Unify QByteArray::MaxSize and MaxAllocSize

We have established the maximum size qAllocMore can deal with in
commit 880986be23 and we should use
it.

The maximum size for byte arrays is reduced by one byte as with
the previous code we could make qAllocMore produce ((1 << 31) - extra)
by passing (1 << 30). That is not a problem for qAllocMore itself
(as long as extra > 0) but it's hard to verify that no related
code casts the total sum back to signed int, which would overflow
to -1.

To make the compiler inline access to the maximum size, a private
enum MaxByteArraySize is provided, which can be used in internal
code.

This fixes the merge of commits
880986be23 and
c70658d301

Change-Id: Idb04856f7c2e53ef383063e7555d3083020ff2b7
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/io/qiodevice.cpp

@@ -39,6 +39,7 @@
 #include "qfile.h"
 #include "qstringlist.h"
 #include "qdir.h"
+#include "private/qbytearray_p.h"
 
 #include <algorithm>
 
@@ -941,9 +942,9 @@ QByteArray QIODevice::read(qint64 maxSize)
     Q_UNUSED(d);
 #endif
 
-    if (quint64(maxSize) >= QByteArray::MaxSize) {
+    if (maxSize >= MaxByteArraySize) {
         checkWarnMessage(this, "read", "maxSize argument exceeds QByteArray size limit");
-        maxSize = QByteArray::MaxSize - 1;
+        maxSize = MaxByteArraySize - 1;
     }
 
     qint64 readBytes = 0;
@@ -995,7 +996,7 @@ QByteArray QIODevice::readAll()
 
     // flush internal read buffer
     if (!(d->openMode & Text) && !d->buffer.isEmpty()) {
-        if (quint64(d->buffer.size()) >= QByteArray::MaxSize)
+        if (d->buffer.size() >= MaxByteArraySize)
             return QByteArray();
         result = d->buffer.readAll();
         readBytes = result.size();
@@ -1008,7 +1009,7 @@ QByteArray QIODevice::readAll()
         // Size is unknown, read incrementally.
         qint64 readResult;
         do {
-            if (quint64(readBytes) + QIODEVICE_BUFFERSIZE >= QByteArray::MaxSize) {
+            if (readBytes + QIODEVICE_BUFFERSIZE >= MaxByteArraySize) {
                 // If resize would fail, don't read more, return what we have.
                 break;
             }
@@ -1020,7 +1021,7 @@ QByteArray QIODevice::readAll()
     } else {
         // Read it all in one go.
         // If resize fails, don't read anything.
-        if (quint64(readBytes + theSize - d->pos) >= QByteArray::MaxSize)
+        if (readBytes + theSize - d->pos >= MaxByteArraySize)
             return QByteArray();
         result.resize(int(readBytes + theSize - d->pos));
         readBytes += read(result.data() + readBytes, result.size() - readBytes);
@@ -1178,9 +1179,9 @@ QByteArray QIODevice::readLine(qint64 maxSize)
     Q_UNUSED(d);
 #endif
 
-    if (quint64(maxSize) >= QByteArray::MaxSize) {
+    if (maxSize >= MaxByteArraySize) {
         qWarning("QIODevice::read: maxSize argument exceeds QByteArray size limit");
-        maxSize = QByteArray::MaxSize - 1;
+        maxSize = MaxByteArraySize - 1;
     }
 
     result.resize(int(maxSize));
@@ -1188,7 +1189,7 @@ QByteArray QIODevice::readLine(qint64 maxSize)
     if (!result.size()) {
         // If resize fails or maxSize == 0, read incrementally
         if (maxSize == 0)
-            maxSize = QByteArray::MaxSize - 1;
+            maxSize = MaxByteArraySize - 1;
 
         // The first iteration needs to leave an extra byte for the terminating null
         result.resize(1);

src/corelib/tools/qbytearray.cpp

@@ -41,6 +41,7 @@
 #include "qlocale_p.h"
 #include "qstringalgorithms_p.h"
 #include "qscopedpointer.h"
+#include "qbytearray_p.h"
 #include <qdatastream.h>
 #include <qmath.h>
 
@@ -123,8 +124,8 @@ int qFindByteArray(
 
 int qAllocMore(int alloc, int extra) Q_DECL_NOTHROW
 {
-    Q_ASSERT(alloc >= 0 && extra >= 0);
+    Q_ASSERT(alloc >= 0 && extra >= 0 && extra <= MaxAllocSize);
-    Q_ASSERT_X(uint(alloc) <= QByteArray::MaxSize, "qAllocMore", "Requested size is too large!");
+    Q_ASSERT_X(alloc <= MaxAllocSize - extra, "qAllocMore", "Requested size is too large!");
 
     unsigned nalloc = qNextPowerOfTwo(alloc + extra);
 
@@ -837,16 +838,6 @@ static inline char qToLower(char c)
     \sa QString, QBitArray
 */
 
-/*!
-    \variable QByteArray::MaxSize
-    \internal
-    \since 5.4
-
-    The maximum size of a QByteArray (including a '\0' terminator), in bytes.
-    Also applies to the maximum storage size of QString and QVector, though
-    not the number of elements.
-*/
-
 /*!
     \enum QByteArray::Base64Option
     \since 5.2
@@ -1575,7 +1566,7 @@ void QByteArray::reallocData(uint alloc, Data::AllocationOptions options)
         d = x;
     } else {
         if (options & Data::Grow) {
-            if (alloc > uint(MaxAllocSize) - uint(sizeof(Data)))
+            if (alloc > MaxByteArraySize)
                 qBadAlloc();
             alloc = qAllocMore(alloc, sizeof(Data));
         }

src/corelib/tools/qbytearray.h

@@ -162,9 +162,6 @@ private:
     typedef QTypedArrayData<char> Data;
 
 public:
-    // undocumented:
-    static const quint64 MaxSize = (1 << 30) - sizeof(Data);
-
     enum Base64Option {
         Base64Encoding = 0,
         Base64UrlEncoding = 1,

src/corelib/tools/qbytearray_p.h

@@ -0,0 +1,61 @@
+/****************************************************************************
+**
+** Copyright (C) 2015 The Qt Company Ltd.
+** Contact: http://www.qt.io/licensing/
+**
+** This file is part of the QtCore module of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL21$
+** Commercial License Usage
+** Licensees holding valid commercial Qt licenses may use this file in
+** accordance with the commercial license agreement provided with the
+** Software or, alternatively, in accordance with the terms contained in
+** a written agreement between you and The Qt Company. For licensing terms
+** and conditions see http://www.qt.io/terms-conditions. For further
+** information use the contact form at http://www.qt.io/contact-us.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 or version 3 as published by the Free
+** Software Foundation and appearing in the file LICENSE.LGPLv21 and
+** LICENSE.LGPLv3 included in the packaging of this file. Please review the
+** following information to ensure the GNU Lesser General Public License
+** requirements will be met: https://www.gnu.org/licenses/lgpl.html and
+** http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** As a special exception, The Qt Company gives you certain additional
+** rights. These rights are described in The Qt Company LGPL Exception
+** version 1.1, included in the file LGPL_EXCEPTION.txt in this package.
+**
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+#ifndef QBYTEARRAY_P_H
+#define QBYTEARRAY_P_H
+
+//
+//  W A R N I N G
+//  -------------
+//
+// This file is not part of the Qt API.  It exists for the convenience
+// of other Qt classes.  This header file may change from version to
+// version without notice, or even be removed.
+//
+// We mean it.
+//
+
+#include <QtCore/qbytearray.h>
+#include <QtCore/qtypetraits.h>
+#include "qtools_p.h"
+
+QT_BEGIN_NAMESPACE
+
+enum {
+    // Define as enum to force inlining. Don't expose MaxAllocSize in a public header.
+    MaxByteArraySize = MaxAllocSize - sizeof(QtPrivate::remove_pointer<QByteArray::DataPtr>::type)
+};
+
+QT_END_NAMESPACE
+
+#endif // QBYTEARRAY_P_H

src/corelib/tools/qringbuffer.cpp

@@ -33,6 +33,7 @@
 ****************************************************************************/
 
 #include "private/qringbuffer_p.h"
+#include "private/qbytearray_p.h"
 #include <string.h>
 
 QT_BEGIN_NAMESPACE
@@ -79,7 +80,7 @@ void QRingBuffer::free(qint64 bytes)
                     clear(); // try to minify/squeeze us
                 }
             } else {
-                Q_ASSERT(quint64(bytes) < QByteArray::MaxSize);
+                Q_ASSERT(bytes < MaxByteArraySize);
                 head += int(bytes);
                 bufferSize -= bytes;
             }
@@ -96,14 +97,14 @@ void QRingBuffer::free(qint64 bytes)
 
 char *QRingBuffer::reserve(qint64 bytes)
 {
-    if (bytes <= 0 || quint64(bytes) >= QByteArray::MaxSize)
+    if (bytes <= 0 || bytes >= MaxByteArraySize)
         return 0;
 
     const qint64 newSize = bytes + tail;
     // if need buffer reallocation
     if (newSize > buffers.last().size()) {
         if (newSize > buffers.last().capacity() && (tail >= basicBlockSize
-                || quint64(newSize) >= QByteArray::MaxSize)) {
+                || newSize >= MaxByteArraySize)) {
             // shrink this buffer to its current size
             buffers.last().resize(tail);
 
@@ -117,7 +118,7 @@ char *QRingBuffer::reserve(qint64 bytes)
 
     char *writePtr = buffers.last().data() + tail;
     bufferSize += bytes;
-    Q_ASSERT(quint64(bytes) < QByteArray::MaxSize);
+    Q_ASSERT(bytes < MaxByteArraySize);
     tail += int(bytes);
     return writePtr;
 }
@@ -129,7 +130,7 @@ char *QRingBuffer::reserve(qint64 bytes)
 */
 char *QRingBuffer::reserveFront(qint64 bytes)
 {
-    if (bytes <= 0 || quint64(bytes) >= QByteArray::MaxSize)
+    if (bytes <= 0 || bytes >= MaxByteArraySize)
         return 0;
 
     if (head < bytes) {
@@ -163,7 +164,7 @@ void QRingBuffer::chop(qint64 bytes)
                     clear(); // try to minify/squeeze us
                 }
             } else {
-                Q_ASSERT(quint64(bytes) < QByteArray::MaxSize);
+                Q_ASSERT(bytes < MaxByteArraySize);
                 tail -= int(bytes);
                 bufferSize -= bytes;
             }

src/corelib/tools/tools.pri

@@ -9,6 +9,7 @@ HEADERS +=  \
         tools/qarraydatapointer.h \
         tools/qbitarray.h \
         tools/qbytearray.h \
+        tools/qbytearray_p.h \
         tools/qbytearraylist.h \
         tools/qbytearraymatcher.h \
         tools/qbytedata_p.h \