From bb290ab7cbd6af7b38de87e89c0906f65ec2c631 Mon Sep 17 00:00:00 2001
From: Kevin Matz <kevin@company235.com>
Date: Sat, 28 Aug 2021 12:23:20 -0400
Subject: [PATCH] validate incoming sequence number

---
 protocols/sacn/receiver.cpp | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/protocols/sacn/receiver.cpp b/protocols/sacn/receiver.cpp
index c6430fa..93ef31a 100644
--- a/protocols/sacn/receiver.cpp
+++ b/protocols/sacn/receiver.cpp
@@ -26,6 +26,8 @@
 #include "receiver.h"
 #include "config.h"
 
+#include <limits>
+
 namespace sACN {
 
 /**
@@ -220,6 +222,29 @@ void Receiver::dataFrameHandler(ACN::PDU::Message<DATA::Pdu> frame) {
   if (source->sync_address != 0)
       subscribe(source->sync_address);
 
+  /// > \cite sACN 6.2.5 E1.31 Data Packet: Sequence Number
+  /// > In a routed network environment it is possible for packets to be
+  /// > received in a different order to the one in which they were sent. The
+  /// > sequence number allows receivers or diagnostic equipment to detect out
+  /// > of sequence or lost packets.
+  /// Assume that sources transmitting a sequence number of 0 do not support
+  /// sequencing.
+  if (source->sequence_number != 0 && universe->provenance())
+    {
+      auto seq = source->sequence_number;
+      auto old = universe->provenance()->sequence_number;
+      auto hasWrapped = [seq, old] () {
+          auto threshold = std::numeric_limits<typeof(old)>::max() * 0.9;
+          if (seq < old && old > threshold)
+            return true;
+          return false;
+        };
+      if (seq != old + 1)
+        ; // missed packet!
+      if (seq <= old && !hasWrapped())
+        return; // out of sequence packet!
+    }
+
   // PDU data will be a block of DMP
   auto block = static_cast<ACN::PDU::Block<ACN::DMP::Pdu>*>(frame->data());
   for (auto const &dmp : *block->pdu)