From 355d5591952b6ce7f8e1e78d95601bebb38ef372 Mon Sep 17 00:00:00 2001
From: Alain Zscheile <zseri.devel@ytrizja.de>
Date: Sun, 27 Nov 2022 21:52:41 +0100
Subject: [PATCH] coalesce drop notifications

---
 lib/floof.ex | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/lib/floof.ex b/lib/floof.ex
index 3dd95eb..2ae8e06 100644
--- a/lib/floof.ex
+++ b/lib/floof.ex
@@ -94,6 +94,11 @@ defmodule Floof do
 
           {backlog, sesskey}
 
+        {:fwddrop, dcdhash} ->
+          to_drop = coalesce_fwddrops(MapSet.new(dcdhash))
+          :ok = send_summary(client, :drop, to_drop)
+          {backlog, sesskey}
+
         {:SessionPushed, sesskey} ->
           sesskeys = coalesce_sesspushes([sesskey])
           [sesskey | _] = sesskeys
@@ -180,9 +185,9 @@ defmodule Floof do
 
       {:xfer, xf} ->
         mhash = Floof.Message.emit(xf)
-        # notify the remote end that we successfully consumed the message
-        # non-fatal if this fails
-        send_summary(client, :drop, [mhash])
+        # the following indirection is necessary
+        # to reduce the amount of 'drop' notifications
+        send(self(), {:fwddrop, mhash})
         {backlog, sesskey}
     end
   end
@@ -210,6 +215,14 @@ defmodule Floof do
     end
   end
 
+  defp coalesce_fwddrops(to_drop) do
+    receive do
+      {:fwddrop, dcdhash} -> coalesce_fwddrops(MapSet.put(to_drop, dcdhash))
+    after
+      10 -> to_drop
+    end
+  end
+
   defp partition_hashes(xs) do
     xs
     |> Floof.DistributorSeen.have_we_multi()