Add an example for leader election based multiple controller

examples/leader_example/.formatter.exs

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+# Used by "mix format"
+[
+  inputs: ["mix.exs", "{config,lib,test}/**/*.{ex,exs}"]
+]

examples/leader_example/.gitignore

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+# The directory Mix will write compiled artifacts to.
+/_build/
+
+# If you run "mix test --cover", coverage assets end up here.
+/cover/
+
+# The directory Mix downloads your dependencies sources to.
+/deps/
+
+# Where 3rd-party dependencies like ExDoc output generated docs.
+/doc/
+
+# Ignore .fetch files in case you like to edit your project deps locally.
+/.fetch
+
+# If the VM crashes, it generates a dump, let's ignore it too.
+erl_crash.dump
+
+# Also ignore archive artifacts (built via "mix archive.build").
+*.ez
+
+# Ignore package tarball (built via "mix hex.build").
+leader_example-*.tar
+

examples/leader_example/README.md

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+# LeaderExample
+
+**TODO: Add description**
+
+## Installation
+
+If [available in Hex](https://hex.pm/docs/publish), the package can be installed
+by adding `leader_example` to your list of dependencies in `mix.exs`:
+
+```elixir
+def deps do
+  [
+    {:leader_example, "~> 0.1.0"}
+  ]
+end
+```
+
+Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)
+and published on [HexDocs](https://hexdocs.pm). Once published, the docs can
+be found at [https://hexdocs.pm/leader_example](https://hexdocs.pm/leader_example).
+

examples/leader_example/config/config.exs

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+# This file is responsible for configuring your application
+# and its dependencies with the aid of the Mix.Config module.
+use Mix.Config
+
+config :libcluster,
+  topologies: [
+    gossip_example: [
+      strategy: Cluster.Strategy.Gossip,
+      config: [
+        port: 45_892,
+        if_addr: {0, 0, 0, 0},
+        multicast_addr: {230, 1, 1, 251},
+        multicast_ttl: 1]]]
+
+config :logger,
+  level: :debug,
+  format: "$date $time [$level] $metadata$message\n",
+  metadata: [:application],
+  handle_otp_reports: true
+
+import_config "#{Mix.env}.exs"

examples/leader_example/config/dev.exs

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+# This file is responsible for configuring your application
+# and its dependencies with the aid of the Mix.Config module.
+use Mix.Config

examples/leader_example/config/node1.exs

@@ -0,0 +1,9 @@
+use Mix.Config
+
+config :tres,
+  protocol:        :tcp,
+  port:            6653,
+  max_connections: 10,
+  num_acceptors:   10,
+  callback_module: LeaderExample.Leader,
+  callback_args:   []

examples/leader_example/config/node2.exs

@@ -0,0 +1,9 @@
+use Mix.Config
+
+config :tres,
+  protocol:        :tcp,
+  port:            6633,
+  max_connections: 10,
+  num_acceptors:   10,
+  callback_module: LeaderExample.Leader,
+  callback_args:   []

examples/leader_example/lib/leader_example/application.ex

@@ -0,0 +1,20 @@
+defmodule LeaderExample.Application do
+  # See https://hexdocs.pm/elixir/Application.html
+  # for more information on OTP Applications
+  @moduledoc false
+
+  use Application
+
+  def start(_type, _args) do
+    # List all child processes to be supervised
+    children = [
+      # Starts a worker by calling: LeaderExample.Worker.start_link(arg)
+      # {LeaderExample.Worker, arg},
+    ]
+
+    # See https://hexdocs.pm/elixir/Supervisor.html
+    # for other strategies and supported options
+    opts = [strategy: :one_for_one, name: LeaderExample.Supervisor]
+    Supervisor.start_link(children, opts)
+  end
+end

examples/leader_example/lib/leader_example/leader.ex

@@ -0,0 +1,77 @@
+defmodule LeaderExample.Leader do
+  use Tres.Controller
+
+  @behaviour :locks_leader
+
+  require Logger
+
+  def start_link(datapath_id, args) do
+    :locks_leader.start_link(__MODULE__, [datapath_id, args], [])
+  end
+
+  def init([{datapath_id, _aux_id}, _args]) do
+    :ok = Logger.debug("Switch Ready: datapath_id: #{inspect(datapath_id)}")
+    :ok = role_request(datapath_id, role: :slave, generation_id: 0)
+    {:ok, %{am_leader: false, gen_id: 0, datapath_id: datapath_id}}
+  end
+
+  def elected(state, _info, _cand) do
+    :ok = Logger.info("Elected: #{inspect(Node.self)} for #{state.datapath_id} gen_id: #{state.gen_id}")
+    :ok = role_request(state.datapath_id, role: :master, generation_id: state.gen_id)
+    {:ok, {:elected, {Node.self(), state.gen_id + 1}}, %{state|am_leader: true}}
+  end
+
+  def surrendered(%{am_leader: true} = state, {:elected, {_node, next_gen_id}}, _info) do
+    :ok = Logger.info("network split possible detected")
+    :ok = role_request(state.datapath_id, role: :slave, generation_id: state.gen_id)
+    {:ok, %{state|am_leader: false, gen_id: next_gen_id}}
+  end
+
+  def surrendered(state, {:elected, {node, next_gen_id}}, _info) do
+    :ok = Logger.info("Surrendered: elected node is #{node} for #{state.datapath_id}")
+    :ok = role_request(state.datapath_id, role: :slave, generation_id: state.gen_id)
+    {:ok, %{state|am_leader: false, gen_id: next_gen_id}}
+  end
+
+  def handle_DOWN(_pid, state, _info) do
+    :ok = Logger.warn("DOWN detected")
+    {:ok, state}
+  end
+
+  def handle_leader_call(msg, from, state, _info) do
+    :ok = Logger.info("leader call with: #{inspect(msg)} from: #{inspect(from)} on #{Node.self()}")
+    {:reply, :ok, state}
+  end
+
+  def handle_leader_cast(_msg, state, _info) do
+    {:ok, state}
+  end
+
+  def from_leader(_from_leader, state, _info) do
+    {:ok, state}
+  end
+
+  def handle_call(_msg, _from, state, _info) do
+    {:reply, :ok, state}
+  end
+
+  def handle_cast(_msg, state, _info) do
+    {:noreply, state}
+  end
+
+  def handle_info(%Role.Reply{datapath_id: dpid} = role, %{datapath_id: dpid} = state, _info) do
+    :ok = Logger.info("#{Node.self()} is on #{role.role} for #{dpid}")
+    {:noreply, state}
+  end
+  def handle_info(_msg, state, _info) do
+    {:noreply, state}
+  end
+
+  def code_change(_from_vsn, state, _info, _extra) do
+    {:ok, state}
+  end
+
+  def terminate(_reason, _state) do
+    :ok
+  end
+end

examples/leader_example/mix.exs

@@ -0,0 +1,25 @@
+defmodule LeaderExample.MixProject do
+  use Mix.Project
+
+  def project do
+    [
+      app: :leader_example,
+      version: "0.1.0",
+      elixir: "~> 1.6",
+      deps: deps()
+    ]
+  end
+
+  def application do
+    [
+      extra_applications: [:logger, :libcluster, :locks, :tres],
+      mod: {LeaderExample.Application, []}
+    ]
+  end
+
+  defp deps do
+    [{:locks, "~> 0.2.0"},
+     {:libcluster, "~> 2.3.0"},
+     {:tres, path: "../../../tres"}]
+  end
+end

examples/leader_example/mix.lock

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+%{
+  "eovsdb": {:git, "https://github.com/shun159/eovsdb.git", "1ff1572708d72fd25631c681f2102407903252a3", [branch: "master"]},
+  "jsone": {:git, "https://github.com/sile/jsone.git", "eecc9666c7165e1870b78a7a762549ae8d1c391b", [tag: "1.2.1"]},
+  "libcluster": {:hex, :libcluster, "2.3.0", "d2fb8e8b2054a4a0c7faf7ced7c41dd13f7b49cce689590d37ecf30098e1b344", [:mix], [{:poison, "~> 3.0", [hex: :poison, repo: "hexpm", optional: false]}], "hexpm"},
+  "locks": {:hex, :locks, "0.2.0", "c8a5db52bdbfacfcc979b38920adb2ab8909fa7fb36015ddff6b753d1c950b92", [:rebar3], [{:plain_fsm, "1.4.1", [hex: :plain_fsm, repo: "hexpm", optional: false]}], "hexpm"},
+  "plain_fsm": {:hex, :plain_fsm, "1.4.1", "47e9bf6ac9322fc7586fb6df8de7198391e93764571c75165f2c45b27acde1d0", [:rebar3], [], "hexpm"},
+  "poison": {:hex, :poison, "3.1.0", "d9eb636610e096f86f25d9a46f35a9facac35609a7591b3be3326e99a0484665", [:mix], [], "hexpm"},
+  "ranch": {:hex, :ranch, "1.4.0", "10272f95da79340fa7e8774ba7930b901713d272905d0012b06ca6d994f8826b", [:rebar3], [], "hexpm"},
+  "uuid": {:git, "https://github.com/avtobiff/erlang-uuid.git", "585c2474afb4a597ae8c8bf6d21e5a9c73f18e0b", [tag: "v0.5.0"]},
+}

examples/leader_example/test/leader_example_test.exs

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+defmodule LeaderExampleTest do
+  use ExUnit.Case
+  doctest LeaderExample
+
+  test "greets the world" do
+    assert LeaderExample.hello() == :world
+  end
+end

examples/leader_example/test/test_helper.exs

@@ -0,0 +1 @@
+ExUnit.start()

lib/tres/message_helper.ex

@@ -93,6 +93,16 @@ defmodule Tres.MessageHelper do
 
         send_message(group_mod, datapath_id)
       end
+
+      defp role_request(datapath_id, options) do
+        role_request =
+          Openflow.Role.Request.new(
+            role: options[:role] || :nochange,
+            generation_id: options[:generation_id] || 0
+          )
+
+        send_message(role_request, datapath_id)
+      end
     end
   end
 end