qtenvironmentvariables.cpp

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// Copyright (C) 2022 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
 
#include "qtenvironmentvariables.h"
#include "qtenvironmentvariables_p.h"
 
#include <qplatformdefs.h>
#include <QtCore/qbytearray.h>
#include <QtCore/qmutex.h>
#include <QtCore/qstring.h>
#include <QtCore/qvarlengtharray.h>
 
#include <QtCore/private/qlocking_p.h>
 
QT_BEGIN_NAMESPACE
 
// In the C runtime on all platforms access to the environment is not thread-safe. We
// add thread-safety for the Qt wrappers.
Q_CONSTINIT static QBasicMutex environmentMutex;
 
QByteArray qgetenv(const char *varName)
{
    const auto locker = qt_scoped_lock(environmentMutex);
#ifdef Q_CC_MSVC
    size_t requiredSize = 0;
    QByteArray buffer;
    getenv_s(&requiredSize, 0, 0, varName);
    if (requiredSize == 0)
        return buffer;
    buffer.resize(qsizetype(requiredSize));
    getenv_s(&requiredSize, buffer.data(), requiredSize, varName);
    // requiredSize includes the terminating null, which we don't want.
    Q_ASSERT(buffer.endsWith('\0'));
    buffer.chop(1);
    return buffer;
#else
    return QByteArray(::getenv(varName));
#endif
}
 
QString qEnvironmentVariable(const char *varName, const QString &defaultValue)
{
#if defined(Q_OS_WIN)
    QVarLengthArray<wchar_t, 32> wname(qsizetype(strlen(varName)) + 1);
    for (qsizetype i = 0; i < wname.size(); ++i) // wname.size() is correct: will copy terminating null
        wname[i] = uchar(varName[i]);
    size_t requiredSize = 0;
    auto locker = qt_unique_lock(environmentMutex);
    _wgetenv_s(&requiredSize, 0, 0, wname.data());
    if (requiredSize == 0)
        return defaultValue;
    QString buffer(qsizetype(requiredSize), Qt::Uninitialized);
    _wgetenv_s(&requiredSize, reinterpret_cast<wchar_t *>(buffer.data()), requiredSize,
               wname.data());
    locker.unlock();
    // requiredSize includes the terminating null, which we don't want.
    Q_ASSERT(buffer.endsWith(QChar(u'\0')));
    buffer.chop(1);
    return buffer;
#else
    QByteArray value = qgetenv(varName);
    if (value.isNull())
        return defaultValue;
// duplicated in qfile.h (QFile::decodeName)
#if defined(Q_OS_DARWIN)
    return QString::fromUtf8(value).normalized(QString::NormalizationForm_C);
#else // other Unix
    return QString::fromLocal8Bit(value);
#endif
#endif
}
 
QString qEnvironmentVariable(const char *varName)
{
    return qEnvironmentVariable(varName, QString());
}
 
bool qEnvironmentVariableIsEmpty(const char *varName) noexcept
{
    const auto locker = qt_scoped_lock(environmentMutex);
#ifdef Q_CC_MSVC
    // we provide a buffer that can only hold the empty string, so
    // when the env.var isn't empty, we'll get an ERANGE error (buffer
    // too small):
    size_t dummy;
    char buffer = '\0';
    return getenv_s(&dummy, &buffer, 1, varName) != ERANGE;
#else
    const char * const value = ::getenv(varName);
    return !value || !*value;
#endif
}
 
int qEnvironmentVariableIntValue(const char *varName, bool *ok) noexcept
{
    static const int NumBinaryDigitsPerOctalDigit = 3;
    static const int MaxDigitsForOctalInt =
        (std::numeric_limits<uint>::digits + NumBinaryDigitsPerOctalDigit - 1) / NumBinaryDigitsPerOctalDigit;
 
    const auto locker = qt_scoped_lock(environmentMutex);
    size_t size;
#ifdef Q_CC_MSVC
    // we provide a buffer that can hold any int value:
    char buffer[MaxDigitsForOctalInt + 2]; // +1 for NUL +1 for optional '-'
    size_t dummy;
    if (getenv_s(&dummy, buffer, sizeof buffer, varName) != 0) {
        if (ok)
            *ok = false;
        return 0;
    }
    size = strlen(buffer);
#else
    const char * const buffer = ::getenv(varName);
    if (!buffer || (size = strlen(buffer)) > MaxDigitsForOctalInt + 2) {
        if (ok)
            *ok = false;
        return 0;
    }
#endif
    return QByteArrayView(buffer, size).toInt(ok, 0);
}
 
bool qEnvironmentVariableIsSet(const char *varName) noexcept
{
    const auto locker = qt_scoped_lock(environmentMutex);
#ifdef Q_CC_MSVC
    size_t requiredSize = 0;
    (void)getenv_s(&requiredSize, 0, 0, varName);
    return requiredSize != 0;
#else
    return ::getenv(varName) != nullptr;
#endif
}
 
bool qputenv(const char *varName, QByteArrayView raw)
{
    auto protect = [](const char *str) { return str ? str : ""; };
 
    std::string value{protect(raw.data()), size_t(raw.size())}; // NUL-terminates w/SSO
 
#if defined(Q_CC_MSVC)
    const auto locker = qt_scoped_lock(environmentMutex);
    return _putenv_s(varName, value.data()) == 0;
#elif (defined(_POSIX_VERSION) && (_POSIX_VERSION-0) >= 200112L) || defined(Q_OS_HAIKU)
    // POSIX.1-2001 has setenv
    const auto locker = qt_scoped_lock(environmentMutex);
    return setenv(varName, value.data(), true) == 0;
#else
    std::string buffer;
    buffer += protect(varName);
    buffer += '=';
    buffer += value;
    char *envVar = qstrdup(buffer.data());
    int result = [&] {
        const auto locker = qt_scoped_lock(environmentMutex);
        return putenv(envVar);
    }();
    if (result != 0) // error. we have to delete the string.
        delete[] envVar;
    return result == 0;
#endif
}
 
bool qunsetenv(const char *varName)
{
#if defined(Q_CC_MSVC)
    const auto locker = qt_scoped_lock(environmentMutex);
    return _putenv_s(varName, "") == 0;
#elif (defined(_POSIX_VERSION) && (_POSIX_VERSION-0) >= 200112L) || defined(Q_OS_BSD4) || defined(Q_OS_HAIKU)
    // POSIX.1-2001, BSD and Haiku have unsetenv
    const auto locker = qt_scoped_lock(environmentMutex);
    return unsetenv(varName) == 0;
#elif defined(Q_CC_MINGW)
    // On mingw, putenv("var=") removes "var" from the environment
    QByteArray buffer(varName);
    buffer += '=';
    const auto locker = qt_scoped_lock(environmentMutex);
    return putenv(buffer.constData()) == 0;
#else
    // Fallback to putenv("var=") which will insert an empty var into the
    // environment and leak it
    QByteArray buffer(varName);
    buffer += '=';
    char *envVar = qstrdup(buffer.constData());
    const auto locker = qt_scoped_lock(environmentMutex);
    return putenv(envVar) == 0;
#endif
}
 
/* Various time-related APIs that need to consult system settings also need
   protection with the same lock as the environment, since those system settings
   include part of the environment (principally TZ).
 
   First, tzset(), which POSIX explicitly says accesses the environment.
*/
void qTzSet()
{
    const auto locker = qt_scoped_lock(environmentMutex);
#if defined(Q_OS_WIN)
    _tzset();
#else
    tzset();
#endif // Q_OS_WIN
}
 
/* Wrap mktime(), which is specified to behave as if it called tzset(), hence
   shares its implicit environment-dependence.
*/
time_t qMkTime(struct tm *when)
{
    const auto locker = qt_scoped_lock(environmentMutex);
    return mktime(when);
}
 
/* For localtime(), POSIX mandates that it behave as if it called tzset().
   For the alternatives to it, we need (if only for compatibility) to do the
   same explicitly, which should ensure a re-parse of timezone info.
*/
bool qLocalTime(time_t utc, struct tm *local)
{
    const auto locker = qt_scoped_lock(environmentMutex);
#if defined(Q_OS_WIN)
    // The doc of localtime_s() says that it corrects for the same things
    // _tzset() sets the globals for, but QTBUG-109974 reveals a need for an
    // explicit call, all the same.
    _tzset();
    return !localtime_s(local, &utc);
#elif QT_CONFIG(thread) && defined(_POSIX_THREAD_SAFE_FUNCTIONS)
    // Use the reentrant version of localtime() where available, as it is
    // thread-safe and doesn't use a shared static data area.
    // As localtime_r() is not specified to work as if it called tzset(),
    // make an explicit call.
    tzset();
    if (tm *res = localtime_r(&utc, local)) {
        Q_ASSERT(res == local);
        Q_UNUSED(res);
        return true;
    }
    return false;
#else
    // POSIX mandates that localtime() behaves as if it called tzset().
    // Returns shared static data which may be overwritten at any time (albeit
    // our lock probably keeps it safe). So copy the result promptly:
    if (tm *res = localtime(&utc)) {
        *local = *res;
        return true;
    }
    return false;
#endif
}
 
/* Access to the tzname[] global in one thread is UB if any other is calling
   tzset() or anything that behaves as if it called tzset(). So also lock this
   access to prevent such collisions.
 
   Parameter dstIndex must be 1 for DST or 0 for standard time.
   Returns the relevant form of the name of local-time's zone.
*/
QString qTzName(int dstIndex)
{
    char name[512];
    bool ok;
#if defined(Q_CC_MSVC)
    size_t s = 0;
    {
        const auto locker = qt_scoped_lock(environmentMutex);
        ok = _get_tzname(&s, name, 512, dstIndex) != 0;
    }
#else
    {
        const auto locker = qt_scoped_lock(environmentMutex);
        const char *const src = tzname[dstIndex];
        ok = src != nullptr;
        if (ok)
            memcpy(name, src, std::min(sizeof(name), strlen(src) + 1));
    }
#endif // Q_OS_WIN
    return ok ? QString::fromLocal8Bit(name) : QString();
}
 
QT_END_NAMESPACE