Mark connection as not good when error on cancellation confirmation

mssql.go

@@ -228,6 +228,8 @@ func (c *Conn) checkBadConn(ctx context.Context, err error, mayRetry bool) error
 		return nil
 	case io.EOF:
 		c.connectionGood = false
+	case ErrorCancelConfirmation:
+		c.connectionGood = false
 	case driver.ErrBadConn:
 		// It is an internal programming error if driver.ErrBadConn
 		// is ever passed to this function. driver.ErrBadConn should
@@ -874,6 +876,7 @@ func (r *Rows) ColumnTypeLength(index int) (int64, bool) {
 // It should return
 // the precision and scale for decimal types. If not applicable, ok should be false.
 // The following are examples of returned values for various types:
+//
 //   decimal(38, 4)    (38, 4, true)
 //   int               (0, 0, false)
 //   decimal           (math.MaxInt64, math.MaxInt64, true)

token.go

@@ -85,6 +85,8 @@ const (
 	// TODO implement more flags
 )
 
+var ErrorCancelConfirmation = errors.New("did not get cancellation confirmation from the server")
+
 // interface for all tokens
 type tokenStruct interface{}
 
@@ -934,7 +936,7 @@ func (t tokenProcessor) nextToken() (tokenStruct, error) {
 		}
 		// we did not get cancellation confirmation, something is not
 		// right, this connection is not usable anymore
-		return nil, errors.New("did not get cancellation confirmation from the server")
+		return nil, ErrorCancelConfirmation
 	}
 }