QHttpMultiPart: fix data corruption in readData method

When readData() is called repeatedly, we need to keep track which
part of the multipart message we are currently reading from.
Hereby we also need to take the boundary size into account, and not
only the size of the multipart; otherwise we would skip a not
completely read part. This would then later lead to advancing the
read pointer by negative indexes and data loss.

Task-number: QTBUG-32534
Change-Id: Ibb6dff16adaf4ea67181d23d1d0c8459e33a0ed0
Reviewed-by: Jonathan Liu <net147@gmail.com>
Reviewed-by: Shane Kearns <shane.kearns@accenture.com>

src/network/access/qhttpmultipart.cpp

@@ -497,7 +497,8 @@ qint64 QHttpMultiPartIODevice::readData(char *data, qint64 maxSize)
 
     // skip the parts we have already read
     while (index < multiPart->parts.count() &&
-           readPointer >= partOffsets.at(index) + multiPart->parts.at(index).d->size())
+           readPointer >= partOffsets.at(index) + multiPart->parts.at(index).d->size()
+           + multiPart->boundary.count() + 6) // 6 == 2 boundary dashes, \r\n after boundary, \r\n after multipart
         index++;
 
     // read the data

tests/auto/network/access/qnetworkreply/tst_qnetworkreply.cpp

@@ -221,6 +221,7 @@ private Q_SLOTS:
     void postToHttpSynchronous();
     void postToHttpMultipart_data();
     void postToHttpMultipart();
+    void multipartSkipIndices(); // QTBUG-32534
 #ifndef QT_NO_SSL
     void putToHttps_data();
     void putToHttps();
@@ -2382,6 +2383,49 @@ void tst_QNetworkReply::postToHttpMultipart()
     QCOMPARE(replyData, expectedReplyData);
 }
 
+void tst_QNetworkReply::multipartSkipIndices() // QTBUG-32534
+{
+    QHttpMultiPart *multiPart = new QHttpMultiPart(QHttpMultiPart::MixedType);
+    QUrl url("http://" + QtNetworkSettings::serverName() + "/qtest/cgi-bin/multipart.cgi");
+    QNetworkRequest request(url);
+    QList<QByteArray> parts;
+    parts << QByteArray(56083, 'X') << QByteArray(468, 'X') << QByteArray(24952, 'X');
+
+    QHttpPart part1;
+    part1.setHeader(QNetworkRequest::ContentDispositionHeader, "form-data; name=\"field1\"; filename=\"aaaa.bin\"");
+    part1.setHeader(QNetworkRequest::ContentTypeHeader, "application/octet-stream");
+    part1.setBody(parts.at(0));
+    multiPart->append(part1);
+
+    QHttpPart part2;
+    part2.setHeader(QNetworkRequest::ContentDispositionHeader, "form-data; name=\"field2\"; filename=\"bbbb.txt\"");
+    part2.setHeader(QNetworkRequest::ContentTypeHeader, "text/plain");
+    part2.setBody(parts.at(1));
+    multiPart->append(part2);
+
+    QHttpPart part3;
+    part3.setHeader(QNetworkRequest::ContentDispositionHeader, "form-data; name=\"text-3\"; filename=\"cccc.txt\"");
+    part3.setHeader(QNetworkRequest::ContentTypeHeader, "text/plain");
+    part3.setBody(parts.at(2));
+    multiPart->append(part3);
+
+    QNetworkReplyPtr reply;
+    RUN_REQUEST(runMultipartRequest(request, reply, multiPart, "POST"));
+
+    QCOMPARE(reply->error(), QNetworkReply::NoError);
+
+    QCOMPARE(reply->attribute(QNetworkRequest::HttpStatusCodeAttribute).toInt(), 200); // 200 Ok
+    QByteArray line;
+    int partIndex = 0;
+    while ((line = reply->readLine()) != QByteArray("")) {
+        if (line.startsWith("content:")) {
+            // before, the 3rd part would return garbled output at the end
+            QCOMPARE("content: " + parts[partIndex++] + "\n", line);
+        }
+    }
+    multiPart->deleteLater();
+}
+
 void tst_QNetworkReply::putToHttpMultipart_data()
 {
     postToHttpMultipart_data();