Section 3.9 of the Fedora Specification defines a new interaction pattern for external content. The Fedora 4.x interaction is defined here: https://wiki.duraspace.org/display/FEDORA4x/External+Content. In a short the external content handling interaction is triggered via the use of a special variation of the ContentType header. The new interaction, defined in https://fcrepo.github.io/fcrepo-specification/#external-content , uses a link header instead.
Building on https://jira.duraspace.org/browse/FCREPO-2749, the task here is to add support for proxying an external binary (LDP-NR) that happens to exist on a local file system, using in a PUT or POST with the following header:
Link: <file:///home/foo/file> ;
If there is no type attribute, use the media type obtained when accessing the external content via the specified scheme (e.g. the Content-Type header for external content accessed via http). Otherwise use default media type (application/octet-stream).
When serving requests for the the newly created resource, servers should use the recorded location and mime type from the above header to deliver the content via a proxied connection.