net: implement ECN handling, rfc6040 stylefd/propagate-DSCP-bits

To decide whether we should use the compatibility mode or the normal
mode with a peer, we use the handshake messages as a signaling channel.

If we receive the expected ECN bits, it most likely means they're
running a compatible version.

Signed-off-by: Florent Daigniere <nextgens@freenetproject.org>

1 files changed, 9 insertions, 0 deletions

diff --git a/peer.go b/peer.go
index 96cfa61..642a0ee 100644
--- a/peer.go
+++ b/peer.go
@@ -15,6 +15,14 @@ import (
 
 const (
 	PeerRoutineNumber = 3
+
+	DiffServAF41          = 0x88 // AF41
+	NotECNTransport       = 0x00 // Not-ECT (Not ECN-Capable Transport)
+	ECNTransport1         = 0x01 // ECT(1) (ECN-Capable Transport(1))
+	ECNTransport0         = 0x02 // ECT(0) (ECN-Capable Transport(0))
+	CongestionExperienced = 0x03 // CE (Congestion Experienced)
+
+	HandshakeDSCP = DiffServAF41 | ECNTransport0 // AF41, plus 10 ECN
 )
 
 type Peer struct {
@@ -25,6 +33,7 @@ type Peer struct {
 	device                      *Device
 	endpoint                    Endpoint
 	persistentKeepaliveInterval uint16
+	isECNConfirmed              AtomicBool
 
 	// This must be 64-bit aligned, so make sure the above members come out to even alignment and pad accordingly
 	stats struct {