Preserve STATUS_MYSQL_CONNECTION_COMPRESSION after connection reset

In MySQL_Connection::reset() we were forgetting the value of
STATUS_MYSQL_CONNECTION_COMPRESSION.
De-facto disabling compression if it was enabled.

lib/mysql_connection.cpp

@@ -2779,9 +2779,12 @@ int MySQL_Connection::async_send_simple_command(short event, char *stmt, unsigne
 
 void MySQL_Connection::reset() {
 	bool old_no_multiplex_hg = get_status(STATUS_MYSQL_CONNECTION_NO_MULTIPLEX_HG);
+	bool old_compress = get_status(STATUS_MYSQL_CONNECTION_COMPRESSION);
 	status_flags=0;
 	// reconfigure STATUS_MYSQL_CONNECTION_NO_MULTIPLEX_HG
 	set_status(old_no_multiplex_hg,STATUS_MYSQL_CONNECTION_NO_MULTIPLEX_HG);
+	// reconfigure STATUS_MYSQL_CONNECTION_COMPRESSION
+	set_status(old_compress,STATUS_MYSQL_CONNECTION_COMPRESSION);
 	reusable=true;
 	options.last_set_autocommit=-1; // never sent
 

test/tap/tests/reg_test_4158_change_user-t.cpp

@@ -0,0 +1,115 @@
+/**
+ * @file reg_test_4158_change_user-t.cpp
+ * @brief This test verifies COM_CHANGE_USER and COM_RESET_CONNECTION with compression
+ *
+ * @details It run COM_CHANGE_USER and COM_RESET_CONNECTION with compression.
+ * This seems broken in 2.x (not sure yet in which version the regression was
+ * first introduced), while working fine in 1.4
+ */
+
+#include "mysql.h"
+
+#include "proxysql_utils.h"
+#include "tap.h"
+#include "utils.h"
+
+#include <unistd.h>
+#include <iostream>
+
+using std::string;
+
+//#include "json.hpp"
+//using nlohmann::json;
+
+
+using namespace std;
+
+int loop1 = 3;
+int loop2 = 3;
+
+CommandLine cl;
+
+int work_mysql() {
+	MYSQL* proxy = mysql_init(NULL);
+	if (!mysql_real_connect(proxy, cl.host, cl.username, cl.password, NULL, cl.port, NULL, CLIENT_COMPRESS)) {
+		fprintf(stderr, "File %s, line %d, Error: %s\n", __FILE__, __LINE__, mysql_error(proxy));
+		return EXIT_FAILURE;
+	}
+
+	for (int j=0; j < loop1 ; j++) {
+		diag("We run multiple queries just to verify that the connection is still healthy after the firstone");
+		for (int i=0; i < loop2 ; i++) {
+			MYSQL_QUERY_T(proxy, "SELECT CONNECTION_ID()");
+			MYSQL_RES* myres;
+			myres = mysql_store_result(proxy);
+			int nr = mysql_num_rows(myres);
+			ok(nr == 1, "Rows returned: %d" , nr);
+			mysql_free_result(myres);
+		}
+		int rb;
+		diag("Running mysql_reset_connection()");
+		rb = mysql_reset_connection(proxy);
+		ok(rb == 0 , "mysql_reset_connection(): %s", (rb == 0 ? "OK" : mysql_error(proxy)));
+		diag("Running mysql_change_user()");
+		rb = mysql_change_user(proxy, cl.username, cl.password, NULL);
+		ok(rb == 0 , "mysql_change_user(): %s", (rb == 0 ? "OK" : mysql_error(proxy)));
+	}
+	mysql_close(proxy);
+	return 0;
+}
+
+void * work(void *arg) {
+	work_mysql(); // this return an int
+	return NULL;
+}
+
+int main(int, char**) {
+
+	plan(loop1 * (loop2 + 2));
+
+	if (cl.getEnv()) {
+		diag("Failed to get the required environmental variables.");
+		return EXIT_FAILURE;
+	}
+
+/*
+	// PLACEHOLDER
+	MYSQL* admin = mysql_init(NULL);
+	if (!mysql_real_connect(admin, cl.host, cl.admin_username, cl.admin_password, NULL, cl.admin_port, NULL, 0)) {
+		fprintf(stderr, "File %s, line %d, Error: %s\n", __FILE__, __LINE__, mysql_error(admin));
+		return EXIT_FAILURE;
+	}
+
+	MYSQL_QUERY_T(admin, "LOAD MYSQL VARIABLES TO RUNTIME");
+
+	mysql_close(admin);
+*/
+
+	// we run the test on a separate thread because we have a built-in timeout
+	pthread_t thread_id;
+	if (pthread_create(&thread_id, NULL, work, NULL)) {
+		fprintf(stderr, "Error calling pthread_create()");
+		return EXIT_FAILURE; 
+	}
+
+	int timeout = 10; // this is the timeout for the whole TAP test
+	if (timeout != 0) {
+		int tr = 0;
+		while (timeout != 0) {
+			sleep(1);
+			tr = pthread_tryjoin_np(thread_id, NULL);
+			if (tr == 0) {
+				timeout = 0;
+			} else {
+				timeout--;
+				diag("Waiting up to %d seconds", timeout);
+			}
+		}
+	} else {
+		// if timeout == 0 , the timeout is disabled
+		// This is useful during debugging, while running the TAP test in gdb
+		diag("Built-in timeout DISABLED");
+		pthread_join(thread_id, NULL);
+	}
+	return exit_status();
+}