Investigating the possibility to support HTTP or WebDAV for the LFC, in order to provide a standard user-friendly access method to catalogues.

Background

The LFC provides a file system view of the repository of a community or working group. Beside meta-data, it stores the different locations of the replicas of a file. Those replicas might be highly distributed. The endpoints are storage elements making the data available through different protocols. The goal of this object is to evaluate the possibility to browse through the LFC and download the data from the storage elements transparently with standard Internet tools (e.g. browsers, curl, wget). This requirement is not so much of interest for WLCG mass operation but more for interactive groups or communities.

Expected issues

Although the objective sounds rather straightforward and very useful, it could require a lot of efforts. One of the issues is the way file replicas are addressed in the catalogue. In LFC, replica locations are expressed by a Storage URL, which doesn’t yet contain the information on the Transfer URL. The transfer URL theoretically only provides the location and transfer protocol, which is only valid for particular time or a single transfer. The TURL, for EMI storage elements, is negotiated through the SRM protocols. Another unsolved issue is that the TURL would have to be returned to the system after the transfer, in order to free resource. Standard client tools don’t support the return TURL operation. The figure below sketches a possible request flow from a standard browser via the LFC to the final storage location of the requested data.

-- PatrickFuhrmann - 03-Aug-2011