From 142dcb777f5d5a514ab35d747c6ba7c781819e7e Mon Sep 17 00:00:00 2001
From: MikaAK <mika@kalathil.me>
Date: Mon, 21 Aug 2023 23:06:29 -0400
Subject: [PATCH] fix: make sure we detect content type and set properly or
 allow it to pass through if set

---
 lib/request_cache/plug.ex | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/lib/request_cache/plug.ex b/lib/request_cache/plug.ex
index 0da3cc7..703e50d 100644
--- a/lib/request_cache/plug.ex
+++ b/lib/request_cache/plug.ex
@@ -16,6 +16,8 @@ defmodule RequestCache.Plug do
   # This is compile time so we can check quicker
   @graphql_paths RequestCache.Config.graphql_paths()
   @request_cache_header "rc-cache-status"
+  @json_regex ~r/^(\[|\{)(.*|\n)*(\]|\})$/
+  @html_regex ~r/<!DOCTYPE\s+html>/i
 
   @impl Plug
   def init(opts), do: opts
@@ -95,10 +97,23 @@ defmodule RequestCache.Plug do
     conn
     |> Plug.Conn.halt()
     |> Plug.Conn.put_resp_header(@request_cache_header, "HIT")
-    |> Plug.Conn.put_resp_content_type("application/json")
+    |> maybe_put_content_type(result)
     |> Plug.Conn.send_resp(200, result)
   end
 
+  defp maybe_put_content_type(conn, result) do
+    case Plug.Conn.get_resp_header(conn, "content-type") do
+      [_ | _] -> conn
+      [] ->
+        cond do
+          result =~ @json_regex -> Plug.Conn.put_resp_content_type(conn, "application/json")
+          result =~ @html_regex -> Plug.Conn.put_resp_content_type(conn, "text/html")
+
+          true -> conn
+        end
+    end
+  end
+
   defp rest_cache_key(%Plug.Conn{request_path: path, query_string: query_string}) do
     Util.create_key(path, query_string)
   end