bug mongo: Transaction does not keep its invariant. Hide it from users

Tests: протестировано CI
commit_hash:01bc74240ad70b0db85b092fa56b361057c3b5e9

Author: apolukhin

mongo/include/userver/storages/mongo/pool.hpp

@@ -56,11 +56,6 @@ class Pool {
     /// @throws storages::mongo::MongoException if failed to connect to the mongo server.
     void Ping();
 
-    /// @brief Begin a new transaction
-    /// @return Transaction handle for executing operations within transaction context
-    /// @throws MongoException if transaction cannot be started
-    Transaction BeginTransaction() const;
-
     /// @cond
     // For internal use only
     Pool(
@@ -81,6 +76,13 @@ class Pool {
     /// @endcond
 
 private:
+    // Note: transactions are broken. See tests for more info
+    //
+    /// @brief Begin a new transaction
+    /// @return Transaction handle for executing operations within transaction context
+    /// @throws MongoException if transaction cannot be started
+    Transaction BeginTransaction() const;
+
     std::shared_ptr<impl::PoolImpl> impl_;
 };
 

mongo/src/storages/mongo/transaction_mongotest.cpp

@@ -11,6 +11,8 @@
 
 USERVER_NAMESPACE_BEGIN
 
+#if 0
+
 namespace bson = formats::bson;
 
 // NOLINTNEXTLINE(google-build-using-namespace)
@@ -273,4 +275,47 @@ UTEST_F(MongoTransaction, ParallelTrancactions) {
     EXPECT_THAT(found_docs, ::testing::ElementsAre(bson::MakeDoc("name", "test_user", "age", 30)));
 }
 
+UTEST_F(MongoTransaction, InvalidSessionIdReproducer) {
+    static const std::string kCollectionName = "test_invalid_session_id";
+
+    auto config = MakeTestPoolConfig();
+    config.pool_settings.initial_size = 1;
+    config.pool_settings.max_size = 3;
+    config.pool_settings.idle_limit = 2;
+
+    auto pool = MakePool("userver_mongotest_invalid_session_id", config);
+
+    auto coll = pool.GetCollection(kCollectionName);
+
+    {
+        std::vector<formats::bson::Document> docs;
+        docs.reserve(10);
+        for (int i = 0; i < 10; ++i) {
+            docs.push_back(bson::MakeDoc("foo", "bar", "value", i));
+        }
+        coll.InsertMany(std::move(docs));
+    }
+
+    using formats::bson::MakeDoc;
+
+    auto txn = pool.BeginTransaction();
+    // GetCollection starts a transaction using client_1 from the pool
+    auto coll_txn = txn.GetCollection(kCollectionName);
+
+    // Find uses the same client_1 from the pool because initial_size == 1
+    // and returns a Cursor that holds this client
+    //
+    // TODO: transaction is not usable after that???
+    auto cursor = coll.Find(MakeDoc("foo", "bar"));
+
+    // TODO: Must be fatal or must not compile: two cursors in the same transaction?
+    auto cursor = coll.Find(MakeDoc("foo", "bar"));
+
+    // TODO: Must be fatal or must not compile: executing not in a transaction
+    UASSERT_THROW( coll_txn.InsertOne(MakeDoc("foo", "bar", "value", 11)) );
+    txn.Commit();
+}
+
+#endif
+
 USERVER_NAMESPACE_END