Resources fixes and improvements

- Fix getting page description
- Fix fetching metadata from Twitter (thx @marienfressinaud)
- Improve error handling

Signed-off-by: Thomas Citharel <tcit@tcit.fr>

lib/graphql/resolvers/resource.ex

@@ -118,6 +118,9 @@ defmodule Mobilizon.GraphQL.Resolvers.Resource do
            ) do
       {:ok, resource}
     else
+      {:error, _} ->
+        {:error, dgettext("errors", "Error while creating resource")}
+
       {:own_check, _} ->
         {:error, dgettext("errors", "Parent resource doesn't belong to this group")}
 
@@ -201,8 +204,12 @@ defmodule Mobilizon.GraphQL.Resolvers.Resource do
       {:ok, data} when is_map(data) ->
         {:ok, struct(Metadata, data)}
 
-      {:error, _err} ->
+      {:error, :invalid_parsed_data} ->
+        {:error, dgettext("errors", "Unable to fetch resource details from this URL.")}
+
+      {:error, err} ->
         Logger.warn("Error while fetching preview from #{inspect(resource_url)}")
+        Logger.debug(inspect(err))
         {:error, :unknown_resource}
     end
   end

lib/service/rich_media/parser.ex

@@ -57,7 +57,7 @@ defmodule Mobilizon.Service.RichMedia.Parser do
 
   @spec parse_url(String.t(), Enum.t()) :: {:ok, map()} | {:error, any()}
   defp parse_url(url, options \\ []) do
-    user_agent = Keyword.get(options, :user_agent, Config.instance_user_agent())
+    user_agent = Keyword.get(options, :user_agent, default_user_agent(url))
     headers = [{"User-Agent", user_agent}]
     Logger.debug("Fetching content at address #{inspect(url)}")
 
@@ -212,7 +212,8 @@ defmodule Mobilizon.Service.RichMedia.Parser do
   end
 
   defp check_parsed_data(data) do
-    {:error, "Found metadata was invalid or incomplete: #{inspect(data)}"}
+    Logger.debug("Found metadata was invalid or incomplete: #{inspect(data)}")
+    {:error, :invalid_parsed_data}
   end
 
   defp clean_parsed_data(data) do
@@ -293,4 +294,17 @@ defmodule Mobilizon.Service.RichMedia.Parser do
   end
 
   defp check_remote_picture_path(data), do: data
+
+  # Twitter requires a well-know crawler user-agent to show server-rendered data
+  defp default_user_agent("https://twitter.com/" <> _) do
+    "Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)"
+  end
+
+  defp default_user_agent("https://mobile.twitter.com/" <> _) do
+    "Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)"
+  end
+
+  defp default_user_agent(_url) do
+    Config.instance_user_agent()
+  end
 end

lib/service/rich_media/parsers/meta_tags_parser.ex

@@ -70,8 +70,14 @@ defmodule Mobilizon.Service.RichMedia.Parsers.MetaTagsParser do
 
   defp maybe_put_description(meta, html) when meta != %{} do
     case get_page_description(html) do
-      "" -> meta
-      description -> Map.put_new(meta, :description, description)
+      "" ->
+        meta
+
+      descriptions when is_list(descriptions) and length(descriptions) > 0 ->
+        Map.put_new(meta, :description, hd(descriptions))
+
+      description ->
+        Map.put_new(meta, :description, description)
     end
   end