I tried to publish XMI file (using Modeshape's REST client) into /files directory, but I was unsuccessful as I've got HTTP 400 error with message "java.lang.IllegalStateException: java.io.IOException: Not in GZIP format".

When I looked into files directory on the server, there was a node with a specified filename created, this node also has jcr:content node, but jcr:content node has no jcr:data node.

However , when I tried to publish CSV file (using the same client) I was successful and file was created under the /files directory.