Function check_known_capabilities 

pub fn check_known_capabilities<S: AsRef<str>>(
    req: &JmapRequest,
    known: &[S],
) -> Result<(), JmapError>

Validate that every capability URI in req.using is in the known set.

RFC 8620 §3.3 requires the server to return an unknownCapability error (HTTP 400) if the request declares a capability the server does not support. This library cannot enforce that check because it has no knowledge of which capabilities a given deployment supports — that is the caller’s responsibility.

Call this immediately after parse_request and map any Err to an HTTP 400 response using crate::request_error.

Errors

Returns JmapError::unknown_capability_with_detail for the first URI in req.using that is not present in known. If all URIs are known, returns Ok(()).

Example

let req = JmapRequest::new(
    vec!["urn:ietf:params:jmap:core".into()],
    vec![],
    None,
);
let known = &["urn:ietf:params:jmap:core", "urn:ietf:params:jmap:mail"];
check_known_capabilities(&req, known).expect("all URIs in known — Ok(()) expected (doctest)");