mcp_utils/server/
mrtr.rs

1use rmcp::model::{ClientCapabilities, ElicitRequestParams, ErrorData, InputRequest, InputRequests, InputResponses};
2use serde::de::DeserializeOwned;
3
4pub const ELICITATION_UNSUPPORTED: &str = "This tool needs to ask the user for input, but the connected client does not support \
5     interactive input (MCP elicitation over protocol 2026-07-28 or newer).";
6
7pub fn input_requests_supported(capabilities: Option<&ClientCapabilities>, requests: &InputRequests) -> bool {
8    requests.values().all(|request| capabilities.is_some_and(|capabilities| supports_input(capabilities, request)))
9}
10
11/// Deserialize one keyed response from a complete MRTR response batch.
12pub fn parse_response<T: DeserializeOwned>(responses: &InputResponses, key: &str) -> Result<T, ErrorData> {
13    let response = responses
14        .get(key)
15        .ok_or_else(|| ErrorData::invalid_params(format!("missing input response for '{key}'"), None))?;
16    serde_json::from_value(response.clone())
17        .map_err(|e| ErrorData::invalid_params(format!("invalid input response for '{key}': {e}"), None))
18}
19
20fn supports_input(capabilities: &ClientCapabilities, request: &InputRequest) -> bool {
21    #[allow(unreachable_patterns)]
22    match request {
23        InputRequest::CreateMessage(_) => capabilities.sampling.is_some(),
24        InputRequest::Elicitation(request) => supports_elicitation(capabilities, &request.params),
25        InputRequest::ListRoots(_) => capabilities.roots.is_some(),
26        _ => false,
27    }
28}
29
30fn supports_elicitation(capabilities: &ClientCapabilities, params: &ElicitRequestParams) -> bool {
31    #[allow(unreachable_patterns)]
32    match params {
33        ElicitRequestParams::FormElicitationParams { .. } => capabilities
34            .elicitation
35            .as_ref()
36            .is_some_and(|elicitation| elicitation.form.is_some() || elicitation.url.is_none()),
37        ElicitRequestParams::UrlElicitationParams { .. } => {
38            capabilities.elicitation.as_ref().is_some_and(|elicitation| elicitation.url.is_some())
39        }
40        _ => false,
41    }
42}
43
44#[cfg(test)]
45mod tests {
46    use super::*;
47    use rmcp::model::{
48        ClientCapabilities, ElicitRequest, ElicitRequestParams, ElicitationCapability, ElicitationSchema,
49        FormElicitationCapability, InputRequest, UrlElicitationCapability,
50    };
51    use serde_json::json;
52
53    #[test]
54    fn validates_capabilities_against_every_request_in_the_batch() {
55        let requests = InputRequests::from([
56            ("form".to_string(), elicitation("Form")),
57            ("url".to_string(), url_elicitation("URL")),
58        ]);
59        let mut capabilities = ClientCapabilities::default();
60        capabilities.elicitation = Some(ElicitationCapability::new().with_form(FormElicitationCapability::new()));
61
62        assert!(!input_requests_supported(Some(&capabilities), &requests));
63    }
64
65    #[test]
66    fn validates_a_mixed_elicitation_batch_when_all_capabilities_are_present() {
67        let requests = InputRequests::from([
68            ("form".to_string(), elicitation("Form")),
69            ("url".to_string(), url_elicitation("URL")),
70        ]);
71        let mut capabilities = ClientCapabilities::default();
72        capabilities.elicitation = Some(
73            ElicitationCapability::new()
74                .with_form(FormElicitationCapability::new())
75                .with_url(UrlElicitationCapability::new()),
76        );
77
78        assert!(input_requests_supported(Some(&capabilities), &requests));
79    }
80
81    #[test]
82    fn parse_response_deserializes_a_key_from_the_batch() {
83        let responses = InputResponses::from([("answer".to_string(), json!(42))]);
84
85        assert_eq!(parse_response::<u64>(&responses, "answer").unwrap(), 42);
86    }
87
88    #[test]
89    fn parse_response_rejects_a_missing_key() {
90        let error = parse_response::<u64>(&InputResponses::new(), "answer").unwrap_err();
91
92        assert_eq!(error.message, "missing input response for 'answer'");
93    }
94
95    fn elicitation(message: &str) -> InputRequest {
96        InputRequest::Elicitation(ElicitRequest::new(ElicitRequestParams::FormElicitationParams {
97            meta: None,
98            message: message.to_string(),
99            requested_schema: ElicitationSchema::builder().build().unwrap(),
100        }))
101    }
102
103    fn url_elicitation(message: &str) -> InputRequest {
104        InputRequest::Elicitation(ElicitRequest::new(ElicitRequestParams::UrlElicitationParams {
105            meta: None,
106            message: message.to_string(),
107            url: "https://example.com/input".to_string(),
108            elicitation_id: "id".to_string(),
109        }))
110    }
111}
mcp_utils/server/mrtr.rs

mcp_utils/server/
mrtr.rs
