Split off serialization and key functions to their own packages.

filter/dscache/dscache.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 dscache
 
 import (
         "bytes"
         "crypto/sha1"
         "encoding/base64"
         "fmt"
         "time"
 
         "github.com/luci/gae/service/datastore"
+        "github.com/luci/gae/service/datastore/serialize"
 )
 
 var (
         // InstanceEnabledStatic allows you to statically (e.g. in an init() function)
         // bypass this filter by setting it to false. This takes effect when the
         // application calls IsGloballyEnabled.
         InstanceEnabledStatic = true
 
         // LockTimeSeconds is the number of seconds that a "lock" memcache entry will
         // have its expiration set to. It's set to just over half of the frontend
@@ skipping 73 matching lines @@
         ItemUKNONWN FlagValue = iota
         ItemHasData
         ItemHasLock
 )
 
 func MakeMemcacheKey(shard int, k datastore.Key) string {
         return fmt.Sprintf(KeyFormat, shard, HashKey(k))
 }
 
 func HashKey(k datastore.Key) string {
-        // errs can't happen, since we're using a byte buffer.
+        dgst := sha1.Sum(serialize.ToBytes(k))
         buf := bytes.Buffer{}
-        _ = datastore.WriteKey(&buf, datastore.WithoutContext, k)
-        dgst := sha1.Sum(buf.Bytes())
-        buf.Reset()
         enc := base64.NewEncoder(base64.StdEncoding, &buf)
         _, _ = enc.Write(dgst[:])
         enc.Close()
         return buf.String()[:buf.Len()-Sha1B64Padding]
 }