Merge pull request #58 from pingcap/siddontang/fix-session-string-panic

tidb: fix string() panic if txn is nil

Author: ngaut

session.go

@@ -111,7 +111,11 @@ func (s *session) String() string {
 		"userName":   s.userName,
 		"currDBName": db.GetCurrentSchema(s),
 		"sid":        s.sid,
-		"txn":        s.txn.String(),
+	}
+
+	if s.txn != nil {
+		// if txn is committed or rolled back, txn is nil.
+		data["txn"] = s.txn.String()
 	}
 
 	b, _ := json.MarshalIndent(data, "", "  ")

tidb_test.go

@@ -348,6 +348,14 @@ func (s *testSessionSuite) TestAffectedRows(c *C) {
 
 }
 
+func (s *testSessionSuite) TestString(c *C) {
+	store := newStore(c, s.dbName)
+	se := newSession(c, store, s.dbName)
+	sessionExec(c, se, "select 1")
+	// here to check the panic bug in String() when txn is nil after committed.
+	c.Log(se.String())
+}
+
 func (s *testSessionSuite) TestResultField(c *C) {
 	store := newStore(c, s.dbName)
 	se := newSession(c, store, s.dbName)