From 3c384c1b7617f00a5222733e22e7b6cf7550c7fa Mon Sep 17 00:00:00 2001
From: FloatingGhost <hannah@coffee-and-dreams.uk>
Date: Wed, 20 Dec 2023 16:45:35 +0000
Subject: [PATCH] Add ratelimit backoff to HTTP get

---
 lib/pleroma/http/backoff.ex        | 21 ++++++++++++++++-----
 test/pleroma/http/backoff_test.exs | 22 +++++++++++++++++++++-
 2 files changed, 37 insertions(+), 6 deletions(-)

diff --git a/lib/pleroma/http/backoff.ex b/lib/pleroma/http/backoff.ex
index d47d2ea6b..cba6c0c17 100644
--- a/lib/pleroma/http/backoff.ex
+++ b/lib/pleroma/http/backoff.ex
@@ -9,14 +9,24 @@ defmodule Pleroma.HTTP.Backoff 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
+    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 ->
-        DateTime.utc_now()
-        |> Timex.shift(seconds: 5 * 60)
+        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)
-        stamp
+        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
 
@@ -28,7 +38,8 @@ defmodule Pleroma.HTTP.Backoff 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
+
+    case @cachex.get(@backoff_cache, host) do
       {:ok, nil} ->
         case HTTP.get(url, headers, options) do
           {:ok, env} ->
diff --git a/test/pleroma/http/backoff_test.exs b/test/pleroma/http/backoff_test.exs
index e8a571e87..b50a4c458 100644
--- a/test/pleroma/http/backoff_test.exs
+++ b/test/pleroma/http/backoff_test.exs
@@ -9,6 +9,7 @@ defmodule Pleroma.HTTP.BackoffTest 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
@@ -29,6 +30,25 @@ defmodule Pleroma.HTTP.BackoffTest do
       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
+
+    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