From 858d528cc1b551e23850a4b65eb43e44a2a18cf4 Mon Sep 17 00:00:00 2001
From: Mark Felder <feld@feld.me>
Date: Tue, 4 Jun 2024 22:44:56 -0400
Subject: [PATCH] Allow Cowboy to stream the response instead of chunk it

---
 changelog.d/cowboy-stream-chunked.fix |  1 +
 lib/pleroma/reverse_proxy.ex          | 16 +++++++++++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)
 create mode 100644 changelog.d/cowboy-stream-chunked.fix

diff --git a/changelog.d/cowboy-stream-chunked.fix b/changelog.d/cowboy-stream-chunked.fix
new file mode 100644
index 000000000..07211bf18
--- /dev/null
+++ b/changelog.d/cowboy-stream-chunked.fix
@@ -0,0 +1 @@
+Restore Cowboy's ability to stream MediaProxy responses without Chunked encoding.
diff --git a/lib/pleroma/reverse_proxy.ex b/lib/pleroma/reverse_proxy.ex
index 4d13e51fc..8aec4ae58 100644
--- a/lib/pleroma/reverse_proxy.ex
+++ b/lib/pleroma/reverse_proxy.ex
@@ -8,7 +8,7 @@ defmodule Pleroma.ReverseProxy do
                       ~w(if-unmodified-since if-none-match) ++ @range_headers
   @resp_cache_headers ~w(etag date last-modified)
   @keep_resp_headers @resp_cache_headers ++
-                       ~w(content-type content-disposition content-encoding) ++
+                       ~w(content-length content-type content-disposition content-encoding) ++
                        ~w(content-range accept-ranges vary)
   @default_cache_control_header "public, max-age=1209600"
   @valid_resp_codes [200, 206, 304]
@@ -180,6 +180,7 @@ defmodule Pleroma.ReverseProxy do
     result =
       conn
       |> put_resp_headers(build_resp_headers(headers, opts))
+      |> streaming_compat
       |> send_chunked(status)
       |> chunk_reply(client, opts)
 
@@ -417,4 +418,17 @@ defmodule Pleroma.ReverseProxy do
 
     @cachex.put(:failed_proxy_url_cache, url, true, ttl: ttl)
   end
+
+  # When Cowboy handles a chunked response with a content-length header it streams
+  # over HTTP 1.1 instead of chunking. Bandit cannot stream over HTTP 1.1 so the header
+  # must be stripped or it breaks RFC compliance for Transfer Encoding: Chunked. RFC9112§6.2
+  #
+  # HTTP2 is always streamed for all adapters.
+  defp streaming_compat(conn) do
+    with Phoenix.Endpoint.Cowboy2Adapter <- Pleroma.Web.Endpoint.config(:adapter) do
+      conn
+    else
+      _ -> delete_resp_header(conn, "content-length")
+    end
+  end
 end