conn: fix database info leaking problem (#3699)

server/conn.go

@@ -317,6 +317,12 @@ func (cc *clientConn) readHandshakeResponse() error {
 			return errors.Trace(errAccessDenied.GenByArgs(cc.user, host, "YES"))
 		}
 	}
+	if cc.dbname != "" {
+		_, err = cc.ctx.Execute("use " + cc.dbname)
+		if err != nil {
+			return errors.Trace(err)
+		}
+	}
 	cc.ctx.SetSessionManager(cc.server)
 	return nil
 }

server/driver_tidb.go

@@ -129,12 +129,6 @@ func (qd *TiDBDriver) OpenCtx(connID uint64, capability uint32, collation uint8,
 	}
 	session.SetClientCapability(capability)
 	session.SetConnectionID(connID)
-	if dbname != "" {
-		_, err = session.Execute("use " + dbname)
-		if err != nil {
-			return nil, errors.Trace(err)
-		}
-	}
 	tc := &TiDBContext{
 		session:   session,
 		currentDB: dbname,

server/server_test.go

@@ -487,6 +487,24 @@ func runTestAuth(c *C) {
 	})
 }
 
+func runTestIssue3682(c *C) {
+	runTests(c, dsn, func(dbt *DBTest) {
+		dbt.mustExec(`CREATE USER 'abc'@'%' IDENTIFIED BY '123';`)
+		dbt.mustExec(`FLUSH PRIVILEGES;`)
+	})
+	newDsn := "abc:123@tcp(127.0.0.1:4001)/test?strict=true"
+	runTests(c, newDsn, func(dbt *DBTest) {
+		dbt.mustExec(`USE mysql;`)
+	})
+	wrongDsn := "abc:456@tcp(127.0.0.1:4001)/a_database_not_exist?strict=true"
+	db, err := sql.Open("mysql", wrongDsn)
+	c.Assert(err, IsNil)
+	defer db.Close()
+	err = db.Ping()
+	c.Assert(err, NotNil)
+	c.Assert(err.Error(), Equals, "Error 1045: Access denied for user 'abc'@'127.0.0.1' (using password: YES)")
+}
+
 func runTestIssues(c *C) {
 	// For issue #263
 	unExistsSchemaDsn := "root@tcp(localhost:4001)/unexists_schema?strict=true"

server/tidb_test.go

@@ -160,3 +160,7 @@ func (ts *TidbTestSuite) TestIssue3680(c *C) {
 	c.Assert(err, NotNil)
 	c.Assert(err.Error(), Equals, "Error 1045: Access denied for user 'non_existing_user'@'127.0.0.1' (using password: YES)")
 }
+
+func (ts *TidbTestSuite) TestIssue3682(c *C) {
+	runTestIssue3682(c)
+}