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   1 # Pleroma: A lightweight social networking server
   2 # Copyright © 2017-2021 Pleroma Authors <https://pleroma.social/>
   3 # SPDX-License-Identifier: AGPL-3.0-only
   4
   5 defmodule Pleroma.Web.Plugs.IdempotencyPlug do
   6   import Phoenix.Controller, only: [json: 2]
   7   import Plug.Conn
   8
   9   @behaviour Plug
  10
  11   @cachex Pleroma.Config.get([:cachex, :provider], Cachex)
  12
  13   @impl true
  14   def init(opts), do: opts
  15
  16   # Sending idempotency keys in `GET` and `DELETE` requests has no effect
  17   # and should be avoided, as these requests are idempotent by definition.
  18
  19   @impl true
  20   def call(%{method: method} = conn, _) when method in ["POST", "PUT", "PATCH"] do
  21     case get_req_header(conn, "idempotency-key") do
  22       [key] -> process_request(conn, key)
  23       _ -> conn
  24     end
  25   end
  26
  27   def call(conn, _), do: conn
  28
  29   def process_request(conn, key) do
  30     case @cachex.get(:idempotency_cache, key) do
  31       {:ok, nil} ->
  32         cache_resposnse(conn, key)
  33
  34       {:ok, record} ->
  35         send_cached(conn, key, record)
  36
  37       {atom, message} when atom in [:ignore, :error] ->
  38         render_error(conn, message)
  39     end
  40   end
  41
  42   defp cache_resposnse(conn, key) do
  43     register_before_send(conn, fn conn ->
  44       [request_id] = get_resp_header(conn, "x-request-id")
  45       content_type = get_content_type(conn)
  46
  47       record = {request_id, content_type, conn.status, conn.resp_body}
  48       {:ok, _} = @cachex.put(:idempotency_cache, key, record)
  49
  50       conn
  51       |> put_resp_header("idempotency-key", key)
  52       |> put_resp_header("x-original-request-id", request_id)
  53     end)
  54   end
  55
  56   defp send_cached(conn, key, record) do
  57     {request_id, content_type, status, body} = record
  58
  59     conn
  60     |> put_resp_header("idempotency-key", key)
  61     |> put_resp_header("idempotent-replayed", "true")
  62     |> put_resp_header("x-original-request-id", request_id)
  63     |> put_resp_content_type(content_type)
  64     |> send_resp(status, body)
  65     |> halt()
  66   end
  67
  68   defp render_error(conn, message) do
  69     conn
  70     |> put_status(:unprocessable_entity)
  71     |> json(%{error: message})
  72     |> halt()
  73   end
  74
  75   defp get_content_type(conn) do
  76     [content_type] = get_resp_header(conn, "content-type")
  77
  78     if String.contains?(content_type, ";") do
  79       content_type
  80       |> String.split(";")
  81       |> hd()
  82     else
  83       content_type
  84     end
  85   end
  86 end