QLockFile: make sure we encode the hostname as UTF-8 in the lock file

We chose to use UTF-8 as it allows us to ensure there's no mistaking the
hostname in case the locale is changed, if the host name contains
characters outside of US-ASCII.

But this didn't work because the code that wrote the hostname always
used the local 8-bit codec instead of UTF-8. On Unix, we used the
result of gethostname(3) directly, which is supposedly on the locale codec.
This commit doesn't fix Windows, which requires _wgetenv, the plan being
to encapsulate that with a qEnvironmentVariable() method.

[ChangeLog][QtCore][QLockFile] Fixed a bug that caused QLockFile not to
recognize a stale lock file if the machine's hostname contained non-US-
ASCII characters, on Unix. A Windows fix is still pending.

Task-number: QTBUG-49640
Change-Id: Ib9d045544ff370ec901626658a84ec4e6575fe21
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 2 insertions, 11 deletions

diff --git a/src/corelib/io/qlockfile_unix.cpp b/src/corelib/io/qlockfile_unix.cpp
index 82beb15912..3a80014c00 100644
--- a/src/corelib/io/qlockfile_unix.cpp
+++ b/src/corelib/io/qlockfile_unix.cpp
@@ -81,15 +81,6 @@
 
 QT_BEGIN_NAMESPACE
 
-static QByteArray localHostName() // from QHostInfo::localHostName(), modified to return a QByteArray
-{
-    QByteArray hostName(512, Qt::Uninitialized);
-    if (gethostname(hostName.data(), hostName.size()) == -1)
-        return QByteArray();
-    hostName.truncate(strlen(hostName.data()));
-    return hostName;
-}
-
 // ### merge into qt_safe_write?
 static qint64 qt_write_loop(int fd, const char *data, qint64 len)
 {
@@ -185,7 +176,7 @@ QLockFile::LockError QLockFilePrivate::tryLock_sys()
     // Use operator% from the fast builder to avoid multiple memory allocations.
     QByteArray fileData = QByteArray::number(QCoreApplication::applicationPid()) % '\n'
                           % QCoreApplication::applicationName().toUtf8() % '\n'
-                          % localHostName() % '\n';
+                          % QSysInfo::machineHostName().toUtf8() % '\n';
 
     const QByteArray lockFileName = QFile::encodeName(fileName);
     const int fd = qt_safe_open(lockFileName.constData(), O_WRONLY | O_CREAT | O_EXCL, 0666);
@@ -242,7 +233,7 @@ bool QLockFilePrivate::isApparentlyStale() const
     qint64 pid;
     QString hostname, appname;
     if (getLockInfo(&pid, &hostname, &appname)) {
-        if (hostname.isEmpty() || hostname == QString::fromLocal8Bit(localHostName())) {
+        if (hostname.isEmpty() || hostname == QSysInfo::machineHostName()) {
             if (::kill(pid, 0) == -1 && errno == ESRCH)
                 return true; // PID doesn't exist anymore
             const QString processName = processNameByPid(pid);