clacks/lib/clacks/activitypub/fetcher.ex

defmodule Clacks.ActivityPub.Fetcher do
  require Logger

  @spec fetch_actor(id :: String.t()) :: map() | nil
  def fetch_actor(id) do
    %{host: id_host} = URI.parse(id)

    with %{"type" => type, "id" => remote_id} = actor <- fetch(id),
         "person" <- String.downcase(type),
         %{host: ^id_host} <- URI.parse(remote_id) do
      actor
    else
      _ ->
        nil
    end
  end

  @spec fetch_object(id :: String.t()) :: map() | nil
  def fetch_object(id) do
    %{host: id_host} = URI.parse(id)

    with %{"actor" => remote_actor} = object <- fetch(id),
         %{host: ^id_host} <- URI.parse(remote_actor) do
      object
    else
      _ ->
        nil
    end
  end

  @spec fetch_activity(id :: String.t()) :: map() | nil
  def fetch_activity(id) do
    fetch_object(id)
  end

  @spec fetch(uri :: String.t()) :: map() | nil
  defp fetch(uri) do
    Logger.debug("Attempting to fetch AP object at #{uri}")

    headers = [Accept: "application/activity+json, application/ld+json"]
    opts = [hackney: Application.get_env(:clacks, :hackney_opts, [])]

    with {:ok, %HTTPoison.Response{status_code: status_code, body: body}}
         when status_code in 200..299 <-
           HTTPoison.get(uri, headers, opts),
         {:ok, data} <- Jason.decode(body) do
      data
    else
      {:ok, %HTTPoison.Response{}} ->
        nil

      {:error, reason} ->
        Logger.warn("Couldn't fetch AP object at #{uri}: #{inspect(reason)}")
        nil
    end
  end
end