PropagateDownload: Don't discard the body of error message

We want to keep the body so we can get the message from it
(Issue #6459)

TestDownload::testErrorMessage did not fail because the FakeErrorReply
did not emit readyRead and did not implement bytesAvailable.

Author: ogoffart

src/libsync/propagatedownload.cpp

@@ -165,6 +165,9 @@ void GETFileJob::slotMetaDataChanged()
     // If the status code isn't 2xx, don't write the reply body to the file.
     // For any error: handle it when the job is finished, not here.
     if (httpStatus / 100 != 2) {
+        // Disable the buffer limit, as we don't limit the bandwidth for error messages.
+        // (We are only going to do a readAll() at the end.)
+        reply()->setReadBufferSize(0);
         _device->close();
         return;
     }
@@ -268,7 +271,7 @@ void GETFileJob::slotReadyRead()
     int bufferSize = qMin(1024 * 8ll, reply()->bytesAvailable());
     QByteArray buffer(bufferSize, Qt::Uninitialized);
 
-    while (reply()->bytesAvailable() > 0) {
+    while (reply()->bytesAvailable() > 0 && _saveBodyToFile) {
         if (_bandwidthChoked) {
             qCWarning(lcGetJob) << "Download choked";
             break;
@@ -292,7 +295,7 @@ void GETFileJob::slotReadyRead()
             return;
         }
 
-        if (_device->isOpen() && _saveBodyToFile) {
+        if (_device->isOpen()) {
             qint64 w = _device->write(buffer.constData(), r);
             if (w != r) {
                 _errorString = _device->errorString();
@@ -304,7 +307,7 @@ void GETFileJob::slotReadyRead()
         }
     }
 
-    if (reply()->isFinished() && reply()->bytesAvailable() == 0) {
+    if (reply()->isFinished() && (reply()->bytesAvailable() == 0 || !_saveBodyToFile)) {
         qCDebug(lcGetJob) << "Actually finished!";
         if (_bandwidthManager) {
             _bandwidthManager->unregisterDownloadJob(this);

test/syncenginetestutils.h

@@ -728,6 +728,8 @@ class FakeErrorReply : public QNetworkReply
         setAttribute(QNetworkRequest::HttpStatusCodeAttribute, _httpErrorCode);
         setError(InternalServerError, "Internal Server Fake Error");
         emit metaDataChanged();
+        emit readyRead();
+        setFinished(true);
         emit finished();
     }
 
@@ -738,6 +740,9 @@ class FakeErrorReply : public QNetworkReply
         _body = _body.mid(max);
         return max;
     }
+    qint64 bytesAvailable() const override {
+        return _body.size();
+    }
 
     int _httpErrorCode;
     QByteArray _body;