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   1 # Pleroma: A lightweight social networking server
   2 # Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
   3 # SPDX-License-Identifier: AGPL-3.0-only
   4
   5 defmodule Pleroma.Plugs.IdempotencyPlug do
   6   import Phoenix.Controller, only: [json: 2]
   7   import Plug.Conn
   8
   9   @behaviour Plug
  10
  11   @impl true
  12   def init(opts), do: opts
  13
  14   # Sending idempotency keys in `GET` and `DELETE` requests has no effect
  15   # and should be avoided, as these requests are idempotent by definition.
  16
  17   @impl true
  18   def call(%{method: method} = conn, _) when method in ["POST", "PUT", "PATCH"] do
  19     case get_req_header(conn, "idempotency-key") do
  20       [key] -> process_request(conn, key)
  21       _ -> conn
  22     end
  23   end
  24
  25   def call(conn, _), do: conn
  26
  27   def process_request(conn, key) do
  28     case Cachex.get(:idempotency_cache, key) do
  29       {:ok, nil} ->
  30         cache_resposnse(conn, key)
  31
  32       {:ok, record} ->
  33         send_cached(conn, key, record)
  34
  35       {atom, message} when atom in [:ignore, :error] ->
  36         render_error(conn, message)
  37     end
  38   end
  39
  40   defp cache_resposnse(conn, key) do
  41     register_before_send(conn, fn conn ->
  42       [request_id] = get_resp_header(conn, "x-request-id")
  43       content_type = get_content_type(conn)
  44
  45       record = {request_id, content_type, conn.status, conn.resp_body}
  46       {:ok, _} = Cachex.put(:idempotency_cache, key, record)
  47
  48       conn
  49       |> put_resp_header("idempotency-key", key)
  50       |> put_resp_header("x-original-request-id", request_id)
  51     end)
  52   end
  53
  54   defp send_cached(conn, key, record) do
  55     {request_id, content_type, status, body} = record
  56
  57     conn
  58     |> put_resp_header("idempotency-key", key)
  59     |> put_resp_header("idempotent-replayed", "true")
  60     |> put_resp_header("x-original-request-id", request_id)
  61     |> put_resp_content_type(content_type)
  62     |> send_resp(status, body)
  63     |> halt()
  64   end
  65
  66   defp render_error(conn, message) do
  67     conn
  68     |> put_status(:unprocessable_entity)
  69     |> json(%{error: message})
  70     |> halt()
  71   end
  72
  73   defp get_content_type(conn) do
  74     [content_type] = get_resp_header(conn, "content-type")
  75
  76     if String.contains?(content_type, ";") do
  77       content_type
  78       |> String.split(";")
  79       |> hd()
  80     else
  81       content_type
  82     end
  83   end
  84 end