Mach’s Message’s structure might look like as following:
- Fix-length header
- Variable-length data section
Note: In Version 2.5, there is an 8 KB size limit on the data section. However, such limitation had been lifted by Version 3.0.
The fix-length header will contain the following information:
- the destination’s port name
- the reply port name where reply messages should be sent
- the length of the message
In the data section, there could be a variety of typed data objects being stored, such as simple type (numbers or characters), port rights, pointers to out-of-line data.