From 1b95684cf04ff4b419921ffd791d12a3dda415b2 Mon Sep 17 00:00:00 2001
From: Alexey Ivanov <rbtz@dropbox.com>
Date: Fri, 15 Nov 2019 16:20:01 -0800
Subject: [PATCH 1/2] runtime: added standard library compatibility to
 RandomGenerator

Signed-off-by: Alexey Ivanov <rbtz@dropbox.com>
---
 include/envoy/runtime/runtime.h          | 23 ++++++++++++++++++++++-
 test/common/runtime/runtime_impl_test.cc | 17 +++++++++++++++++
 2 files changed, 39 insertions(+), 1 deletion(-)

diff --git a/include/envoy/runtime/runtime.h b/include/envoy/runtime/runtime.h
index 6494289402dfb..71efd7c7939dc 100644
--- a/include/envoy/runtime/runtime.h
+++ b/include/envoy/runtime/runtime.h
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <cstdint>
+#include <limits>
 #include <memory>
 #include <string>
 #include <unordered_map>
@@ -30,10 +31,30 @@ class RandomGenerator {
 public:
   virtual ~RandomGenerator() = default;
 
+  using result_type = uint64_t;
+
   /**
    * @return uint64_t a new random number.
    */
-  virtual uint64_t random() PURE;
+  virtual result_type random() PURE;
+
+  /*
+   * @return the smallest value that `operator()` may return. The value is
+   * strictly less than `max()`.
+   */
+  constexpr static result_type min() noexcept { return std::numeric_limits<result_type>::min(); };
+
+  /*
+   * @return the largest value that `operator()` may return. The value is
+   * strictly greater than `min()`.
+   */
+  constexpr static result_type max() noexcept { return std::numeric_limits<result_type>::max(); };
+
+  /*
+   * @return a value in the closed interval `[min(), max()]`. Has amortized
+   * constant complexity.
+   */
+  result_type operator()() { return result_type(random()); };
 
   /**
    * @return std::string containing uuid4 of 36 char length.
diff --git a/test/common/runtime/runtime_impl_test.cc b/test/common/runtime/runtime_impl_test.cc
index e53097f5d74b1..d591e3b6d7638 100644
--- a/test/common/runtime/runtime_impl_test.cc
+++ b/test/common/runtime/runtime_impl_test.cc
@@ -48,6 +48,23 @@ TEST(Random, SanityCheckOfUniquenessRandom) {
   EXPECT_EQ(num_of_results, results.size());
 }
 
+TEST(Random, SanityCheckOfStdLibRandom) {
+  Runtime::RandomGeneratorImpl random;
+
+  static const auto num_of_items = 100;
+  std::vector<uint64_t> v(num_of_items);
+  std::iota(v.begin(), v.end(), 0);
+
+  static const auto num_of_checks = 10000;
+  for (size_t i = 0; i < num_of_checks; ++i) {
+    const auto prev = v;
+    std::shuffle(v.begin(), v.end(), random);
+    EXPECT_EQ(v.size(), prev.size());
+    EXPECT_NE(v, prev);
+    EXPECT_FALSE(std::is_sorted(v.begin(), v.end()));
+  }
+}
+
 TEST(UUID, CheckLengthOfUUID) {
   RandomGeneratorImpl random;
 

From 170b95e443e2f4489878718ed1e40b4104f0619f Mon Sep 17 00:00:00 2001
From: Alexey Ivanov <rbtz@dropbox.com>
Date: Tue, 26 Nov 2019 01:25:02 -0800
Subject: [PATCH 2/2] clang-tidy: add lint

Signed-off-by: Alexey Ivanov <rbtz@dropbox.com>
---
 include/envoy/runtime/runtime.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/envoy/runtime/runtime.h b/include/envoy/runtime/runtime.h
index 71efd7c7939dc..7eda91473c904 100644
--- a/include/envoy/runtime/runtime.h
+++ b/include/envoy/runtime/runtime.h
@@ -31,7 +31,7 @@ class RandomGenerator {
 public:
   virtual ~RandomGenerator() = default;
 
-  using result_type = uint64_t;
+  using result_type = uint64_t; // NOLINT(readability-identifier-naming)
 
   /**
    * @return uint64_t a new random number.