From 6fdd986bd9d9eacdfa6210605eb63371136d0e55 Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Tue, 20 Sep 2022 12:21:12 +0200
Subject: [PATCH] QPdfEngine: port from raw zlib to qCompress()
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Hotfix for disappearing zlib symbols caused by QTBUG-104972
and QTBUG-106542 fixes, to be merged later on.

Pick-to: 6.4 6.3 6.2
Change-Id: I21e0bf13c866fa7bb45c7587c81e7fddddad90f9
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>
---
 src/gui/painting/qpdf.cpp | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/src/gui/painting/qpdf.cpp b/src/gui/painting/qpdf.cpp
index 28d4216de9..848769d5b2 100644
--- a/src/gui/painting/qpdf.cpp
+++ b/src/gui/painting/qpdf.cpp
@@ -2280,16 +2280,15 @@ int QPdfEnginePrivate::writeCompressed(const char *src, int len)
 {
 #ifndef QT_NO_COMPRESS
     if (do_compress) {
-        uLongf destLen = len + len/100 + 13; // zlib requirement
-        Bytef* dest = new Bytef[destLen];
-        if (Z_OK == ::compress(dest, &destLen, (const Bytef*) src, (uLongf)len)) {
-            stream->writeRawData((const char*)dest, destLen);
+        const QByteArray data = qCompress(reinterpret_cast<const uchar *>(src), len);
+        constexpr qsizetype HeaderSize = 4;
+        if (!data.isNull()) {
+            stream->writeRawData(data.data() + HeaderSize, data.size() - HeaderSize);
+            len = data.size() - HeaderSize;
         } else {
             qWarning("QPdfStream::writeCompressed: Error in compress()");
-            destLen = 0;
+            len = 0;
         }
-        delete [] dest;
-        len = destLen;
     } else
 #endif
     {