fix parsing prepare response (#1057)

* fix parsing prepare response https://dev.mysql.com/doc/dev/mysql-server/9.3.0/page_protocol_com_stmt_prepare.html warnings is optional from server, & is preceded by a reserved byte * WarningsNum

Author: serprex

client/client_test.go

@@ -269,6 +269,7 @@ func (s *clientTestSuite) testStmt_DropTable() {
 
 stmt, err := s.c.Prepare(str)
 require.NoError(s.T(), err)
+require.Zero(s.T(), stmt.WarningsNum())
 
 defer stmt.Close()
 

client/stmt.go

@@ -265,9 +265,14 @@ func (c *Conn) Prepare(query string) (*Stmt, error) {
 s.params = int(binary.LittleEndian.Uint16(data[pos:]))
 pos += 2
 
-// warnings
-s.warnings = int(binary.LittleEndian.Uint16(data[pos:]))
-// pos += 2
+// reserved
+pos += 1
+
+if len(data) >= 12 {
+// warnings
+s.warnings = int(binary.LittleEndian.Uint16(data[pos:]))
+// pos += 2
+}
 
 if s.params > 0 {
 if err := s.conn.readUntilEOF(); err != nil {