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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -1,147 +1,2 @@ | ||
| defmodule MBTA.Cache do | ||
| @moduledoc """ | ||
| Cache HTTP responses from MBTA. | ||
| Static data such as schedules and stops do not change frequently. However, | ||
| we do want to check in with the API periodically to make sure we have the | ||
| most recent data. This module stores the previous HTTP responses, and can | ||
| return them if the server says that the data is unchanged. | ||
| """ | ||
|
|
||
| require Logger | ||
|
|
||
| use GenServer | ||
|
|
||
| alias HTTPoison.Response | ||
|
|
||
| @type url :: String.t() | ||
| @type params :: Enumerable.t() | ||
|
|
||
| def start_link(opts \\ []) do | ||
| opts = Keyword.put_new(opts, :name, __MODULE__) | ||
| GenServer.start_link(__MODULE__, opts, opts) | ||
| end | ||
|
|
||
| @doc """ | ||
| Given a URL, parameters, and an HTTP response: | ||
| - If the HTTP response is a 304 Not Modified, return the previously cached response | ||
| - If the HTTP response is a 200, 400, or 404, cache it and return the response | ||
| - If the HTTP response is anything else, try to return a cached response, otherwise return the response as-is | ||
| """ | ||
| @spec cache_response(url, params, Response.t()) :: | ||
| {:ok, Response.t()} | {:error, :no_cached_response} | ||
| def cache_response(name \\ __MODULE__, url, params, response) | ||
|
|
||
| def cache_response(name, url, params, %{status_code: 304}) do | ||
| lookup_cached_response(name, url, params) | ||
| rescue | ||
| ArgumentError -> | ||
| {:error, :no_cached_response} | ||
| end | ||
|
|
||
| def cache_response(name, url, params, %{status_code: status_code} = response) | ||
| when status_code in [200, 400, 404] do | ||
| key = {url, params} | ||
| last_modified = header(response, "last-modified") | ||
| true = :ets.insert(name, {key, last_modified, response, now()}) | ||
| {:ok, response} | ||
| end | ||
|
|
||
| def cache_response(name, url, params, response) do | ||
| lookup_cached_response(name, url, params) | ||
| rescue | ||
| ArgumentError -> | ||
| {:ok, response} | ||
| end | ||
|
|
||
| defp lookup_cached_response(name, url, params) do | ||
| key = {url, params} | ||
| element = :ets.lookup_element(name, key, 3) | ||
| :ets.update_element(name, key, {4, now()}) | ||
| {:ok, element} | ||
| end | ||
|
|
||
| @doc """ | ||
| Return a list of cache headers for the given URL/parameters. | ||
| """ | ||
| @spec cache_headers(url, params) :: [{String.t(), String.t()}] | ||
| def cache_headers(name \\ __MODULE__, url, params) do | ||
| last_modfied = :ets.lookup_element(name, {url, params}, 2) | ||
| [{"if-modified-since", last_modfied}] | ||
| rescue | ||
| ArgumentError -> | ||
| [] | ||
| end | ||
|
|
||
| defp header(%{headers: headers}, header) do | ||
| case Enum.find(headers, &(String.downcase(elem(&1, 0)) == header)) do | ||
| {_, value} -> value | ||
| nil -> nil | ||
| end | ||
| end | ||
|
|
||
| @doc "Expire the least-recently-used cache items" | ||
| @spec expire!() :: :ok | ||
| def expire!(name \\ __MODULE__) do | ||
| GenServer.call(name, :expire!) | ||
| end | ||
|
|
||
| @impl GenServer | ||
| def init(opts) do | ||
| name = Keyword.fetch!(opts, :name) | ||
|
|
||
| ^name = | ||
| :ets.new(name, [ | ||
| :set, | ||
| :named_table, | ||
| :public, | ||
| {:read_concurrency, true}, | ||
| {:write_concurrency, true} | ||
| ]) | ||
|
|
||
| timeout = Keyword.get(opts, :timeout, 60_000) | ||
| Process.send_after(self(), :expire, timeout) | ||
| size = Keyword.get(opts, :size, Application.get_env(:dotcom, :v3_api_cache_size)) | ||
| {:ok, %{name: name, size: size, timeout: timeout}} | ||
| end | ||
|
|
||
| @impl GenServer | ||
| def handle_call(:expire!, _from, state) do | ||
| :ok = do_expire(state) | ||
| {:reply, :ok, state} | ||
| end | ||
|
|
||
| @impl GenServer | ||
| def handle_info(:expire, state) do | ||
| :ok = do_expire(state) | ||
| Process.send_after(self(), :expire, state.timeout) | ||
| {:noreply, state} | ||
| end | ||
|
|
||
| defp do_expire(%{name: name, size: size}) do | ||
| current_size = :ets.info(name, :size) | ||
|
|
||
| _ = | ||
| Logger.info(fn -> | ||
| "#{name} report - size=#{current_size} max_size=#{size} memory=#{:ets.info(name, :memory)}" | ||
| end) | ||
|
|
||
| if current_size > size do | ||
| # keep half of the cache, so that we don't bounce around clearing the | ||
| # cache each minute | ||
| keep = div(size, 2) | ||
|
|
||
| name | ||
| |> :ets.match({:"$2", :_, :_, :"$1"}) | ||
| |> Enum.sort(&>=/2) | ||
| |> Enum.drop(keep) | ||
| |> Enum.each(fn [_lru, key] -> :ets.delete(name, key) end) | ||
| else | ||
| :ok | ||
| end | ||
| end | ||
|
|
||
| defp now do | ||
| System.monotonic_time() | ||
| end | ||
| end |
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