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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.ReverseProxy do
   6   @range_headers ~w(range if-range)
   7   @keep_req_headers ~w(accept accept-encoding cache-control if-modified-since) ++
   8                       ~w(if-unmodified-since if-none-match) ++ @range_headers
   9   @resp_cache_headers ~w(etag date last-modified)
  10   @keep_resp_headers @resp_cache_headers ++
  11                        ~w(content-length content-type content-disposition content-encoding) ++
  12                        ~w(content-range accept-ranges vary)
  13   @default_cache_control_header "public, max-age=1209600"
  14   @valid_resp_codes [200, 206, 304]
  15   @max_read_duration :timer.seconds(30)
  16   @max_body_length :infinity
  17   @failed_request_ttl :timer.seconds(60)
  18   @methods ~w(GET HEAD)
  19
  20   @cachex Pleroma.Config.get([:cachex, :provider], Cachex)
  21
  22   def max_read_duration_default, do: @max_read_duration
  23   def default_cache_control_header, do: @default_cache_control_header
  24
  25   @moduledoc """
  26   A reverse proxy.
  27
  28       Pleroma.ReverseProxy.call(conn, url, options)
  29
  30   It is not meant to be added into a plug pipeline, but to be called from another plug or controller.
  31
  32   Supports `#{inspect(@methods)}` HTTP methods, and only allows `#{inspect(@valid_resp_codes)}` status codes.
  33
  34   Responses are chunked to the client while downloading from the upstream.
  35
  36   Some request / responses headers are preserved:
  37
  38   * request: `#{inspect(@keep_req_headers)}`
  39   * response: `#{inspect(@keep_resp_headers)}`
  40
  41   Options:
  42
  43   * `redirect_on_failure` (default `false`). Redirects the client to the real remote URL if there's any HTTP
  44   errors. Any error during body processing will not be redirected as the response is chunked. This may expose
  45   remote URL, clients IPs, ….
  46
  47   * `max_body_length` (default `#{inspect(@max_body_length)}`): limits the content length to be approximately the
  48   specified length. It is validated with the `content-length` header and also verified when proxying.
  49
  50   * `max_read_duration` (default `#{inspect(@max_read_duration)}` ms): the total time the connection is allowed to
  51   read from the remote upstream.
  52
  53   * `failed_request_ttl` (default `#{inspect(@failed_request_ttl)}` ms): the time the failed request is cached and cannot be retried.
  54
  55   * `inline_content_types`:
  56     * `true` will not alter `content-disposition` (up to the upstream),
  57     * `false` will add `content-disposition: attachment` to any request,
  58     * a list of whitelisted content types
  59
  60   * `req_headers`, `resp_headers` additional headers.
  61
  62   * `http`: options for [hackney](https://github.com/benoitc/hackney) or [gun](https://github.com/ninenines/gun).
  63
  64   """
  65   @default_options [pool: :media]
  66
  67   @inline_content_types [
  68     "image/gif",
  69     "image/jpeg",
  70     "image/jpg",
  71     "image/png",
  72     "image/svg+xml",
  73     "audio/mpeg",
  74     "audio/mp3",
  75     "video/webm",
  76     "video/mp4",
  77     "video/quicktime"
  78   ]
  79
  80   require Logger
  81   import Plug.Conn
  82
  83   @type option() ::
  84           {:max_read_duration, :timer.time() | :infinity}
  85           | {:max_body_length, non_neg_integer() | :infinity}
  86           | {:failed_request_ttl, :timer.time() | :infinity}
  87           | {:http, []}
  88           | {:req_headers, [{String.t(), String.t()}]}
  89           | {:resp_headers, [{String.t(), String.t()}]}
  90           | {:inline_content_types, boolean() | [String.t()]}
  91           | {:redirect_on_failure, boolean()}
  92
  93   @spec call(Plug.Conn.t(), url :: String.t(), [option()]) :: Plug.Conn.t()
  94   def call(_conn, _url, _opts \\ [])
  95
  96   def call(conn = %{method: method}, url, opts) when method in @methods do
  97     client_opts = Keyword.merge(@default_options, Keyword.get(opts, :http, []))
  98
  99     req_headers = build_req_headers(conn.req_headers, opts)
 100
 101     opts =
 102       if filename = Pleroma.Web.MediaProxy.filename(url) do
 103         Keyword.put_new(opts, :attachment_name, filename)
 104       else
 105         opts
 106       end
 107
 108     with {:ok, nil} <- @cachex.get(:failed_proxy_url_cache, url),
 109          {:ok, code, headers, client} <- request(method, url, req_headers, client_opts),
 110          :ok <-
 111            header_length_constraint(
 112              headers,
 113              Keyword.get(opts, :max_body_length, @max_body_length)
 114            ) do
 115       response(conn, client, url, code, headers, opts)
 116     else
 117       {:ok, true} ->
 118         conn
 119         |> error_or_redirect(url, 500, "Request failed", opts)
 120         |> halt()
 121
 122       {:ok, code, headers} ->
 123         head_response(conn, url, code, headers, opts)
 124         |> halt()
 125
 126       {:error, {:invalid_http_response, code}} ->
 127         Logger.error("#{__MODULE__}: request to #{inspect(url)} failed with HTTP status #{code}")
 128         track_failed_url(url, code, opts)
 129
 130         conn
 131         |> error_or_redirect(
 132           url,
 133           code,
 134           "Request failed: " <> Plug.Conn.Status.reason_phrase(code),
 135           opts
 136         )
 137         |> halt()
 138
 139       {:error, error} ->
 140         Logger.error("#{__MODULE__}: request to #{inspect(url)} failed: #{inspect(error)}")
 141         track_failed_url(url, error, opts)
 142
 143         conn
 144         |> error_or_redirect(url, 500, "Request failed", opts)
 145         |> halt()
 146     end
 147   end
 148
 149   def call(conn, _, _) do
 150     conn
 151     |> send_resp(400, Plug.Conn.Status.reason_phrase(400))
 152     |> halt()
 153   end
 154
 155   defp request(method, url, headers, opts) do
 156     Logger.debug("#{__MODULE__} #{method} #{url} #{inspect(headers)}")
 157     method = method |> String.downcase() |> String.to_existing_atom()
 158
 159     case client().request(method, url, headers, "", opts) do
 160       {:ok, code, headers, client} when code in @valid_resp_codes ->
 161         {:ok, code, downcase_headers(headers), client}
 162
 163       {:ok, code, headers} when code in @valid_resp_codes ->
 164         {:ok, code, downcase_headers(headers)}
 165
 166       {:ok, code, _, _} ->
 167         {:error, {:invalid_http_response, code}}
 168
 169       {:ok, code, _} ->
 170         {:error, {:invalid_http_response, code}}
 171
 172       {:error, error} ->
 173         {:error, error}
 174     end
 175   end
 176
 177   defp response(conn, client, url, status, headers, opts) do
 178     Logger.debug("#{__MODULE__} #{status} #{url} #{inspect(headers)}")
 179
 180     result =
 181       conn
 182       |> put_resp_headers(build_resp_headers(headers, opts))
 183       |> send_chunked(status)
 184       |> chunk_reply(client, opts)
 185
 186     case result do
 187       {:ok, conn} ->
 188         halt(conn)
 189
 190       {:error, :closed, conn} ->
 191         client().close(client)
 192         halt(conn)
 193
 194       {:error, error, conn} ->
 195         Logger.warn(
 196           "#{__MODULE__} request to #{url} failed while reading/chunking: #{inspect(error)}"
 197         )
 198
 199         client().close(client)
 200         halt(conn)
 201     end
 202   end
 203
 204   defp chunk_reply(conn, client, opts) do
 205     chunk_reply(conn, client, opts, 0, 0)
 206   end
 207
 208   defp chunk_reply(conn, client, opts, sent_so_far, duration) do
 209     with {:ok, duration} <-
 210            check_read_duration(
 211              duration,
 212              Keyword.get(opts, :max_read_duration, @max_read_duration)
 213            ),
 214          {:ok, data, client} <- client().stream_body(client),
 215          {:ok, duration} <- increase_read_duration(duration),
 216          sent_so_far = sent_so_far + byte_size(data),
 217          :ok <-
 218            body_size_constraint(
 219              sent_so_far,
 220              Keyword.get(opts, :max_body_length, @max_body_length)
 221            ),
 222          {:ok, conn} <- chunk(conn, data) do
 223       chunk_reply(conn, client, opts, sent_so_far, duration)
 224     else
 225       :done -> {:ok, conn}
 226       {:error, error} -> {:error, error, conn}
 227     end
 228   end
 229
 230   defp head_response(conn, url, code, headers, opts) do
 231     Logger.debug("#{__MODULE__} #{code} #{url} #{inspect(headers)}")
 232
 233     conn
 234     |> put_resp_headers(build_resp_headers(headers, opts))
 235     |> send_resp(code, "")
 236   end
 237
 238   defp error_or_redirect(conn, url, code, body, opts) do
 239     if Keyword.get(opts, :redirect_on_failure, false) do
 240       conn
 241       |> Phoenix.Controller.redirect(external: url)
 242       |> halt()
 243     else
 244       conn
 245       |> send_resp(code, body)
 246       |> halt
 247     end
 248   end
 249
 250   defp downcase_headers(headers) do
 251     Enum.map(headers, fn {k, v} ->
 252       {String.downcase(k), v}
 253     end)
 254   end
 255
 256   defp get_content_type(headers) do
 257     {_, content_type} =
 258       List.keyfind(headers, "content-type", 0, {"content-type", "application/octet-stream"})
 259
 260     [content_type | _] = String.split(content_type, ";")
 261     content_type
 262   end
 263
 264   defp put_resp_headers(conn, headers) do
 265     Enum.reduce(headers, conn, fn {k, v}, conn ->
 266       put_resp_header(conn, k, v)
 267     end)
 268   end
 269
 270   defp build_req_headers(headers, opts) do
 271     headers
 272     |> downcase_headers()
 273     |> Enum.filter(fn {k, _} -> k in @keep_req_headers end)
 274     |> build_req_range_or_encoding_header(opts)
 275     |> build_req_user_agent_header(opts)
 276     |> Keyword.merge(Keyword.get(opts, :req_headers, []))
 277   end
 278
 279   # Disable content-encoding if any @range_headers are requested (see #1823).
 280   defp build_req_range_or_encoding_header(headers, _opts) do
 281     range? = Enum.any?(headers, fn {header, _} -> Enum.member?(@range_headers, header) end)
 282
 283     if range? && List.keymember?(headers, "accept-encoding", 0) do
 284       List.keydelete(headers, "accept-encoding", 0)
 285     else
 286       headers
 287     end
 288   end
 289
 290   defp build_req_user_agent_header(headers, _opts) do
 291     List.keystore(
 292       headers,
 293       "user-agent",
 294       0,
 295       {"user-agent", Pleroma.Application.user_agent()}
 296     )
 297   end
 298
 299   defp build_resp_headers(headers, opts) do
 300     headers
 301     |> Enum.filter(fn {k, _} -> k in @keep_resp_headers end)
 302     |> build_resp_cache_headers(opts)
 303     |> build_resp_content_disposition_header(opts)
 304     |> Keyword.merge(Keyword.get(opts, :resp_headers, []))
 305   end
 306
 307   defp build_resp_cache_headers(headers, _opts) do
 308     has_cache? = Enum.any?(headers, fn {k, _} -> k in @resp_cache_headers end)
 309
 310     cond do
 311       has_cache? ->
 312         # There's caching header present but no cache-control -- we need to set our own
 313         # as Plug defaults to "max-age=0, private, must-revalidate"
 314         List.keystore(
 315           headers,
 316           "cache-control",
 317           0,
 318           {"cache-control", @default_cache_control_header}
 319         )
 320
 321       true ->
 322         List.keystore(
 323           headers,
 324           "cache-control",
 325           0,
 326           {"cache-control", @default_cache_control_header}
 327         )
 328     end
 329   end
 330
 331   defp build_resp_content_disposition_header(headers, opts) do
 332     opt = Keyword.get(opts, :inline_content_types, @inline_content_types)
 333
 334     content_type = get_content_type(headers)
 335
 336     attachment? =
 337       cond do
 338         is_list(opt) && !Enum.member?(opt, content_type) -> true
 339         opt == false -> true
 340         true -> false
 341       end
 342
 343     if attachment? do
 344       name =
 345         try do
 346           {{"content-disposition", content_disposition_string}, _} =
 347             List.keytake(headers, "content-disposition", 0)
 348
 349           [name | _] =
 350             Regex.run(
 351               ~r/filename="((?:[^"\\]|\\.)*)"/u,
 352               content_disposition_string || "",
 353               capture: :all_but_first
 354             )
 355
 356           name
 357         rescue
 358           MatchError -> Keyword.get(opts, :attachment_name, "attachment")
 359         end
 360
 361       disposition = "attachment; filename=\"#{name}\""
 362
 363       List.keystore(headers, "content-disposition", 0, {"content-disposition", disposition})
 364     else
 365       headers
 366     end
 367   end
 368
 369   defp header_length_constraint(headers, limit) when is_integer(limit) and limit > 0 do
 370     with {_, size} <- List.keyfind(headers, "content-length", 0),
 371          {size, _} <- Integer.parse(size),
 372          true <- size <= limit do
 373       :ok
 374     else
 375       false ->
 376         {:error, :body_too_large}
 377
 378       _ ->
 379         :ok
 380     end
 381   end
 382
 383   defp header_length_constraint(_, _), do: :ok
 384
 385   defp body_size_constraint(size, limit) when is_integer(limit) and limit > 0 and size >= limit do
 386     {:error, :body_too_large}
 387   end
 388
 389   defp body_size_constraint(_, _), do: :ok
 390
 391   defp check_read_duration(nil = _duration, max), do: check_read_duration(@max_read_duration, max)
 392
 393   defp check_read_duration(duration, max)
 394        when is_integer(duration) and is_integer(max) and max > 0 do
 395     if duration > max do
 396       {:error, :read_duration_exceeded}
 397     else
 398       {:ok, {duration, :erlang.system_time(:millisecond)}}
 399     end
 400   end
 401
 402   defp check_read_duration(_, _), do: {:ok, :no_duration_limit, :no_duration_limit}
 403
 404   defp increase_read_duration({previous_duration, started})
 405        when is_integer(previous_duration) and is_integer(started) do
 406     duration = :erlang.system_time(:millisecond) - started
 407     {:ok, previous_duration + duration}
 408   end
 409
 410   defp increase_read_duration(_) do
 411     {:ok, :no_duration_limit, :no_duration_limit}
 412   end
 413
 414   defp client, do: Pleroma.ReverseProxy.Client
 415
 416   defp track_failed_url(url, error, opts) do
 417     ttl =
 418       unless error in [:body_too_large, 400, 204] do
 419         Keyword.get(opts, :failed_request_ttl, @failed_request_ttl)
 420       else
 421         nil
 422       end
 423
 424     @cachex.put(:failed_proxy_url_cache, url, true, ttl: ttl)
 425   end
 426 end