[Owncloud] Chunked Upload Problem

[Klaas Freitag]

Hi,

here is something all clients (also the Webinterface-Client) should 
think about when they use chunked upload.

As you might know the chunked upload "protocol" [1] we agreed on uses a 
http header to indicate that chunked upload is in progress.

Problems happen if there are proxies or whatever gangsters on the way 
between client and server that filter out these headers without further 
notice. Than the server has no chance to detect that chunked upload is 
in progress.

With the sync client we have found a way to detect that: If there are 
more than one chunk and the server returns an etag after the first 
chunk, that can mean two things:
a) The server does not see the chunk header and created that file with 
the chunk name, which is the error.
b) The server already knew all parts and the one transmitted was the 
last missing. Thats cool and no file with the chunk filename is created.

If that happens, we send an DELETE request on the chunk file name. If 
that succeeds we have the error condition and can not do chunking. If 
the remove fails, we have case b) and all is fine.

If we had the server returning the header it would have been easier, but 
to late now. Maybe next time.

best,

Klaas

[1] https://github.com/owncloud/core/wiki/spec:-big-file-chunking