Previewing proxy proof of concept

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

@@ -358,6 +358,7 @@ def render("attachment.json", %{attachment: attachment}) 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
@@ -373,7 +374,7 @@ def render("attachment.json", %{attachment: attachment}) 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 @@ def url(url) 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())
@@ -54,6 +62,17 @@ def encode_url(url) do
     build_url(sig64, base64, filename(url))
   end
 
+  def encode_preview_url(url) do
+    base64 = Base.url_encode64(url, @base64_opts)
+
+    sig64 =
+      base64
+      |> signed_url
+      |> Base.url_encode64(@base64_opts)
+
+    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
@@ -82,4 +101,17 @@ def build_url(sig_base64, url_base64, filename \\ nil) do
     |> Enum.filter(& &1)
     |> Path.join()
   end
+
+  def build_preview_url(sig_base64, url_base64, filename \\ nil) do
+    [
+      Pleroma.Config.get([:media_proxy, :base_url], Web.base_url()),
+      "proxy",
+      "preview",
+      sig_base64,
+      url_base64,
+      filename
+    ]
+    |> Enum.filter(& &1)
+    |> Path.join()
+  end
 end

lib/pleroma/web/media_proxy/media_proxy_controller.ex

@@ -27,6 +27,33 @@ def remote(conn, %{"sig" => sig64, "url" => url64} = params) do
     end
   end
 
+  def preview(conn, %{"sig" => sig64, "url" => url64} = params) do
+    with config <- Pleroma.Config.get([:media_proxy], []),
+         true <- Keyword.get(config, :enabled, false),
+         {:ok, url} <- MediaProxy.decode_url(sig64, url64),
+         :ok <- filename_matches(params, conn.request_path, url),
+         {:ok, %{body: body}} = _tesla <- Tesla.get(url) do
+      path = Mogrify.temporary_path_for(%{path: url})
+      File.write!(path, body)
+
+      Mogrify.open(path)
+      |> Mogrify.resize_to_limit("400x200")
+      |> Mogrify.save(in_place: true)
+
+      conn
+      |> send_file(200, path)
+    else
+      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_url(sig64, url64, filename))
+    end
+  end
+
   def filename_matches(%{"filename" => _} = _, path, url) do
     filename = MediaProxy.filename(url)
 

lib/pleroma/web/router.ex

@@ -640,6 +640,9 @@ defmodule Pleroma.Web.Router do
   scope "/proxy/", Pleroma.Web.MediaProxy do
     pipe_through(:remote_media)
 
+    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