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// Copyright 2015 The LUCI Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package memcache
import (
type key int
var (
memcacheKey key
memcacheFilterKey key = 1
// RawFactory is the function signature for RawFactory methods compatible with
// SetRawFactory.
type RawFactory func(context.Context) RawInterface
// RawFilter is the function signature for a RawFilter MC implementation. It
// gets the current MC implementation, and returns a new MC implementation
// backed by the one passed in.
type RawFilter func(context.Context, RawInterface) RawInterface
// getUnfiltered gets gets the RawInterface implementation from context without
// any of the filters applied.
func getUnfiltered(c context.Context) RawInterface {
if f, ok := c.Value(memcacheKey).(RawFactory); ok && f != nil {
return f(c)
return nil
// Raw gets the current memcache implementation from the context.
func Raw(c context.Context) RawInterface {
ret := getUnfiltered(c)
if ret == nil {
return nil
for _, f := range getCurFilters(c) {
ret = f(c, ret)
return ret
// SetRawFactory sets the function to produce RawInterface instances, as returned by
// the Get method.
func SetRawFactory(c context.Context, mcf RawFactory) context.Context {
return context.WithValue(c, memcacheKey, mcf)
// SetRaw sets the current RawInterface object in the context. Useful for testing
// with a quick mock. This is just a shorthand SetRawFactory invocation to SetRaw
// a RawFactory which always returns the same object.
func SetRaw(c context.Context, mc RawInterface) context.Context {
return SetRawFactory(c, func(context.Context) RawInterface { return mc })
func getCurFilters(c context.Context) []RawFilter {
curFiltsI := c.Value(memcacheFilterKey)
if curFiltsI != nil {
return curFiltsI.([]RawFilter)
return nil
// AddRawFilters adds RawInterface filters to the context.
func AddRawFilters(c context.Context, filts ...RawFilter) context.Context {
if len(filts) == 0 {
return c
cur := getCurFilters(c)
newFilts := make([]RawFilter, 0, len(cur)+len(filts))
newFilts = append(newFilts, getCurFilters(c)...)
newFilts = append(newFilts, filts...)
return context.WithValue(c, memcacheFilterKey, newFilts)