// Copyright (C) 2016 The Qt Company Ltd.

// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only

// Qt-Security score:significant reason:trusted-data

//#define QHOSTINFO_DEBUG

#include "qhostinfo_p.h"

#include <qbytearray.h>

#include <qfile.h>

#include <qplatformdefs.h>

#include <qurl.h>

#include <sys/types.h>

#include <netdb.h>

#include <netinet/in.h>

#if QT_CONFIG(libresolv)

#  include <resolv.h>

#endif

#ifndef _PATH_RESCONF

#  define _PATH_RESCONF "/etc/resolv.conf"

#endif

QT_BEGIN_NAMESPACE

using namespace Qt::StringLiterals;

static void maybeRefreshResolver()

{

#if defined(RES_NORELOAD)

    // If RES_NORELOAD is defined, then the libc is capable of watching

    // /etc/resolv.conf for changes and reloading as necessary. So accept

    // whatever is configured.

    return;

#elif defined(Q_OS_DARWIN)

    // Apple's libsystem_info.dylib:getaddrinfo() uses the

    // libsystem_dnssd.dylib to resolve hostnames. Using res_init() has no

    // effect on it and is thread-unsafe.

    return;

#elif defined(Q_OS_FREEBSD)

    // FreeBSD automatically refreshes:

    // https://github.com/freebsd/freebsd-src/blob/b3fe5d932264445cbf9a1c4eab01afb6179b499b/lib/libc/resolv/res_state.c#L69

    return;

#elif defined(Q_OS_OPENBSD)

    // OpenBSD automatically refreshes:

    // https://github.com/ligurio/openbsd-src/blob/b1ce0da17da254cc15b8aff25b3d55d3c7a82cec/lib/libc/asr/asr.c#L367

    return;

#elif defined(Q_OS_QNX)

    // res_init() is not thread-safe; executing it leads to state corruption.

    // Whether it reloads resolv.conf on its own is unknown.

    return;

#endif

#if QT_CONFIG(libresolv)

    // OSes known or thought to reach here: AIX, NetBSD, Solaris,

    // Linux with MUSL (though res_init() does nothing and is unnecessary)

    Q_CONSTINIT static QT_STATBUF lastStat = {};

    Q_CONSTINIT static QBasicMutex mutex = {};

    if (QT_STATBUF st; QT_STAT(_PATH_RESCONF, &st) == 0) {

        QMutexLocker locker(&mutex);

        bool refresh = false;

        if ((_res.options & RES_INIT) == 0)

            refresh = true;

        else if (lastStat.st_ctime != st.st_ctime)

            refresh = true;     // file was updated

        else if (lastStat.st_dev != st.st_dev || lastStat.st_ino != st.st_ino)

            refresh = true;     // file was replaced

        if (refresh) {

            lastStat = st;

            res_init();

        }

    }

#endif

}

QHostInfo QHostInfoAgent::fromName(const QString &hostName)

{

    QHostInfo results;

#if defined(QHOSTINFO_DEBUG)

    qDebug("QHostInfoAgent::fromName(%s) looking up...",

           hostName.toLatin1().constData());

#endif

    maybeRefreshResolver();

    QHostAddress address;

    if (address.setAddress(hostName))

        return reverseLookup(address);

    return lookup(hostName);

}

QString QHostInfo::localDomainName()

{

#if QT_CONFIG(libresolv)

    auto domainNameFromRes = [](res_state r) {

        QString domainName;

        if (r->defdname[0])

            domainName = QUrl::fromAce(r->defdname);

        if (domainName.isEmpty())

            domainName = QUrl::fromAce(r->dnsrch[0]);

        return domainName;

    };

    std::remove_pointer_t<res_state> state = {};

    if (res_ninit(&state) == 0) {

        // using thread-safe version

        auto guard = qScopeGuard([&] { res_nclose(&state); });

        return domainNameFromRes(&state);

    }

    // using thread-unsafe version

    maybeRefreshResolver();

    return domainNameFromRes(&_res);

#endif  // !QT_CONFIG(libresolv)

    // nothing worked, try doing it by ourselves:

    QFile resolvconf;

    resolvconf.setFileName(_PATH_RESCONF ""_L1);

    if (!resolvconf.open(QIODevice::ReadOnly))

        return QString();       // failure

    QString domainName;

    QByteArray lineArray;

    while (resolvconf.readLineInto(&lineArray)) {

        QByteArrayView line = QByteArrayView(lineArray).trimmed();

        constexpr QByteArrayView domainWithSpace = "domain ";

        if (line.startsWith(domainWithSpace))

            return QUrl::fromAce(line.mid(domainWithSpace.size()).trimmed().toByteArray());

        // in case there's no "domain" line, fall back to the first "search" entry

        constexpr QByteArrayView searchWithSpace = "search ";

        if (domainName.isEmpty() && line.startsWith(searchWithSpace)) {

            QByteArrayView searchDomain = line.mid(searchWithSpace.size()).trimmed();

            int pos = searchDomain.indexOf(' ');

            if (pos != -1)

                searchDomain.truncate(pos);

            domainName = QUrl::fromAce(searchDomain.toByteArray());

        }

    }

    // return the fallen-back-to searched domain

    return domainName;

}

QT_END_NAMESPACE