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a4851ee76f
This PR implements the "reverse path" of handling TURN traffic, i.e. UDP datagrams that arrive on an allocation port and need to be wrapped in a channel-data message to be sent to the TURN client. In order to achieve that, I had to rewrite most of the TURN code to not use the `etherparse` crate. I couldn't quite figure out the details but the eBPF verifier rejected my code in mysterious ways that I didn't understand. Commenting out random code-paths seemed to make it happy but all code-paths combined caused an error. Eventually, I decided that we simply have to use less abstractions to implement the same logic. All the "parsing" code is now using types inspired by `network-types`. The only modification here is that we use byte-arrays within our structs in order to directly receive them in big-endian ordering. `network-types` uses `u16`s and `u32`s which get interpreted as little-endian on x86. Instead of converting around between the endianness, constructing those values where we want them using the right endianness is deemed much simpler. I opened an issue with upstream which - if accepted - will allow us to remove our own structs and instead depend on upstream again. I also had to aggressively add `#[inline(always)]` to several functions, otherwise the compiler would not optimise away our function calls, causing the linker and / or eBPF verifier to fail. This PR also fixes numerous bugs that I've found in the already existing eBPF code. The number of bugs makes me question how this has been working so far at all! - We did not swap the Ethernet source and destination MAC address when re-routing the packet. The integration-test didn't catch this because it only operates on the loopback interface. Further testing on staging should allow us to confirm that this is indeed working now. - The UDP checksum update did not incorporate the new src and dst port. The integration-test didnt' catch that because it has UDP checksumming disabled. We need to have that disabled in the test because UDP checksumming is typically offloaded to the NIC and packets on the loopback interface never leave the device. Related: https://github.com/vadorovsky/network-types/issues/32. Related: #7518