Using POST to add  I ↓Membersto Web Distributed Authoring and Versioning (WebDAV) Collections

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The Hypertext Transfer Protocol (HTTP) Extensions for the Web Distributed Authoring and Versioning (WebDAV) do not define the behavior for the "POST" method when applied to collections, as the base specification (HTTP) leaves implementers lots of freedom for the semantics of "POST".¶

This has lead to a situation where many WebDAV servers do not implement POST for collections at all, although it is well suited to be used for the purpose of adding new members to a collection, where the server remains in control of the newly assigned URL. As a matter of fact, the Atom Publishing Protocol (AtomPub) uses POST exactly for that purpose. On the other hand, WebDAV-based protocols such as the Calendar Extensions to WebDAV (CalDAV) frequently require clients to pick a unique URL, although the server could easily perform that task.¶

This specification defines a discovery mechanism through which servers can advertise support for POST requests with the aforementioned "add collection member" semantics.¶

9.5 POST for Collections ¶

Since by definition the actual function performed by POST is determined by the server and often depends on the particular resource, the behavior of POST when applied to collections cannot be meaningfully modified because it is largely undefined. Thus, the semantics of POST are unmodified when applied to a collection.¶

9.2 Creating Resources with POST ¶

To add members to a Collection, clients send POST requests to the URI of the Collection.¶

5.3.2 Creating Calendar Object Resources ¶

...¶

When servers create new resources, it's not hard for the server to choose an unmapped URI. It's slightly tougher for clients, because a client might not want to examine all resources in the collection and might not want to lock the entire collection to ensure that a new resource isn't created with a name collision. (...)¶

This specification defines a discovery mechanism through which servers can advertise support for POST requests with the aforementioned "add collection member" semantics.¶

The terminology used here follows that in the WebDAV specification ([RFC4918]).¶

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].¶

This document uses XML DTD fragments ([XML]) as a purely notational convention. In particular: ¶

• Element names use the namespace "http://purl.org/NET/webdav/post#". When an XML element type in this namespace is referenced in this document outside of the context of an XML fragment, the string "p:" will be prefixed to the element name. [ns: With sufficient support from the WebDAV WG's former mailing list and/or the IESG Applications Area the property defined later on could potentially be moved into the DAV: namespace.]
• Element ordering is irrelevant.
• Extension elements/attributes (elements/attributes not already defined as valid child elements) may be added anywhere, except when explicitly stated otherwise.

Due to the reasons stated in Section 1, clients can not rely on a specific server behavior when POST is applied to a collection. This problem is addressed by this specification by allowing servers to advertise a URI that has the desired "add member" semantics.¶

Note that ↑ I ↓servers that already use POST for a different purpose can just expose a different URI for that purpose. Other servers can just advertise the collection's own URI, thus avoiding ↑ I ↓to mintminting another URI for a limited purpose.¶

This document does not introduce any new internationalization considerations beyond those discussed in Section 20 of [RFC4918].¶

This specification does not require any actions from IANA.¶

All security considerations connected to HTTP/WebDAV and XML apply for this specification as well, namely, [RFC4918] (Section 20) and [RFC3470] (Section 7).¶

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