CHANGELOG.md

@@ -35,6 +35,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Issue leading to Mastodon bot accounts being rejected
 - Scope misdetection of remote posts resulting from not recognising
   JSON-LD-compacted forms of public scope; affected e.g. federation with bovine
+- Ratelimits encountered when fetching objects are now respected; 429 responses will cause a backoff when we get one.
 
 ## Removed
 - ActivityPub Client-To-Server write API endpoints have been disabled;

lib/pleroma/application.ex

@@ -179,7 +179,8 @@ defp cachex_children do
       build_cachex("translations", default_ttl: :timer.hours(24 * 30), limit: 2500),
       build_cachex("instances", default_ttl: :timer.hours(24), ttl_interval: 1000, limit: 2500),
       build_cachex("request_signatures", default_ttl: :timer.hours(24 * 30), limit: 3000),
-      build_cachex("rel_me", default_ttl: :timer.hours(24 * 30), limit: 300)
+      build_cachex("rel_me", default_ttl: :timer.hours(24 * 30), limit: 300),
+      build_cachex("http_backoff", default_ttl: :timer.hours(24 * 30), limit: 10000)
     ]
   end
 

lib/pleroma/http/backoff.ex

@@ -0,0 +1,121 @@
+defmodule Pleroma.HTTP.Backoff do
+  alias Pleroma.HTTP
+  require Logger
+
+  @cachex Pleroma.Config.get([:cachex, :provider], Cachex)
+  @backoff_cache :http_backoff_cache
+
+  # attempt to parse a timestamp from a header
+  # returns nil if it can't parse the timestamp
+  @spec timestamp_or_nil(binary) :: DateTime.t() | nil
+  defp timestamp_or_nil(header) do
+    case DateTime.from_iso8601(header) do
+      {:ok, stamp, _} ->
+        stamp
+
+      _ ->
+        nil
+    end
+  end
+
+  # attempt to parse the x-ratelimit-reset header from the headers
+  @spec x_ratelimit_reset(headers :: list) :: DateTime.t() | nil
+  defp x_ratelimit_reset(headers) do
+    with {_header, value} <- List.keyfind(headers, "x-ratelimit-reset", 0),
+         true <- is_binary(value) do
+      timestamp_or_nil(value)
+    else
+      _ ->
+        nil
+    end
+  end
+
+  # attempt to parse the Retry-After header from the headers
+  # this can be either a timestamp _or_ a number of seconds to wait!
+  # we'll return a datetime if we can parse it, or nil if we can't
+  @spec retry_after(headers :: list) :: DateTime.t() | nil
+  defp retry_after(headers) do
+    with {_header, value} <- List.keyfind(headers, "retry-after", 0),
+         true <- is_binary(value) do
+      # first, see if it's an integer
+      case Integer.parse(value) do
+        {seconds, ""} ->
+          Logger.debug("Parsed Retry-After header: #{seconds} seconds")
+          DateTime.utc_now() |> Timex.shift(seconds: seconds)
+
+        _ ->
+          # if it's not an integer, try to parse it as a timestamp
+          timestamp_or_nil(value)
+      end
+    else
+      _ ->
+        nil
+    end
+  end
+
+  # given a set of headers, will attempt to find the next backoff timestamp
+  # if it can't find one, it will default to 5 minutes from now
+  @spec next_backoff_timestamp(%{headers: list}) :: DateTime.t()
+  defp next_backoff_timestamp(%{headers: headers}) when is_list(headers) do
+    default_5_minute_backoff =
+      DateTime.utc_now()
+      |> Timex.shift(seconds: 5 * 60)
+
+    backoff =
+      [&x_ratelimit_reset/1, &retry_after/1]
+      |> Enum.map(& &1.(headers))
+      |> Enum.find(&(&1 != nil))
+
+    if is_nil(backoff) do
+      Logger.debug("No backoff headers found, defaulting to 5 minutes from now")
+      default_5_minute_backoff
+    else
+      Logger.debug("Found backoff header, will back off until: #{backoff}")
+      backoff
+    end
+  end
+
+  defp next_backoff_timestamp(_), do: DateTime.utc_now() |> Timex.shift(seconds: 5 * 60)
+
+  # utility function to check the HTTP response for potential backoff headers
+  # will check if we get a 429 or 503 response, and if we do, will back off for a bit
+  @spec check_backoff({:ok | :error, HTTP.Env.t()}, binary()) ::
+          {:ok | :error, HTTP.Env.t()} | {:error, :ratelimit}
+  defp check_backoff({:ok, env}, host) do
+    case env.status do
+      status when status in [429, 503] ->
+        Logger.error("Rate limited on #{host}! Backing off...")
+        timestamp = next_backoff_timestamp(env)
+        ttl = Timex.diff(timestamp, DateTime.utc_now(), :seconds)
+        # we will cache the host for 5 minutes
+        @cachex.put(@backoff_cache, host, true, ttl: ttl)
+        {:error, :ratelimit}
+
+      _ ->
+        {:ok, env}
+    end
+  end
+
+  defp check_backoff(env, _), do: env
+
+  @doc """
+  this acts as a single throughput for all GET requests
+  we will check if the host is in the cache, and if it is, we will automatically fail the request
+  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!
+  """
+  @spec get(binary, list, list) :: {:ok | :error, HTTP.Env.t()} | {:error, :ratelimit}
+  def get(url, headers \\ [], options \\ []) do
+    %{host: host} = URI.parse(url)
+
+    case @cachex.get(@backoff_cache, host) do
+      {:ok, nil} ->
+        url
+        |> HTTP.get(headers, options)
+        |> check_backoff(host)
+
+      _ ->
+        {:error, :ratelimit}
+    end
+  end
+end

lib/pleroma/object/fetcher.ex

@@ -354,7 +354,7 @@ def get_object(id) do
 
     with {:ok, %{body: body, status: code, headers: headers, url: final_url}}
          when code in 200..299 <-
-           HTTP.get(id, headers),
+           HTTP.Backoff.get(id, headers),
          remote_host <-
            URI.parse(final_url).host,
          {:cross_domain_redirect, false} <-

lib/pleroma/web/web_finger.ex

@@ -160,7 +160,8 @@ def find_lrdd_template(domain) do
     # WebFinger is restricted to HTTPS - https://tools.ietf.org/html/rfc7033#section-9.1
     meta_url = "https://#{domain}/.well-known/host-meta"
 
-    with {:ok, %{status: status, body: body}} when status in 200..299 <- HTTP.get(meta_url) do
+    with {:ok, %{status: status, body: body}} when status in 200..299 <-
+           HTTP.Backoff.get(meta_url) do
       get_template_from_xml(body)
     else
       error ->
@@ -197,7 +198,7 @@ def finger(account) do
 
     with address when is_binary(address) <- get_address_from_domain(domain, encoded_account),
          {:ok, %{status: status, body: body, headers: headers}} when status in 200..299 <-
-           HTTP.get(
+           HTTP.Backoff.get(
              address,
              [{"accept", "application/xrd+xml,application/jrd+json"}]
            ) do

test/pleroma/http/backoff_test.exs

@@ -0,0 +1,105 @@
+defmodule Pleroma.HTTP.BackoffTest do
+  @backoff_cache :http_backoff_cache
+  use Pleroma.DataCase, async: false
+  alias Pleroma.HTTP.Backoff
+
+  defp within_tolerance?(ttl, expected) do
+    ttl > expected - 10 and ttl < expected + 10
+  end
+
+  describe "get/3" do
+    test "should return {:ok, env} when not rate limited" do
+      Tesla.Mock.mock_global(fn
+        %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
+
+    test "should return {:error, env} when rate limited" do
+      # Shove a value into the cache to simulate a rate limit
+      Cachex.put(@backoff_cache, "akkoma.dev", true)
+      assert {:error, :ratelimit} = Backoff.get("https://akkoma.dev/api/v1/instance")
+    end
+
+    test "should insert a value into the cache when rate limited" do
+      Tesla.Mock.mock_global(fn
+        %Tesla.Env{url: "https://ratelimited.dev/api/v1/instance"} ->
+          {:ok, %Tesla.Env{status: 429, body: "Rate limited"}}
+      end)
+
+      assert {:error, :ratelimit} = Backoff.get("https://ratelimited.dev/api/v1/instance")
+      assert {:ok, true} = Cachex.get(@backoff_cache, "ratelimited.dev")
+    end
+
+    test "should insert a value into the cache when rate limited with a 503 response" do
+      Tesla.Mock.mock_global(fn
+        %Tesla.Env{url: "https://ratelimited.dev/api/v1/instance"} ->
+          {:ok, %Tesla.Env{status: 503, body: "Rate limited"}}
+      end)
+
+      assert {:error, :ratelimit} = Backoff.get("https://ratelimited.dev/api/v1/instance")
+      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, :ratelimit} = Backoff.get("https://ratelimited.dev/api/v1/instance")
+      assert {:ok, true} = Cachex.get(@backoff_cache, "ratelimited.dev")
+      {:ok, ttl} = Cachex.ttl(@backoff_cache, "ratelimited.dev")
+      assert within_tolerance?(ttl, 600)
+    end
+
+    test "should parse the value of retry-after when it's a timestamp" 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: [{"retry-after", ten_minutes_from_now}]
+           }}
+      end)
+
+      assert {:error, :ratelimit} = Backoff.get("https://ratelimited.dev/api/v1/instance")
+      assert {:ok, true} = Cachex.get(@backoff_cache, "ratelimited.dev")
+      {:ok, ttl} = Cachex.ttl(@backoff_cache, "ratelimited.dev")
+      assert within_tolerance?(ttl, 600)
+    end
+
+    test "should parse the value of retry-after when it's a number of seconds" do
+      Tesla.Mock.mock_global(fn
+        %Tesla.Env{url: "https://ratelimited.dev/api/v1/instance"} ->
+          {:ok,
+           %Tesla.Env{
+             status: 429,
+             body: "Rate limited",
+             headers: [{"retry-after", "600"}]
+           }}
+      end)
+
+      assert {:error, :ratelimit} = Backoff.get("https://ratelimited.dev/api/v1/instance")
+      assert {:ok, true} = Cachex.get(@backoff_cache, "ratelimited.dev")
+      # assert that the value is 10 minutes from now
+      {:ok, ttl} = Cachex.ttl(@backoff_cache, "ratelimited.dev")
+      assert within_tolerance?(ttl, 600)
+    end
+  end
+end