path: root/netwerk/system/win32/nsNotifyAddrListener.cpp

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* vim:set et sw=4 ts=4: */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

// We define this to make our use of inet_ntoa() pass. The "proper" function
// inet_ntop() doesn't exist on Windows XP.
#define _WINSOCK_DEPRECATED_NO_WARNINGS

#include <stdarg.h>
#include <windef.h>
#include <winbase.h>
#include <wingdi.h>
#include <winuser.h>
#include <ole2.h>
#include <netcon.h>
#include <objbase.h>
#include <winsock2.h>
#include <ws2ipdef.h>
#include <tcpmib.h>
#include <iphlpapi.h>
#include <netioapi.h>
#include <iprtrmib.h>
#include "plstr.h"
#include "mozilla/Logging.h"
#include "nsThreadUtils.h"
#include "nsIObserverService.h"
#include "nsServiceManagerUtils.h"
#include "nsNotifyAddrListener.h"
#include "nsString.h"
#include "nsAutoPtr.h"
#include "mozilla/Services.h"
#include "nsCRT.h"
#include "mozilla/Preferences.h"
#include "mozilla/SHA1.h"
#include "mozilla/Base64.h"
#include "mozilla/Telemetry.h"

#include <iptypes.h>
#include <iphlpapi.h>

using namespace mozilla;

static LazyLogModule gNotifyAddrLog("nsNotifyAddr");
#define LOG(args) MOZ_LOG(gNotifyAddrLog, mozilla::LogLevel::Debug, args)

static HMODULE sNetshell;
static decltype(NcFreeNetconProperties)* sNcFreeNetconProperties;

static HMODULE sIphlpapi;
static decltype(NotifyIpInterfaceChange)* sNotifyIpInterfaceChange;
static decltype(CancelMibChangeNotify2)* sCancelMibChangeNotify2;

#define NETWORK_NOTIFY_CHANGED_PREF "network.notify.changed"
#define NETWORK_NOTIFY_IPV6_PREF "network.notify.IPv6"

// period during which to absorb subsequent network change events, in
// milliseconds
static const unsigned int kNetworkChangeCoalescingPeriod  = 1000;

static void InitIphlpapi(void)
{
    if (!sIphlpapi) {
        sIphlpapi = LoadLibraryW(L"Iphlpapi.dll");
        if (sIphlpapi) {
            sNotifyIpInterfaceChange = (decltype(NotifyIpInterfaceChange)*)
                GetProcAddress(sIphlpapi, "NotifyIpInterfaceChange");
            sCancelMibChangeNotify2 = (decltype(CancelMibChangeNotify2)*)
                GetProcAddress(sIphlpapi, "CancelMibChangeNotify2");
        } else {
            NS_WARNING("Failed to load Iphlpapi.dll - cannot detect network"
                       " changes!");
        }
    }
}

static void InitNetshellLibrary(void)
{
    if (!sNetshell) {
        sNetshell = LoadLibraryW(L"Netshell.dll");
        if (sNetshell) {
            sNcFreeNetconProperties = (decltype(NcFreeNetconProperties)*)
                GetProcAddress(sNetshell, "NcFreeNetconProperties");
        }
    }
}

static void FreeDynamicLibraries(void)
{
    if (sNetshell) {
        sNcFreeNetconProperties = nullptr;
        FreeLibrary(sNetshell);
        sNetshell = nullptr;
    }
    if (sIphlpapi) {
        sNotifyIpInterfaceChange = nullptr;
        sCancelMibChangeNotify2 = nullptr;
        FreeLibrary(sIphlpapi);
        sIphlpapi = nullptr;
    }
}

NS_IMPL_ISUPPORTS(nsNotifyAddrListener,
                  nsINetworkLinkService,
                  nsIRunnable,
                  nsIObserver)

nsNotifyAddrListener::nsNotifyAddrListener()
    : mLinkUp(true)  // assume true by default
    , mStatusKnown(false)
    , mCheckAttempted(false)
    , mCheckEvent(nullptr)
    , mShutdown(false)
    , mIPInterfaceChecksum(0)
    , mAllowChangedEvent(true)
    , mIPv6Changes(false)
    , mCoalescingActive(false)
{
    InitIphlpapi();
}

nsNotifyAddrListener::~nsNotifyAddrListener()
{
    NS_ASSERTION(!mThread, "nsNotifyAddrListener thread shutdown failed");
    FreeDynamicLibraries();
}

NS_IMETHODIMP
nsNotifyAddrListener::GetIsLinkUp(bool *aIsUp)
{
    if (!mCheckAttempted && !mStatusKnown) {
        mCheckAttempted = true;
        CheckLinkStatus();
    }

    *aIsUp = mLinkUp;
    return NS_OK;
}

NS_IMETHODIMP
nsNotifyAddrListener::GetLinkStatusKnown(bool *aIsUp)
{
    *aIsUp = mStatusKnown;
    return NS_OK;
}

NS_IMETHODIMP
nsNotifyAddrListener::GetLinkType(uint32_t *aLinkType)
{
    NS_ENSURE_ARG_POINTER(aLinkType);

    // XXX This function has not yet been implemented for this platform
    *aLinkType = nsINetworkLinkService::LINK_TYPE_UNKNOWN;
    return NS_OK;
}

static bool macAddr(BYTE addr[], DWORD len, char *buf, size_t buflen)
{
    buf[0] = '\0';
    if (!addr || !len || (len * 3 > buflen)) {
        return false;
    }

    for (DWORD i = 0; i < len; ++i) {
        sprintf_s(buf + (i * 3), sizeof(buf + (i * 3)),
                  "%02x%s", addr[i], (i == len-1) ? "" : ":");
    }
    return true;
}

bool nsNotifyAddrListener::findMac(char *gateway)
{
    // query for buffer size needed
    DWORD dwActualSize = 0;
    bool found = FALSE;

    // GetIpNetTable gets the IPv4 to physical address mapping table
    DWORD status = GetIpNetTable(NULL, &dwActualSize, FALSE);
    if (status == ERROR_INSUFFICIENT_BUFFER) {
        // the expected route, now with a known buffer size
        UniquePtr <char[]>buf(new char[dwActualSize]);
        PMIB_IPNETTABLE pIpNetTable =
            reinterpret_cast<PMIB_IPNETTABLE>(&buf[0]);

        status = GetIpNetTable(pIpNetTable, &dwActualSize, FALSE);

        if (status == NO_ERROR) {
            for (DWORD i = 0; i < pIpNetTable->dwNumEntries; ++i) {
                DWORD dwCurrIndex = pIpNetTable->table[i].dwIndex;
                char hw[256];

                if (!macAddr(pIpNetTable->table[i].bPhysAddr,
                             pIpNetTable->table[i].dwPhysAddrLen,
                             hw, sizeof(hw))) {
                    // failed to get the MAC
                    continue;
                }

                struct in_addr addr;
                addr.s_addr = pIpNetTable->table[i].dwAddr;

                if (!strcmp(gateway, inet_ntoa(addr))) {
                    LOG(("networkid: MAC %s\n", hw));
                    nsAutoCString mac(hw);
                    // This 'addition' could potentially be a
                    // fixed number from the profile or something.
                    nsAutoCString addition("local-rubbish");
                    nsAutoCString output;
                    SHA1Sum sha1;
                    nsCString combined(mac + addition);
                    sha1.update(combined.get(), combined.Length());
                    uint8_t digest[SHA1Sum::kHashSize];
                    sha1.finish(digest);
                    nsCString newString(reinterpret_cast<char*>(digest),
                                        SHA1Sum::kHashSize);
                    Base64Encode(newString, output);
                    LOG(("networkid: id %s\n", output.get()));
                    if (mNetworkId != output) {
                        // new id
                        Telemetry::Accumulate(Telemetry::NETWORK_ID, 1);
                        mNetworkId = output;
                    }
                    else {
                        // same id
                        Telemetry::Accumulate(Telemetry::NETWORK_ID, 2);
                    }
                    found = true;
                    break;
                }
            }
        }
    }
    return found;
}

// returns 'true' when the gw is found and stored
static bool defaultgw(char *aGateway, size_t aGatewayLen)
{
    PMIB_IPFORWARDTABLE pIpForwardTable = NULL;

    DWORD dwSize = 0;
    if (GetIpForwardTable(NULL, &dwSize, 0) != ERROR_INSUFFICIENT_BUFFER) {
        return false;
    }

    UniquePtr <char[]>buf(new char[dwSize]);
    pIpForwardTable = reinterpret_cast<PMIB_IPFORWARDTABLE>(&buf[0]);

    // Note that the IPv4 addresses returned in GetIpForwardTable entries are
    // in network byte order

    DWORD retVal = GetIpForwardTable(pIpForwardTable, &dwSize, 0);
    if (retVal == NO_ERROR) {
        for (unsigned int i = 0; i < pIpForwardTable->dwNumEntries; ++i) {
            // Convert IPv4 addresses to strings
            struct in_addr IpAddr;
            IpAddr.S_un.S_addr = static_cast<u_long>
                (pIpForwardTable->table[i].dwForwardDest);
            char *ipStr = inet_ntoa(IpAddr);
            if (ipStr && !strcmp("0.0.0.0", ipStr)) {
                // Default gateway!
                IpAddr.S_un.S_addr = static_cast<u_long>
                    (pIpForwardTable->table[i].dwForwardNextHop);
                ipStr = inet_ntoa(IpAddr);
                if (ipStr) {
                    strcpy_s(aGateway, aGatewayLen, ipStr);
                    return true;
                }
            }
        } // for loop
    }

    return false;
}

//
// Figure out the current "network identification" string.
//
// It detects the IP of the default gateway in the routing table, then the MAC
// address of that IP in the ARP table before it hashes that string (to avoid
// information leakage).
//
void nsNotifyAddrListener::calculateNetworkId(void)
{
    bool found = FALSE;
    char gateway[128];
    if (defaultgw(gateway, sizeof(gateway) )) {
        found = findMac(gateway);
    }
    if (!found) {
        // no id
        Telemetry::Accumulate(Telemetry::NETWORK_ID, 0);
    }
}

// Static Callback function for NotifyIpInterfaceChange API.
static void WINAPI OnInterfaceChange(PVOID callerContext,
                                     PMIB_IPINTERFACE_ROW row,
                                     MIB_NOTIFICATION_TYPE notificationType)
{
    nsNotifyAddrListener *notify = static_cast<nsNotifyAddrListener*>(callerContext);
    notify->CheckLinkStatus();
}

DWORD
nsNotifyAddrListener::nextCoalesceWaitTime()
{
    // check if coalescing period should continue
    double period = (TimeStamp::Now() - mChangeTime).ToMilliseconds();
    if (period >= kNetworkChangeCoalescingPeriod) {
        calculateNetworkId();
        SendEvent(NS_NETWORK_LINK_DATA_CHANGED);
        mCoalescingActive = false;
        return INFINITE; // return default
    } else {
        // wait no longer than to the end of the period
        return static_cast<DWORD>
            (kNetworkChangeCoalescingPeriod - period);
    }
}

NS_IMETHODIMP
nsNotifyAddrListener::Run()
{
    PR_SetCurrentThreadName("Link Monitor");

    mStartTime = TimeStamp::Now();

    calculateNetworkId();

    DWORD waitTime = INFINITE;

    if (!sNotifyIpInterfaceChange || !sCancelMibChangeNotify2 || !mIPv6Changes) {
        // For Windows versions which are older than Vista which lack
        // NotifyIpInterfaceChange. Note this means no IPv6 support.
        HANDLE ev = CreateEvent(nullptr, FALSE, FALSE, nullptr);
        NS_ENSURE_TRUE(ev, NS_ERROR_OUT_OF_MEMORY);

        HANDLE handles[2] = { ev, mCheckEvent };
        OVERLAPPED overlapped = { 0 };
        bool shuttingDown = false;

        overlapped.hEvent = ev;
        while (!shuttingDown) {
            HANDLE h;
            DWORD ret = NotifyAddrChange(&h, &overlapped);

            if (ret == ERROR_IO_PENDING) {
                ret = WaitForMultipleObjects(2, handles, FALSE, waitTime);
                if (ret == WAIT_OBJECT_0) {
                    CheckLinkStatus();
                } else if (!mShutdown) {
                    waitTime = nextCoalesceWaitTime();
                } else {
                    shuttingDown = true;
                }
            } else {
                shuttingDown = true;
            }
        }
        CloseHandle(ev);
    } else {
        // Windows Vista and newer versions.
        HANDLE interfacechange;
        // The callback will simply invoke CheckLinkStatus()
        DWORD ret = sNotifyIpInterfaceChange(
            AF_UNSPEC, // IPv4 and IPv6
            (PIPINTERFACE_CHANGE_CALLBACK)OnInterfaceChange,
            this,  // pass to callback
            false, // no initial notification
            &interfacechange);

        if (ret == NO_ERROR) {
            do {
                ret = WaitForSingleObject(mCheckEvent, waitTime);
                if (!mShutdown) {
                    waitTime = nextCoalesceWaitTime();
                }
                else {
                    break;
                }
            } while (ret != WAIT_FAILED);
            sCancelMibChangeNotify2(interfacechange);
        } else {
            LOG(("Link Monitor: sNotifyIpInterfaceChange returned %d\n",
                 (int)ret));
        }
    }
    return NS_OK;
}

NS_IMETHODIMP
nsNotifyAddrListener::Observe(nsISupports *subject,
                              const char *topic,
                              const char16_t *data)
{
    if (!strcmp("xpcom-shutdown-threads", topic))
        Shutdown();

    return NS_OK;
}

nsresult
nsNotifyAddrListener::Init(void)
{
    nsCOMPtr<nsIObserverService> observerService =
        mozilla::services::GetObserverService();
    if (!observerService)
        return NS_ERROR_FAILURE;

    nsresult rv = observerService->AddObserver(this, "xpcom-shutdown-threads",
                                               false);
    NS_ENSURE_SUCCESS(rv, rv);

    Preferences::AddBoolVarCache(&mAllowChangedEvent,
                                 NETWORK_NOTIFY_CHANGED_PREF, true);
    Preferences::AddBoolVarCache(&mIPv6Changes,
                                 NETWORK_NOTIFY_IPV6_PREF, false);

    mCheckEvent = CreateEvent(nullptr, FALSE, FALSE, nullptr);
    NS_ENSURE_TRUE(mCheckEvent, NS_ERROR_OUT_OF_MEMORY);

    rv = NS_NewThread(getter_AddRefs(mThread), this);
    NS_ENSURE_SUCCESS(rv, rv);

    return NS_OK;
}

nsresult
nsNotifyAddrListener::Shutdown(void)
{
    // remove xpcom shutdown observer
    nsCOMPtr<nsIObserverService> observerService =
        mozilla::services::GetObserverService();
    if (observerService)
        observerService->RemoveObserver(this, "xpcom-shutdown-threads");

    if (!mCheckEvent)
        return NS_OK;

    mShutdown = true;
    SetEvent(mCheckEvent);

    nsresult rv = mThread ? mThread->Shutdown() : NS_OK;

    // Have to break the cycle here, otherwise nsNotifyAddrListener holds
    // onto the thread and the thread holds onto the nsNotifyAddrListener
    // via its mRunnable
    mThread = nullptr;

    CloseHandle(mCheckEvent);
    mCheckEvent = nullptr;

    return rv;
}

/*
 * A network event has been registered. Delay the actual sending of the event
 * for a while and absorb subsequent events in the mean time in an effort to
 * squash potentially many triggers into a single event.
 * Only ever called from the same thread.
 */
nsresult
nsNotifyAddrListener::NetworkChanged()
{
    if (mCoalescingActive) {
        LOG(("NetworkChanged: absorbed an event (coalescing active)\n"));
    } else {
        // A fresh trigger!
        mChangeTime = TimeStamp::Now();
        mCoalescingActive = true;
        SetEvent(mCheckEvent);
        LOG(("NetworkChanged: coalescing period started\n"));
    }
    return NS_OK;
}

/* Sends the given event.  Assumes aEventID never goes out of scope (static
 * strings are ideal).
 */
nsresult
nsNotifyAddrListener::SendEvent(const char *aEventID)
{
    if (!aEventID)
        return NS_ERROR_NULL_POINTER;

    LOG(("SendEvent: network is '%s'\n", aEventID));

    nsresult rv;
    nsCOMPtr<nsIRunnable> event = new ChangeEvent(this, aEventID);
    if (NS_FAILED(rv = NS_DispatchToMainThread(event)))
        NS_WARNING("Failed to dispatch ChangeEvent");
    return rv;
}

NS_IMETHODIMP
nsNotifyAddrListener::ChangeEvent::Run()
{
    nsCOMPtr<nsIObserverService> observerService =
        mozilla::services::GetObserverService();
    if (observerService)
        observerService->NotifyObservers(
                mService, NS_NETWORK_LINK_TOPIC,
                NS_ConvertASCIItoUTF16(mEventID).get());
    return NS_OK;
}


// Bug 465158 features an explanation for this check. ICS being "Internet
// Connection Sharing). The description says it is always IP address
// 192.168.0.1 for this case.
bool
nsNotifyAddrListener::CheckICSGateway(PIP_ADAPTER_ADDRESSES aAdapter)
{
    if (!aAdapter->FirstUnicastAddress)
        return false;

    LPSOCKADDR aAddress = aAdapter->FirstUnicastAddress->Address.lpSockaddr;
    if (!aAddress)
        return false;

    PSOCKADDR_IN in_addr = (PSOCKADDR_IN)aAddress;
    bool isGateway = (aAddress->sa_family == AF_INET &&
        in_addr->sin_addr.S_un.S_un_b.s_b1 == 192 &&
        in_addr->sin_addr.S_un.S_un_b.s_b2 == 168 &&
        in_addr->sin_addr.S_un.S_un_b.s_b3 == 0 &&
        in_addr->sin_addr.S_un.S_un_b.s_b4 == 1);

    if (isGateway)
      isGateway = CheckICSStatus(aAdapter->FriendlyName);

    return isGateway;
}

bool
nsNotifyAddrListener::CheckICSStatus(PWCHAR aAdapterName)
{
    InitNetshellLibrary();

    // This method enumerates all privately shared connections and checks if some
    // of them has the same name as the one provided in aAdapterName. If such
    // connection is found in the collection the adapter is used as ICS gateway
    bool isICSGatewayAdapter = false;

    HRESULT hr;
    RefPtr<INetSharingManager> netSharingManager;
    hr = CoCreateInstance(
                CLSID_NetSharingManager,
                nullptr,
                CLSCTX_INPROC_SERVER,
                IID_INetSharingManager,
                getter_AddRefs(netSharingManager));

    RefPtr<INetSharingPrivateConnectionCollection> privateCollection;
    if (SUCCEEDED(hr)) {
        hr = netSharingManager->get_EnumPrivateConnections(
                    ICSSC_DEFAULT,
                    getter_AddRefs(privateCollection));
    }

    RefPtr<IEnumNetSharingPrivateConnection> privateEnum;
    if (SUCCEEDED(hr)) {
        RefPtr<IUnknown> privateEnumUnknown;
        hr = privateCollection->get__NewEnum(getter_AddRefs(privateEnumUnknown));
        if (SUCCEEDED(hr)) {
            hr = privateEnumUnknown->QueryInterface(
                        IID_IEnumNetSharingPrivateConnection,
                        getter_AddRefs(privateEnum));
        }
    }

    if (SUCCEEDED(hr)) {
        ULONG fetched;
        VARIANT connectionVariant;
        while (!isICSGatewayAdapter &&
               SUCCEEDED(hr = privateEnum->Next(1, &connectionVariant,
               &fetched)) &&
               fetched) {
            if (connectionVariant.vt != VT_UNKNOWN) {
                // We should call VariantClear here but it needs to link
                // with oleaut32.lib that produces a Ts incrase about 10ms
                // that is undesired. As it is quit unlikely the result would
                // be of a different type anyway, let's pass the variant
                // unfreed here.
                NS_ERROR("Variant of unexpected type, expecting VT_UNKNOWN, we probably leak it!");
                continue;
            }

            RefPtr<INetConnection> connection;
            if (SUCCEEDED(connectionVariant.punkVal->QueryInterface(
                              IID_INetConnection,
                              getter_AddRefs(connection)))) {
                connectionVariant.punkVal->Release();

                NETCON_PROPERTIES *properties;
                if (SUCCEEDED(connection->GetProperties(&properties))) {
                    if (!wcscmp(properties->pszwName, aAdapterName))
                        isICSGatewayAdapter = true;

                    if (sNcFreeNetconProperties)
                        sNcFreeNetconProperties(properties);
                }
            }
        }
    }

    return isICSGatewayAdapter;
}

DWORD
nsNotifyAddrListener::CheckAdaptersAddresses(void)
{
    ULONG len = 16384;

    PIP_ADAPTER_ADDRESSES adapterList = (PIP_ADAPTER_ADDRESSES) moz_xmalloc(len);

    ULONG flags = GAA_FLAG_SKIP_DNS_SERVER|GAA_FLAG_SKIP_MULTICAST|
        GAA_FLAG_SKIP_ANYCAST;

    DWORD ret = GetAdaptersAddresses(AF_UNSPEC, flags, nullptr, adapterList, &len);
    if (ret == ERROR_BUFFER_OVERFLOW) {
        free(adapterList);
        adapterList = static_cast<PIP_ADAPTER_ADDRESSES> (moz_xmalloc(len));

        ret = GetAdaptersAddresses(AF_UNSPEC, flags, nullptr, adapterList, &len);
    }

    if (FAILED(CoInitializeEx(nullptr, COINIT_MULTITHREADED))) {
        free(adapterList);
        return ERROR_NOT_SUPPORTED;
    }

    //
    // Since NotifyIpInterfaceChange() signals a change more often than we
    // think is a worthy change, we checksum the entire state of all interfaces
    // that are UP. If the checksum is the same as previous check, nothing
    // of interest changed!
    //
    ULONG sum = 0;

    if (ret == ERROR_SUCCESS) {
        bool linkUp = false;

        for (PIP_ADAPTER_ADDRESSES adapter = adapterList; adapter;
             adapter = adapter->Next) {
            if (adapter->OperStatus != IfOperStatusUp ||
                !adapter->FirstUnicastAddress ||
                adapter->IfType == IF_TYPE_SOFTWARE_LOOPBACK ||
                CheckICSGateway(adapter) ) {
                continue;
            }

            // Add chars from AdapterName to the checksum.
            for (int i = 0; adapter->AdapterName[i]; ++i) {
                sum <<= 2;
                sum += adapter->AdapterName[i];
            }

            // Add bytes from each socket address to the checksum.
            for (PIP_ADAPTER_UNICAST_ADDRESS pip = adapter->FirstUnicastAddress;
                 pip; pip = pip->Next) {
                SOCKET_ADDRESS *sockAddr = &pip->Address;
                for (int i = 0; i < sockAddr->iSockaddrLength; ++i) {
                    sum += (reinterpret_cast<unsigned char *>
                            (sockAddr->lpSockaddr))[i];
                }
            }
            linkUp = true;
        }
        mLinkUp = linkUp;
        mStatusKnown = true;
    }
    free(adapterList);

    if (mLinkUp) {
        /* Store the checksum only if one or more interfaces are up */
        mIPInterfaceChecksum = sum;
    }

    CoUninitialize();

    return ret;
}

/**
 * Checks the status of all network adapters.  If one is up and has a valid IP
 * address, sets mLinkUp to true.  Sets mStatusKnown to true if the link status
 * is definitive.
 */
void
nsNotifyAddrListener::CheckLinkStatus(void)
{
    DWORD ret;
    const char *event;
    bool prevLinkUp = mLinkUp;
    ULONG prevCsum = mIPInterfaceChecksum;

    LOG(("check status of all network adapters\n"));

    // The CheckAdaptersAddresses call is very expensive (~650 milliseconds),
    // so we don't want to call it synchronously. Instead, we just start up
    // assuming we have a network link, but we'll report that the status is
    // unknown.
    if (NS_IsMainThread()) {
        NS_WARNING("CheckLinkStatus called on main thread! No check "
                   "performed. Assuming link is up, status is unknown.");
        mLinkUp = true;

        if (!mStatusKnown) {
            event = NS_NETWORK_LINK_DATA_UNKNOWN;
        } else if (!prevLinkUp) {
            event = NS_NETWORK_LINK_DATA_UP;
        } else {
            // Known status and it was already UP
            event = nullptr;
        }

        if (event) {
            SendEvent(event);
        }
    } else {
        ret = CheckAdaptersAddresses();
        if (ret != ERROR_SUCCESS) {
            mLinkUp = true;
        }

        if (mLinkUp && (prevCsum != mIPInterfaceChecksum)) {
            TimeDuration since = TimeStamp::Now() - mStartTime;

            // Network is online. Topology has changed. Always send CHANGED
            // before UP - if allowed to and having cooled down.
            if (mAllowChangedEvent && (since.ToMilliseconds() > 2000)) {
                NetworkChanged();
            }
        }
        if (prevLinkUp != mLinkUp) {
            // UP/DOWN status changed, send appropriate UP/DOWN event
            SendEvent(mLinkUp ?
                      NS_NETWORK_LINK_DATA_UP : NS_NETWORK_LINK_DATA_DOWN);
        }
    }
}