Refactor rollback in commit

Rollback cannot be called in Commit as the function
that watches the context for cancelation assumes it
is only ever called once. Calling it multiple times
hangs the goroutine.

This is an alternative to #829.

Fixes #731 and #848
Replaces #829

Signed-off-by: Jay Mundrawala <[email protected]>

Author: Jay Mundrawala

conn.go

@@ -549,7 +549,7 @@ func (cn *conn) Commit() (err error) {
 	// would get the same behaviour if you issued a COMMIT in a failed
 	// transaction, so it's also the least surprising thing to do here.
 	if cn.txnStatus == txnStatusInFailedTransaction {
-		if err := cn.Rollback(); err != nil {
+		if err := cn.rollback(); err != nil {
 			return err
 		}
 		return ErrInFailedTransaction
@@ -576,7 +576,10 @@ func (cn *conn) Rollback() (err error) {
 		return driver.ErrBadConn
 	}
 	defer cn.errRecover(&err)
+	return cn.rollback()
+}
 
+func (cn *conn) rollback() (err error) {
 	cn.checkIsInTransaction(true)
 	_, commandTag, err := cn.simpleExec("ROLLBACK")
 	if err != nil {

go19_test.go

@@ -67,3 +67,25 @@ func TestPing(t *testing.T) {
 		t.Fatalf("expected error %s, instead got %s", driver.ErrBadConn, err)
 	}
 }
+
+func TestCommitInFailedTransactionWithCancelContext(t *testing.T) {
+	db := openTestConn(t)
+	defer db.Close()
+
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+
+	txn, err := db.BeginTx(ctx, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	rows, err := txn.Query("SELECT error")
+	if err == nil {
+		rows.Close()
+		t.Fatal("expected failure")
+	}
+	err = txn.Commit()
+	if err != ErrInFailedTransaction {
+		t.Fatalf("expected ErrInFailedTransaction; got %#v", err)
+	}
+}