qputenv: port to QByteArrayView

The vast majority of in-tree users pass simple and short C string
literals as the value. By porting to QByteArrayView, we document that
we'll accept non-NUL-terminated data, and do the NUL-termination
internally, using SSO'ed std::string, saving memory allocations in the
common case of short strings.

I didn't bother to check which direction std::string takes for
nullptrs these days (there was a change accepted in that area for
C++20 or 23), so play it safe and protect against them.

Follow-up to

Task-number: QTBUG-105302
Change-Id: I2369acc62f1d5cbc26135396cfe0602d8c75300c
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

4 files changed, 27 insertions, 13 deletions

diff --git a/src/corelib/compat/removed_api.cpp b/src/corelib/compat/removed_api.cpp
index 2b864ad41f..aa1a496f0f 100644
--- a/src/corelib/compat/removed_api.cpp
+++ b/src/corelib/compat/removed_api.cpp
@@ -285,6 +285,13 @@ QT_WARNING_POP
 
 #if QT_CORE_REMOVED_SINCE(6, 5)
 
+#include "qenvironmentvariables.h"
+
+bool qputenv(const char *varName, const QByteArray &value)
+{
+    return qputenv(varName, qToByteArrayViewIgnoringNull(value));
+}
+
 #include "qmetatype.h"
 
 int QMetaType::idHelper() const
diff --git a/src/corelib/global/qenvironmentvariables.cpp b/src/corelib/global/qenvironmentvariables.cpp
index d3d963e52e..4860913327 100644
--- a/src/corelib/global/qenvironmentvariables.cpp
+++ b/src/corelib/global/qenvironmentvariables.cpp
@@ -243,6 +243,7 @@ bool qEnvironmentVariableIsSet(const char *varName) noexcept
 }
 
 /*!
+    \fn bool qputenv(const char *varName, QByteArrayView value)
     \relates <QEnvironmentVariables>
 
     This function sets the \a value of the environment variable named
@@ -258,30 +259,30 @@ bool qEnvironmentVariableIsSet(const char *varName) noexcept
     uses the replacement function in VC, and calls the standard C
     library's implementation on all other platforms.
 
+    \note In Qt versions prior to 6.5, the \a value argument was QByteArray,
+    not QByteArrayView.
+
     \sa qgetenv(), qEnvironmentVariable()
 */
-bool qputenv(const char *varName, const QByteArray &value)
+bool qputenv(const char *varName, QByteArrayView raw)
 {
-    // protect against non-NUL-terminated QByteArrays:
-    if (!const_cast<QByteArray&>(value).data_ptr()->isMutable()) {
-        QByteArray copy(value);
-        copy.reserve(copy.size() + 1); // ensures NUL termination (and isMutable() even for size==0
-                                       // (unlike detach()) to avoid infinite recursion)
-        return qputenv(varName, copy);
-    }
+    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.constData()) == 0;
+    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.constData(), true) == 0;
+    return setenv(varName, value.data(), true) == 0;
 #else
-    QByteArray buffer(varName);
+    std::string buffer;
+    buffer += protect(varName);
     buffer += '=';
     buffer += value;
-    char *envVar = qstrdup(buffer.constData());
+    char *envVar = qstrdup(buffer.data());
     int result = [&] {
         const auto locker = qt_scoped_lock(environmentMutex);
         return putenv(envVar);
diff --git a/src/corelib/global/qenvironmentvariables.h b/src/corelib/global/qenvironmentvariables.h
index cde51c9ba1..78fea255d3 100644
--- a/src/corelib/global/qenvironmentvariables.h
+++ b/src/corelib/global/qenvironmentvariables.h
@@ -5,6 +5,7 @@
 #define QENVIRONMENTVARIABLES_H
 
 #include <QtCore/qglobal.h>
+#include <QtCore/qtdeprecationmarkers.h>
 
 #if 0
 #pragma qt_class(QEnvironmentVariables)
@@ -14,11 +15,16 @@
 QT_BEGIN_NAMESPACE
 
 class QByteArray;
+class QByteArrayView;
+
 Q_CORE_EXPORT QByteArray qgetenv(const char *varName);
 // need it as two functions because QString is only forward-declared here
 Q_CORE_EXPORT QString qEnvironmentVariable(const char *varName);
 Q_CORE_EXPORT QString qEnvironmentVariable(const char *varName, const QString &defaultValue);
+#if QT_CORE_REMOVED_SINCE(6, 5)
 Q_CORE_EXPORT bool qputenv(const char *varName, const QByteArray &value);
+#endif
+Q_CORE_EXPORT bool qputenv(const char *varName, QByteArrayView value);
 Q_CORE_EXPORT bool qunsetenv(const char *varName);
 
 Q_CORE_EXPORT bool qEnvironmentVariableIsEmpty(const char *varName) noexcept;
diff --git a/src/gui/opengl/platform/unix/qglxconvenience.cpp b/src/gui/opengl/platform/unix/qglxconvenience.cpp
index a756caf343..ce70818042 100644
--- a/src/gui/opengl/platform/unix/qglxconvenience.cpp
+++ b/src/gui/opengl/platform/unix/qglxconvenience.cpp
@@ -124,7 +124,7 @@ struct QXcbSoftwareOpenGLEnforcer {
         }
 
         if (forceSoftwareOpenGL)
-            qputenv("LIBGL_ALWAYS_SOFTWARE", QByteArrayLiteral("1"));
+            qputenv("LIBGL_ALWAYS_SOFTWARE", "1");
     }
 
     ~QXcbSoftwareOpenGLEnforcer() {