fix(ttl): report -2 when a container key has become empty

src/storage/redis_db.cc

@@ -244,6 +244,14 @@ rocksdb::Status Database::TTL(engine::Context &ctx, const Slice &user_key, int64
   Metadata metadata(kRedisNone, false);
   s = metadata.Decode(value);
   if (!s.ok()) return s;
+  // Report -2 when the metadata is expired, so that TTL stays consistent with
+  // EXISTS and TYPE which also rely on Metadata::Expired(). This also covers
+  // containers whose metadata is kept but treated as expired once empty (e.g. a
+  // hash whose last field was deleted, leaving size == 0 but expire == 0).
+  if (metadata.Expired()) {
+    *ttl = -2;
+    return rocksdb::Status::OK();
+  }
   *ttl = metadata.TTL();
 
   return rocksdb::Status::OK();

tests/cppunit/types/hash_test.cc

@@ -271,6 +271,34 @@ TEST_F(RedisHashTest, GetAndSet) {
   s = hash_->Del(*ctx_, key_);
 }
 
+TEST_F(RedisHashTest, TTLReportsKeyGoneAfterDeletingLastField) {
+  uint64_t ret = 0;
+  auto s = hash_->Set(*ctx_, key_, fields_[0], values_[0], &ret);
+  EXPECT_TRUE(s.ok() && ret == 1);
+
+  redis::Database db(storage_.get(), "hash_ns");
+  int64_t ttl = 0;
+  // The hash holds a live field but has no key-level expire, so TTL is -1.
+  s = db.TTL(*ctx_, key_, &ttl);
+  EXPECT_TRUE(s.ok());
+  EXPECT_EQ(-1, ttl);
+
+  // Deleting the last field leaves an empty hash whose metadata is still stored.
+  // TTL must report -2 (key does not exist) to stay consistent with EXISTS,
+  // instead of -1 leaked from the leftover metadata.
+  s = hash_->Delete(*ctx_, key_, {fields_[0]}, &ret);
+  EXPECT_TRUE(s.ok() && ret == 1);
+
+  uint32_t exists = 0;
+  s = db.Exists(*ctx_, {Slice(key_)}, &exists);
+  EXPECT_TRUE(s.ok());
+  EXPECT_EQ(0u, exists);
+
+  s = db.TTL(*ctx_, key_, &ttl);
+  EXPECT_TRUE(s.ok());
+  EXPECT_EQ(-2, ttl);
+}
+
 TEST_F(RedisHashTest, MGetAndMSet) {
   uint64_t ret = 0;
   std::vector<FieldValue> fvs;

tests/gocase/unit/type/hash/hash_test.go

@@ -584,6 +584,10 @@ var testHash = func(t *testing.T, configs util.KvrocksServerConfigs) {
 		rdb.HMSet(ctx, "myhash", []string{"a", "1", "b", "2", "c", "3"})
 		require.Equal(t, int64(3), rdb.HDel(ctx, "myhash", "a", "b", "c", "d", "e").Val())
 		require.Equal(t, int64(0), rdb.Exists(ctx, "myhash").Val())
+		// TTL and PTTL must report -2 (key does not exist) once the last field is
+		// deleted, consistent with EXISTS, instead of -1 from the leftover metadata.
+		require.EqualValues(t, -2, rdb.TTL(ctx, "myhash").Val())
+		require.EqualValues(t, -2, rdb.PTTL(ctx, "myhash").Val())
 	})
 
 	t.Run("HEXISTS", func(t *testing.T) {