4 files changed, 60 insertions, 18 deletions

diff --git a/src/network/access/qnetworkaccessbackend_p.h b/src/network/access/qnetworkaccessbackend_p.h
index 830ec7e..eab011c 100644
--- a/src/network/access/qnetworkaccessbackend_p.h
+++ b/src/network/access/qnetworkaccessbackend_p.h
@@ -162,6 +162,10 @@ public:
     // This will possibly enable buffering of the upload data.
     virtual bool needsResetableUploadData() { return false; }
 
+    // Returns true if backend is able to resume downloads.
+    virtual bool canResume() const { return false; }
+    virtual void setResumeOffset(quint64 offset) { Q_UNUSED(offset); }
+
 protected:
     // Create the device used for reading the upload data
     QNonContiguousByteDevice* createUploadByteDevice();
diff --git a/src/network/access/qnetworkaccesshttpbackend.cpp b/src/network/access/qnetworkaccesshttpbackend.cpp
index 8e02723..aa6a820 100644
--- a/src/network/access/qnetworkaccesshttpbackend.cpp
+++ b/src/network/access/qnetworkaccesshttpbackend.cpp
@@ -296,6 +296,7 @@ QNetworkAccessHttpBackend::QNetworkAccessHttpBackend()
 #ifndef QT_NO_OPENSSL
     , pendingSslConfiguration(0), pendingIgnoreAllSslErrors(false)
 #endif
+    , resumeOffset(0)
 {
 }
 
@@ -533,6 +534,28 @@ void QNetworkAccessHttpBackend::postRequest()
     httpRequest.setUrl(url());
 
     QList<QByteArray> headers = request().rawHeaderList();
+    if (resumeOffset != 0) {
+        if (headers.contains("Range")) {
+            // Need to adjust resume offset for user specified range
+
+            headers.removeOne("Range");
+
+            // We've already verified that requestRange starts with "bytes=", see canResume.
+            QByteArray requestRange = request().rawHeader("Range").mid(6);
+
+            int index = requestRange.indexOf('-');
+
+            quint64 requestStartOffset = requestRange.left(index).toULongLong();
+            quint64 requestEndOffset = requestRange.mid(index + 1).toULongLong();
+
+            requestRange = "bytes=" + QByteArray::number(resumeOffset + requestStartOffset) +
+                           '-' + QByteArray::number(requestEndOffset);
+
+            httpRequest.setHeaderField("Range", requestRange);
+        } else {
+            httpRequest.setHeaderField("Range", "bytes=" + QByteArray::number(resumeOffset) + '-');
+        }
+    }
     foreach (const QByteArray &header, headers)
         httpRequest.setHeaderField(header, request().rawHeader(header));
 
@@ -1108,6 +1131,31 @@ QNetworkCacheMetaData QNetworkAccessHttpBackend::fetchCacheMetaData(const QNetwo
     return metaData;
 }
 
+bool QNetworkAccessHttpBackend::canResume() const
+{
+    // Only GET operation supports resuming.
+    if (operation() != QNetworkAccessManager::GetOperation)
+        return false;
+
+    // Can only resume if server/resource supports Range header.
+    if (httpReply->headerField("Accept-Ranges", "none") == "none")
+        return false;
+
+    // We only support resuming for byte ranges.
+    if (request().hasRawHeader("Range")) {
+        QByteArray range = request().rawHeader("Range");
+        if (!range.startsWith("bytes="))
+            return false;
+    }
+
+    return true;
+}
+
+void QNetworkAccessHttpBackend::setResumeOffset(quint64 offset)
+{
+    resumeOffset = offset;
+}
+
 QT_END_NAMESPACE
 
 #endif // QT_NO_HTTP
diff --git a/src/network/access/qnetworkaccesshttpbackend_p.h b/src/network/access/qnetworkaccesshttpbackend_p.h
index 0eaf003..e5cc0ab 100644
--- a/src/network/access/qnetworkaccesshttpbackend_p.h
+++ b/src/network/access/qnetworkaccesshttpbackend_p.h
@@ -99,6 +99,9 @@ public:
     // we return true since HTTP needs to send PUT/POST data again after having authenticated
     bool needsResetableUploadData() { return true; }
 
+    bool canResume() const;
+    void setResumeOffset(quint64 offset);
+
 private slots:
     void replyReadyRead();
     void replyFinished();
@@ -120,6 +123,8 @@ private:
     QList<QSslError> pendingIgnoreSslErrorsList;
 #endif
 
+    quint64 resumeOffset;
+
     void disconnectFromHttp();
     void setupConnection();
     void validateCache(QHttpNetworkRequest &httpRequest, bool &loadedFromCache);
diff --git a/src/network/access/qnetworkreplyimpl.cpp b/src/network/access/qnetworkreplyimpl.cpp
index 7f66b25..2906caa 100644
--- a/src/network/access/qnetworkreplyimpl.cpp
+++ b/src/network/access/qnetworkreplyimpl.cpp
@@ -497,15 +497,6 @@ void QNetworkReplyImplPrivate::appendDownstreamData(QByteDataBuffer &data)
     QPointer<QNetworkReplyImpl> qq = q;
 
     QVariant totalSize = cookedHeaders.value(QNetworkRequest::ContentLengthHeader);
-    if (totalSize.isNull()) {
-        RawHeadersList::ConstIterator it = findRawHeader("Content-Range");
-        if (it != rawHeaders.constEnd()) {
-            int index = it->second.lastIndexOf('/');
-            if (index != -1)
-                totalSize = it->second.mid(index + 1).toLongLong() - preMigrationDownloaded;
-        }
-    }
-
     if (preMigrationDownloaded != Q_INT64_C(-1))
         totalSize = totalSize.toLongLong() + preMigrationDownloaded;
     pauseNotificationHandling();
@@ -812,8 +803,8 @@ bool QNetworkReplyImplPrivate::migrateBackend()
     if (state == Finished || state == Aborted)
         return true;
 
-    // Resume only supported by http backend, not migrating.
-    if (!qobject_cast<QNetworkAccessHttpBackend *>(backend))
+    // Backend does not support resuming download.
+    if (!backend->canResume())
         return false;
 
     // Request has outgoing data, not migrating.
@@ -824,11 +815,6 @@ bool QNetworkReplyImplPrivate::migrateBackend()
     if (copyDevice)
         return true;
 
-    // Range header is not supported by server/resource, can't migrate.
-    RawHeadersList::ConstIterator it = findRawHeader("Accept-Ranges");
-    if (it == rawHeaders.constEnd() || it->second == "none")
-        return false;
-
     state = QNetworkReplyImplPrivate::Reconnecting;
 
     if (backend) {
@@ -841,13 +827,12 @@ bool QNetworkReplyImplPrivate::migrateBackend()
 
     preMigrationDownloaded = bytesDownloaded;
 
-    request.setRawHeader("Range", "bytes=" + QByteArray::number(preMigrationDownloaded) + '-');
-
     backend = manager->d_func()->findBackend(operation, request);
 
     if (backend) {
         backend->setParent(q);
         backend->reply = this;
+        backend->setResumeOffset(bytesDownloaded);
     }
 
     if (qobject_cast<QNetworkAccessHttpBackend *>(backend)) {