Support for abstract unix domain sockets for Linux

[mar...@aporeto.com]

Hi there,

To improve a feature that I’m working on for my company, we require support for abstract unix domain sockets. In our initial tests - all using golang grpc servers and clients - it all just worked out of the box by just specifying a URI like `unix:@abstract_socket_name`.

However, trying to use `google_grpc` now from within envoyproxy failed. After a lot of debugging and actually doing some digging, I found out that there is actually no support for abstract unix sockets within the core / C++ implementation of gRPC. There was an issue here which got closed because it got stale: https://github.com/grpc/grpc/pull/21278

Now I have already done a manual patch of gRPC and a custom compile of envoy to test that I can actually make it work (and it works), however, I’d ideally like to get that merged upstream of course.

So I started to put a PR together here: https://github.com/grpc/grpc/issues/4677
 
However, there is a couple of things that I'm not sure about: for example where and how to add tests for it, also, with a bigger project like gRPC, how can I get that PR into the right hands, etc., and also just in general: is that a feature that you actually want to support in the core (imho it's valuable as it is already supported in other implementations which can be confusing).

Cheers
Marcus

[Sanjay Pujare]

Marcus,

4677 is the stale issue and 21278 is your PR (you had them switched). I do believe the feature is valuable/useful so your PR is great. 

Regarding your question about adding tests etc hopefully markdroth or veblush will answer them in the PR?