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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 mail
import (
type key int
var (
serviceKey key
serviceFilterKey key = 1
// Factory is the function signature for factory methods compatible with
// SetFactory.
type Factory func(context.Context) RawInterface
// Filter is the function signature for a filter mail implementation. It
// gets the current mail implementation, and returns a new mail implementation
// backed by the one passed in.
type Filter 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(serviceKey).(Factory); ok && f != nil {
return f(c)
return nil
func getCurFilters(c context.Context) []Filter {
curFiltsI := c.Value(serviceFilterKey)
if curFiltsI != nil {
return curFiltsI.([]Filter)
return nil
// Raw pulls the raw mail service implementation from context or nil if it
// wasn't set.
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
// SetFactory sets the function to produce mail.RawInterface instances,
// as returned by the Get method.
func SetFactory(c context.Context, f Factory) context.Context {
return context.WithValue(c, serviceKey, f)
// Set sets the mail service in this 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, u RawInterface) context.Context {
return SetFactory(c, func(context.Context) RawInterface { return u })
// AddFilters adds RawInterface 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, serviceFilterKey, newFilts)