Use QIODevice::readLineInto() instead of readLine() in loops

Most of the callers of QIODevice::readLine() are reading a device line
by line in a loop. Instead, use one QByteArray and modify it in every
iteration using QIODevice::readLineInto().

Use a QByteArrayView instead of QByteArray when calling trimmed() as
it's an expensive operation.

Fixes: QTBUG-103108
Change-Id: Ic1af487a2fbf352cc21d76a41717944d034d3709
Reviewed-by: Marc Mutz <[email protected]>
Reviewed-by: Thiago Macieira <[email protected]>

8 files changed, 24 insertions, 23 deletions

diff --git a/src/corelib/mimetypes/qmimeprovider.cpp b/src/corelib/mimetypes/qmimeprovider.cpp
index 0a3d858486c..d12449c3988 100644
--- a/src/corelib/mimetypes/qmimeprovider.cpp
+++ b/src/corelib/mimetypes/qmimeprovider.cpp
@@ -458,8 +458,8 @@ void QMimeBinaryProvider::loadMimeTypeList()
         // So we have to parse the plain-text files called "types".
         QFile file(m_directory + QStringView(u"/types"));
         if (file.open(QIODevice::ReadOnly)) {
-            while (!file.atEnd()) {
-                const QByteArray line = file.readLine();
+            QByteArray line;
+            while (file.readLineInto(&line)) {
                 auto lineView = QByteArrayView(line);
                 if (lineView.endsWith('\n'))
                     lineView.chop(1);
diff --git a/src/corelib/time/qtimezoneprivate_tz.cpp b/src/corelib/time/qtimezoneprivate_tz.cpp
index 23916be1792..4a238110e9d 100644
--- a/src/corelib/time/qtimezoneprivate_tz.cpp
+++ b/src/corelib/time/qtimezoneprivate_tz.cpp
@@ -88,12 +88,12 @@ static QTzTimeZoneHash loadTzTimeZones()
         return QTzTimeZoneHash();
 
     QTzTimeZoneHash zonesHash;
-    while (!tzif.atEnd()) {
-        const QByteArray line = tzif.readLine().trimmed();
-        if (line.isEmpty() || line.at(0) == '#') // Ignore empty or comment
+    QByteArray line;
+    while (tzif.readLineInto(&line)) {
+        QByteArrayView text = QByteArrayView(line).trimmed();
+        if (text.isEmpty() || text.at(0) == '#') // Ignore empty or comment
             continue;
         // Data rows are tab-separated columns Region, Coordinates, ID, Optional Comments
-        QByteArrayView text(line);
         int cut = text.indexOf('\t');
         if (Q_LIKELY(cut > 0)) {
             QTzTimeZone zone;
diff --git a/src/network/kernel/qhostinfo_unix.cpp b/src/network/kernel/qhostinfo_unix.cpp
index 80d386a13d9..3b0e2d333aa 100644
--- a/src/network/kernel/qhostinfo_unix.cpp
+++ b/src/network/kernel/qhostinfo_unix.cpp
@@ -123,8 +123,8 @@ QString QHostInfo::localDomainName()
         return QString();       // failure
 
     QString domainName;
-    while (!resolvconf.atEnd()) {
-        const QByteArray lineArray = resolvconf.readLine();
+    QByteArray lineArray;
+    while (resolvconf.readLineInto(&lineArray)) {
         QByteArrayView line = QByteArrayView(lineArray).trimmed();
         constexpr QByteArrayView domainWithSpace = "domain ";
         if (line.startsWith(domainWithSpace))
diff --git a/src/plugins/platforminputcontexts/ibus/qibusplatforminputcontext.cpp b/src/plugins/platforminputcontexts/ibus/qibusplatforminputcontext.cpp
index 00c7884cda2..c38cb289c19 100644
--- a/src/plugins/platforminputcontexts/ibus/qibusplatforminputcontext.cpp
+++ b/src/plugins/platforminputcontexts/ibus/qibusplatforminputcontext.cpp
@@ -776,11 +776,12 @@ void QIBusPlatformInputContextPrivate::createConnection()
     if (!file.open(QFile::ReadOnly))
         return;
 
-    QByteArray address;
+    QByteArrayView address;
     int pid = -1;
+    QByteArray lineArray;
 
-    while (!file.atEnd()) {
-        QByteArray line = file.readLine().trimmed();
+    while (file.readLineInto(&lineArray)) {
+        QByteArrayView line = QByteArrayView(lineArray).trimmed();
         if (line.startsWith('#'))
             continue;
 
diff --git a/src/testlib/qbenchmarkvalgrind.cpp b/src/testlib/qbenchmarkvalgrind.cpp
index 1663c5d28d2..33479f135d7 100644
--- a/src/testlib/qbenchmarkvalgrind.cpp
+++ b/src/testlib/qbenchmarkvalgrind.cpp
@@ -60,8 +60,8 @@ qint64 QBenchmarkValgrindUtils::extractResult(const QString &fileName)
     Q_UNUSED(openOk);
 
     std::optional<qint64> val = std::nullopt;
-    while (!file.atEnd()) {
-        const QByteArray line = file.readLine();
+    QByteArray line;
+    while (file.readLineInto(&line)) {
         constexpr QByteArrayView tag = "summary: ";
         if (line.startsWith(tag)) {
             const auto maybeNumber = line.data() + tag.size();
diff --git a/src/testlib/qtestblacklist.cpp b/src/testlib/qtestblacklist.cpp
index 7d848b3f1c3..7567e467469 100644
--- a/src/testlib/qtestblacklist.cpp
+++ b/src/testlib/qtestblacklist.cpp
@@ -252,9 +252,9 @@ void parseBlackList()
         return;
 
     QByteArray function;
+    QByteArray line;
 
-    while (!ignored.atEnd()) {
-        QByteArray line = ignored.readLine();
+    while (ignored.readLineInto(&line)) {
         const int commentPosition = line.indexOf('#');
         if (commentPosition >= 0)
             line.truncate(commentPosition);
diff --git a/src/tools/androiddeployqt/main.cpp b/src/tools/androiddeployqt/main.cpp
index 98324ab5b25..cf13c5e781a 100644
--- a/src/tools/androiddeployqt/main.cpp
+++ b/src/tools/androiddeployqt/main.cpp
@@ -2837,8 +2837,9 @@ QStringList getLibraryProjectsInOutputFolder(const Options &options)
 
     QFile file(options.outputDirectory + "/project.properties"_L1);
     if (file.open(QIODevice::ReadOnly)) {
-        while (!file.atEnd()) {
-            QByteArray line = file.readLine().trimmed();
+        QByteArray lineArray;
+        while (file.readLineInto(&lineArray)) {
+            QByteArrayView line = QByteArrayView(lineArray).trimmed();
             if (line.startsWith("android.library.reference")) {
                 int equalSignIndex = line.indexOf('=');
                 if (equalSignIndex >= 0) {
@@ -2913,8 +2914,8 @@ static bool mergeGradleProperties(const QString &path, GradleProperties properti
 
     QFile oldFile(oldPathStr);
     if (oldFile.open(QIODevice::ReadOnly)) {
-        while (!oldFile.atEnd()) {
-            QByteArray line(oldFile.readLine());
+        QByteArray line;
+        while (oldFile.readLineInto(&line)) {
             QList<QByteArray> prop(line.split('='));
             if (prop.size() > 1) {
                 GradleProperties::iterator it = properties.find(prop.at(0).trimmed());
diff --git a/src/tools/windeployqt/utils.cpp b/src/tools/windeployqt/utils.cpp
index 25b4a9788b2..ea32346c65f 100644
--- a/src/tools/windeployqt/utils.cpp
+++ b/src/tools/windeployqt/utils.cpp
@@ -225,10 +225,9 @@ QMap<QString, QString> queryQtPaths(const QString &qtpathsBinary, QString *error
     }
     QFile qconfigPriFile(result.value(QStringLiteral("QT_HOST_DATA")) + QStringLiteral("/mkspecs/qconfig.pri"));
     if (qconfigPriFile.open(QIODevice::ReadOnly | QIODevice::Text)) {
-        while (true) {
-            const QByteArray line = qconfigPriFile.readLine();
-            if (line.isEmpty())
-                break;
+        QByteArray lineArray;
+        while (qconfigPriFile.readLineInto(&lineArray)) {
+            QByteArrayView line = QByteArrayView(lineArray);
             if (line.startsWith("QT_LIBINFIX")) {
                 const int pos = line.indexOf('=');
                 if (pos >= 0) {