Create a more random approach to uuid generation (#868)

* Create a more random approach to uuid generation
* Add two additional test cases for Uuid

sdk/core/azure-core/inc/azure/core/uuid.hpp

@@ -21,7 +21,7 @@ namespace Azure { namespace Core {
   class Uuid {
 
   private:
-    static const int UuidSize = 16;
+    static constexpr int UuidSize = 16;
 
     uint8_t m_uuid[UuidSize];
     // The UUID reserved variants.
@@ -74,12 +74,14 @@ namespace Azure { namespace Core {
     static Uuid CreateUuid()
     {
       std::random_device rd;
-      std::mt19937 gen(rd());
 
       uint8_t uuid[UuidSize] = {};
 
       for (int i = 0; i < UuidSize; i += 4)
-        *reinterpret_cast<uint32_t*>(uuid + i) = gen();
+      {
+        const uint32_t x = rd();
+        std::memcpy(uuid + i, &x, 4);
+      }
 
       // SetVariant to ReservedRFC4122
       uuid[8] = (uuid[8] | ReservedRFC4122) & 0x7F;

sdk/core/azure-core/test/ut/uuid.cpp

@@ -4,7 +4,7 @@
 #include "gtest/gtest.h"
 #include <azure/core/uuid.hpp>
 #include <string>
-#include <vector>
+#include <set>
 
 using namespace Azure::Core;
 
@@ -13,3 +13,60 @@ TEST(Uuid, Basic)
   auto uuid = Uuid::CreateUuid();
   EXPECT_TRUE(uuid.GetUuidString().length() == 36);
 }
+
+TEST(Uuid, Randomness) 
+{ 
+  const int size = 100000;
+  std::set<std::string> uuids;
+  for (int i = 0; i < size; i++)
+  {
+    auto ret = uuids.insert(Uuid::CreateUuid().GetUuidString());
+    //If the value already exists in the set then the insert will fail
+    // ret.second == false means the insert failed.
+    EXPECT_TRUE(ret.second);
+  }
+  EXPECT_TRUE(uuids.size() == size);
+}
+
+TEST(Uuid, separatorPosition)
+{
+  auto uuidKey = Uuid::CreateUuid().GetUuidString();
+  // validate expected format '8-4-4-4-12'
+  EXPECT_PRED5(
+      [](std::string const& uuidKey, char pos1, char pos2, char pos3, char pos4) {
+        return pos1 == pos2 && pos1 == pos3 && pos1 == pos4 && pos1 == '-';
+      },
+      uuidKey,
+      uuidKey[8],
+      uuidKey[13],
+      uuidKey[18],
+      uuidKey[23]);
+}
+
+TEST(Uuid, validChars)
+{
+  auto uuidKey = Uuid::CreateUuid().GetUuidString();
+  // validate valid chars and separators count
+  EXPECT_PRED2(
+      [](std::string const& uuidKey, int expectedSeparators) {
+        int separatorsCount = 0;
+        for (int index = 0; index < uuidKey.size(); index++)
+        {
+          if (uuidKey[index] == '-')
+          {
+            separatorsCount++;
+            continue;
+          }
+          else if (!((uuidKey[index] >= '0' && uuidKey[index] <= '9')
+                     || (uuidKey[index] >= 'a' && uuidKey[index] <= 'f')
+                     || (uuidKey[index] >= 'A' && uuidKey[index] <= 'F')))
+          {
+            // invalid char found
+            return false;
+          }
+        }
+        return separatorsCount == expectedSeparators;
+      },
+      uuidKey,
+      4);
+}