For an example, try to "Export Route" (download button in the left-hand menu) from osm routing service:
MiniBrowser will report "Download failed: Load request cancelled"
I've found the problem, and it's not a Soup issue (soup is not even used for Blobs), but GTK+ specific one. The problem is that GTK+ API uses URIs for download destination paths, and passes that uris to the WebKit internals. But WebKit expects download destination location to be a local path. This is not a problem for normal downloads, because the soup backend handles the cases of download destination being a URI and a path. For blob downloads NetworkDataTaskBlob is used, and it always expects the download destination to be a local path, failing in FileSystem::openFile() when a URI is passed. We need to keep using local files internally and convert to URIs only when exposing those paths to the API.
Created attachment 312598 [details]
Thanks for the patch. If this patch contains new public API please make sure it follows the guidelines for new WebKit2 GTK+ API. See http://trac.webkit.org/wiki/WebKitGTK/AddingNewWebKit2API
Thank you Carlos, tested with Openrouteservice the Blob downloads now work in Minibrowser.
But the patch hasn't landed, do not close bugs with unreviewed patches, please.
Committed r218185: <http://trac.webkit.org/changeset/218185>