From 787d178b19587731fa9e78d37a053bd75308eba6 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Mon, 4 Apr 2022 16:49:03 +0200
Subject: [PATCH] QBuffer: optimize seek()-past-end-of-buffer
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
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Use new QByteArray::resize(n, ch) method to resize the buffer
directly, instead of first allocating a QByteArray full of NULs and
then using public write() API to append it.

Change-Id: Ibdb082b970de0ba24534a570ecb23304c5f1470c
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
---
 src/corelib/io/qbuffer.cpp | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/src/corelib/io/qbuffer.cpp b/src/corelib/io/qbuffer.cpp
index 2b53f09796..8e1888d893 100644
--- a/src/corelib/io/qbuffer.cpp
+++ b/src/corelib/io/qbuffer.cpp
@@ -363,16 +363,15 @@ bool QBuffer::seek(qint64 pos)
     const auto oldBufSize = d->buf->size();
     constexpr qint64 MaxSeekPos = (std::numeric_limits<decltype(oldBufSize)>::max)();
     if (pos <= MaxSeekPos && pos > oldBufSize && isWritable()) {
-        if (seek(d->buf->size())) {
-            const qint64 gapSize = pos - d->buf->size();
-            if (write(QByteArray(gapSize, 0)) != gapSize) {
-                qWarning("QBuffer::seek: Unable to fill gap");
-                return false;
-            }
-        } else {
+        QT_TRY {
+            d->buf->resize(qsizetype(pos), '\0');
+        } QT_CATCH(const std::bad_alloc &) {} // swallow, failure case is handled below
+        if (d->buf->size() != pos) {
+            qWarning("QBuffer::seek: Unable to fill gap");
             return false;
         }
-    } else if (pos > d->buf->size() || pos < 0) {
+    }
+    if (pos > d->buf->size() || pos < 0) {
         qWarning("QBuffer::seek: Invalid pos: %lld", pos);
         return false;
     }