add comments

packets.go

@@ -131,7 +131,9 @@ func (mc *mysqlConn) writePacket(data []byte) error {
 			}
 			return err
 		}
-		if n != size+4 {
+		if n != 4+size {
+			// io.Writer(b) must return a non-nil error if it cannot write len(b) bytes.
+			// The io.ErrShortWrite error is used to indicate that this rule has not been followed.
 			mc.cleanup()
 			return io.ErrShortWrite
 		}
@@ -142,7 +144,6 @@ func (mc *mysqlConn) writePacket(data []byte) error {
 		}
 		pktLen -= size
 		data = data[size:]
-		continue
 	}
 }