teac

defmodule Teac.Plug.CacheBodyReader do
  @moduledoc """
  A `Plug.Parsers` body reader that caches the raw request body in `conn.assigns`.

  Use this with `Plug.Parsers` in your Phoenix `Endpoint` so that
  `Teac.Plug.EventSub` can verify the Twitch HMAC signature after the body
  has already been parsed.

  ## Endpoint configuration

      plug Plug.Parsers,
        parsers: [:urlencoded, :multipart, :json],
        pass: ["*/*"],
        body_reader: {Teac.Plug.CacheBodyReader, :read_body, []},
        json_decoder: JSON

  The raw body is stored under `conn.assigns[:raw_body]` as a binary string.
  """

  def read_body(conn, opts) do
    case Plug.Conn.read_body(conn, opts) do
      {:ok, body, conn} ->
        conn = Plug.Conn.assign(conn, :raw_body, body)
        {:ok, body, conn}

      {:more, partial, conn} ->
        # For large bodies, accumulate chunks. Webhook payloads are small so
        # this path is rarely hit, but we handle it for correctness.
        conn = Plug.Conn.assign(conn, :raw_body, partial)
        {:more, partial, conn}

      other ->
        other
    end
  end
end