Retry fetching mapped host port when a container is created

[hexedpackets]

I've been running into a race condition where the host port mapping is not available right after a container is created. Attempting to inspect the container too quickly results in a JSON blob that looks roughly like:

  "NetworkSettings" => %{
    "Ports" => %{
      "8080/tcp" => []
  },

which in turn results in the following exception:

09:48:03.330 module=gen_server [error] GenServer #PID<0.554.0> terminating
** (BadMapError) expected a map, got: nil
    (elixir 1.16.3) lib/map.ex:535: Map.get(nil, "HostPort", nil)
    (excontainers 0.3.0) lib/docker/container_state.ex:34: anonymous fn/1 in Docker.ContainerState.port_mapping/1
    (elixir 1.16.3) lib/enum.ex:1708: anonymous fn/3 in Enum.map/2
    (stdlib 4.3.1.4) maps.erl:411: :maps.fold_1/3
    (elixir 1.16.3) lib/enum.ex:2540: Enum.map/2
    (excontainers 0.3.0) lib/docker/container_state.ex:34: Docker.ContainerState.port_mapping/1
    (excontainers 0.3.0) lib/docker/container_state.ex:28: Docker.ContainerState.parse_docker_response/1
    (excontainers 0.3.0) lib/docker/api/containers.ex:50: Docker.Api.Containers.inspect/1
Last message (from Excontainers.ResourcesReaper): {:mapped_port, 8080}
** (EXIT from #PID<0.93.0>) exited in: GenServer.call(#PID<0.554.0>, {:mapped_port, 8080}, 5000)
    ** (EXIT) an exception was raised:
        ** (BadMapError) expected a map, got: nil
            (elixir 1.16.3) lib/map.ex:535: Map.get(nil, "HostPort", nil)
            (excontainers 0.3.0) lib/docker/container_state.ex:34: anonymous fn/1 in Docker.ContainerState.port_mapping/1
            (elixir 1.16.3) lib/enum.ex:1708: anonymous fn/3 in Enum.map/2
            (stdlib 4.3.1.4) maps.erl:411: :maps.fold_1/3
            (elixir 1.16.3) lib/enum.ex:2540: Enum.map/2
            (excontainers 0.3.0) lib/docker/container_state.ex:34: Docker.ContainerState.port_mapping/1
            (excontainers 0.3.0) lib/docker/container_state.ex:28: Docker.ContainerState.parse_docker_response/1
            (excontainers 0.3.0) lib/docker/api/containers.ex:50: Docker.Api.Containers.inspect/1

I see this error very frequently with the ResourcesReaper container, but I don't think it's specific to that. Retrying after a small delay seems to consistently resolve the problem. This PR implements retry logic for all calls to Docker.Containers.mapped_port/2

As a side note, the tests are failing for me both with and without this change.

[dallagi]

Thanks @hexedpackets for the contribution!

I'm gonna merge this, but note that excontainers is currently not maintained, and I'd suggest you to consider switching to testcontainers-elixir instead.

I've never used it but it seems to be maintained and it should be pretty similar API-wise, since when it started it borrowed much of the code from this project.