SI File Transfer (XEP-0096) XEP-0096: SI File Transfer <https://xmpp.org/extensions/xep-0096.html>. defines mechanisms for transferring files between Jabber users, and defines the preferred approach for file transfers in Jabber applications. Unfortunately, the mechanisms defined therein require that both the sender and recipient be online at the same time. However, sometimes it is desirable for the sender to initiate a file transfer while the recipient is offline. One way to make this possible is for the sender to upload the file to a unique URL, then inform the recipient of the URL. The sender could do this by uploading the file to their own web server, but not everyone has their own web server. Fortunately, there is a well-defined protocol for such file management operations: a set of HTTP extensions known as WebDAV and defined in RFC 2518 RFC 2518: HTTP Extensions for Distributed Authoring -- WEBDAV <http://tools.ietf.org/html/rfc2518>. (see also the revision-in-progress, rfc2518bis RFC 2518: HTTP Extensions for Distributed Authoring -- WebDAV <http://tools.ietf.org/html/draft-ietf-webdav-rfc2518bis>.).

The use case in which the recipient is offline is the main motivation for this document. Another WebDAV use case presents itself in environments that use, or even require, WebDAV for file transfers using other protocols (e.g., files attached to email messages). The usual rationale for such deployments is virus-checking: the file is put onto the WebDAV server (either by an end-user or a script that, for example, strips attached files off email messages) and then checked for viruses; only after the virus check successfully completes is the recipient allowed to retrieve the file. A further benefit of such deployments is that it enables the sender to provide the file to multiple recipients. Thus the approach defined herein provides the added benefit of being usable in generic WebDAV environments as well.

This document addresses the following requirements:

1. Enable file transfers when recipient is offline.
2. Use WebDAV for file puts and gets.

This document inherits terms from RFC 2518 RFC 2518: HTTP Extensions for Distributed Authoring -- WEBDAV <http://tools.ietf.org/html/rfc2518>., RFC 2616 RFC 2616: Hypertext Transport Protocol -- HTTP/1.1 <http://tools.ietf.org/html/rfc2616>., and RFC 2617 RFC 2617: HTTP Authentication: Basic and Digest Access Authentication <http://tools.ietf.org/html/rfc2617>..

The client SHOULD attempt to PUT the file on the server. Alternatively, the client MAY first attempt one or more HEAD requests to determine a unique URL. The PUT request MUST include an "If-None-Match" header as well as an "Authorization" header that specifies appropriate authentication information.

Prior to storing the file, the server MUST verify the user's authentication credentials via any supported method. When the file is stored, the server also MUST set the owner "live" property to ensure that only the user that originally posted this file is allowed to modify the file in any way. Other users MAY be allowed to see properties and retrieve the file (upon authentication) but MUST NOT be able to perform operations such as DELETE, MOVE, and PROPPATCH.

In the absence of any other authorization method (e.g., RFC 3744 RFC 3744: Web Distributed Authoring and Versioning (WebDAV) Access Control Protocol <http://tools.ietf.org/html/rfc3744>. or Security Assertion Markup Language Security Assertion Markup Language <http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=security>.) in use by the deployed WebDAV server, the client SHOULD perform a PROPPATCH request to set the list of Jabber IDs authorized to retrieve this file, and the server MUST NOT allow access until this configuration is completed.

Note: The semantics of the JID list defined above are:

• If a JID is a bare JID (no resource), any fully-qualified form of that JID may access this resource (in the example above, this means that any resource of juliet@capulet.com may access this URL).
• If a JID includes a resource identifier, only that specific JID may access this URL (in the example above, this means that only the JID benvolio@montague.net/home may access this URL; benvolio@montague.net/other may not).
• If both a full JID and a bare JID are specified in a single JID list, the bare JID takes precedence.

The server responds when the properties have been updated. This is typically a 207 (MultiPart) response, which means that the body can contain multiple status codes, as shown in the following example.

Now that the file is available via WebDAV and the client has specified what Jabber IDs may access the URL, the sender sends a message to the target user(s) containing the URL of the file, encapsulated via Out-of-Band Data (XEP-0066) XEP-0066: Out of Band Data <https://xmpp.org/extensions/xep-0066.html>.. (The example below shows the file being sent to multiple users using the Extended Stanza Addressing (XEP-0033) XEP-0033: Extended Stanza Addressing <https://xmpp.org/extensions/xep-0033.html>. protocol.)