Hello.

I have encountered what I believe isn't a good behaviour from the library. As you can see on the minimum example below, firstly I've tried to insert String to the UInt64 column, and I get an exception with text: DB::Exception: Cannot convert: String to UInt64. That's good.

However, when I try to insert correct data as a second step, I also get an exception saying: Unexpected packet Data received from client. Do I need to reset the client somehow after an exception happened? I would expect to successfully insert the correct data even after the first failure. Example:

int main() {
	clickhouse::Client client(clickhouse::ClientOptions().SetHost("localhost").SetPassword("clickhouse"));
	client.Execute("CREATE DATABASE IF NOT EXISTS test");
	client.Execute("CREATE TABLE IF NOT EXISTS test.numbers (id UInt64) ENGINE = Memory");

	clickhouse::Block block_bad;
	auto id_column_bad = std::make_shared<clickhouse::ColumnString>();
	id_column_bad->Append("Foo");
	block_bad.AppendColumn("id", id_column_bad);
	try
	{
		client.Insert("test.numbers", block_bad);
	}
	catch (const std::exception& e)
	{
		// says "arrived at 1: DB::Exception: Cannot convert: String to UInt64"
		printf("arrived at 1: %s\n", e.what());
	}

	clickhouse::Block block_good;
	auto id_column_good = std::make_shared<clickhouse::ColumnUInt64>();
	id_column_good->Append(1);
	block_good.AppendColumn("id", id_column_good);
	try
	{
		client.Insert("test.numbers", block_good);
	}
	catch (const std::exception& e)
	{
		// says "arrived at 2: DB::Exception: Unexpected packet Data received from client"
		printf("arrived at 2: %s\n", e.what());
	}
}

Initially I have discovered this issue in my code, but it was slightly different: the second attempt to insert the same incorrect data (I have a retrial mechanism in the code to mitigate possible network issues) led me to an infinite wait in client.Insert(..) function. After debugging a little I have found out that the library does not actually send a request to the server in that case: BufferedOutput::DoFlush function skips the if body completely. After that it tries to read the response from the server, but it never comes because there was no request.

Unfortunately, I could not reproduce the original issue with a minumum example, but I believe it can have something in common with the two exceptions case I've described in the beginning.