From 3549ce35ff905467c90bb3396b3c4a126fe0dd7f Mon Sep 17 00:00:00 2001
From: Paul Lorenz <paul.lorenz@netfoundry.io>
Date: Mon, 27 Jun 2022 14:28:40 -0400
Subject: [PATCH] Prevent payload which has looped back to sender from being
 acked

---
 router/xgress/link_receive_buffer.go | 5 +++--
 router/xgress/messages.go            | 8 ++++----
 router/xgress/messages_test.go       | 4 ++--
 router/xgress/xgress.go              | 5 ++++-
 4 files changed, 13 insertions(+), 9 deletions(-)

diff --git a/router/xgress/link_receive_buffer.go b/router/xgress/link_receive_buffer.go
index c2fbc1116..62d0211a5 100644
--- a/router/xgress/link_receive_buffer.go
+++ b/router/xgress/link_receive_buffer.go
@@ -107,8 +107,9 @@ func (buffer *LinkReceiveBuffer) Inspect() *inspect.XgressRecvBufferDetail {
 
 func (buffer *LinkReceiveBuffer) inspectComplete() *inspect.XgressRecvBufferDetail {
 	nextPayload := "none"
-	if head := buffer.PeekHead(); head != nil {
-		nextPayload = fmt.Sprintf("%v", head.Sequence)
+	if head := buffer.tree.LeftValue(); head != nil {
+		payload := head.(*Payload)
+		nextPayload = fmt.Sprintf("%v", payload.Sequence)
 	}
 
 	return &inspect.XgressRecvBufferDetail{
diff --git a/router/xgress/messages.go b/router/xgress/messages.go
index 987377fa3..f5d05808f 100644
--- a/router/xgress/messages.go
+++ b/router/xgress/messages.go
@@ -66,7 +66,7 @@ type PayloadFlag uint32
 
 const (
 	PayloadFlagCircuitEnd   PayloadFlag = 1
-	PayloadFlagEgress       PayloadFlag = 2
+	PayloadFlagOriginator   PayloadFlag = 2
 	PayloadFlagCircuitStart PayloadFlag = 4
 )
 
@@ -86,7 +86,7 @@ func (header *Header) GetFlags() string {
 }
 
 func (header *Header) GetOriginator() Originator {
-	if isPayloadFlagSet(header.Flags, PayloadFlagEgress) {
+	if isPayloadFlagSet(header.Flags, PayloadFlagOriginator) {
 		return Terminator
 	}
 	return Initiator
@@ -267,9 +267,9 @@ func (payload *Payload) IsCircuitStartFlagSet() bool {
 
 func SetOriginatorFlag(flags uint32, originator Originator) uint32 {
 	if originator == Initiator {
-		return ^uint32(PayloadFlagEgress) & flags
+		return ^uint32(PayloadFlagOriginator) & flags
 	}
-	return uint32(PayloadFlagEgress) | flags
+	return uint32(PayloadFlagOriginator) | flags
 }
 
 func (payload *Payload) GetLoggerFields() logrus.Fields {
diff --git a/router/xgress/messages_test.go b/router/xgress/messages_test.go
index 9d54f99e1..d3bd7b191 100644
--- a/router/xgress/messages_test.go
+++ b/router/xgress/messages_test.go
@@ -55,14 +55,14 @@ func TestSetOriginatorFlag(t *testing.T) {
 				flags:      0,
 				originator: Terminator,
 			},
-			want: uint32(PayloadFlagEgress),
+			want: uint32(PayloadFlagOriginator),
 		},
 		{name: "set end of circuit to egress",
 			args: args{
 				flags:      uint32(PayloadFlagCircuitEnd),
 				originator: Terminator,
 			},
-			want: uint32(PayloadFlagCircuitEnd) | uint32(PayloadFlagEgress),
+			want: uint32(PayloadFlagCircuitEnd) | uint32(PayloadFlagOriginator),
 		},
 	}
 	for _, tt := range tests {
diff --git a/router/xgress/xgress.go b/router/xgress/xgress.go
index 3dea1ef10..c1d1bf873 100644
--- a/router/xgress/xgress.go
+++ b/router/xgress/xgress.go
@@ -564,7 +564,10 @@ func (self *Xgress) nextReceiveSequence() int32 {
 func (self *Xgress) PayloadReceived(payload *Payload) {
 	log := pfxlog.ContextLogger(self.Label()).WithFields(payload.GetLoggerFields())
 	log.Debug("payload received")
-	if self.linkRxBuffer.ReceiveUnordered(payload, self.Options.RxBufferSize) {
+	if self.originator == payload.GetOriginator() {
+		// a payload sent from this xgress has arrived back at this xgress, instead of the other end
+		log.Warn("ouroboros (circuit cycle) detected, dropping payload")
+	} else if self.linkRxBuffer.ReceiveUnordered(payload, self.Options.RxBufferSize) {
 		log.Debug("ready to acknowledge")
 
 		ack := NewAcknowledgement(self.circuitId, self.originator)