Initial implementation of image preview proxy. Media proxy tests refactoring.

lib/pleroma/helpers/mogrify_helper.ex

@@ -0,0 +1,25 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Helpers.MogrifyHelper do
+  @moduledoc """
+  Handles common Mogrify operations.
+  """
+
+  @spec store_as_temporary_file(String.t(), binary()) :: {:ok, String.t()} | {:error, atom()}
+  @doc "Stores binary content fetched from specified URL as a temporary file."
+  def store_as_temporary_file(url, body) do
+    path = Mogrify.temporary_path_for(%{path: url})
+    with :ok <- File.write(path, body), do: {:ok, path}
+  end
+
+  @spec store_as_temporary_file(String.t(), String.t()) :: Mogrify.Image.t() | any()
+  @doc "Modifies file at specified path by resizing to specified limit dimensions."
+  def in_place_resize_to_limit(path, resize_dimensions) do
+    path
+    |> Mogrify.open()
+    |> Mogrify.resize_to_limit(resize_dimensions)
+    |> Mogrify.save(in_place: true)
+  end
+end

lib/pleroma/web/mastodon_api/views/status_view.ex

@@ -419,6 +419,7 @@ defmodule Pleroma.Web.MastodonAPI.StatusView do
     [attachment_url | _] = attachment["url"]
     media_type = attachment_url["mediaType"] || attachment_url["mimeType"] || "image"
     href = attachment_url["href"] |> MediaProxy.url()
+    href_preview = attachment_url["href"] |> MediaProxy.preview_url()
 
     type =
       cond do
@@ -434,7 +435,7 @@ defmodule Pleroma.Web.MastodonAPI.StatusView do
       id: to_string(attachment["id"] || hash_id),
       url: href,
       remote_url: href,
-      preview_url: href,
+      preview_url: href_preview,
       text_url: href,
       type: type,
       description: attachment["name"],

lib/pleroma/web/media_proxy/media_proxy.ex

@@ -20,6 +20,14 @@ defmodule Pleroma.Web.MediaProxy do
     end
   end
 
+  def preview_url(url) do
+    if disabled?() or whitelisted?(url) do
+      url
+    else
+      encode_preview_url(url)
+    end
+  end
+
   defp disabled?, do: !Config.get([:media_proxy, :enabled], false)
 
   defp local?(url), do: String.starts_with?(url, Pleroma.Web.base_url())
@@ -43,17 +51,29 @@ defmodule Pleroma.Web.MediaProxy do
     end)
   end
 
-  def encode_url(url) do
+  defp base64_sig64(url) do
     base64 = Base.url_encode64(url, @base64_opts)
 
     sig64 =
       base64
-      |> signed_url
+      |> signed_url()
       |> Base.url_encode64(@base64_opts)
 
+    {base64, sig64}
+  end
+
+  def encode_url(url) do
+    {base64, sig64} = base64_sig64(url)
+
     build_url(sig64, base64, filename(url))
   end
 
+  def encode_preview_url(url) do
+    {base64, sig64} = base64_sig64(url)
+
+    build_preview_url(sig64, base64, filename(url))
+  end
+
   def decode_url(sig, url) do
     with {:ok, sig} <- Base.url_decode64(sig, @base64_opts),
          signature when signature == sig <- signed_url(url) do
@@ -71,10 +91,10 @@ defmodule Pleroma.Web.MediaProxy do
     if path = URI.parse(url_or_path).path, do: Path.basename(path)
   end
 
-  def build_url(sig_base64, url_base64, filename \\ nil) do
+  defp proxy_url(path, sig_base64, url_base64, filename) do
     [
       Pleroma.Config.get([:media_proxy, :base_url], Web.base_url()),
-      "proxy",
+      path,
       sig_base64,
       url_base64,
       filename
@@ -82,4 +102,29 @@ defmodule Pleroma.Web.MediaProxy do
     |> Enum.filter(& &1)
     |> Path.join()
   end
+
+  def build_url(sig_base64, url_base64, filename \\ nil) do
+    proxy_url("proxy", sig_base64, url_base64, filename)
+  end
+
+  def build_preview_url(sig_base64, url_base64, filename \\ nil) do
+    proxy_url("proxy/preview", sig_base64, url_base64, filename)
+  end
+
+  def filename_matches(%{"filename" => _} = _, path, url) do
+    filename = filename(url)
+
+    if filename && not basename_matches?(path, filename) do
+      {:wrong_filename, filename}
+    else
+      :ok
+    end
+  end
+
+  def filename_matches(_, _, _), do: :ok
+
+  defp basename_matches?(path, filename) do
+    basename = Path.basename(path)
+    basename == filename or URI.decode(basename) == filename or URI.encode(basename) == filename
+  end
 end

lib/pleroma/web/media_proxy/media_proxy_controller.ex

@@ -5,19 +5,21 @@
 defmodule Pleroma.Web.MediaProxy.MediaProxyController do
   use Pleroma.Web, :controller
 
+  alias Pleroma.Config
+  alias Pleroma.Helpers.MogrifyHelper
   alias Pleroma.ReverseProxy
   alias Pleroma.Web.MediaProxy
 
   @default_proxy_opts [max_body_length: 25 * 1_048_576, http: [follow_redirect: true]]
 
   def remote(conn, %{"sig" => sig64, "url" => url64} = params) do
-    with config <- Pleroma.Config.get([:media_proxy], []),
-         true <- Keyword.get(config, :enabled, false),
+    with config <- Config.get([:media_proxy], []),
+         {_, true} <- {:enabled, Keyword.get(config, :enabled, false)},
          {:ok, url} <- MediaProxy.decode_url(sig64, url64),
-         :ok <- filename_matches(params, conn.request_path, url) do
+         :ok <- MediaProxy.filename_matches(params, conn.request_path, url) do
       ReverseProxy.call(conn, url, Keyword.get(config, :proxy_opts, @default_proxy_opts))
     else
-      false ->
+      {:enabled, false} ->
         send_resp(conn, 404, Plug.Conn.Status.reason_phrase(404))
 
       {:error, :invalid_signature} ->
@@ -28,20 +30,68 @@ defmodule Pleroma.Web.MediaProxy.MediaProxyController do
     end
   end
 
-  def filename_matches(%{"filename" => _} = _, path, url) do
-    filename = MediaProxy.filename(url)
-
-    if filename && does_not_match(path, filename) do
-      {:wrong_filename, filename}
+  def preview(conn, %{"sig" => sig64, "url" => url64} = params) do
+    with {_, true} <- {:enabled, Config.get([:media_preview_proxy, :enabled], false)},
+         {:ok, url} <- MediaProxy.decode_url(sig64, url64),
+         :ok <- MediaProxy.filename_matches(params, conn.request_path, url) do
+      handle_preview(conn, url)
     else
-      :ok
+      {:enabled, false} ->
+        send_resp(conn, 404, Plug.Conn.Status.reason_phrase(404))
+
+      {:error, :invalid_signature} ->
+        send_resp(conn, 403, Plug.Conn.Status.reason_phrase(403))
+
+      {:wrong_filename, filename} ->
+        redirect(conn, external: MediaProxy.build_preview_url(sig64, url64, filename))
     end
   end
 
-  def filename_matches(_, _, _), do: :ok
+  defp handle_preview(conn, url) do
+    with {:ok, %{status: status} = head_response} when status in 200..299 <- Tesla.head(url),
+         {_, true} <- {:acceptable_content_length, acceptable_body_length?(head_response)} do
+      content_type = Tesla.get_header(head_response, "content-type")
+      handle_preview(content_type, conn, url)
+    else
+      {_, %{status: status}} ->
+        send_resp(conn, :failed_dependency, "Can't fetch HTTP headers (HTTP #{status}).")
 
-  defp does_not_match(path, filename) do
-    basename = Path.basename(path)
-    basename != filename and URI.decode(basename) != filename and URI.encode(basename) != filename
+      {:acceptable_content_length, false} ->
+        send_resp(conn, :unprocessable_entity, "Source file size exceeds limit.")
+    end
+  end
+
+  defp handle_preview("image/" <> _, %{params: params} = conn, url) do
+    with {:ok, %{status: status, body: body}} when status in 200..299 <- Tesla.get(url),
+         {:ok, path} <- MogrifyHelper.store_as_temporary_file(url, body),
+         resize_dimensions <-
+           Map.get(
+             params,
+             "limit_dimensions",
+             Config.get([:media_preview_proxy, :limit_dimensions])
+           ),
+         %Mogrify.Image{} <- MogrifyHelper.in_place_resize_to_limit(path, resize_dimensions) do
+      send_file(conn, 200, path)
+    else
+      {_, %{status: _}} ->
+        send_resp(conn, :failed_dependency, "Can't fetch the image.")
+
+      _ ->
+        send_resp(conn, :failed_dependency, "Can't handle image preview.")
+    end
+  end
+
+  defp handle_preview(content_type, conn, _url) do
+    send_resp(conn, :unprocessable_entity, "Unsupported content type: #{content_type}.")
+  end
+
+  defp acceptable_body_length?(head_response) do
+    max_body_length = Config.get([:media_preview_proxy, :max_body_length], nil)
+    content_length = Tesla.get_header(head_response, "content-length")
+    content_length = with {int, _} <- Integer.parse(content_length), do: int
+
+    content_length == :error or
+      max_body_length in [nil, :infinity] or
+      content_length <= max_body_length
   end
 end

lib/pleroma/web/router.ex

@@ -663,6 +663,8 @@ defmodule Pleroma.Web.Router do
   end
 
   scope "/proxy/", Pleroma.Web.MediaProxy do
+    get("/preview/:sig/:url", MediaProxyController, :preview)
+    get("/preview/:sig/:url/:filename", MediaProxyController, :preview)
     get("/:sig/:url", MediaProxyController, :remote)
     get("/:sig/:url/:filename", MediaProxyController, :remote)
   end