Add server/cache support to gaeconfig.

appengine/gaeconfig/cache.go

Index: appengine/gaeconfig/cache.go
diff --git a/appengine/gaeconfig/cache.go b/appengine/gaeconfig/cache.go
deleted file mode 100644
index 731aab93de00eac29de15c658ebd7f0ca2acd471..0000000000000000000000000000000000000000
--- a/appengine/gaeconfig/cache.go
+++ /dev/null
@@ -1,97 +0,0 @@
-// Copyright 2015 The LUCI Authors. All rights reserved.
-// Use of this source code is governed under the Apache License, Version 2.0
-// that can be found in the LICENSE file.
-
-package gaeconfig
-
-import (
-	"bytes"
-	"encoding/binary"
-	"fmt"
-	"time"
-
-	ds "github.com/luci/gae/service/datastore"
-	mc "github.com/luci/gae/service/memcache"
-	"github.com/luci/luci-go/common/clock"
-	"github.com/luci/luci-go/common/config"
-	"github.com/luci/luci-go/common/config/filters/caching"
-	"github.com/luci/luci-go/common/data/caching/proccache"
-	log "github.com/luci/luci-go/common/logging"
-
-	"golang.org/x/net/context"
-)
-
-// WrapWithCache wraps config client with proccache-and-memcache-caching layer.
-func WrapWithCache(cfg config.Interface, expire time.Duration) config.Interface {
-	return caching.Wrap(cfg, caching.Options{
-		Cache:      &cache{},
-		Expiration: expire,
-	})
-}
-
-type cache struct{}
-
-type proccacheKey string
-
-func (c *cache) Store(ctx context.Context, baseKey string, expire time.Duration, value []byte) {
-	k := cacheKey(baseKey)
-
-	proccache.Put(ctx, k, value, expire)
-
-	// value in memcache is [varint(expiration_ts.Millis) ++ value]
-	// value in proccache is [value]
-	//
-	// This is because memcache doesn't populate the .Expiration field of the
-	// memcache Item on Get operations :(
-	stamp := ds.TimeToInt(clock.Now(ctx).UTC().Add(expire))
-	buf := make([]byte, binary.MaxVarintLen64)
-	value = append(buf[:binary.PutVarint(buf, stamp)], value...)
-
-	itm := mc.NewItem(ctx, string(k)).SetExpiration(expire).SetValue(value)
-	if err := mc.Set(ctx, itm); err != nil {
-		log.Fields{
-			log.ErrorKey: err,
-			"key":        baseKey,
-			"expire":     expire,
-		}.Warningf(ctx, "Failed to store cache value.")
-	}
-}
-
-func (c *cache) Retrieve(ctx context.Context, baseKey string) []byte {
-	k := cacheKey(baseKey)
-	ret, err := proccache.GetOrMake(ctx, k, func() (value interface{}, exp time.Duration, err error) {
-		item, err := mc.GetKey(ctx, string(k))
-		if err != nil {
-			if err != mc.ErrCacheMiss {
-				log.Fields{
-					log.ErrorKey: err,
-					"key":        baseKey,
-				}.Warningf(ctx, "Failed to retrieve memcache value.")
-			}
-			return
-		}
-
-		buf := bytes.NewBuffer(item.Value())
-		expStamp, err := binary.ReadVarint(buf)
-		if err != nil {
-			log.Fields{
-				log.ErrorKey: err,
-				"key":        baseKey,
-			}.Warningf(ctx, "Failed to decode stamp in memcache value.")
-			return
-		}
-
-		// proccache will ignore this value if exp is in the past
-		exp = ds.IntToTime(expStamp).Sub(clock.Now(ctx))
-		value = buf.Bytes()
-		return
-	})
-	if err != nil {
-		return nil
-	}
-	return ret.([]byte)
-}
-
-func cacheKey(baseKey string) proccacheKey {
-	return proccacheKey(fmt.Sprintf("luci-config:v2:%s", baseKey))
-}