Also handle case where seqnums around u16::MAX-16

Author: pthatcher

src/transport_feedbacks/transport_layer_nack/mod.rs

@@ -230,12 +230,13 @@ pub fn nack_pairs_from_sequence_numbers(seq_nos: &[u16]) -> Vec<NackPair> {
         if seq == nack_pair.packet_id {
             continue;
         }
-        if seq <= nack_pair.packet_id || seq - nack_pair.packet_id > 16 {
+        if seq <= nack_pair.packet_id || seq > nack_pair.packet_id.saturating_add(16) {
             pairs.push(nack_pair.clone());
             nack_pair.packet_id = seq;
             continue;
         }
 
+        // Subtraction here is safe because the above checks that seqnum > nack_pair.packet_id.
         nack_pair.lost_packets |= 1 << (seq - nack_pair.packet_id - 1);
     }
 

src/transport_feedbacks/transport_layer_nack/transport_layer_nack_test.rs

@@ -305,7 +305,7 @@ fn test_transport_layer_nack_pair_generation() {
         ),
         (
             "Multiple Ranges, Multiple NACKPair (with rollover)",
-            vec![100, 117, 65535, 0, 1, 99],
+            vec![100, 117, 65534, 65535, 0, 1, 99],
             vec![
                 NackPair {
                     packet_id: 100,
@@ -316,8 +316,8 @@ fn test_transport_layer_nack_pair_generation() {
                     lost_packets: 0,
                 },
                 NackPair {
-                    packet_id: 65535,
-                    lost_packets: 0,
+                    packet_id: 65534,
+                    lost_packets: 1,
                 },
                 NackPair {
                     packet_id: 0,