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The aeron_udp_channel_transport_stct::bindings_clientd is only found be used in aeron_udp_channel_transport_init function which set the bindings_clientd to NULL without further operations. Except some modification and assert in test cases.

In the test case, it is assigned as struct aeron_test_udp_bindings_state_stct, which containes some state counter.

What role does this data member play in Aeron? What is the proper usage of bindings_clientd?

Avalon
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TL;DR unless you are writing a custom network binding don't concern yourself with this field.

The Aeron C driver has support for adding different network bindings implementations (see aeron_udp_channel_transport_bindings_stct). In the OSS repo there is only support for traditional OS (Linux, Mac, Windows) networking. However, if a user wanted to add an additional implementation that used a different network API and needed to carry some implementation specific information on each transport instance, this would be the field to add it to. In theory for the UDP implementation, it could be refactored towards having a structure that held the file descriptors here.

The test driver carries some state information in that field so that behaviour can be asserted within the tests. There also exists commercial extensions to the C driver (e.g. for DPDK) that make use of this field too.

Michael Barker
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  • Thank you so much for the official reply! Is there any mailing list or some disussion group to communicate the dev problem about aeron? – Avalon Nov 08 '22 at 01:39
  • General questions about usage should be asked here. Bugs & issues can be raised on the Github repository. The Github repsository README.md has contact details for sales if you want to pay for commercial support. – Michael Barker Nov 08 '22 at 06:35
  • If we want to implement a custom network binding (not UDP), should we reuse the ```aeron_udp_channel_transport_stct```, ```aeron_udp_channel_transport_bindings_stct```, or we have to create some brand new structs and functions? From what layer or part of the project's code base should we design the new transport binding? Because in the code, ```aeron_driver_context_stct::udp_channel_outgoing_interceptor_bindings``` seems embeded deeply with the aeron driver. – Avalon Nov 17 '22 at 08:10
  • For a new binding you need to provide a struct of type `aeron_udp_channel_transport_bindings_stct` with implementations of all of the specified function pointers. A very bare-bones example is the binding used in the test code: https://github.com/real-logic/aeron/blob/master/aeron-driver/src/test/c/aeron_test_udp_bindings.h – Michael Barker Nov 18 '22 at 07:52
  • The outgoing and incoming interceptors are also pluggable, we use these for some commercial extensions like encryption. We also use them to generate loss in some test to validate redelivery. – Michael Barker Nov 18 '22 at 08:01