3 files changed, 90 insertions, 23 deletions
diff --git a/lib/pleroma/plugs/idempotency_plug.ex b/lib/pleroma/plugs/idempotency_plug.ex
new file mode 100644
index 000000000..e99c5d279
--- /dev/null
+++ b/lib/pleroma/plugs/idempotency_plug.ex
@@ -0,0 +1,84 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2019 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Plugs.IdempotencyPlug do
+  import Phoenix.Controller, only: [json: 2]
+  import Plug.Conn
+
+  @behaviour Plug
+
+  @impl true
+  def init(opts), do: opts
+
+  # Sending idempotency keys in `GET` and `DELETE` requests has no effect
+  # and should be avoided, as these requests are idempotent by definition.
+
+  @impl true
+  def call(%{method: method} = conn, _) when method in ["POST", "PUT", "PATCH"] do
+    case get_req_header(conn, "idempotency-key") do
+      [key] -> process_request(conn, key)
+      _ -> conn
+    end
+  end
+
+  def call(conn, _), do: conn
+
+  def process_request(conn, key) do
+    case Cachex.get(:idempotency_cache, key) do
+      {:ok, nil} ->
+        cache_resposnse(conn, key)
+
+      {:ok, record} ->
+        send_cached(conn, key, record)
+
+      {atom, message} when atom in [:ignore, :error] ->
+        render_error(conn, message)
+    end
+  end
+
+  defp cache_resposnse(conn, key) do
+    register_before_send(conn, fn conn ->
+      [request_id] = get_resp_header(conn, "x-request-id")
+      content_type = get_content_type(conn)
+
+      record = {request_id, content_type, conn.status, conn.resp_body}
+      {:ok, _} = Cachex.put(:idempotency_cache, key, record)
+
+      conn
+      |> put_resp_header("idempotency-key", key)
+      |> put_resp_header("x-original-request-id", request_id)
+    end)
+  end
+
+  defp send_cached(conn, key, record) do
+    {request_id, content_type, status, body} = record
+
+    conn
+    |> put_resp_header("idempotency-key", key)
+    |> put_resp_header("idempotent-replayed", "true")
+    |> put_resp_header("x-original-request-id", request_id)
+    |> put_resp_content_type(content_type)
+    |> send_resp(status, body)
+    |> halt()
+  end
+
+  defp render_error(conn, message) do
+    conn
+    |> put_status(:unprocessable_entity)
+    |> json(%{error: message})
+    |> halt()
+  end
+
+  defp get_content_type(conn) do
+    [content_type] = get_resp_header(conn, "content-type")
+
+    if String.contains?(content_type, ";") do
+      content_type
+      |> String.split(";")
+      |> hd()
+    else
+      content_type
+    end
+  end
+end
diff --git a/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex b/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex
index 9b9eca2a1..7cdba4cc0 100644
--- a/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex
+++ b/lib/pleroma/web/mastodon_api/mastodon_api_controller.ex
@@ -561,18 +561,13 @@ defmodule Pleroma.Web.MastodonAPI.MastodonAPIController do
     else
       params = Map.drop(params, ["scheduled_at"])
 
-      case get_cached_status_or_post(conn, params) do
-        {:ignore, message} ->
-          conn
-          |> put_status(422)
-          |> json(%{error: message})
-
+      case CommonAPI.post(user, params) do
         {:error, message} ->
           conn
-          |> put_status(422)
+          |> put_status(:unprocessable_entity)
           |> json(%{error: message})
 
-        {_, activity} ->
+        {:ok, activity} ->
           conn
           |> put_view(StatusView)
           |> try_render("status.json", %{activity: activity, for: user, as: :activity})
@@ -580,21 +575,6 @@ defmodule Pleroma.Web.MastodonAPI.MastodonAPIController do
     end
   end
 
-  defp get_cached_status_or_post(%{assigns: %{user: user}} = conn, params) do
-    idempotency_key =
-      case get_req_header(conn, "idempotency-key") do
-        [key] -> key
-        _ -> Ecto.UUID.generate()
-      end
-
-    Cachex.fetch(:idempotency_cache, idempotency_key, fn _ ->
-      case CommonAPI.post(user, params) do
-        {:ok, activity} -> activity
-        {:error, message} -> {:ignore, message}
-      end
-    end)
-  end
-
   def delete_status(%{assigns: %{user: user}} = conn, %{"id" => id}) do
     with {:ok, %Activity{}} <- CommonAPI.delete(id, user) do
       json(conn, %{})
diff --git a/lib/pleroma/web/router.ex b/lib/pleroma/web/router.ex
index c504116b6..055289dc5 100644
--- a/lib/pleroma/web/router.ex
+++ b/lib/pleroma/web/router.ex
@@ -27,6 +27,7 @@ defmodule Pleroma.Web.Router do
     plug(Pleroma.Plugs.UserEnabledPlug)
     plug(Pleroma.Plugs.SetUserSessionIdPlug)
     plug(Pleroma.Plugs.EnsureUserKeyPlug)
+    plug(Pleroma.Plugs.IdempotencyPlug)
   end
 
   pipeline :authenticated_api do
@@ -41,6 +42,7 @@ defmodule Pleroma.Web.Router do
     plug(Pleroma.Plugs.UserEnabledPlug)
     plug(Pleroma.Plugs.SetUserSessionIdPlug)
     plug(Pleroma.Plugs.EnsureAuthenticatedPlug)
+    plug(Pleroma.Plugs.IdempotencyPlug)
   end
 
   pipeline :admin_api do
@@ -57,6 +59,7 @@ defmodule Pleroma.Web.Router do
     plug(Pleroma.Plugs.SetUserSessionIdPlug)
     plug(Pleroma.Plugs.EnsureAuthenticatedPlug)
     plug(Pleroma.Plugs.UserIsAdminPlug)
+    plug(Pleroma.Plugs.IdempotencyPlug)
   end
 
   pipeline :mastodon_html do