From 2f97c28add27dcc6c3d26fd65323f0a0f3f77fe8 Mon Sep 17 00:00:00 2001
From: Alain Zscheile <zseri.devel@ytrizja.de>
Date: Thu, 24 Nov 2022 01:33:43 +0100
Subject: [PATCH] allow subscribing to sessions

---
 asn1/FloofProtocol.asn1      |  9 +++++++--
 lib/floof.ex                 | 31 +++++++++++++++++++++++++++----
 lib/floof/session_manager.ex | 28 ++++++++++++++++++++++++----
 3 files changed, 58 insertions(+), 10 deletions(-)

diff --git a/asn1/FloofProtocol.asn1 b/asn1/FloofProtocol.asn1
index 9bcfcd3..052546e 100644
--- a/asn1/FloofProtocol.asn1
+++ b/asn1/FloofProtocol.asn1
@@ -60,6 +60,10 @@ XferBlob ::= SEQUENCE {
   data      OCTET STRING
 }
 
+SessionModify ::= CHOICE {
+  attach [0] OCTET STRING
+}
+
 SummaryDirection ::= ENUMERATED {
   pull (0),
   rejectpush (1),
@@ -72,8 +76,9 @@ Summary    ::= SEQUENCE {
 }
 
 ProtoMessage ::= CHOICE {
-  summary   [0] Summary,
-  xfer      [1] XferBlob
+  session   [0] SessionModify,
+  summary   [1] Summary,
+  xfer      [2] XferBlob
 }
 
 END
diff --git a/lib/floof.ex b/lib/floof.ex
index f095b0f..870bc1e 100644
--- a/lib/floof.ex
+++ b/lib/floof.ex
@@ -31,8 +31,8 @@ defmodule Floof do
     receive do
       {:tcp, _, message} ->
         {:ok, dcd} = :FloofProtocol.decode(:ProtoMessage, message)
-        backlog2 = handle_incoming(client, backlog, dcd)
-        serve(client, backlog2)
+        backlog = handle_incoming(client, backlog, dcd)
+        serve(client, backlog)
       {:fwdxfer, dcdmessage} ->
         dcdid = get_xfer_id dcdmessage
         handle_outgoing(client, dcdid)
@@ -42,6 +42,14 @@ defmodule Floof do
         {:ok, encd} = :FloofProtocol.encode(:ProtoMessage, {:summary, dat})
         :ok = client.send(encd)
         serve(client, backlog)
+      {:SessionPushed, key} ->
+        {backlog, added_ids} = extract_backlog(key, backlog, [])
+        for id <- added_ids do
+          dat = {:Summary, :requestpull, id}
+          {:ok, encd} = :FloofProtocol.encode(:ProtoMessage, {:summary, dat})
+          :ok = client.send(encd)
+        end
+        serve(client, backlog)
       x -> Logger.warn("unable to handle request: #{inspect(x)}")
         serve(client, backlog)
     end
@@ -50,10 +58,17 @@ defmodule Floof do
   defp handle_incoming(client, backlog, dcd) do
     Logger.debug("got packet #{inspect(dcd)}")
     case dcd do
+      {:session, {:SessionModify, {:attach, key}}} ->
+        if Floof.SessionManager.attach(key, self()) do
+          send self(), {:SessionPushed, key}
+          backlog
+        else
+          backlog
+        end
       {:summary, {:Summary, direction, id}} ->
         case direction do
           :requestpull ->
-            send(Floof.Distributor, {:havewe, self(), id})
+            send Floof.Distributor, {:havewe, self(), id}
             backlog
           :pull ->
             case List.keytake(backlog, id, 0) do
@@ -67,7 +82,7 @@ defmodule Floof do
             List.keydelete(backlog, id, 0)
         end
       {:xfer, xf} ->
-        send(Floof.Distributor, xf)
+        send Floof.Distributor, xf
         backlog
     end
   end
@@ -82,4 +97,12 @@ defmodule Floof do
     {:ok, {:XferInner, id, _, _, _, _}} = :FloofProtocol.decode(:XferInner, xfinner)
     id
   end
+
+  defp extract_backlog(key, backlog, added_ids) do
+    case Floof.SessionManager.pop(key) do
+      :empty -> {backlog, added_ids}
+      {:value, {id, entry}} ->
+        extract_backlog(key, [{id, entry} | backlog], [id | added_ids])
+    end
+  end
 end
diff --git a/lib/floof/session_manager.ex b/lib/floof/session_manager.ex
index b7d4852..59302a6 100644
--- a/lib/floof/session_manager.ex
+++ b/lib/floof/session_manager.ex
@@ -5,11 +5,23 @@ defmodule Floof.SessionManager do
     Agent.start_link(fn -> initial_value end, name: __MODULE__)
   end
 
+  def attach(key, pid) do
+    Agent.get_and_update(__MODULE__, fn state ->
+      Map.get_and_update(state, key, fn q ->
+        {_, q2} = entry_dfl(q)
+        {:queue.is_empty(q2), {pid, q2}}
+      end)
+    end)
+  end
+
   def push(key, value) do
     Agent.cast(__MODULE__, fn state ->
-      {_, state2} = Map.get_and_update(state, key, fn q ->
-        q2 = if q == nil do :queue.new() else q end
-        {nil, :queue.cons(value, q2)} end)
+      {sub, state2} = Map.get_and_update(state, key, fn q ->
+        {sub, q2} = entry_dfl(q)
+        {sub, {sub, :queue.cons(value, q2)}} end)
+      if sub != nil do
+        send(sub, {:SessionPushed, key})
+      end
       state2
     end)
   end
@@ -17,7 +29,11 @@ defmodule Floof.SessionManager do
   def pop(key) do
     Agent.get_and_update(__MODULE__, fn state ->
       {tmp, state} = Map.get_and_update(state, key, fn q ->
-        if q == nil do :pop else :queue.out_r(q) end
+        if q == nil do :pop else
+          {sub, q2} = q
+          {got, q3} = :queue.out_r(q2)
+          {got, {sub, q3}}
+        end
       end)
       retval = case tmp do
         nil -> :empty
@@ -26,4 +42,8 @@ defmodule Floof.SessionManager do
       {retval, state}
     end, :infinity)
   end
+
+  defp entry_dfl(got) do
+    if got == nil do {nil, :queue.new()} else got end
+  end
 end