/* $Id: HostDnsServiceWin.cpp 98292 2023-01-25 01:14:53Z vboxsync $ */
/** @file
 * Host DNS listener for Windows.
 */

/*
 * Copyright (C) 2014-2023 Oracle and/or its affiliates.
 *
 * This file is part of VirtualBox base platform packages, as
 * available from https://www.virtualbox.org.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation, in version 3 of the
 * License.
 *
 * 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, see <https://www.gnu.org/licenses>.
 *
 * SPDX-License-Identifier: GPL-3.0-only
 */

/*
 * XXX: need <winsock2.h> to reveal IP_ADAPTER_ADDRESSES in
 * <iptypes.h> and it must be included before <windows.h>, which is
 * pulled in by IPRT headers.
 */
#include <iprt/win/winsock2.h>

#include "../HostDnsService.h"

#include <VBox/com/string.h>
#include <VBox/com/ptr.h>

#include <iprt/assert.h>
#include <iprt/errcore.h>
#include <VBox/log.h>

#include <iprt/win/windows.h>
#include <windns.h>
#include <iptypes.h>
#include <iprt/win/iphlpapi.h>

#include <algorithm>
#include <iprt/sanitized/sstream>
#include <iprt/sanitized/string>
#include <vector>


DECLINLINE(int) registerNotification(const HKEY &hKey, HANDLE &hEvent)
{
    LONG lrc = RegNotifyChangeKeyValue(hKey,
                                       TRUE,
                                       REG_NOTIFY_CHANGE_LAST_SET,
                                       hEvent,
                                       TRUE);
    AssertMsgReturn(lrc == ERROR_SUCCESS,
                    ("Failed to register event on the key. Please debug me!"),
                    VERR_INTERNAL_ERROR);

    return VINF_SUCCESS;
}

static void appendTokenizedStrings(std::vector<std::string> &vecStrings, const std::string &strToAppend, char chDelim = ' ')
{
    if (strToAppend.empty())
        return;

    std::istringstream stream(strToAppend);
    std::string substr;

    while (std::getline(stream, substr, chDelim))
    {
        if (substr.empty())
            continue;

        if (std::find(vecStrings.cbegin(), vecStrings.cend(), substr) != vecStrings.cend())
            continue;

        vecStrings.push_back(substr);
    }
}


struct HostDnsServiceWin::Data
{
    HKEY hKeyTcpipParameters;
    bool fTimerArmed;

#define DATA_SHUTDOWN_EVENT   0
#define DATA_DNS_UPDATE_EVENT 1
#define DATA_TIMER            2
#define DATA_MAX_EVENT        3
    HANDLE haDataEvent[DATA_MAX_EVENT];

    Data()
    {
        hKeyTcpipParameters = NULL;
        fTimerArmed = false;

        for (size_t i = 0; i < DATA_MAX_EVENT; ++i)
            haDataEvent[i] = NULL;
    }

    ~Data()
    {
        if (hKeyTcpipParameters != NULL)
            RegCloseKey(hKeyTcpipParameters);

        for (size_t i = 0; i < DATA_MAX_EVENT; ++i)
            if (haDataEvent[i] != NULL)
                CloseHandle(haDataEvent[i]);
    }
};


HostDnsServiceWin::HostDnsServiceWin()
    : HostDnsServiceBase(true)
{
    m = new Data();
}

HostDnsServiceWin::~HostDnsServiceWin()
{
    if (m != NULL)
        delete m;
}

HRESULT HostDnsServiceWin::init(HostDnsMonitorProxy *pProxy)
{
    if (m == NULL)
        return E_FAIL;

    bool fRc = true;
    LONG lRc = RegOpenKeyExW(HKEY_LOCAL_MACHINE,
                             L"SYSTEM\\CurrentControlSet\\Services\\Tcpip\\Parameters",
                             0,
                             KEY_READ|KEY_NOTIFY,
                             &m->hKeyTcpipParameters);
    if (lRc != ERROR_SUCCESS)
    {
        LogRel(("HostDnsServiceWin: failed to open key Tcpip\\Parameters (error %d)\n", lRc));
        fRc = false;
    }
    else
    {
        for (size_t i = 0; i < DATA_MAX_EVENT; ++i)
        {
            HANDLE h;

            if (i ==  DATA_TIMER)
                h = CreateWaitableTimer(NULL, FALSE, NULL);
            else
                h = CreateEvent(NULL, TRUE, FALSE, NULL);

            if (h == NULL)
            {
                LogRel(("HostDnsServiceWin: failed to create event (error %d)\n", GetLastError()));
                fRc = false;
                break;
            }

            m->haDataEvent[i] = h;
        }
    }

    if (!fRc)
        return E_FAIL;

    HRESULT hrc = HostDnsServiceBase::init(pProxy);
    if (FAILED(hrc))
        return hrc;

    return updateInfo();
}

void HostDnsServiceWin::uninit(void)
{
    HostDnsServiceBase::uninit();
}

int HostDnsServiceWin::monitorThreadShutdown(RTMSINTERVAL uTimeoutMs)
{
    RT_NOREF(uTimeoutMs);

    AssertPtr(m);
    SetEvent(m->haDataEvent[DATA_SHUTDOWN_EVENT]);
    /** @todo r=andy Wait for thread? Check vrc here. Timeouts? */

    return VINF_SUCCESS;
}

int HostDnsServiceWin::monitorThreadProc(void)
{
    Assert(m != NULL);

    registerNotification(m->hKeyTcpipParameters,
                         m->haDataEvent[DATA_DNS_UPDATE_EVENT]);

    onMonitorThreadInitDone();

    for (;;)
    {
        DWORD dwReady;

        dwReady = WaitForMultipleObjects(DATA_MAX_EVENT, m->haDataEvent,
                                         FALSE, INFINITE);

        if (dwReady == WAIT_OBJECT_0 + DATA_SHUTDOWN_EVENT)
            break;

        if (dwReady == WAIT_OBJECT_0 + DATA_DNS_UPDATE_EVENT)
        {
            /*
             * Registry updates for multiple values are not atomic, so
             * wait a bit to avoid racing and reading partial update.
             */
            if (!m->fTimerArmed)
            {
                LARGE_INTEGER delay; /* in 100ns units */
                delay.QuadPart = -2 * 1000 * 1000 * 10LL; /* relative: 2s */

                BOOL ok = SetWaitableTimer(m->haDataEvent[DATA_TIMER], &delay,
                                           0, NULL, NULL, FALSE);
                if (ok)
                {
                    m->fTimerArmed = true;
                }
                else
                {
                    LogRel(("HostDnsServiceWin: failed to arm timer (error %d)\n", GetLastError()));
                    updateInfo();
                }
            }

            ResetEvent(m->haDataEvent[DATA_DNS_UPDATE_EVENT]);
            registerNotification(m->hKeyTcpipParameters,
                                 m->haDataEvent[DATA_DNS_UPDATE_EVENT]);
        }
        else if (dwReady == WAIT_OBJECT_0 + DATA_TIMER)
        {
            m->fTimerArmed = false;
            updateInfo();
        }
        else if (dwReady == WAIT_FAILED)
        {
            LogRel(("HostDnsServiceWin: WaitForMultipleObjects failed: error %d\n", GetLastError()));
            return VERR_INTERNAL_ERROR;
        }
        else
        {
            LogRel(("HostDnsServiceWin: WaitForMultipleObjects unexpected return value %d\n", dwReady));
            return VERR_INTERNAL_ERROR;
        }
    }

    return VINF_SUCCESS;
}

HRESULT HostDnsServiceWin::updateInfo(void)
{
    HostDnsInformation info;

    std::string strDomain;
    std::string strSearchList;  /* NB: comma separated, no spaces */

    /*
     * We ignore "DhcpDomain" key here since it's not stable.  If
     * there are two active interfaces that use DHCP (in particular
     * when host uses OpenVPN) then DHCP ACKs will take turns updating
     * that key.  Instead we call GetAdaptersAddresses() below (which
     * is what ipconfig.exe seems to do).
     */
    for (DWORD regIndex = 0; /**/; ++regIndex)
    {
        char keyName[256];
        DWORD cbKeyName = sizeof(keyName);
        DWORD keyType = 0;
        char keyData[1024];
        DWORD cbKeyData = sizeof(keyData);

/** @todo use unicode API. This isn't UTF-8 clean!   */
        LSTATUS lrc = RegEnumValueA(m->hKeyTcpipParameters, regIndex,
                                    keyName, &cbKeyName, 0,
                                    &keyType, (LPBYTE)keyData, &cbKeyData);

        if (lrc == ERROR_NO_MORE_ITEMS)
            break;

        if (lrc == ERROR_MORE_DATA) /* buffer too small; handle? */
            continue;

        if (lrc != ERROR_SUCCESS)
        {
            LogRel2(("HostDnsServiceWin: RegEnumValue error %d\n", (int)lrc));
            return E_FAIL;
        }

        if (keyType != REG_SZ)
            continue;

        if (cbKeyData > 0 && keyData[cbKeyData - 1] == '\0')
            --cbKeyData;     /* don't count trailing NUL if present */

        if (RTStrICmp("Domain", keyName) == 0)
        {
            strDomain.assign(keyData, cbKeyData);
            LogRel2(("HostDnsServiceWin: Domain=\"%s\"\n", strDomain.c_str()));
        }
        else if (RTStrICmp("DhcpDomain", keyName) == 0)
        {
            std::string strDhcpDomain(keyData, cbKeyData);
            LogRel2(("HostDnsServiceWin: DhcpDomain=\"%s\"\n", strDhcpDomain.c_str()));
        }
        else if (RTStrICmp("SearchList", keyName) == 0)
        {
            strSearchList.assign(keyData, cbKeyData);
            LogRel2(("HostDnsServiceWin: SearchList=\"%s\"\n", strSearchList.c_str()));
        }
    }

    /* statically configured domain name */
    if (!strDomain.empty())
    {
        info.domain = strDomain;
        info.searchList.push_back(strDomain);
    }

    /* statically configured search list */
    if (!strSearchList.empty())
        appendTokenizedStrings(info.searchList, strSearchList, ',');

    /*
     * When name servers are configured statically it seems that the
     * value of Tcpip\Parameters\NameServer is NOT set, inly interface
     * specific NameServer value is (which triggers notification for
     * us to pick up the change).  Fortunately, DnsApi seems to do the
     * right thing there.
     */
    DNS_STATUS status;
    PIP4_ARRAY pIp4Array = NULL;

    // NB: must be set on input it seems, despite docs' claim to the contrary.
    DWORD cbBuffer = sizeof(&pIp4Array);

    status = DnsQueryConfig(DnsConfigDnsServerList,
                            DNS_CONFIG_FLAG_ALLOC, NULL, NULL,
                            &pIp4Array, &cbBuffer);

    if (status == NO_ERROR && pIp4Array != NULL)
    {
        for (DWORD i = 0; i < pIp4Array->AddrCount; ++i)
        {
            char szAddrStr[16] = "";
            RTStrPrintf(szAddrStr, sizeof(szAddrStr), "%RTnaipv4", pIp4Array->AddrArray[i]);

            LogRel2(("HostDnsServiceWin: server %d: %s\n", i+1,  szAddrStr));
            info.servers.push_back(szAddrStr);
        }

        LocalFree(pIp4Array);
    }


    /**
     * DnsQueryConfig(DnsConfigSearchList, ...) is not implemented.
     * Call GetAdaptersAddresses() that orders the returned list
     * appropriately and collect IP_ADAPTER_ADDRESSES::DnsSuffix.
     */
    do {
        PIP_ADAPTER_ADDRESSES pAddrBuf = NULL;
        ULONG cbAddrBuf = 8 * 1024;
        bool fReallocated = false;
        ULONG err;

        pAddrBuf = (PIP_ADAPTER_ADDRESSES) malloc(cbAddrBuf);
        if (pAddrBuf == NULL)
        {
            LogRel2(("HostDnsServiceWin: failed to allocate %zu bytes"
                     " of GetAdaptersAddresses buffer\n",
                     (size_t)cbAddrBuf));
            break;
        }

        while (pAddrBuf != NULL)
        {
            ULONG cbAddrBufProvided = cbAddrBuf;

            err = GetAdaptersAddresses(AF_UNSPEC,
                                         GAA_FLAG_SKIP_ANYCAST
                                       | GAA_FLAG_SKIP_MULTICAST,
                                       NULL,
                                       pAddrBuf, &cbAddrBuf);
            if (err == NO_ERROR)
            {
                break;
            }
            else if (err == ERROR_BUFFER_OVERFLOW)
            {
                LogRel2(("HostDnsServiceWin: provided GetAdaptersAddresses with %zu"
                         " but asked again for %zu bytes\n",
                         (size_t)cbAddrBufProvided, (size_t)cbAddrBuf));

                if (RT_UNLIKELY(fReallocated)) /* what? again?! */
                {
                    LogRel2(("HostDnsServiceWin: ... not going to realloc again\n"));
                    free(pAddrBuf);
                    pAddrBuf = NULL;
                    break;
                }

                PIP_ADAPTER_ADDRESSES pNewBuf = (PIP_ADAPTER_ADDRESSES) realloc(pAddrBuf, cbAddrBuf);
                if (pNewBuf == NULL)
                {
                    LogRel2(("HostDnsServiceWin: failed to reallocate %zu bytes\n", (size_t)cbAddrBuf));
                    free(pAddrBuf);
                    pAddrBuf = NULL;
                    break;
                }

                /* try again */
                pAddrBuf = pNewBuf; /* cbAddrBuf already updated */
                fReallocated = true;
            }
            else
            {
                LogRel2(("HostDnsServiceWin: GetAdaptersAddresses error %d\n", err));
                free(pAddrBuf);
                pAddrBuf = NULL;
                break;
            }
        }

        if (pAddrBuf == NULL)
            break;

        for (PIP_ADAPTER_ADDRESSES pAdp = pAddrBuf; pAdp != NULL; pAdp = pAdp->Next)
        {
            LogRel2(("HostDnsServiceWin: %ls (status %u) ...\n",
                     pAdp->FriendlyName ? pAdp->FriendlyName : L"(null)", pAdp->OperStatus));

            if (pAdp->OperStatus != IfOperStatusUp)
                continue;

            if (pAdp->DnsSuffix == NULL || *pAdp->DnsSuffix == L'\0')
                continue;

            char *pszDnsSuffix = NULL;
            int vrc = RTUtf16ToUtf8Ex(pAdp->DnsSuffix, RTSTR_MAX, &pszDnsSuffix, 0, /* allocate */ NULL);
            if (RT_FAILURE(vrc))
            {
                LogRel2(("HostDnsServiceWin: failed to convert DNS suffix \"%ls\": %Rrc\n", pAdp->DnsSuffix, vrc));
                continue;
            }

            AssertContinue(pszDnsSuffix != NULL);
            AssertContinue(*pszDnsSuffix != '\0');
            LogRel2(("HostDnsServiceWin: ... suffix = \"%s\"\n", pszDnsSuffix));

            appendTokenizedStrings(info.searchList, pszDnsSuffix);
            RTStrFree(pszDnsSuffix);
        }

        free(pAddrBuf);
    } while (0);


    if (info.domain.empty() && !info.searchList.empty())
        info.domain = info.searchList[0];

    if (info.searchList.size() == 1)
        info.searchList.clear();

    HostDnsServiceBase::setInfo(info);

    return S_OK;
}