quic: expose retransmit counts to JS

Allows monitoring the number of times packets have to be
retransmitted because of loss or delayed ack. An implementation
experiencing a high number of retransmits may need to be torn
down or mitigated in some way. This allows the user code to keep
track. Later, we may want to add a setting that enforces a maximum
number of retransmissions before failing a connection.

Fixes: #78
PR-URL: #207
Reviewed-By: #207

lib/internal/quic/core.js

@@ -150,6 +150,8 @@ const {
     IDX_QUIC_SESSION_STATS_STREAMS_IN_COUNT,
     IDX_QUIC_SESSION_STATS_STREAMS_OUT_COUNT,
     IDX_QUIC_SESSION_STATS_KEYUPDATE_COUNT,
+    IDX_QUIC_SESSION_STATS_LOSS_RETRANSMIT_COUNT,
+    IDX_QUIC_SESSION_STATS_ACK_DELAY_RETRANSMIT_COUNT,
     IDX_QUIC_SESSION_STATS_MAX_BYTES_IN_FLIGHT,
     ERR_INVALID_REMOTE_TRANSPORT_PARAMS,
     ERR_INVALID_TLS_SESSION_TICKET,
@@ -1864,6 +1866,16 @@ class QuicSession extends EventEmitter {
     return stats[IDX_QUIC_SESSION_STATS_MAX_BYTES_IN_FLIGHT];
   }
 
+  get lossRetransmitCount() {
+    const stats = this.#stats || this[kHandle].stats;
+    return stats[IDX_QUIC_SESSION_STATS_LOSS_RETRANSMIT_COUNT];
+  }
+
+  get ackDelayRetransmitCount() {
+    const stats = this.#stats || this[kHandle].stats;
+    return stats[IDX_QUIC_SESSION_STATS_ACK_DELAY_RETRANSMIT_COUNT];
+  }
+
   get peerInitiatedStreamCount() {
     const stats = this.#stats || this[kHandle].stats;
     return stats[IDX_QUIC_SESSION_STATS_STREAMS_IN_COUNT];