Split off serialization and key functions to their own packages.

filter/dscache/serialize.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"
         "compress/zlib"
         "io/ioutil"
 
         ds "github.com/luci/gae/service/datastore"
+        "github.com/luci/gae/service/datastore/serialize"
 )
 
 func encodeItemValue(pm ds.PropertyMap) []byte {
         pm, _ = pm.Save(false)
 
         buf := bytes.Buffer{}
         // errs can't happen, since we're using a byte buffer.
         _ = buf.WriteByte(byte(NoCompression))
-        _ = pm.Write(&buf, ds.WithoutContext)
+        _ = serialize.WritePropertyMap(&buf, serialize.WithoutContext, pm)
 
         data := buf.Bytes()
         if buf.Len() > CompressionThreshold {
                 buf2 := bytes.NewBuffer(make([]byte, 0, len(data)))
                 _ = buf2.WriteByte(byte(ZlibCompression))
                 writer := zlib.NewWriter(buf2)
                 _, _ = writer.Write(data[1:]) // skip the NoCompression byte
                 writer.Close()
                 data = buf2.Bytes()
         }
@@ skipping 16 matching lines @@
                 if err != nil {
                         return nil, err
                 }
                 defer reader.Close()
                 data, err := ioutil.ReadAll(reader)
                 if err != nil {
                         return nil, err
                 }
                 buf = bytes.NewBuffer(data)
         }
-        ret := ds.PropertyMap{}
-        err = ret.Read(buf, ds.WithoutContext, ns, aid)
-        return ret, err
+        return serialize.ReadPropertyMap(buf, serialize.WithoutContext, ns, aid)
 }