go/mysql: conn.go: Fix read-after-recycle bug of the packet byte buff…

…er in COM_STMT_SEND_LONG_DATA.

Back ports vitessio@24820d8

go/mysql/conn.go

@@ -1236,7 +1236,7 @@ func (c *Conn) handleNextCommand(ctx context.Context, handler Handler) error {
 			return err
 		}
 	case ComStmtSendLongData:
-		stmtID, paramID, chunkData, ok := c.parseComStmtSendLongData(data)
+		stmtID, paramID, chunk, ok := c.parseComStmtSendLongData(data)
 		c.recycleReadPacket()
 		if !ok {
 			err := fmt.Errorf("error parsing statement send long data from client %v, returning error: %v", c.ConnectionID, data)
@@ -1259,9 +1259,6 @@ func (c *Conn) handleNextCommand(ctx context.Context, handler Handler) error {
 			return err
 		}
 
-		chunk := make([]byte, len(chunkData))
-		copy(chunk, chunkData)
-
 		key := fmt.Sprintf("v%d", paramID+1)
 		if val, ok := prepare.BindVars[key]; ok {
 			val.Value = append(val.Value, chunk...)

go/mysql/query.go

@@ -933,7 +933,11 @@ func (c *Conn) parseComStmtSendLongData(data []byte) (uint32, uint16, []byte, bo
 		return 0, 0, nil, false
 	}
 
-	return statementID, paramID, data[pos:], true
+	chunkData := data[pos:]
+	chunk := make([]byte, len(chunkData))
+	copy(chunk, chunkData)
+
+	return statementID, paramID, chunk, true
 }
 
 func (c *Conn) parseComStmtClose(data []byte) (uint32, bool) {