From 6a71074b4b8998dac41022fa4619a54659732304 Mon Sep 17 00:00:00 2001
From: Thomas Kolb <thomas@tkolb.de>
Date: Mon, 30 Dec 2019 12:19:00 +0100
Subject: [PATCH] UDPProto: added "ack request" + response packets

The ACK request packet contains a sequence number which is echoed back
to the client in a simple UDP packet. By evaluating the difference
between sent and received sequence number, the client can control how
much data is buffered on the way to the ESP.
---
 include/UDPProto.h |  3 ++-
 src/UDPProto.cpp   | 27 ++++++++++++++++-----------
 2 files changed, 18 insertions(+), 12 deletions(-)

diff --git a/include/UDPProto.h b/include/UDPProto.h
index 855a800..14fbf18 100644
--- a/include/UDPProto.h
+++ b/include/UDPProto.h
@@ -11,7 +11,8 @@ public:
         SET_COLOUR = 0,
         FADE_COLOUR = 1,
         ADD_COLOUR = 2,
-        SET_FADESTEP = 3
+        SET_FADESTEP = 3,
+        ACK_REQUEST = 255
     };
 
     UDPProto(Fader *fader);
diff --git a/src/UDPProto.cpp b/src/UDPProto.cpp
index 4b83156..a7ce39d 100644
--- a/src/UDPProto.cpp
+++ b/src/UDPProto.cpp
@@ -27,12 +27,7 @@ bool UDPProto::check(void)
 {
 	int packetSize = m_udpServer.parsePacket();
 	if(packetSize) {
-		byte buf[1024];
-		int len;
-		while((len = m_udpServer.read(buf, 1024)) == 1024) {
-			// do nothing
-		}
-		m_udpServer.endPacket();
+		m_udpServer.flush();
 		return true;
 	} else {
 		return false;
@@ -45,6 +40,8 @@ bool UDPProto::loop(void)
 	byte action, strip, module, r, g, b, w;
 	int len;
 
+	int32_t seq = -1;
+
 	int packetSize = m_udpServer.parsePacket();
 	if(packetSize)
 	{
@@ -87,16 +84,24 @@ bool UDPProto::loop(void)
 					m_fader->set_fadestep(r); // red channel contains the fadestep in this case
 					break;
 
+                case ACK_REQUEST:
+					seq = ((int32_t)r) << 8 | (int32_t)g;
+
 				default:
 					break;
 			}
 		}
 		// send a reply, to the IP address and port that sent us the packet we received
-		/*
-		ws2801UDP.beginPacket(ws2801UDP.remoteIP(), ws2801UDP.remotePort());
-		ws2801UDP.write("OK\n");
-		*/
-		m_udpServer.endPacket();
+		if(seq >= 0) {
+			uint8_t data[2];
+			data[0] = (seq >> 8) & 0xFF;
+			data[1] = seq & 0xFF;
+			m_udpServer.beginPacket(m_udpServer.remoteIP(), m_udpServer.remotePort());
+			m_udpServer.write(data, 2);
+			m_udpServer.endPacket();
+		}
+
+		m_udpServer.flush();
 
 		return true; // processed a packet
 	} else {