4 files changed, 20 insertions, 8 deletions

diff --git a/logic/net/CacheDownload.cpp b/logic/net/CacheDownload.cpp
index 6a76a4ae..309eb345 100644
--- a/logic/net/CacheDownload.cpp
+++ b/logic/net/CacheDownload.cpp
@@ -33,7 +33,11 @@ void CacheDownload::start()
 	}
 	QLOG_INFO() << "Downloading " << m_url.toString();
 	QNetworkRequest request(m_url);
-	request.setRawHeader(QString("If-None-Match").toLatin1(), m_entry->etag.toLatin1());
+	if(m_entry->remote_changed_timestamp.size())
+		request.setRawHeader(QString("If-Modified-Since").toLatin1(), m_entry->remote_changed_timestamp.toLatin1());
+	if(m_entry->etag.size())
+		request.setRawHeader(QString("If-None-Match").toLatin1(), m_entry->etag.toLatin1());
+
 	request.setHeader(QNetworkRequest::UserAgentHeader,"MultiMC/5.0 (Cached)");
 
 	auto worker = MMC->qnam();
@@ -87,7 +91,11 @@ void CacheDownload::downloadFinished()
 		QFileInfo output_file_info(m_target_path);
 
 		m_entry->etag = m_reply->rawHeader("ETag").constData();
-		m_entry->last_changed_timestamp =
+		if(m_reply->hasRawHeader("Last-Modified"))
+		{
+			m_entry->remote_changed_timestamp = m_reply->rawHeader("Last-Modified").constData();
+		}
+		m_entry->local_changed_timestamp =
 			output_file_info.lastModified().toUTC().toMSecsSinceEpoch();
 		m_entry->stale = false;
 		MMC->metacache()->updateEntry(m_entry);
diff --git a/logic/net/ForgeXzDownload.cpp b/logic/net/ForgeXzDownload.cpp
index 3ec2155b..0e5287d8 100644
--- a/logic/net/ForgeXzDownload.cpp
+++ b/logic/net/ForgeXzDownload.cpp
@@ -269,7 +269,7 @@ void ForgeXzDownload::decompressAndInstall()
 	
 	QFileInfo output_file_info(m_target_path);
 	m_entry->etag = m_reply->rawHeader("ETag").constData();
-	m_entry->last_changed_timestamp =
+	m_entry->local_changed_timestamp =
 		output_file_info.lastModified().toUTC().toMSecsSinceEpoch();
 	m_entry->stale = false;
 	MMC->metacache()->updateEntry(m_entry);
diff --git a/logic/net/HttpMetaCache.cpp b/logic/net/HttpMetaCache.cpp
index 9c642a0f..5ba5b98d 100644
--- a/logic/net/HttpMetaCache.cpp
+++ b/logic/net/HttpMetaCache.cpp
@@ -82,7 +82,7 @@ MetaEntryPtr HttpMetaCache::resolveEntry ( QString base, QString resource_path,
 	
 	// if the file changed, check md5sum
 	qint64 file_last_changed = finfo.lastModified().toUTC().toMSecsSinceEpoch();
-	if(file_last_changed != entry->last_changed_timestamp)
+	if(file_last_changed != entry->local_changed_timestamp)
 	{
 		QFile input(real_path);
 		input.open(QIODevice::ReadOnly);
@@ -93,7 +93,7 @@ MetaEntryPtr HttpMetaCache::resolveEntry ( QString base, QString resource_path,
 			return staleEntry(base, resource_path);
 		}
 		// md5sums matched... keep entry and save the new state to file
-		entry->last_changed_timestamp = file_last_changed;
+		entry->local_changed_timestamp = file_last_changed;
 		SaveEventually();
 	}
 
@@ -184,7 +184,8 @@ void HttpMetaCache::Load()
 		QString path = foo->path = element_obj.value("path").toString();
 		foo->md5sum = element_obj.value("md5sum").toString();
 		foo->etag = element_obj.value("etag").toString();
-		foo->last_changed_timestamp = element_obj.value("last_changed_timestamp").toDouble();
+		foo->local_changed_timestamp = element_obj.value("last_changed_timestamp").toDouble();
+		foo->remote_changed_timestamp = element_obj.value("remote_changed_timestamp").toString();
 		// presumed innocent until closer examination
 		foo->stale = false;
 		entrymap.entry_list[path] = MetaEntryPtr( foo );
@@ -215,7 +216,9 @@ void HttpMetaCache::SaveNow()
 			entryObj.insert("path", QJsonValue(entry->path));
 			entryObj.insert("md5sum", QJsonValue(entry->md5sum));
 			entryObj.insert("etag", QJsonValue(entry->etag));
-			entryObj.insert("last_changed_timestamp", QJsonValue(double(entry->last_changed_timestamp)));
+			entryObj.insert("last_changed_timestamp", QJsonValue(double(entry->local_changed_timestamp)));
+			if(!entry->remote_changed_timestamp.isEmpty())
+				entryObj.insert("remote_changed_timestamp", QJsonValue(entry->remote_changed_timestamp));
 			entriesArr.append(entryObj);
 		}
 	}
diff --git a/logic/net/HttpMetaCache.h b/logic/net/HttpMetaCache.h
index 8107839e..557d9298 100644
--- a/logic/net/HttpMetaCache.h
+++ b/logic/net/HttpMetaCache.h
@@ -10,7 +10,8 @@ struct MetaEntry
 	QString path;
 	QString md5sum;
 	QString etag;
-	qint64 last_changed_timestamp = 0;
+	qint64 local_changed_timestamp = 0;
+	QString remote_changed_timestamp; // QString for now, RFC 2822 encoded time
 	bool stale = true;
 	QString getFullPath();
 };