[frameworks/karchive] src: kzip: write data in chunks

Git commit f33d70da6ed7afa5d0b7b04542f689297b0a1714 by George Florea Bănuș.
Committed on 30/07/2026 at 15:40.
Pushed by georgefb into branch 'master'.

kzip: write data in chunks

z_stream::avail_in is a uint32_t and only supports input sizes up to UINT32_MAX

a chunk size of "2 * 1024 * 1024" was chosen because it was the fastest
in a simple benchmark that consisted of creating a ZIP archive
containing a single 5 GB file; each chunk size was tested only once

         64 * 1024:  82867 ms elapsed
        256 * 1024:  82535 ms elapsed
       1024 * 1024:  74614 ms elapsed
   2 * 1024 * 1024:  72103 ms elapsed
   5 * 1024 * 1024:  79815 ms elapsed
1024 * 1024 * 1024:  82510 ms elapsed

M  +20   -3    src/kzip.cpp

https://invent.kde.org/frameworks/karchive/-/commit/f33d70da6ed7afa5d0b7b04542f689297b0a1714

diff --git a/src/kzip.cpp b/src/kzip.cpp
index 27e0a2c..2faf812 100644
--- a/src/kzip.cpp
+++ b/src/kzip.cpp
@@ -1526,11 +1526,28 @@ bool KZip::doWriteData(const char *data, qint64 size)
 
     // crc to be calculated over uncompressed stuff...
     // and they didn't mention it in their docs...
-    d->m_crc = crc32(d->m_crc, (const Bytef *)data, size);
+    quint32 crc = d->m_crc;
+
+    constexpr qint64 chunkSize = 2 * 1024 * 1024;
+    qint64 totalWritten = 0;
+    while (totalWritten < size) {
+        qint64 chunk = std::min(chunkSize, size - totalWritten);
+
+        crc = crc32(crc, reinterpret_cast<const Bytef *>(data + totalWritten), static_cast<quint32>(chunk));
+
+        qint64 currentWritten = d->m_currentDev->write(data + totalWritten, chunk);
+        if (currentWritten != chunk) {
+            setErrorString(tr("Error writing data chunk: %1").arg(d->m_currentDev->errorString()));
+            return false;
+        }
+
+        totalWritten += currentWritten;
+    }
+
+    d->m_crc = crc;
 
-    qint64 written = d->m_currentDev->write(data, size);
     // qCDebug(KArchiveLog) << "wrote" << size << "bytes.";
-    const bool ok = written == size;
+    const bool ok = totalWritten == size;
 
     if (!ok) {
         setErrorString(tr("Error writing data: %1").arg(d->m_currentDev->errorString()));