508 Loop Detected
508 Loop Detected is a status code that’s introduced by an
extension of the WebDAV specification.
The specific extension adds support for a ‘Binding’ feature. WebDAV itself
is a bit like a filesystem protocol over HTTP, and the Binding extension
adds support for a ‘hardlink’-like feature via the BIND and UNBIND
methods.
WebDAV has a few features that allows a client to get information from a server and ask for an entire directory tree. The binding extension makes it possible to make a link from 1 resource, and create the target somewhere in it’s own tree.
This makes it hypothetically possible to create a directory structure that’s ‘infinitely deep’, because it always keeps looping back into itself.
When this happens, a server can respond with 508 Loop Detected to tell a
client it’s not possible to return a result of infinite size.
It’s extremely rate to run into it, as there’s few WebDAV servers that implement support for it.
HTTP/1.1 508 Loop Detected
Content-Type: text/plain
There was a loop detected in the directory tree, which means that we're not
able to return a full directory tree.
Should I use this?
Maybe. Even though this is a WebDAV feature, other types of APIs might have support for a feature that allows recursively linking structures. If such an API also has a feature to flatten and return entire trees, this status code could be appropriate and doesn’t hurt.
Although, the choice of the 5xx status code is a little odd. If a system allows recurively linking structures, and the user requested this, it’s really the client that’s at fault.
References
- RFC5842, Section 7.2 - 508 Loop Detected.