context.Context {
-        return SetFactory(c, func(context.Context) Interface { return rds })
-}
-
-func getCurFilters(c context.Context) []Filter {
-        curFiltsI := c.Value(rawDatastoreFilterKey)
-        if curFiltsI != nil {
-                return curFiltsI.([]Filter)
-        }
-        return nil
-}
-
-// AddFilters adds Interface filters to the context.
-func AddFilters(c context.Context, filts ...Filter) context.Context {
-        if len(filts) == 0 {
-                return c
-        }
-        cur := getCurFilters(c)
-        newFilts := make([]Filter, 0, len(cur)+len(filts))
-        newFilts = append(newFilts, getCurFilters(c)...)
-        newFilts = append(newFilts, filts...)
-        return context.WithValue(c, rawDatastoreFilterKey, newFilts)
-}