How can I count ESTABLISHED connections in Go?

Question

I'm trying to do basically this in Go:

netstat -an | grep 2375 -c

I need to count the number of connections to the Docker daemon in my regression test for a connection leak bug. However, because I run this in multiple places in different OS (local dev box, CI, etc), I cannot rely on the "netstat" tool, so I wonder how can I do this in a more programmatic way in Go?

I looked around the net package and could not find anything that would help. There are some libraries that basically replace netstat:

https://github.com/drael/GOnetstat https://github.com/dominikh/netstat-nat

But they are not cross-platform compliant (Mac and *nix). Any idea how can I achieve this?

Answer 1

In linux this info is exposed in the /proc filesystem. Use os.Getpid and query the info in /proc/<pid>/fd. Most likely a simple count is good here, if you need more see the proc man page.

Cross platform compatibility for this kind of thing is going to be roll your own, as the ways of identifying open fd's for a process are very per platform. If you simply need to compile, and pass some tests for this on non linux platforms you can use Go's per platform support to make this a no-op on other platforms, or implement an appropriate solution.