wifi: fix iterator invalidation in WifiMacQueue::Insert

If pos == begin(), it may be invalidated before inserting if DROP_OLDEST
policy is used and queue is full.

Add fix for this case and a test for it.

src/wifi/model/wifi-mac-queue.cc

@@ -154,7 +154,16 @@ WifiMacQueue::Insert (ConstIterator pos, Ptr<WifiMacQueueItem> item)
   if (m_dropPolicy == DROP_OLDEST)
     {
       NS_LOG_DEBUG ("Remove the oldest item in the queue");
-      DoRemove (begin ());
+      if (pos == begin ())
+        {
+          // Avoid invalidating pos
+          DoRemove (begin ());
+          pos = begin ();
+        }
+      else
+        {
+          DoRemove (begin ());
+        }
     }
 
   return DoEnqueue (pos, item);

src/wifi/test/wifi-mac-queue.cc

@@ -0,0 +1,121 @@
+/* -*- Mode:C++; c-file-style:"gnu"; indent-tabs-mode:nil; -*- */
+/*
+ * Copyright (c) 2021 IITP RAS
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation;
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
+ *
+ * Author: Alexander Krotov <krotov@iitp.ru>
+ */
+
+#include "ns3/test.h"
+#include "ns3/wifi-mac-queue.h"
+
+using namespace ns3;
+
+/**
+ * \ingroup wifi-test
+ * \ingroup tests
+ *
+ * \brief Test DROP_OLDEST setting.
+ *
+ * This test verifies the correctness of DROP_OLDEST policy when packets
+ * are pushed into the front of the queue. This case is not handled
+ * by the underlying ns3::Queue<WifiMacQueueItem>.
+ */
+class WifiMacQueueDropOldestTest : public TestCase
+{
+public:
+  /**
+   * \brief Constructor
+   */
+  WifiMacQueueDropOldestTest ();
+
+  void DoRun () override;
+};
+
+WifiMacQueueDropOldestTest::WifiMacQueueDropOldestTest()
+  : TestCase ("Test DROP_OLDEST setting")
+{
+}
+
+void
+WifiMacQueueDropOldestTest::DoRun ()
+{
+  auto wifiMacQueue = CreateObject<WifiMacQueue> ();
+  wifiMacQueue->SetMaxSize (QueueSize ("5p"));
+  wifiMacQueue->SetAttribute ("DropPolicy", EnumValue (WifiMacQueue::DROP_OLDEST));
+
+  // Initialize the queue with 5 packets.
+  std::vector<uint64_t> packetUids;
+  for (uint32_t i = 0; i < 5; i++)
+    {
+      WifiMacHeader header;
+      auto packet = Create<Packet> ();
+      auto item = Create<WifiMacQueueItem> (packet, header);
+      wifiMacQueue->PushFront (item);
+
+      packetUids.push_back (packet->GetUid ());
+    }
+
+  // Check that all elements are inserted successfully.
+  auto it = wifiMacQueue->begin ();
+  NS_TEST_EXPECT_MSG_EQ (wifiMacQueue->GetNPackets (), 5, "Queue has unexpected number of elements");
+  for (uint32_t i = 5; i > 0; i--)
+    {
+      NS_TEST_EXPECT_MSG_EQ ((*it)->GetPacket ()->GetUid (),
+                             packetUids.at (i - 1),
+                             "Stored packet is not the expected one");
+      it++;
+    }
+
+  // Push another element in front of the queue.
+  WifiMacHeader header;
+  auto packet = Create<Packet> ();
+  auto item = Create<WifiMacQueueItem> (packet, header);
+  wifiMacQueue->PushFront (item);
+
+  // Update the vector of expected packet UIDs.
+  packetUids.at (4) = packet->GetUid ();
+
+  // Check that front packet was replaced correctly.
+  it = wifiMacQueue->begin ();
+  NS_TEST_EXPECT_MSG_EQ (wifiMacQueue->GetNPackets (), 5, "Queue has unexpected number of elements");
+  for (uint32_t i = 5; i > 0; i--)
+    {
+      NS_TEST_EXPECT_MSG_EQ ((*it)->GetPacket ()->GetUid (),
+                             packetUids.at (i - 1),
+                             "Stored packet is not the expected one");
+      it++;
+    }
+}
+
+/**
+ * \ingroup wifi-test
+ * \ingroup tests
+ *
+ * \brief Wifi MAC Queue Test Suite
+ */
+class WifiMacQueueTestSuite : public TestSuite
+{
+  public:
+    WifiMacQueueTestSuite ();
+};
+
+WifiMacQueueTestSuite::WifiMacQueueTestSuite ()
+  : TestSuite ("wifi-mac-queue", UNIT)
+{
+  AddTestCase (new WifiMacQueueDropOldestTest, TestCase::QUICK);
+}
+
+static WifiMacQueueTestSuite g_wifiMacQueueTestSuite; ///< the test suite

src/wifi/wscript

@@ -124,7 +124,8 @@ def build(bld):
         'test/wifi-phy-thresholds-test.cc',
         'test/wifi-phy-reception-test.cc',
         'test/inter-bss-test-suite.cc',
-        'test/wifi-phy-ofdma-test.cc'
+        'test/wifi-phy-ofdma-test.cc',
+        'test/wifi-mac-queue.cc',
         ]
 
     # Tests encapsulating example programs should be listed here