feat: switch to Mint as the default HTTP producer

Mint uses a no-process architecture, which fits better with
Concentrate's one-process-per-HTTP-endpoint model.

config/config.exs

@@ -73,6 +73,6 @@ config :concentrate,
   file_tap: [
     enabled?: false
   ],
-  http_producer: Concentrate.Producer.HTTPoison
+  http_producer: Concentrate.Producer.Mint
 
 import_config "#{Mix.env()}.exs"

lib/concentrate/producer/mint.ex

@@ -0,0 +1,374 @@
+defmodule Concentrate.Producer.Mint do
+  @moduledoc """
+  HTTP producer implementation using Mint.
+  """
+  use GenStage
+  require Logger
+  alias Mint.HTTP
+  @start_link_opts ~w(name)a
+  @default_fetch_after 5_000
+  @default_timeout 30_000
+  @default_transport_opts [timeout: @default_timeout]
+  @default_headers %{"accept-encoding" => "gzip"}
+
+  defmodule State do
+    @moduledoc false
+
+    defstruct [
+      :url,
+      :parser,
+      fetch_after: nil,
+      opts: %{},
+      transport_opts: [],
+      headers: %{},
+      conn: :not_connected,
+      ref: :not_connected,
+      demand: 0,
+      response: nil,
+      events: []
+    ]
+  end
+
+  alias __MODULE__.State
+
+  def start_link({url, opts}) when is_binary(url) and is_list(opts) do
+    {start_link_opts, opts} = Keyword.split(opts, @start_link_opts)
+    GenStage.start_link(__MODULE__, {url, opts}, start_link_opts)
+  end
+
+  @impl GenStage
+  def init({url, opts}) do
+    opts = Map.new(opts)
+
+    parser =
+      case Map.fetch!(opts, :parser) do
+        module when is_atom(module) ->
+          &module.parse(&1, [])
+
+        {module, opts} when is_atom(module) and is_list(opts) ->
+          &module.parse(&1, opts)
+
+        fun when is_function(fun, 1) ->
+          fun
+      end
+
+    state = %State{
+      url: url,
+      parser: parser,
+      fetch_after: Map.get(opts, :fetch_after, @default_fetch_after),
+      transport_opts:
+        Keyword.take(Map.get(opts, :get_opts, @default_transport_opts), ~w(timeout send_timeout)a),
+      headers: Map.merge(@default_headers, Map.get(opts, :headers, %{})),
+      opts: opts
+    }
+
+    {
+      :producer,
+      state,
+      dispatcher: GenStage.BroadcastDispatcher
+    }
+  end
+
+  @impl GenStage
+  def handle_demand(new_demand, %{demand: existing_demand} = state) do
+    demand = new_demand + existing_demand
+    state = %{state | demand: demand}
+
+    state =
+      if existing_demand == 0 do
+        make_request(state, state.url)
+      else
+        state
+      end
+
+    {:noreply, [], state}
+  end
+
+  @impl GenStage
+  def handle_info({:fetch, url}, state) do
+    state =
+      if state.demand > 0 do
+        make_request(state, url)
+      else
+        state
+      end
+
+    {:noreply, [], state}
+  end
+
+  def handle_info({:fetch_timeout, ref}, %{ref: ref} = state) do
+    log_message(:warn, state, fn -> "fetch timed out, disconnecting" end)
+
+    _ =
+      if state.conn != :not_connected and HTTP.open?(state.conn) do
+        HTTP.close(state.conn)
+      end
+
+    state = %{state | conn: :not_connected, ref: nil}
+    state = fetch_again!(state)
+    {:noreply, [], state}
+  end
+
+  def handle_info({:fetch_timeout, _}, state) do
+    {:noreply, [], state}
+  end
+
+  def handle_info(message, state) do
+    state =
+      case HTTP.stream(state.conn, message) do
+        {:ok, conn, responses} ->
+          Enum.reduce(responses, %{state | conn: conn}, &handle_responses/2)
+
+        {:error, conn, error, _responses} ->
+          log_message(:warn, state, fn ->
+            "HTTP error error=#{inspect(error)}
+            "
+          end)
+
+          state = %{state | conn: conn, ref: nil}
+          fetch_again!(state)
+
+        :unknown ->
+          log_message(:warn, state, fn -> "unknown message message=#{inspect(message)}" end)
+          state
+      end
+
+    {:noreply, Enum.reverse(state.events), %{state | events: []}}
+  end
+
+  def handle_responses({:status, ref, status}, %{ref: ref} = state) do
+    %{state | response: {status, [], []}}
+  end
+
+  def handle_responses({:headers, ref, headers}, %{ref: ref} = state) do
+    {status, old_headers, body} = state.response
+
+    cache_headers =
+      Enum.reduce(headers, state.headers, fn {header, value}, acc ->
+        case String.downcase(header) do
+          "last-modified" ->
+            Map.put(acc, "if-modified-since", value)
+
+          "etag" ->
+            Map.put(acc, "if-none-match", value)
+
+          _ ->
+            acc
+        end
+      end)
+
+    # don't use if-none-match if we already have if-modified-since
+    cache_headers =
+      case cache_headers do
+        %{"if-modified-since" => _, "if-none-match" => _} ->
+          Map.delete(cache_headers, "if-none-match")
+
+        _ ->
+          cache_headers
+      end
+
+    %{state | response: {status, headers ++ old_headers, body}, headers: cache_headers}
+  end
+
+  def handle_responses({:data, ref, data}, %{ref: ref} = state) do
+    {status, headers, body} = state.response
+
+    %{state | response: {status, headers, [body | data]}}
+  end
+
+  def handle_responses({:done, ref}, %{ref: ref} = state) do
+    {status, headers, body} = state.response
+    handle_http_response(state, status, headers, body)
+  end
+
+  def handle_responses(response, state) do
+    log_message(:warn, state, fn ->
+      "unexpected response=#{inspect(response)}"
+    end)
+
+    state
+  end
+
+  def make_request(state, url) do
+    state = connect(state, url)
+
+    if state.conn != :not_connected do
+      {_, _, _, path} = parse_url(url)
+      {:ok, conn, ref} = HTTP.request(state.conn, "GET", path, Map.to_list(state.headers), "")
+
+      Process.send_after(
+        self(),
+        {:fetch_timeout, ref},
+        Keyword.get(state.transport_opts, :timeout)
+      )
+
+      %{state | conn: conn, ref: ref}
+    else
+      fetch_again!(state)
+    end
+  end
+
+  defp connect(%{conn: :not_connected} = state, url) do
+    {scheme, host, port, _} = parse_url(url)
+
+    case HTTP.connect(scheme, host, port,
+           transport_opts: state.transport_opts,
+           protocols: [:http1]
+         ) do
+      {:ok, conn} ->
+        %{state | conn: conn}
+
+      {:error, _} ->
+        state
+    end
+  end
+
+  defp connect(state, url) do
+    # if HTTP.open?(conn) do
+    #   state
+    # else
+    state
+    |> disconnect()
+    |> connect(url)
+
+    # end
+  end
+
+  defp disconnect(%{conn: conn} = state) do
+    _ = HTTP.close(conn)
+    %{state | conn: :not_connected, ref: :not_connected}
+  end
+
+  defp handle_http_response(state, 200, headers, body) do
+    body = decode_body(body, find_header(headers, "content-encoding"))
+    {time, parsed} = :timer.tc(state.parser, [body])
+
+    log_message(:info, state, fn ->
+      "updated: records=#{length(parsed)} time=#{time / 1000}"
+    end)
+
+    state = %{
+      state
+      | events: [parsed | state.events],
+        demand: max(state.demand - 1, 0),
+        response: nil
+    }
+
+    fetch_again!(state)
+  rescue
+    error ->
+      state = log_parse_error(error, state, System.stacktrace())
+      fetch_again!(state)
+  catch
+    error ->
+      state = log_parse_error(error, state, System.stacktrace())
+      fetch_again!(state)
+  end
+
+  defp handle_http_response(state, redirect, headers, _body) when redirect in [301, 302] do
+    {:ok, location} = find_header(headers, "location")
+    state = disconnect(state)
+
+    if redirect == 301 do
+      state = %{state | url: location}
+      fetch_again!(state, fetch_after: 0)
+    else
+      fetch_again!(state, url: location, fetch_after: 0)
+    end
+  end
+
+  defp handle_http_response(state, 304, _headers, _body) do
+    log_message(:info, state, fn -> "not modified status=304" end)
+    fetch_again!(state)
+  end
+
+  defp handle_http_response(state, 404, _headers, _body) do
+    log_message(:warn, state, fn -> "not found status=404" end)
+    fetch_again!(state)
+  end
+
+  defp decode_body(body, {:ok, "gzip"}) do
+    :zlib.gunzip(body)
+  end
+
+  defp decode_body(body, _) do
+    IO.iodata_to_binary(body)
+  end
+
+  defp fetch_again!(state, opts \\ []) do
+    _ =
+      if state.demand > 0 do
+        url = Keyword.get(opts, :url, state.url)
+        fetch_after = Keyword.get(opts, :fetch_after, state.fetch_after)
+        Process.send_after(self(), {:fetch, url}, fetch_after)
+      end
+
+    state
+  end
+
+  def find_header(headers, query) do
+    value =
+      Enum.find_value(headers, fn {header, value} ->
+        if String.downcase(header) == query do
+          value
+        else
+          nil
+        end
+      end)
+
+    if value do
+      {:ok, value}
+    else
+      :error
+    end
+  end
+
+  defp log_parse_error(error, machine, trace) do
+    _ =
+      Logger.error(fn ->
+        "#{__MODULE__}: parse error url=#{machine.url} error=#{inspect(error)}\n#{
+          Exception.format_stacktrace(trace)
+        }"
+      end)
+
+    machine
+  end
+
+  @doc """
+  Parse URL into the pieces needed for connecting to Mint.
+
+  iex> parse_url("https://mbta.com/developers")
+  {:https, "mbta.com", 443, "/developers"}
+
+  iex> parse_url("http://localhost:8080/path?query=string#fragement")
+  {:http, "localhost", 8080, "/path?query=string"}
+  """
+  def parse_url(url) when is_binary(url) do
+    uri = URI.parse(url)
+
+    scheme =
+      case uri.scheme do
+        "https" -> :https
+        "http" -> :http
+        nil -> :http
+      end
+
+    path =
+      if uri.query do
+        "#{uri.path}?#{uri.query}"
+      else
+        uri.path
+      end
+
+    {scheme, uri.host, uri.port, path}
+  end
+
+  defp log_message(level, state, log_fn) do
+    _ =
+      Logger.log(level, fn ->
+        "#{__MODULE__} #{log_fn.()} url=#{inspect(state.url)}"
+      end)
+
+    :ok
+  end
+end

mix.exs

@@ -71,6 +71,8 @@ defmodule Concentrate.MixProject do
       {:gen_stage, "~> 1.0"},
       {:gpb, "~> 4.7", only: :dev, runtime: false, only: :dev},
       {:httpoison, "~> 1.0"},
+      {:mint, "~> 1.0"},
+      {:castore, "~> 0.1"},
       {:jason, "~> 1.0"},
       {:stream_data, "~> 0.4", only: :test},
       {:tzdata, "~> 1.1.1"}