RFC 5785: Defining Well-Known URIs

This first piece of the discovery stack was published today as an RFC. RFC 5785 defines a registry for new well-known URIs which will provide a standard location for the host-meta document. This work started a year and a half ago as a well-known document called /site-meta, and slowly evolved into a simple registry. While this isn’t a breakthrough idea, it does codify existing behavior and hopefully encourages people to share ideas, discuss proposals, and reusing existing well-known URIs.

Many thanks to my co-author Mark Nottingham for got this ball rolling.

From RFC 5785:

It is increasingly common for Web-based protocols to require the discovery of policy or other information about a host (“site-wide metadata”) before making a request. For example, the Robots Exclusion Protocol specifies a way for automated processes to obtain permission to access resources; likewise, the Platform for Privacy Preferences tells user-agents how to discover privacy policy beforehand.

While there are several ways to access per-resource metadata (e.g., HTTP headers, WebDAV’s PROPFIND), the perceived overhead (either in terms of client-perceived latency and/or deployment difficulties) associated with them often precludes their use in these scenarios.

When this happens, it is common to designate a “well-known location” for such data, so that it can be easily located. However, this approach has the drawback of risking collisions, both with other such designated “well-known locations” and with pre-existing resources.

To address this, this memo defines a path prefix in HTTP(S) URIs for these “well-known locations”, “/.well-known/”. Future specifications that need to define a resource for such site-wide metadata can register their use to avoid collisions and minimise impingement upon sites’ URI space.

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