Add ratelimit backoff to HTTP get

lib/pleroma/http/backoff.ex

@@ -9,14 +9,24 @@ defp next_backoff_timestamp(%{headers: headers}) when is_list(headers) do
     # figure out from the 429 response when we can make the next request
     # mastodon uses the x-ratelimit-reset header, so we will use that!
     # other servers may not, so we'll default to 5 minutes from now if we can't find it
-    case Enum.find_value(headers, fn {"x-ratelimit-reset", value} -> value end) do
-      nil ->
+    default_5_minute_backoff =
       DateTime.utc_now()
       |> Timex.shift(seconds: 5 * 60)
 
+    case Enum.find_value(headers, fn {"x-ratelimit-reset", value} -> value end) do
+      nil ->
+        Logger.error("Rate limited, but couldn't find timestamp! Using default 5 minute backoff until #{default_5_minute_backoff}")
+        default_5_minute_backoff
+
       value ->
-        {:ok, stamp} = DateTime.from_iso8601(value)
+        with {:ok, stamp, _} <- DateTime.from_iso8601(value) do
+          Logger.error("Rate limited until #{stamp}")
           stamp
+        else
+          _ ->
+            Logger.error("Rate limited, but couldn't parse timestamp! Using default 5 minute backoff until #{default_5_minute_backoff}")
+            default_5_minute_backoff
+        end
     end
   end
 
@@ -28,6 +38,7 @@ def get(url, headers \\ [], options \\ []) do
     # this ensures that we don't hammer the server with requests, and instead wait for the backoff to expire
     # this is a very simple implementation, and can be improved upon!
     %{host: host} = URI.parse(url)
+
     case @cachex.get(@backoff_cache, host) do
       {:ok, nil} ->
         case HTTP.get(url, headers, options) do
@@ -49,6 +60,7 @@ def get(url, headers \\ [], options \\ []) do
         end
 
       _ ->
+        Logger.error("Request not made to #{host} because we are rate limited!")
         {:error, %Tesla.Env{status: 429, body: "Rate limited (internal backoff)"}}
     end
   end

test/pleroma/http/backoff_test.exs

@@ -9,6 +9,7 @@ test "should return {:ok, env} when not rate limited" do
         %Tesla.Env{url: "https://akkoma.dev/api/v1/instance"} ->
           {:ok, %Tesla.Env{status: 200, body: "ok"}}
       end)
+
       assert {:ok, env} = Backoff.get("https://akkoma.dev/api/v1/instance")
       assert env.status == 200
     end
@@ -30,5 +31,24 @@ test "should insert a value into the cache when rate limited" do
       assert env.status == 429
       assert {:ok, true} = Cachex.get(@backoff_cache, "ratelimited.dev")
     end
+
+    test "should parse the value of x-ratelimit-reset, if present" do
+      ten_minutes_from_now =
+        DateTime.utc_now() |> Timex.shift(minutes: 10) |> DateTime.to_iso8601()
+
+      Tesla.Mock.mock_global(fn
+        %Tesla.Env{url: "https://ratelimited.dev/api/v1/instance"} ->
+          {:ok,
+           %Tesla.Env{
+             status: 429,
+             body: "Rate limited",
+             headers: [{"x-ratelimit-reset", ten_minutes_from_now}]
+           }}
+      end)
+
+      assert {:error, env} = Backoff.get("https://ratelimited.dev/api/v1/instance")
+      assert env.status == 429
+      assert {:ok, true} = Cachex.get(@backoff_cache, "ratelimited.dev")
+    end
   end
 end