always discard already seen packets

lib/floof/distributor.ex

@@ -60,21 +60,28 @@ defmodule Floof.Distributor do
 
   @impl true
   def handle_cast({:xfer, {origin, dcdhash, dcd, attrs}}, state) do
-    if check_incoming(dstate(state, :fconf), dcd, attrs) do
+    # we split the state such that only the parts necessary get
+    # copied into the spawned-off process
+    fconf = dstate(state, :fconf)
+
+    if check_incoming(fconf, dcdhash, dcd, attrs) do
+      trgs = MapSet.delete(dstate(state, :trgs), origin)
+      Floof.DistributorSeen.mark_seen(dcdhash)
+
+      # spawn a separate process to avoid blocking the queue
+      # we only block the queue above for the check + seen marker
       spawn_link(fn ->
         {:XferBlob, source, ttl, old_markers, signature, data} = dcd
-        set_markers = fconfig(dstate(state, :fconf), :set_markers)
+        set_markers = fconfig(fconf, :set_markers)
         new_markers = Enum.uniq(set_markers ++ old_markers)
         dcd2 = {:XferBlob, source, ttl, new_markers, signature, data}
 
-        for trg <- MapSet.delete(dstate(state, :trgs), origin) do
+        for trg <- trgs do
           send(trg, {:fwdxfer, {dcdhash, dcd2}})
         end
 
         Floof.SessionManager.set_for_all(dcdhash, dcd2, origin)
       end)
-
-      Floof.DistributorSeen.mark_seen(dcdhash)
     end
 
     {:noreply, state}
@@ -85,7 +92,7 @@ defmodule Floof.Distributor do
     {:noreply, dstate(state, trgs: MapSet.delete(dstate(state, :trgs), pid))}
   end
 
-  defp check_incoming(fconf, dcd, attrs) do
+  defp check_incoming(fconf, dcdhash, dcd, attrs) do
     {:XferBlob, source, ttl, _, {:Signature, sigalgo, sigval}, xfinner} = dcd
 
     case sigalgo do
@@ -94,6 +101,10 @@ defmodule Floof.Distributor do
         case get_pubkey(fconf, source) do
           {:ok, :ed25519, pubkey} ->
             cond do
+              Floof.DistributorSeen.have_we(dcdhash) ->
+                # we can ignore this packet, its content was already processed
+                false
+
               not :enacl.sign_verify_detached(sigval, xfinner, pubkey) ->
                 Logger.error("packet signature invalid for #{inspect(xfinner)}")
                 false