RAPPOR implementation

components/variations/metrics_util.cc

 // Copyright (c) 2012 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 "components/variations/metrics_util.h"
 
+#include "base/logging.h"
+#include "base/md5.h"
 #include "base/sha1.h"
 #include "base/sys_byteorder.h"
 
 namespace metrics {
 
+namespace {
+
+// Converts the 8-byte prefix of an MD5 hash into a uint64 value.
+inline uint64 HashToUInt64(const std::string& hash) {
+  uint64 value;
+  DCHECK_GE(hash.size(), sizeof(value));
+  memcpy(&value, hash.data(), sizeof(value));
+  return base::HostToNet64(value);
+}
+
+}  // namespace
+
 uint32 HashName(const std::string& name) {
   // SHA-1 is designed to produce a uniformly random spread in its output space,
   // even for nearly-identical inputs.
   unsigned char sha1_hash[base::kSHA1Length];
   base::SHA1HashBytes(reinterpret_cast<const unsigned char*>(name.c_str()),
                       name.size(),
                       sha1_hash);
 
   uint32 bits;
   COMPILE_ASSERT(sizeof(bits) < sizeof(sha1_hash), need_more_data);
   memcpy(&bits, sha1_hash, sizeof(bits));
 
   return base::ByteSwapToLE32(bits);
 }
 
+uint64 HashMetricName(const std::string& name) {
+  // Create an MD5 hash of the given |name|, represented as a byte buffer
+  // encoded as an std::string.
+  base::MD5Context context;
+  base::MD5Init(&context);
+  base::MD5Update(&context, name);
+
+  base::MD5Digest digest;
+  base::MD5Final(&digest, &context);
+
+  std::string hash_str(reinterpret_cast<char*>(digest.a), arraysize(digest.a));
+  uint64 hash = HashToUInt64(hash_str);

[Alexei Svitkine (slow), 2014/02/05 18:07:01]

Nit: Just return this directly.

[Steven Holte, 2014/02/05 22:44:37]

Done.

+
+  return hash;
+}
+
 }  // namespace metrics