tidb-server: Fix issue 263

Open tidb connect with dsn which contains unexists schema causes a
panic.
Fix issue pingcap#263

tidb-server/server/conn.go

@@ -107,7 +107,10 @@ func (cc *clientConn) Close() error {
 	delete(cc.server.clients, cc.connectionID)
 	cc.server.rwlock.Unlock()
 	cc.conn.Close()
-	return cc.ctx.Close()
+	if cc.ctx != nil {
+		return cc.ctx.Close()
+	}
+	return nil
 }
 
 func (cc *clientConn) writeInitialHandshake() error {

tidb-server/server/server_test.go

@@ -236,3 +236,15 @@ func runTestAuth(c *C) {
 	c.Assert(err, NotNil, Commentf("Wrong password should be failed"))
 	db.Close()
 }
+
+func runTestIssues(c *C) {
+	// For issue #263
+	unExistsSchemaDsn := "root@tcp(localhost:4001)/unexists_schema?strict=true"
+	db, err := sql.Open("mysql", unExistsSchemaDsn)
+	c.Assert(db, NotNil)
+	c.Assert(err, IsNil)
+	// Open may just validate its arguments without creating a connection to the database. To verify that the data source name is valid, call Ping.
+	err = db.Ping()
+	c.Assert(err, NotNil, Commentf("Connecting to an unexists schema should be error"))
+	db.Close()
+}

tidb-server/server/tidb_test.go

@@ -71,3 +71,7 @@ func (ts *TidbTestSuite) TestConcurrentUpdate(c *C) {
 func (ts *TidbTestSuite) TestAuth(c *C) {
 	runTestAuth(c)
 }
+
+func (ts *TidbTestSuite) TestIssues(c *C) {
+	runTestIssues(c)
+}