kmx.io/ex_ovh/lib/hubic/cache.ex

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• Hash : 0633245f
  Author :
  Date : 2016-02-07T18:41:33
  

  Change httpotion options to a map type. Also general cleanup.

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• lib/hubic/cache.ex

• defmodule ExOvh.Hubic.Cache do
    @moduledoc ~s"""
    Caches the access_token and provides a simple get_token() api to other modules through one function get_token()
    Caches the hubic config map.
  
    Maintains the access token so that:
    - State is maintained in gen_server state but gen_server could be a bottleneck so it is also copied to a public ets table.
    - So state is also stored in an ets table and is quickly and globally retrievable.
    - State in :ets and :gen_server should be synchronised.
    - It is automatically refreshed in the background when it expires
    - If the gen_server crashes, it will attempt to re-establish the access token
    - The refresh token by attempting the following:
      - 1. Firstly, try to recuperate the refresh_token from a dets entry.
      - 2. Secondly, by checking for the refresh_token in the config secret file.
    - If both of the above methods fail, then ultimately the gen_server will crash and the user
      will have to retrieve another refresh_token using the `mix hubic` task
  
    tokens is a map with the following structure:
    - `%{
         :lock => :true,
         "access_token" => "access_token",
         "expires_in" => 21600,
         "refresh_token" => "refresh_token",
         "token_type" => "Bearer"
      }`
    """
    use GenServer
    alias ExOvh.Hubic.Auth
    @get_token_retries 20
    @get_token_sleep_interval 300
  
  
    #####################
    # Public
    #####################
  
  
    @doc "Starts the genserver"
    def start_link({client, config, opts}) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      GenServer.start_link(__MODULE__, {client, config, opts}, [name: gen_server_name(client)])
    end
  
  
    @doc "Gets the access_token from the :ets table"
    @spec get_token() :: String.t
    def get_token(), do: get_token(ExOvh, 0)
  
    @doc "Gets the access_token from the :ets table"
    @spec get_token(client :: atom) :: String.t
    def get_token(client), do: get_token(client, 0)
  
    @doc "Retrieves the hubic config map"
    def get_config(client) do
      GenServer.call(gen_server_name(client), :get_config)
    end
  
  
    #####################
    # Genserver Callbacks
    #####################
  
    # trap exits so that terminate callback is invoked
    # the :lock key is to allow for locking during the brief moment that the access token is being refreshed
    def init({client, config, _opts}) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      :erlang.process_flag(:trap_exit, :true)
      create_ets_table(client)
      refresh_token = config.refresh_token
      case refresh_token  do
        :nil -> # RAISE AN EXCEPTION DUE TO UNAVAILABILITY OF THE REFRESH TOKEN
          error = "Valid refresh token not available"
          LoggingUtils.log_return(error, :error)
          raise error
        refresh_token -> # TRY TO GET REFRESH TOKEN FROM THE CONFIG
          tokens = get_latest_tokens(%{"refresh_token" => refresh_token}, config) |> Map.put(:lock, :false)
          :ets.insert(ets_tablename(client), {:tokens, tokens})
          Task.start_link(fn -> monitor_expiry(client, tokens["expires_in"]) end)
          {:ok, {client, config, tokens}}
      end
    end
  
    def handle_call(:add_lock, _from, {client, config, tokens}) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      new_tokens = Map.put(tokens, :lock, :true)
      :ets.insert(ets_tablename(client), {:tokens, new_tokens})
      {:reply, :ok, new_tokens}
    end
  
    def handle_call(:remove_lock, _from, {client, config, tokens}) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      new_tokens = Map.put(tokens, :lock, :false)
      :ets.insert(ets_tablename(client), {:tokens, new_tokens})
      {:reply, :ok, new_tokens}
    end
  
    def handle_call(:update_tokens, _from, {client, config, tokens}) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      new_tokens = get_latest_tokens(tokens, config)
      |> Map.put(tokens, :lock, :false)
      :ets.insert(ets_tablename(client), {:tokens, new_tokens})
      {:reply, :ok, {client, new_tokens}}
    end
  
    def handle_call(:get_config, _from, {client, config, tokens}) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      {:reply, config, {client, config, tokens}}
    end
  
    def handle_call(:stop, _from, {client, config, tokens}) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      {:stop, :shutdown, :ok, {client, config, tokens}}
    end
  
    def terminate(:shutdown, {client, config, tokens}) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      :ets.delete(ets_tablename(client))
      :ok
    end
  
  
    #####################
    # Private
    #####################
  
    defp gen_server_name(client), do: String.to_atom(Atom.to_string(client) <> Atom.to_string(__MODULE__))
    defp ets_tablename(client), do: String.to_atom("Ets" <> Atom.to_string(gen_server_name(client)))
  
    # get the token from the :ets table
    defp get_token(client, index) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      if ets_tablename(client) in :ets.all() do
        [tokens: tokens] = :ets.lookup(ets_tablename(client), :tokens)
        if tokens.lock === :true do
          if index > @get_token_retries do
            raise "Problem retrieving the access token from ets table"
          else
            :timer.sleep(@get_token_sleep_interval)
            get_token(index + 1)
          end
        else
          tokens["access_token"]
        end
      else
        if index > @get_token_retries do
          raise "Problem retrieving the access token from ets table"
        else
          :timer.sleep(@get_token_sleep_interval)
          get_token(index + 1)
        end
      end
    end
  
  
    # Returns a map in following format with the latest tokens:
    # %{"access_token" => "access_token", "expires_in" => 21600, "refresh_token" => "refresh_token", "token_type" => "Bearer"}
    defp get_latest_tokens(tokens, config) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      Auth.get_latest_access_token(tokens["refresh_token"], config)
      |> Map.put("refresh_token", tokens["refresh_token"])
    end
  
    # Recursive function
    # Modifies the gen_server state every time the access_token expiry is within 30 seconds of expiry.
    # expires_in parameter is in seconds
    # This function is used as a worker `Task` everytime the genserver is initialised.
    defp monitor_expiry(client, expires_in) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      interval = (expires_in - 30) * 1000
      :timer.sleep(interval)
      {:reply, :ok, _state} = GenServer.call(gen_server_name(client), :add_lock)
      {:reply, :ok, _state} = GenServer.call(gen_server_name(client), :update_tokens)
      {:reply, :ok, state} = GenServer.call(gen_server_name(client), :remove_lock)
      monitor_expiry(client, state["expires_in"])
    end
  
    # creates the ets table
    defp create_ets_table(client) do
      LoggingUtils.log_mod_func_line(__ENV__, :debug)
      ets_options = [
                     :set, # type
                     :protected, # read - all, write this process only.
                     :named_table,
                     {:heir, :none}, # don't let any process inherit the table. when the ets table dies, it dies.
                     {:write_concurrency, :false},
                     {:read_concurrency, :true}
                    ]
      unless ets_tablename(client) in :ets.all() do
        :ets.new(ets_tablename(client), ets_options)
      end
    end
  
  
  end

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