Add latest seqnum notify to replaydetector

Updates the replay detector interface and implementations to support
indicating whether the accepted packet resulted in an update of the
latest sequence number.

Note: this is not a breaking change as the accept() callback was
previously returning zero values and is now returning one, which can be
ignored if desired. It may cause linter failures in some consumers if
using a strict policy.

Signed-off-by: Daniel Mangum <[email protected]>

replaydetector/replaydetector.go

@@ -8,7 +8,14 @@ package replaydetector
 type ReplayDetector interface {
 	// Check returns true if given sequence number is not replayed.
 	// Call accept() to mark the packet is received properly.
-	Check(seq uint64) (accept func(), ok bool)
+	// The return value of accept() indicates whether the accepted packet is
+	// has the latest observed sequence number.
+	Check(seq uint64) (accept func() bool, ok bool)
+}
+
+// nop is a no-op func that is returned in the case that Check() fails.
+func nop() bool {
+	return false
 }
 
 type slidingWindowDetector struct {
@@ -30,30 +37,33 @@ func New(windowSize uint, maxSeq uint64) ReplayDetector {
 	}
 }
 
-func (d *slidingWindowDetector) Check(seq uint64) (accept func(), ok bool) {
+func (d *slidingWindowDetector) Check(seq uint64) (accept func() bool, ok bool) {
 	if seq > d.maxSeq {
 		// Exceeded upper limit.
-		return func() {}, false
+		return nop, false
 	}
 
 	if seq <= d.latestSeq {
 		if d.latestSeq >= uint64(d.windowSize)+seq {
-			return func() {}, false
+			return nop, false
 		}
 		if d.mask.Bit(uint(d.latestSeq-seq)) != 0 {
 			// The sequence number is duplicated.
-			return func() {}, false
+			return nop, false
 		}
 	}
 
-	return func() {
+	return func() bool {
+		latest := seq == 0
 		if seq > d.latestSeq {
 			// Update the head of the window.
 			d.mask.Lsh(uint(seq - d.latestSeq))
 			d.latestSeq = seq
+			latest = true
 		}
 		diff := (d.latestSeq - seq) % d.maxSeq
 		d.mask.SetBit(uint(diff))
+		return latest
 	}, true
 }
 
@@ -75,10 +85,10 @@ type wrappedSlidingWindowDetector struct {
 	init       bool
 }
 
-func (d *wrappedSlidingWindowDetector) Check(seq uint64) (accept func(), ok bool) {
+func (d *wrappedSlidingWindowDetector) Check(seq uint64) (accept func() bool, ok bool) {
 	if seq > d.maxSeq {
 		// Exceeded upper limit.
-		return func() {}, false
+		return nop, false
 	}
 	if !d.init {
 		if seq != 0 {
@@ -99,21 +109,24 @@ func (d *wrappedSlidingWindowDetector) Check(seq uint64) (accept func(), ok bool
 
 	if diff >= int64(d.windowSize) {
 		// Too old.
-		return func() {}, false
+		return nop, false
 	}
 	if diff >= 0 {
 		if d.mask.Bit(uint(diff)) != 0 {
 			// The sequence number is duplicated.
-			return func() {}, false
+			return nop, false
 		}
 	}
 
-	return func() {
+	return func() bool {
+		latest := false
 		if diff < 0 {
 			// Update the head of the window.
 			d.mask.Lsh(uint(-diff))
 			d.latestSeq = seq
+			latest = true
 		}
 		d.mask.SetBit(uint(d.latestSeq - seq))
+		return latest
 	}, true
 }