Add base::UnguessableToken

base/nonce.h

Index: base/nonce.h
diff --git a/base/nonce.h b/base/nonce.h
new file mode 100644
index 0000000000000000000000000000000000000000..4d3656c41278beddcd041c6e7256d6da29e5c746
--- /dev/null
+++ b/base/nonce.h
@@ -0,0 +1,77 @@
+// Copyright 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.
+
+#ifndef BASE_NONCE_H_
+#define BASE_NONCE_H_
+
+#include <stdint.h>
+#include <string.h>
+#include <tuple>
+
+#include "base/base_export.h"
+#include "base/hash.h"
+
+namespace base {
+
+// An Nonce is a cryptographically strong, randomly generated, unguessable 128
+// bit token.
+//
+// TO CREATE NEW NONCES, ONLY USE GENERATE()!
+// The Generate() function is guaranteed to be cryptographically strong random.
+// Deserialize() is only meant to deserialize Nonces that were created via
+// Generate(), and sent accross processes as two uint64_t.
+class BASE_EXPORT Nonce {
+ public:
+  // Generates a unique, strongly random, unguessable nonce.
+  // USE THIS FUNCTION TO GENERATE NEW NONCES.
+  static Nonce Generate();
+
+  // Returns a nonce built from the high/low bytes provided.
+  // It should only be used in deserialization scenarios.
+  static Nonce Deserialize(uint64_t high, uint64_t low);
+
+  // Creates a null Nonce.

[Tom Sepez, 2016/09/13 18:20:41]

Actually, wouldn't this create an uninitialized nonce?  Do we want to set to
(0,0)?

[tguilbert, 2016/09/13 20:20:19]

It does create a (0,0) Nonce (and I have a UT to make sure it is set to 0). I
updated the comment, and renamed is_null() to is_empty().

[Tom Sepez, 2016/09/13 21:29:39]

Ok, yes if the ctor is called, so your test Nonce().is_empty() will pass, but
what about:

  Nonce nonce;
  nonce.is_empty()

sure you dont wan't a user-defined ctor to cover this case?

+  Nonce() = default;
+
+  bool is_null() const { return high_ == 0 && low_ == 0; }
+
+  uint64_t high() const { return high_; }
+
+  uint64_t low() const { return low_; }
+
+  std::string ToString() const;
+
+  bool operator<(const Nonce& other) const {
+    return std::tie(high_, low_) < std::tie(other.high_, other.low_);
+  }
+
+  bool operator==(const Nonce& other) const {
+    return high_ == other.high_ && low_ == other.low_;
+  }
+
+  bool operator!=(const Nonce& other) const { return !operator==(other); }
+
+ private:
+  Nonce(uint64_t high, uint64_t low);
+
+  // Note: Two uint64_t are used instead of uint8_t[16], in order to have a
+  // simpler ToString() and is_null().
+  uint64_t high_;
+  uint64_t low_;
+};
+
+// For use in std::unorderer_map.
+struct NonceHash {
+  size_t operator()(const base::Nonce& nonce) const {
+    return base::HashInts64(nonce.high(), nonce.low());
+  }
+};
+
+// If base::Nonce is not a POD, the IPC serialization logic should be revisited,
+// since it might no longer be possible to memcpy base::Nonce safely.
+static_assert(std::is_pod<Nonce>::value, "base::Nonce should be of POD type.");
+
+}  // namespace base
+
+#endif  // BASE_NONCE_H_