fix: close transactionCommitter and transactionRollbacker with sync.Once

conn.go

@@ -206,15 +206,9 @@ func (c *connection) BeginTx(ctx context.Context, opts driver.TxOptions) (driver
 			select {
 			default:
 				// do nothing
-			case inout, ok := <-txStmtCh:
-				if !ok {
-					continue
-				}
+			case inout := <-txStmtCh:
 				inouts = append(inouts, inout)
-			case _, ok := <-commitCh:
-				if !ok {
-					continue
-				}
+			case <-commitCh:
 				var inputs []types.ParameterizedStatement
 				for _, inout := range inouts {
 					inputs = append(inputs, inout.input)
@@ -233,10 +227,7 @@ func (c *connection) BeginTx(ctx context.Context, opts driver.TxOptions) (driver
 					inouts[i].output = resp.Item
 				}
 				return
-			case _, ok := <-rollbackCh:
-				if !ok {
-					continue
-				}
+			case <-rollbackCh:
 				return
 			case <-ctx.Done():
 				return

tx.go

@@ -44,7 +44,8 @@ type transactionInOut struct {
 
 // transationStatementPublisher publishes statements in a transaction.
 type transactionStatementPublisher struct {
-	ch chan *transactionInOut
+	ch        chan *transactionInOut
+	closeOnce sync.Once
 }
 
 // publish publishes a statement.
@@ -54,7 +55,9 @@ func (p *transactionStatementPublisher) publish(inout *transactionInOut) {
 
 // close closes the channel.
 func (p *transactionStatementPublisher) close() {
-	close(p.ch)
+	p.closeOnce.Do(func() {
+		close(p.ch)
+	})
 }
 
 // transactionCommitter commits a transaction.
@@ -75,7 +78,9 @@ func (c *transactionCommitter) commit() {
 
 // close closes the channel.
 func (c *transactionCommitter) close() {
-	close(c.ch)
+	c.closeOnce.Do(func() {
+		close(c.ch)
+	})
 }
 
 // transactionRollbacker rolls back a transaction.