Experiment with a compact mode for simple preloaded entries.

net/tools/transport_security_state_generator/trie/trie_writer.cc

 // Copyright (c) 2016 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 "net/tools/transport_security_state_generator/trie/trie_writer.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 #include "net/tools/transport_security_state_generator/trie/trie_bit_buffer.h"
 
 namespace net {
 
 namespace transport_security_state {
 
 namespace {
 
 bool CompareReversedEntries(const std::unique_ptr<ReversedEntry>& lhs,
                             const std::unique_ptr<ReversedEntry>& rhs) {
   return lhs->reversed_name < rhs->reversed_name;
 }
 
+// Returns true if the entry only configures HSTS with includeSubdomains.
+// Such entries, when written, can be represented more compactly, and thus
+// reduce the overall size of the trie.
+bool IsSimpleEntry(const TransportSecurityStateEntry* entry) {
+  return entry->force_https && entry->include_subdomains &&
+         entry->pinset.empty() && !entry->expect_ct && !entry->expect_staple;
+}
+
 }  // namespace
 
 ReversedEntry::ReversedEntry(std::vector<uint8_t> reversed_name,
                              const TransportSecurityStateEntry* entry)
     : reversed_name(reversed_name), entry(entry) {}
 
 ReversedEntry::~ReversedEntry() {}
 
 TrieWriter::TrieWriter(const HuffmanRepresentationTable& huffman_table,
                        const NameIDMap& expect_ct_report_uri_map,
@@ skipping 84 matching lines @@
   writer.WriteChar(kEndOfTableValue, huffman_table_, huffman_builder_);
 
   *position = buffer_.position();
   writer.Flush();
   writer.WriteToBitWriter(&buffer_);
   return true;
 }
 
 bool TrieWriter::WriteEntry(const TransportSecurityStateEntry* entry,
                             TrieBitBuffer* writer) {
+  if (IsSimpleEntry(entry)) {
+    writer->WriteBit(1);
+    return true;
+  } else {
+    writer->WriteBit(0);
+  }
+
   uint8_t include_subdomains = 0;
   if (entry->include_subdomains) {
     include_subdomains = 1;
   }
   writer->WriteBit(include_subdomains);
 
   uint8_t force_https = 0;
   if (entry->force_https) {
     force_https = 1;
   }
@@ skipping 135 matching lines @@
   return buffer_.position();
 }
 
 void TrieWriter::Flush() {
   buffer_.Flush();
 }
 
 }  // namespace transport_security_state
 
 }  // namespace net