postland/lib/activity_pub.ex

defmodule ActivityPub do
  alias ActivityPub.Headers

  def get(url, actor_url, private_key) do
    headers = Headers.signing_headers("GET", url, "", actor_url, private_key)

    Req.new(url: url)
    |> Req.Request.put_header("accept", "application/activity+json")
    |> Req.Request.put_headers(headers)
    |> Req.get()
    |> case do
      {:ok, response} ->
        {:ok, response.body}

      other ->
        other
    end
  end

  def post_activity(sender_id, private_key, inbox, activity) do
    body = Jason.encode!(activity)

    headers =
      Headers.signing_headers(
        "POST",
        inbox,
        body,
        sender_id,
        private_key
      )

    Req.post(inbox, headers: headers, body: body)
  end

  def fetch_actor(actor_id) do
    request =
      Req.new(url: actor_id)
      |> Req.Request.put_header("accept", "application/json")

    case Req.get(request) do
      {:ok, %{status: 200} = result} ->
        {:ok, result.body}

      {:ok, %{status: 404}} ->
        nil

      error ->
        error
    end
  end
end