test: extend coverage of testTransport

tests/testTransport.cpp

@@ -321,3 +321,77 @@ VF_TEST(smoothedRoundTripTimeConvergesOnTheLinkLatency) {
     CHECK_EQ(sender.stats().datagramsLost, static_cast<uint64_t>(0));
 }
 
+VF_TEST(theAckBitfieldConfirmsDatagramsWhoseOwnAckWasLost) {
+    LinkQuality quality;
+    quality.latencyTicks = 1;
+    quality.seed = 0x4242424242424242ull;
+    LoopbackLink link(quality);
+
+    TransportConfig config;
+    config.mtu = 96;
+    config.sendWindow = 32;
+    config.retransmitTimeoutTicks = 1000;
+    Transport sender(link, 0, config);
+    Transport receiver(link, 1, config);
+
+    for (uint32_t i = 0; i < 12; ++i) sender.sendReliable(messageOf(i, 50));
+
+    // Twelve datagrams leave, and the sender never pumps, so not a single ack
+    // has been seen when the burst is complete.
+    sender.flush(0);
+    CHECK_EQ(sender.inFlightDatagramCount(), static_cast<std::size_t>(12));
+    CHECK_EQ(sender.stats().datagramsSent, static_cast<uint64_t>(12));
+    CHECK_EQ(sender.stats().smoothedRttTicks, 0.0);
+
+    // A single hand-built ack: latest is sequence 11, and the history bitfield
+    // covers sequences 10 down to 0. Nothing else ever reaches the sender.
+    receiver.pump(1);
+    Datagram carrier;
+    carrier.sequence = 0;
+    carrier.ackLatest = 11;
+    carrier.ackHistory = 0x7ffu;
+    carrier.ackValid = true;
+    ByteWriter wire;
+    carrier.encode(wire);
+    link.send(1, wire.bytes(), 1);
+
+    sender.pump(2);
+    CHECK_EQ(sender.inFlightDatagramCount(), static_cast<std::size_t>(0));
+    CHECK_EQ(sender.unackedFragmentCount(), static_cast<std::size_t>(0));
+    CHECK_EQ(sender.stats().retransmitted, static_cast<uint64_t>(0));
+    CHECK(sender.stats().smoothedRttTicks > 0.0);
+
+    // The whole burst still arrived exactly once, in order.
+    std::vector<uint32_t> order;
+    for (uint64_t tick = 2; tick < 30; ++tick) {
+        receiver.pump(tick);
+        ByteBuffer got;
+        while (receiver.popReliable(got)) order.push_back(indexOf(got));
+    }
+    CHECK_EQ(order.size(), static_cast<std::size_t>(12));
+    for (std::size_t i = 0; i < order.size(); ++i) CHECK_EQ(order[i], static_cast<uint32_t>(i));
+}
+
+VF_TEST(aTransportWithNothingToSendStillAcknowledgesWithoutAnAckStorm) {
+    LinkQuality quality;
+    quality.latencyTicks = 1;
+    quality.seed = 0x0f0f0f0f0f0f0f0full;
+    LoopbackLink link(quality);
+
+    TransportConfig config;
+    config.mtu = 256;
+    config.retransmitTimeoutTicks = 20;
+    Transport sender(link, 0, config);
+    Transport receiver(link, 1, config);
+
+    sender.sendReliable(messageOf(0, 40));
+    for (uint64_t tick = 0; tick < 30; ++tick) stepPair(sender, receiver, tick);
+
+    ByteBuffer got;
+    CHECK(receiver.popReliable(got));
+    CHECK_EQ(indexOf(got), 0u);
+    CHECK_EQ(sender.unackedFragmentCount(), static_cast<std::size_t>(0));
+    // One payload datagram plus at most a handful of bare acks, not one per tick.
+    CHECK(receiver.stats().datagramsSent <= 3u);
+    CHECK(sender.stats().datagramsSent <= 3u);
+}