Refactor a bit.

memcache.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 gae
-
-import (
-        "time"
-
-        "golang.org/x/net/context"
-)
-
-// MCItem is a wrapper around *memcache.Item. Note that the Set* methods all
-// return the original MCItem (e.g. they mutate the original), due to
-// implementation constraints. They return the original item to allow easy
-// chaining, e.g.:
-//   itm := gae.MC(c).NewItem("foo").SetValue([]byte("stuff"))
-type MCItem interface {
-        Key() string
-        Value() []byte
-        Object() interface{}
-        Flags() uint32
-        Expiration() time.Duration
-
-        SetKey(string) MCItem
-        SetValue([]byte) MCItem
-        SetObject(interface{}) MCItem
-        SetFlags(uint32) MCItem
-        SetExpiration(time.Duration) MCItem
-}
-
-// Memcache is the full interface to the memcache service.
-type Memcache interface {
-        NewItem(key string) MCItem
-
-        Add(item MCItem) error
-        Set(item MCItem) error
-        Get(key string) (MCItem, error)
-        Delete(key string) error
-        CompareAndSwap(item MCItem) error
-
-        AddMulti(items []MCItem) error
-        SetMulti(items []MCItem) error
-        GetMulti(keys []string) (map[string]MCItem, error)
-        DeleteMulti(keys []string) error
-        CompareAndSwapMulti(items []MCItem) error
-
-        Increment(key string, delta int64, initialValue uint64) (newValue uint64, err error)
-        IncrementExisting(key string, delta int64) (newValue uint64, err error)
-
-        Flush() error
-
-        Stats() (*MCStatistics, error)
-}
-
-// MCFactory is the function signature for factory methods compatible with
-// SetMCFactory.
-type MCFactory func(context.Context) Memcache
-
-// MCFilter is the function signature for a filter MC implementation. It
-// gets the current MC implementation, and returns a new MC implementation
-// backed by the one passed in.
-type MCFilter func(context.Context, Memcache) Memcache
-
-// GetMCUnfiltered gets gets the Memcache implementation from context without
-// any of the filters applied.
-func GetMCUnfiltered(c context.Context) Memcache {
-        if f, ok := c.Value(memcacheKey).(MCFactory); ok && f != nil {
-                return f(c)
-        }
-        return nil
-}
-
-// GetMC gets the current memcache implementation from the context.
-func GetMC(c context.Context) Memcache {
-        ret := GetMCUnfiltered(c)
-        if ret == nil {
-                return nil
-        }
-        for _, f := range getCurMCFilters(c) {
-                ret = f(c, ret)
-        }
-        return ret
-}
-
-// SetMCFactory sets the function to produce Memcache instances, as returned by
-// the GetMC method.
-func SetMCFactory(c context.Context, mcf MCFactory) context.Context {
-        return context.WithValue(c, memcacheKey, mcf)
-}
-
-// SetMC sets the current Memcache object in the context. Useful for testing
-// with a quick mock. This is just a shorthand SetMCFactory invocation to set
-// a factory which always returns the same object.
-func SetMC(c context.Context, mc Memcache) context.Context {
-        return SetMCFactory(c, func(context.Context) Memcache { return mc })
-}
-
-func getCurMCFilters(c context.Context) []MCFilter {
-        curFiltsI := c.Value(memcacheFilterKey)
-        if curFiltsI != nil {
-                return curFiltsI.([]MCFilter)
-        }
-        return nil
-}
-
-// AddMCFilters adds Memcache filters to the context.
-func AddMCFilters(c context.Context, filts ...MCFilter) context.Context {
-        if len(filts) == 0 {
-                return c
-        }
-        cur := getCurMCFilters(c)
-        newFilts := make([]MCFilter, 0, len(cur)+len(filts))
-        newFilts = append(newFilts, getCurMCFilters(c)...)
-        newFilts = append(newFilts, filts...)
-        return context.WithValue(c, memcacheFilterKey, newFilts)
-}