Adding new TAP test for Clickhouse

Also fixed a bug in Clickhouse module if backend was not present.
Changed some code in SQLite3 TAP test to be reused for Clickhouse testing.

lib/ClickHouse_Server.cpp

@@ -1177,6 +1177,7 @@ bool ClickHouse_Session::init() {
 		co.SetHost(hostname);
 		co.SetPort(atoi(port));
 		co.SetCompressionMethod(CompressionMethod::None);
+		client = NULL;
 		client = new clickhouse::Client(co);
 		ret=true;
 	} catch (const std::exception& e) {

test/tap/tests/modules_server_test.h

@@ -0,0 +1,94 @@
+/**
+ * @brief Extract the current 'MODULE-mysql_ifaces' from ProxySQL config.
+ * @param proxysql_admin An already opened connection to ProxySQL Admin.
+ * @return EXIT_SUCCESS, or one of the following error codes:
+ *   - EINVAL if supplied 'proxysql_admin' is NULL.
+ *   - EXIT_FAILURE in case other operation failed.
+ */
+int get_module_ifaces(MYSQL* proxysql_admin, const std::string varname, std::string& module_ifaces) {
+	if (proxysql_admin == NULL) {
+		return EINVAL;
+	}
+
+	int res = EXIT_FAILURE;
+
+	std::string query = "SELECT * FROM global_variables WHERE Variable_name='" + varname + "'";
+	diag("Running query: %s", query.c_str());
+	MYSQL_QUERY(proxysql_admin, query.c_str());
+
+	MYSQL_RES* admin_res = mysql_store_result(proxysql_admin);
+	if (!admin_res) {
+		diag("'mysql_store_result' at line %d failed: %s", __LINE__, mysql_error(proxysql_admin));
+		goto cleanup;
+	}
+
+	{
+		MYSQL_ROW row = mysql_fetch_row(admin_res);
+		if (!row || row[0] == nullptr || row[1] == nullptr) {
+			diag("'mysql_fetch_row' at line %d returned 'NULL'", __LINE__);
+			res = -1;
+			goto cleanup;
+		}
+
+		std::string _module_ifaces { row[1] };
+		module_ifaces = _module_ifaces;
+		res = EXIT_SUCCESS;
+	}
+
+cleanup:
+
+	return res;
+}
+
+int extract_module_host_port(MYSQL* proxysql_admin, const std::string varname, std::pair<std::string, int>& host_port) {
+	if (proxysql_admin == nullptr) { return EINVAL; }
+	int res = EXIT_SUCCESS;
+
+	std::string module_ifaces {};
+	int ifaces_err = get_module_ifaces(proxysql_admin, varname, module_ifaces);
+
+	// ProxySQL is likely to have been launched without "--MODULE-server" flag
+	if (ifaces_err == -1) {
+		if (varname=="sqliteserver-mysql_ifaces") {
+			diag("ProxySQL was launched without '--sqlite3-server' flag");
+		} else if (varname=="clickhouse-mysql_ifaces") {
+			diag("ProxySQL was launched without '--clickhouse-server' flag");
+		} else {
+			diag("Unknown variable %s", varname.c_str());	
+		}
+		res = EXIT_FAILURE;
+		return res;
+	}
+
+	// Extract the correct port to connect to MODULE server
+	std::string::size_type colon_pos = module_ifaces.find(":");
+	if (colon_pos == std::string::npos) {
+		diag("ProxySQL returned a malformed '%s': %s", varname.c_str(), module_ifaces.c_str());
+		res = EXIT_FAILURE;
+		return res;
+	}
+
+	std::string module_host { module_ifaces.substr(0, colon_pos) };
+	std::string module_port { module_ifaces.substr(colon_pos + 1) };
+
+	// Check that port has valid conversion
+	char* end_pos = nullptr;
+	int i_module_port = std::strtol(module_port.c_str(), &end_pos, 10);
+
+	if (errno == ERANGE || (end_pos != &module_port.back() + 1)) {
+		diag(
+			"ProxySQL returned a invalid port number within '%s': %s",
+			varname.c_str(), module_ifaces.c_str()
+		);
+		res = EXIT_FAILURE;
+		return res;
+	}
+
+	if (res == EXIT_SUCCESS) {
+		host_port = { module_host, i_module_port };
+	}
+
+	return res;
+}
+
+