[Sync] USS: Filter out redundant changes in SMTP.

sync/internal_api/processor_entity_tracker.cc

 // Copyright 2014 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.
 
 #include "sync/internal_api/public/processor_entity_tracker.h"
 
 #include <stdint.h>
 
 #include "base/base64.h"
 #include "base/sha1.h"
 #include "base/time/time.h"
 #include "sync/internal_api/public/non_blocking_sync_common.h"
 #include "sync/syncable/syncable_util.h"
 #include "sync/util/time.h"
 
 namespace syncer_v2 {
 
+namespace {
+
+void HashSpecifics(const sync_pb::EntitySpecifics& specifics,
+                   std::string* hash) {
+  std::string hash_input;
+  specifics.AppendToString(&hash_input);

[skym, 2016/03/28 22:35:38]

Why not use SerializeAsString() inline?

[maxbogue, 2016/03/29 00:32:09]

Because I was just copying from UpdateSpecificsHash() and didn't know that was a
thing :P Done.

+  base::Base64Encode(base::SHA1HashString(hash_input), hash);
+}
+
+}  // namespace
+
 scoped_ptr<ProcessorEntityTracker> ProcessorEntityTracker::CreateNew(
     const std::string& client_tag,
     const std::string& client_tag_hash,
     const std::string& id,
     base::Time creation_time) {
   // Initialize metadata
   sync_pb::EntityMetadata metadata;
   metadata.set_client_tag_hash(client_tag_hash);
   if (!id.empty())
     metadata.set_server_id(id);
@@ skipping 31 matching lines @@
     data->client_tag_hash = metadata_.client_tag_hash();
   }
   commit_data_ = data->PassToPtr();
   DCHECK(HasCommitData());
 }
 
 bool ProcessorEntityTracker::HasCommitData() const {
   return !commit_data_->client_tag_hash.empty();
 }
 
+bool ProcessorEntityTracker::MatchesSpecificsHash(
+    const sync_pb::EntitySpecifics& specifics) const {
+  if (specifics.ByteSize() > 0) {
+    std::string hash;
+    HashSpecifics(specifics, &hash);
+    return hash == metadata_.specifics_hash();
+  } else {
+    return !metadata_.has_specifics_hash();

[skym, 2016/03/28 22:35:38]

What's the reason for this special logic? We don't match specifics hashes for
deletes anyways right?

[maxbogue, 2016/03/29 00:32:09]

Hmm... doesn't seem very important. It should be fine to just set specifics hash
as the empty string. Removed it here and below.

[maxbogue, 2016/03/29 01:02:05]

Update: not below, apparently the logic doesn't return empty string for the
default proto. I've added a DCHECK here that ByteSize > 0 and restored the logic
in UpdateSpecificsHash.

+  }
+}
+
 bool ProcessorEntityTracker::IsUnsynced() const {
   return metadata_.sequence_number() > metadata_.acked_sequence_number();
 }
 
 bool ProcessorEntityTracker::RequiresCommitRequest() const {
   return metadata_.sequence_number() > commit_requested_sequence_number_;
 }
 
 bool ProcessorEntityTracker::RequiresCommitData() const {
   return RequiresCommitRequest() && !HasCommitData() && !metadata_.is_deleted();
@@ skipping 117 matching lines @@
 
 void ProcessorEntityTracker::IncrementSequenceNumber() {
   DCHECK(metadata_.has_sequence_number());
   metadata_.set_sequence_number(metadata_.sequence_number() + 1);
 }
 
 // Update hash string for EntitySpecifics.
 void ProcessorEntityTracker::UpdateSpecificsHash(
     const sync_pb::EntitySpecifics& specifics) {
   if (specifics.ByteSize() > 0) {
-    std::string hash_input;
-    specifics.AppendToString(&hash_input);
-    base::Base64Encode(base::SHA1HashString(hash_input),
-                       metadata_.mutable_specifics_hash());
+    HashSpecifics(specifics, metadata_.mutable_specifics_hash());
   } else {
     metadata_.clear_specifics_hash();
   }
 }
 
 }  // namespace syncer_v2