Initial standalone Recorder+Converter implementation (#1)

* Changes from https://github.com/elixir-webrtc/ex_webrtc/pull/197/files
* Review fixes
* Update README and mix.exs
* Update ex_webrtc dep

Author: sgfn

README.md

@@ -1,3 +1,40 @@
 # ExWebRTC Recorder
 
-TODO WRITEME
+[![Hex.pm](https://img.shields.io/hexpm/v/ex_webrtc_recorder.svg)](https://hex.pm/packages/ex_webrtc_recorder)
+[![API Docs](https://img.shields.io/badge/api-docs-yellow.svg?style=flat)](https://hexdocs.pm/ex_webrtc_recorder)
+
+Records and processes RTP packets sent and received using [ExWebRTC](https://github.com/elixir-webrtc/ex_webrtc).
+
+## Installation
+
+Add `:ex_webrtc_recorder` to your list of dependencies
+
+```elixir
+def deps do
+  [
+    {:ex_webrtc_recorder, "~> 0.1.0"}
+  ]
+end
+```
+
+If you want to use Converter to generate WEBM files from the recordings,
+you need to have the `ffmpeg` binary with the relevant libraries present in `PATH`.
+
+### S3
+
+ExWebRTC Recorder comes with optional support for uploading the recordings to S3-compatible storage,
+but it must be explicitly turned on by adding the following dependencies:
+
+```elixir
+def deps do
+  [
+    {:ex_webrtc_recorder, "~> 0.1.0"},
+    {:ex_aws_s3, "~> 2.5"},
+    {:ex_aws, "~> 2.5"},
+    {:sweet_xml, "~> 0.7"},
+    {:req, "~> 0.5"}         # or any other HTTP client supported by `ex_aws`
+  ]
+end
+```
+
+See `ExWebRTC.Recorder.S3` for more info.

lib/ex_webrtc_recorder.ex

@@ -0,0 +1,351 @@
+defmodule ExWebRTC.Recorder do
+  @moduledoc """
+  Saves received RTP packets to a file for later processing/analysis.
+
+  Dumps raw RTP packets fed to it in a custom format. Use `ExWebRTC.Recorder.Converter` to process them.
+
+  Can optionally upload the saved files to S3-compatible storage.
+  See `ExWebRTC.Recorder.S3` and `t:options/0` for more info.
+  """
+
+  alias ExWebRTC.MediaStreamTrack
+  alias __MODULE__.S3
+
+  require Logger
+
+  use GenServer
+
+  @default_base_dir "./recordings"
+
+  @type recorder :: GenServer.server()
+
+  @typedoc """
+  Options that can be passed to `start_link/1`.
+
+  * `:base_dir` - Base directory where Recorder will save its artifacts. `#{@default_base_dir}` by default.
+  * `:on_start` - Callback that will be executed just after the Recorder is (re)started.
+     It should return the initial list of tracks to be added.
+  * `:controlling_process` - PID of a process where all messages will be sent. `self()` by default.
+  * `:s3_upload_config` - If passed, finished recordings will be uploaded to S3-compatible storage.
+     See `t:ExWebRTC.Recorder.S3.upload_config/0` for more info.
+  """
+  @type option ::
+          {:base_dir, String.t()}
+          | {:on_start, (-> [MediaStreamTrack.t()])}
+          | {:controlling_process, Process.dest()}
+          | {:s3_upload_config, S3.upload_config()}
+
+  @type options :: [option()]
+
+  @typedoc """
+  Messages sent by the `ExWebRTC.Recorder` process to its controlling process.
+
+  * `:upload_complete`, `:upload_failed` - Sent after the completion of the upload task, identified by its reference.
+    Contains the updated manifest with `s3://` scheme URLs to uploaded files.
+  """
+  @type message ::
+          {:ex_webrtc_recorder, pid(),
+           {:upload_complete, S3.upload_task_ref(), __MODULE__.Manifest.t()}
+           | {:upload_failed, S3.upload_task_ref(), __MODULE__.Manifest.t()}}
+
+  # Necessary to start Recorder under a supervisor using `{Recorder, [recorder_opts, gen_server_opts]}`
+  @doc false
+  @spec child_spec(list()) :: Supervisor.child_spec()
+  def child_spec(args) do
+    %{
+      id: __MODULE__,
+      start: {__MODULE__, :start_link, args}
+    }
+  end
+
+  @doc """
+  Starts a new `ExWebRTC.Recorder` process.
+
+  `ExWebRTC.Recorder` is a `GenServer` under the hood, thus this function allows for
+  passing the generic `t:GenServer.options/0` as an argument.
+  """
+  @spec start(options(), GenServer.options()) :: GenServer.on_start()
+  def start(recorder_opts \\ [], gen_server_opts \\ []) do
+    config =
+      recorder_opts
+      |> Keyword.put_new(:controlling_process, self())
+
+    GenServer.start(__MODULE__, config, gen_server_opts)
+  end
+
+  @doc """
+  Starts a new `ExWebRTC.Recorder` process.
+
+  Works identically to `start/2`, but links to the calling process.
+  """
+  @spec start_link(options(), GenServer.options()) :: GenServer.on_start()
+  def start_link(recorder_opts \\ [], gen_server_opts \\ []) do
+    config =
+      recorder_opts
+      |> Keyword.put_new(:controlling_process, self())
+
+    GenServer.start_link(__MODULE__, config, gen_server_opts)
+  end
+
+  @doc """
+  Adds new tracks to the recording.
+
+  Returns the part of the recording manifest that's relevant to the freshly added tracks.
+  See `t:ExWebRTC.Recorder.Manifest.t/0` for more info.
+  """
+  @spec add_tracks(recorder(), [MediaStreamTrack.t()]) :: {:ok, __MODULE__.Manifest.t()}
+  def add_tracks(recorder, tracks) do
+    GenServer.call(recorder, {:add_tracks, tracks})
+  end
+
+  @doc """
+  Records a received packet on the given track.
+  """
+  @spec record(
+          recorder(),
+          MediaStreamTrack.id(),
+          MediaStreamTrack.rid() | nil,
+          ExRTP.Packet.t()
+        ) :: :ok
+  def record(recorder, track_id, rid, %ExRTP.Packet{} = packet) do
+    recv_time = System.monotonic_time(:millisecond)
+    GenServer.cast(recorder, {:record, track_id, rid, recv_time, packet})
+  end
+
+  @doc """
+  Changes the controlling process of this `recorder` process.
+
+  Controlling process is a process that receives all of the messages (described
+  by `t:message/0`) from this Recorder.
+  """
+  @spec controlling_process(recorder(), Process.dest()) :: :ok
+  def controlling_process(recorder, controlling_process) do
+    GenServer.call(recorder, {:controlling_process, controlling_process})
+  end
+
+  @doc """
+  Finishes the recording for the given tracks and optionally uploads the result files.
+
+  Returns the part of the recording manifest that's relevant to the freshly ended tracks.
+  See `t:ExWebRTC.Recorder.Manifest.t/0` for more info.
+
+  If uploads are configured:
+  * Returns the reference to the upload task that was spawned.
+  * Will send the `:upload_complete`/`:upload_failed` message with this reference
+    to the controlling process when the task finishes.
+
+  Note that the manifest returned by this function always contains local paths to files.
+  The updated manifest with `s3://` scheme URLs is sent in the aforementioned message.
+  """
+  @spec end_tracks(recorder(), [MediaStreamTrack.id()]) ::
+          {:ok, __MODULE__.Manifest.t(), S3.upload_task_ref() | nil} | {:error, :tracks_not_found}
+  def end_tracks(recorder, track_ids) do
+    GenServer.call(recorder, {:end_tracks, track_ids})
+  end
+
+  @impl true
+  def init(config) do
+    base_dir =
+      (config[:base_dir] || @default_base_dir)
+      |> Path.join(current_datetime())
+      |> Path.expand()
+
+    :ok = File.mkdir_p!(base_dir)
+    Logger.info("Starting recorder. Recordings will be saved under: #{base_dir}")
+
+    upload_handler =
+      if config[:s3_upload_config] do
+        Logger.info("Recordings will be uploaded to S3")
+        S3.UploadHandler.new(config[:s3_upload_config])
+      end
+
+    state = %{
+      owner: config[:controlling_process],
+      base_dir: base_dir,
+      manifest_path: Path.join(base_dir, "manifest.json"),
+      track_data: %{},
+      upload_handler: upload_handler
+    }
+
+    case config[:on_start] do
+      nil ->
+        {:ok, state}
+
+      callback ->
+        {:ok, state, {:continue, {:on_start, callback}}}
+    end
+  end
+
+  @impl true
+  def handle_continue({:on_start, on_start}, state) do
+    case on_start.() do
+      [] ->
+        {:noreply, state}
+
+      tracks ->
+        {_manifest_diff, state} = do_add_tracks(tracks, state)
+        {:noreply, state}
+    end
+  end
+
+  @impl true
+  def handle_call({:controlling_process, controlling_process}, _from, state) do
+    state = %{state | owner: controlling_process}
+    {:reply, :ok, state}
+  end
+
+  @impl true
+  def handle_call({:add_tracks, tracks}, _from, state) do
+    {manifest_diff, state} = do_add_tracks(tracks, state)
+    {:reply, {:ok, manifest_diff}, state}
+  end
+
+  @impl true
+  def handle_call({:end_tracks, track_ids}, _from, state) do
+    case Enum.filter(track_ids, &Map.has_key?(state.track_data, &1)) do
+      [] ->
+        {:reply, {:error, :tracks_not_found}, state}
+
+      track_ids ->
+        {manifest_diff, ref, state} = do_end_tracks(track_ids, state)
+        {:reply, {:ok, manifest_diff, ref}, state}
+    end
+  end
+
+  @impl true
+  def handle_cast({:record, track_id, rid, recv_time, packet}, state)
+      when is_map_key(state.track_data, track_id) do
+    %{file: file, rid_map: rid_map} = state.track_data[track_id]
+
+    with {:ok, rid_idx} <- Map.fetch(rid_map, rid),
+         false <- is_nil(file) do
+      :ok = IO.binwrite(file, serialize_packet(packet, rid_idx, recv_time))
+    else
+      :error ->
+        Logger.warning("""
+        Tried to save packet for unknown rid. Ignoring. Track id: #{inspect(track_id)}, rid: #{inspect(rid)}.\
+        """)
+
+      true ->
+        Logger.warning("""
+        Tried to save packet for track which has been ended. Ignoring. Track id: #{inspect(track_id)} \
+        """)
+    end
+
+    {:noreply, state}
+  end
+
+  @impl true
+  def handle_cast({:record, track_id, _rid, _recv_time, _packet}, state) do
+    Logger.warning("""
+    Tried to save packet for unknown track id. Ignoring. Track id: #{inspect(track_id)}.\
+    """)
+
+    {:noreply, state}
+  end
+
+  @impl true
+  def handle_info({ref, _res} = task_result, state) when is_reference(ref) do
+    if state.upload_handler do
+      {result, manifest, handler} =
+        S3.UploadHandler.process_result(state.upload_handler, task_result)
+
+      case result do
+        :ok ->
+          send(state.owner, {:ex_webrtc_recorder, self(), {:upload_complete, ref, manifest}})
+
+        {:error, :upload_failed} ->
+          send(state.owner, {:ex_webrtc_recorder, self(), {:upload_failed, ref, manifest}})
+
+        {:error, :unknown_task} ->
+          raise "Upload handler encountered result of unknown task"
+      end
+
+      {:noreply, %{state | upload_handler: handler}}
+    else
+      {:noreply, state}
+    end
+  end
+
+  @impl true
+  def handle_info(_msg, state) do
+    {:noreply, state}
+  end
+
+  defp do_add_tracks(tracks, state) do
+    start_time = DateTime.utc_now()
+
+    new_track_data =
+      Map.new(tracks, fn track ->
+        file_path = Path.join(state.base_dir, "#{track.id}.rtpx")
+
+        track_entry = %{
+          start_time: start_time,
+          kind: track.kind,
+          streams: track.streams,
+          rid_map: (track.rids || [nil]) |> Enum.with_index() |> Map.new(),
+          location: file_path,
+          file: File.open!(file_path, [:write])
+        }
+
+        {track.id, track_entry}
+      end)
+
+    manifest_diff = to_manifest(new_track_data)
+
+    state = %{state | track_data: Map.merge(state.track_data, new_track_data)}
+
+    :ok = File.write!(state.manifest_path, state.track_data |> to_manifest() |> Jason.encode!())
+
+    {manifest_diff, state}
+  end
+
+  defp do_end_tracks(track_ids, state) do
+    # We're keeping entries from `track_data` for ended tracks
+    # because they need to be present in the global manifest,
+    # which gets recreated on each call to `add_tracks`
+    state =
+      Enum.reduce(track_ids, state, fn track_id, state ->
+        %{file: file} = state.track_data[track_id]
+        File.close(file)
+
+        put_in(state, [:track_data, track_id, :file], nil)
+      end)
+
+    manifest_diff = to_manifest(state.track_data, track_ids)
+
+    case state.upload_handler do
+      nil ->
+        {manifest_diff, nil, state}
+
+      handler ->
+        {ref, handler} = S3.UploadHandler.spawn_task(handler, manifest_diff)
+
+        {manifest_diff, ref, %{state | upload_handler: handler}}
+    end
+  end
+
+  defp to_manifest(track_data, track_ids) do
+    track_data |> Map.take(track_ids) |> to_manifest()
+  end
+
+  defp to_manifest(track_data) do
+    Map.new(track_data, fn {id, track} ->
+      {id, Map.delete(track, :file)}
+    end)
+  end
+
+  defp serialize_packet(packet, rid_idx, recv_time) do
+    packet = ExRTP.Packet.encode(packet)
+    packet_size = byte_size(packet)
+    <<rid_idx::8, recv_time::64, packet_size::32, packet::binary>>
+  end
+
+  defp current_datetime() do
+    {{y, mo, d}, {h, m, s}} = :calendar.local_time()
+
+    # e.g. 20240130-120315
+    :io_lib.format("~4..0w~2..0w~2..0w-~2..0w~2..0w~2..0w", [y, mo, d, h, m, s])
+    |> to_string()
+  end
+end