add a check for the result of updating the connection authentication settings

We don't check the result of updating the connection authentication
settings in the conn: reset() method and failure will be detected
only when trying to execute a request. But in programming, it is a
good practice to check the result of the function.
The patch adds a check on the result of updating the connection
authentication settings. On failure, an exception will be thrown.

Author: LeonidVas

mysql/driver.c

@@ -663,9 +663,14 @@ lua_mysql_reset(lua_State *L)
 	const char *user = lua_tostring(L, 2);
 	const char *pass = lua_tostring(L, 3);
 	const char *db = lua_tostring(L, 4);
-	mysql_change_user(raw_conn, user, pass, db);
 
-	return 0;
+	if (mysql_change_user(raw_conn, user, pass, db) == 0) {
+		lua_pushboolean(L, 1);
+	} else {
+		lua_pushboolean(L, 0);
+	}
+
+	return 1;
 }
 
 LUA_API int

mysql/init.lua

@@ -123,7 +123,13 @@ conn_mt = {
                 self.queue:put(false)
                 error('Connection is broken')
             end
-            self.conn:reset(user, pass, db)
+            -- If the update of the connection settings fails, we must set
+            -- the connection to a "broken" state and throw an error.
+            local status = self.conn:reset(user, pass, db)
+            if not status then
+                self.queue:put(false)
+                error('Сonnection settings update failed.')
+            end
             self.queue:put(true)
         end,
 	quote = function(self, value)

test/mysql.test.lua

@@ -431,8 +431,40 @@ local function test_connection_pool(test, pool)
     -- }}}
 end
 
+local function test_connection_reset(test, pool)
+    test:plan(2)
+
+    assert(pool.queue:is_full(), 'test case precondition fails')
+
+    -- Case: valid credentials were used to "reset" the connection
+    test:test('reset connection successfully', function(test)
+        test:plan(1)
+
+        assert(pool.size >= 1, 'test case precondition fails')
+
+        local conn = pool:get()
+        conn:reset(pool.user, pool.pass, pool.db)
+        test:ok(conn:ping(), 'connection "reset" successfully')
+        pool:put(conn)
+    end)
+
+    -- Case: invalid credentials were used to "reset" the connection
+    test:test('reset connection failed', function(test)
+        test:plan(1)
+
+        assert(pool.size >= 1, 'test case precondition fails')
+
+        local conn = pool:get()
+        local check = pcall(conn.reset, conn, "guinea pig", pool.pass, pool.db)
+        test:ok(not check, 'connection "reset" fails')
+        pool:put(conn)
+    end)
+
+    assert(pool.queue:is_full(), 'test case postcondition fails')
+end
+
 local test = tap.test('mysql connector')
-test:plan(6)
+test:plan(7)
 
 test:test('connection old api', test_old_api, conn)
 local pool_conn = p:get()
@@ -442,6 +474,7 @@ test:test('garbage collection', test_gc, p)
 test:test('concurrent connections', test_conn_concurrent, p)
 test:test('int64', test_mysql_int64, p)
 test:test('connection pool', test_connection_pool, p)
+test:test('connection reset', test_connection_reset, p)
 p:close()
 
 os.exit(test:check() and 0 or 1)