Instrument to catch corruption constructing safe-browsing filters.

chrome/browser/safe_browsing/prefix_set.cc

 // Copyright (c) 2011 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 "chrome/browser/safe_browsing/prefix_set.h"
 
 #include <algorithm>
 #include <math.h>
 
 #include "base/file_util.h"
@@ skipping 147 matching lines @@
 
     SBPrefix current = index_[ii].first;
     prefixes->push_back(current);
     for (size_t di = index_[ii].second; di < deltas_end; ++di) {
       current += deltas_[di];
       prefixes->push_back(current);
     }
   }
 }
 
+// NOTE(shess): For debugging potential memory corruption.  I wanted
+// to test that the output of GetPrefixes() matched the checksum over
+// the unique elements in the input to the constructor, but the buffer
+// for GetPrefixes() to write to could itself be corrupted.  That
+// would make it look like GetPrefixes() itself was broken.  At that
+// point my head exploded, so I wrote this.
+SBPrefix PrefixSet::GetPrefixesChecksum() const {
+  SBPrefix checksum = 0;
+
+  for (size_t ii = 0; ii < index_.size(); ++ii) {
+    // The deltas for this |index_| entry run to the next index entry,
+    // or the end of the deltas.
+    const size_t deltas_end =
+        (ii + 1 < index_.size()) ? index_[ii + 1].second : deltas_.size();
+
+    SBPrefix current = index_[ii].first;
+    checksum ^= current;
+    for (size_t di = index_[ii].second; di < deltas_end; ++di) {
+      current += deltas_[di];
+      checksum ^= current;
+    }
+  }
+
+  return checksum;
+}
+
 // static
 PrefixSet* PrefixSet::LoadFile(const FilePath& filter_name) {
   int64 size_64;
   if (!file_util::GetFileSize(filter_name, &size_64))
     return NULL;
   using base::MD5Digest;
   if (size_64 < static_cast<int64>(sizeof(FileHeader) + sizeof(MD5Digest)))
     return NULL;
 
   file_util::ScopedFILE file(file_util::OpenFile(filter_name, "rb"));
@@ skipping 182 matching lines @@
   }
 
   for (size_t di = 0; di < deltas_.size(); ++di) {
     checksum ^= static_cast<uint32>(deltas_[di]);
   }
 
   return checksum == checksum_;
 }
 
 }  // namespace safe_browsing