From 69fcc053bbb9156b8b88116a8dc8cc976148d86d Mon Sep 17 00:00:00 2001
From: Benny Halevy <bhalevy@scylladb.com>
Date: Tue, 15 Feb 2022 13:34:38 +0200
Subject: [PATCH] utils: uuid: add null_uuid

and respective bool predecate and operator
and unit test.

Signed-off-by: Benny Halevy <bhalevy@scylladb.com>
Message-Id: <20220215113438.473400-1-bhalevy@scylladb.com>
---
 test/boost/UUID_test.cc | 22 ++++++++++++++++++++++
 utils/UUID.hh           | 14 ++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/test/boost/UUID_test.cc b/test/boost/UUID_test.cc
index 16c6f8512d..4288912a38 100644
--- a/test/boost/UUID_test.cc
+++ b/test/boost/UUID_test.cc
@@ -234,3 +234,25 @@ BOOST_AUTO_TEST_CASE(test_negate) {
 
     BOOST_REQUIRE(original_uuid == re_negated_uuid);
 }
+
+BOOST_AUTO_TEST_CASE(test_null_uuid) {
+    // Verify that the default-constructed UUID is null
+    utils::UUID uuid;
+    BOOST_CHECK(uuid.is_null());
+    BOOST_CHECK(!uuid);
+
+    // Verify that the null_uuid is indeed null
+    uuid = utils::null_uuid();
+    BOOST_CHECK(uuid.is_null());
+    BOOST_CHECK(!uuid);
+
+    // Verify that a random uuid is not null
+    uuid = utils::make_random_uuid();
+    BOOST_CHECK(!uuid.is_null());
+    BOOST_CHECK(uuid);
+
+    // Verify that a time uuid is not null
+    uuid = utils::UUID_gen::get_time_UUID();
+    BOOST_CHECK(!uuid.is_null());
+    BOOST_CHECK(uuid);
+}
diff --git a/utils/UUID.hh b/utils/UUID.hh
index ff9bac98b9..f27b64c7a3 100644
--- a/utils/UUID.hh
+++ b/utils/UUID.hh
@@ -109,6 +109,16 @@ public:
         return !(*this < v);
     }
 
+    // Valid (non-null) UUIDs always have their version
+    // nibble set to a non-zero value
+    bool is_null() const noexcept {
+        return !most_sig_bits && !least_sig_bits;
+    }
+
+    operator bool() const noexcept {
+        return !is_null();
+    }
+
     bytes serialize() const {
         bytes b(bytes::initialized_later(), serialized_size());
         auto i = b.begin();
@@ -127,6 +137,10 @@ public:
     }
 };
 
+inline UUID null_uuid() noexcept {
+    return UUID();
+}
+
 UUID make_random_uuid();
 
 inline std::strong_ordering uint64_t_tri_compare(uint64_t a, uint64_t b) {