Implement an event-based simulator for QuicConnection

net/quic/core/congestion_control/simulation/queue.cc

+#include "net/quic/core/congestion_control/simulation/queue.h"
+
+namespace net {
+namespace simulation {
+
+Queue::ListenerInterface::~ListenerInterface() {}
+
+Queue::Queue(Simulator* simulator, std::string name, QuicByteCount capacity)
+    : Actor(simulator, name),
+      capacity_(capacity),
+      bytes_queued_(0),
+      listener_(nullptr) {}
+
+void Queue::set_tx_port(ConstrainedPortInterface* port) {
+  tx_port_ = port;
+}
+
+void Queue::AcceptPacket(std::unique_ptr<Packet> packet) {
+  if (packet->size + bytes_queued_ > capacity_) {
+    DVLOG(1) << "Queue [" << name() << "] has received a packet from ["
+             << packet->source << "] to [" << packet->destination
+             << "] which is over capacity.  Dropping it.";
+    DVLOG(1) << "Queue size: " << bytes_queued_ << " out of " << capacity_
+             << ".  Packet size: " << packet->size;
+    return;
+  }
+
+  bytes_queued_ += packet->size;
+  queue_.emplace(std::move(packet));
+  ScheduleNextPacketDequeue();
+}
+
+void Queue::Act() {
+  DCHECK(!queue_.empty());
+  if (tx_port_->TimeUntilAvailable().IsZero()) {
+    DCHECK(bytes_queued_ >= queue_.front()->size);
+    bytes_queued_ -= queue_.front()->size;
+
+    tx_port_->AcceptPacket(std::move(queue_.front()));
+    queue_.pop();
+    if (listener_ != nullptr) {
+      listener_->OnPacketDequeued();
+    }
+  }
+
+  ScheduleNextPacketDequeue();
+}
+
+void Queue::ScheduleNextPacketDequeue() {
+  if (queue_.empty()) {
+    DCHECK_EQ(bytes_queued_, 0);
+    return;
+  }
+
+  Schedule(clock_->Now() + tx_port_->TimeUntilAvailable());
+}
+
+}  // namespace simulation
+}  // namespace net