Appendix B. Notes on HTTP Client Compatibility

Appendix B. Notes on HTTP Client Compatibility

WebDAV was designed to be, and has been found to be, backward-compatible with HTTP 1.1. The PUT and DELETE methods are defined in HTTP and thus may be used by HTTP clients as well as WebDAV-aware clients, but the responses to PUT and DELETE have been extended in this specification in ways that only a WebDAV client would be entirely prepared for. Some theoretical concerns were raised about whether those responses would cause interoperability problems with HTTP-only clients, and this section addresses those concerns.

Since any HTTP client ought to handle unrecognized 400-level and 500-level status codes as errors, the following new status codes should not present any issues: 422, 423, and 507 (424 is also a new status code but it appears only in the body of a Multistatus response.) So, for example, if an HTTP client attempted to PUT or DELETE a locked resource, the 423 Locked response ought to result in a generic error presented to the user.

The 207 Multistatus response is interesting because an HTTP client issuing a DELETE request to a collection might interpret a 207 response as a success, even though it does not realize the resource is a collection and cannot understand that the DELETE operation might have been a complete or partial failure. That interpretation isn't entirely justified, because a 200-level response indicates that the server "received, understood, and accepted" the request, not that the request resulted in complete success.

One option is that a server could treat a DELETE of a collection as an atomic operation, and use either 204 No Content in case of success, or some appropriate error response (400 or 500 level) for an error. This approach would indeed maximize backward compatibility. However, since interoperability tests and working group discussions have not turned up any instances of HTTP clients issuing a DELETE request against a WebDAV collection, this concern is more theoretical than practical. Thus, servers are likely to be completely successful at interoperating with HTTP clients even if they treat any collection DELETE request as a WebDAV request and send a 207 Multi-Status response.

In general, server implementations are encouraged to use the detailed responses and other mechanisms defined in this document rather than make changes for theoretical interoperability concerns.