zf

upload.ex (7264B)

---

 defmodule Plug.UploadError do
   defexception [:message]
 end
 
 defmodule Plug.Upload do
   @moduledoc """
   A server (a `GenServer` specifically) that manages uploaded files.
 
   Uploaded files are stored in a temporary directory
   and removed from that directory after the process that
   requested the file dies.
 
   During the request, files are represented with
   a `Plug.Upload` struct that contains three fields:
 
     * `:path` - the path to the uploaded file on the filesystem
     * `:content_type` - the content type of the uploaded file
     * `:filename` - the filename of the uploaded file given in the request
 
   **Note**: as mentioned in the documentation for `Plug.Parsers`, the `:plug`
   application has to be started in order to upload files and use the
   `Plug.Upload` module.
 
   ## Security
 
   The `:content_type` and `:filename` fields in the `Plug.Upload` struct are
   client-controlled. These values should be validated, via file content
   inspection or similar, before being trusted.
   """
 
   use GenServer
   defstruct [:path, :content_type, :filename]
 
   @type t :: %__MODULE__{
           path: Path.t(),
           filename: binary,
           content_type: binary | nil
         }
 
   @dir_table __MODULE__.Dir
   @path_table __MODULE__.Path
   @max_attempts 10
   @temp_env_vars ~w(PLUG_TMPDIR TMPDIR TMP TEMP)s
 
   @doc """
   Requests a random file to be created in the upload directory
   with the given prefix.
   """
   @spec random_file(binary) ::
           {:ok, binary}
           | {:too_many_attempts, binary, pos_integer}
           | {:no_tmp, [binary]}
   def random_file(prefix) do
     case ensure_tmp() do
       {:ok, tmp} ->
         open_random_file(prefix, tmp, 0)
 
       {:no_tmp, tmps} ->
         {:no_tmp, tmps}
     end
   end
 
   @doc """
   Assign ownership of the given upload file to another process.
 
   Useful if you want to do some work on an uploaded file in another process
   since it means that the file will survive the end of the request.
   """
   @spec give_away(t | binary, pid, pid) :: :ok | {:error, :unknown_path}
   def give_away(upload, to_pid, from_pid \\ self())
 
   def give_away(%__MODULE__{path: path}, to_pid, from_pid) do
     give_away(path, to_pid, from_pid)
   end
 
   def give_away(path, to_pid, from_pid)
       when is_binary(path) and is_pid(to_pid) and is_pid(from_pid) do
     with [{^from_pid, _tmp}] <- :ets.lookup(@dir_table, from_pid),
          true <- path_owner?(from_pid, path) do
       case :ets.lookup(@dir_table, to_pid) do
         [{^to_pid, _tmp}] ->
           :ets.insert(@path_table, {to_pid, path})
           :ets.delete_object(@path_table, {from_pid, path})
 
           :ok
 
         [] ->
           server = plug_server()
           {:ok, tmp} = generate_tmp_dir()
           :ok = GenServer.call(server, {:give_away, to_pid, tmp, path})
           :ets.delete_object(@path_table, {from_pid, path})
           :ok
       end
     else
       _ ->
         {:error, :unknown_path}
     end
   end
 
   defp ensure_tmp() do
     pid = self()
 
     case :ets.lookup(@dir_table, pid) do
       [{^pid, tmp}] ->
         {:ok, tmp}
 
       [] ->
         server = plug_server()
         GenServer.cast(server, {:monitor, pid})
 
         with {:ok, tmp} <- generate_tmp_dir() do
           true = :ets.insert_new(@dir_table, {pid, tmp})
           {:ok, tmp}
         end
     end
   end
 
   defp generate_tmp_dir() do
     tmp_roots = :persistent_term.get(__MODULE__)
     {mega, _, _} = :os.timestamp()
     subdir = "/plug-" <> i(mega)
 
     if tmp = Enum.find_value(tmp_roots, &make_tmp_dir(&1 <> subdir)) do
       {:ok, tmp}
     else
       {:no_tmp, tmp_roots}
     end
   end
 
   defp make_tmp_dir(path) do
     case File.mkdir_p(path) do
       :ok -> path
       {:error, _} -> nil
     end
   end
 
   defp open_random_file(prefix, tmp, attempts) when attempts < @max_attempts do
     path = path(prefix, tmp)
 
     case :file.write_file(path, "", [:write, :raw, :exclusive, :binary]) do
       :ok ->
         :ets.insert(@path_table, {self(), path})
         {:ok, path}
 
       {:error, reason} when reason in [:eexist, :eacces] ->
         open_random_file(prefix, tmp, attempts + 1)
     end
   end
 
   defp open_random_file(_prefix, tmp, attempts) do
     {:too_many_attempts, tmp, attempts}
   end
 
   defp path(prefix, tmp) do
     sec = :os.system_time(:second)
     rand = :rand.uniform(999_999_999_999)
     scheduler_id = :erlang.system_info(:scheduler_id)
     tmp <> "/" <> prefix <> "-" <> i(sec) <> "-" <> i(rand) <> "-" <> i(scheduler_id)
   end
 
   defp path_owner?(pid, path) do
     owned_paths = :ets.lookup(@path_table, pid)
     Enum.any?(owned_paths, fn {_pid, p} -> p == path end)
   end
 
   @compile {:inline, i: 1}
   defp i(integer), do: Integer.to_string(integer)
 
   @doc """
   Requests a random file to be created in the upload directory
   with the given prefix. Raises on failure.
   """
   @spec random_file!(binary) :: binary | no_return
   def random_file!(prefix) do
     case random_file(prefix) do
       {:ok, path} ->
         path
 
       {:too_many_attempts, tmp, attempts} ->
         raise Plug.UploadError,
               "tried #{attempts} times to create an uploaded file at #{tmp} but failed. " <>
                 "Set PLUG_TMPDIR to a directory with write permission"
 
       {:no_tmp, _tmps} ->
         raise Plug.UploadError,
               "could not create a tmp directory to store uploads. " <>
                 "Set PLUG_TMPDIR to a directory with write permission"
     end
   end
 
   defp plug_server do
     Process.whereis(__MODULE__) ||
       raise Plug.UploadError,
             "could not find process Plug.Upload. Have you started the :plug application?"
   end
 
   @doc false
   def start_link(_) do
     GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
   end
 
   ## Callbacks
 
   @impl true
   def init(:ok) do
     Process.flag(:trap_exit, true)
     tmp = Enum.find_value(@temp_env_vars, "/tmp", &System.get_env/1) |> Path.expand()
     cwd = Path.join(File.cwd!(), "tmp")
     :persistent_term.put(__MODULE__, [tmp, cwd])
 
     :ets.new(@dir_table, [:named_table, :public, :set])
     :ets.new(@path_table, [:named_table, :public, :duplicate_bag])
     {:ok, %{}}
   end
 
   @impl true
   def handle_call({:give_away, pid, tmp, path}, _from, state) do
     # Since we are writing in behalf of another process, we need to make sure
     # the monitor and writing to the tables happen within the same operation.
     Process.monitor(pid)
     :ets.insert_new(@dir_table, {pid, tmp})
     :ets.insert(@path_table, {pid, path})
 
     {:reply, :ok, state}
   end
 
   @impl true
   def handle_cast({:monitor, pid}, state) do
     Process.monitor(pid)
     {:noreply, state}
   end
 
   @impl true
   def handle_info({:DOWN, _ref, :process, pid, _reason}, state) do
     case :ets.lookup(@dir_table, pid) do
       [{pid, _tmp}] ->
         :ets.delete(@dir_table, pid)
 
         @path_table
         |> :ets.lookup(pid)
         |> Enum.each(&delete_path/1)
 
         :ets.delete(@path_table, pid)
 
       [] ->
         :ok
     end
 
     {:noreply, state}
   end
 
   def handle_info(_msg, state) do
     {:noreply, state}
   end
 
   @impl true
   def terminate(_reason, _state) do
     folder = fn entry, :ok -> delete_path(entry) end
     :ets.foldl(folder, :ok, @path_table)
   end
 
   defp delete_path({_pid, path}) do
     :file.delete(path)
     :ok
   end
 end