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Merged
danielkov merged 3 commits into from
Oct 19, 2026
Merged

fix(mcp): honor advertised catalog subscription capabilities #41

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dbbb5b0
fix(mcp): honor advertised catalog subscription capabilities
danielkov Oct 19, 2026
3cbd011
test(mcp): retain HTTP stream fixtures through capability assertions
danielkov Oct 19, 2026
30c5b75
fix(mcp): use current transport sink for lazy subscriptions
danielkov Oct 19, 2026
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75 changes: 59 additions & 16 deletions crates/agentkit-mcp/src/lib.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -1648,14 +1648,18 @@ impl McpConnection {
if !resources.is_empty() {
filter.resource_subscriptions = Some(resources.iter().cloned().collect());
}
Some(
subscriptions::SubscriptionController::start(
new_peer.clone(),
filter,
candidate_sink.clone(),
if subscription_filter_is_empty(&filter) {
None
} else {
Some(
subscriptions::SubscriptionController::start(
new_peer.clone(),
filter,
candidate_sink.clone(),
)
.await?,
)
.await?,
)
}
} else {
// Legacy subscriptions are session-scoped and must be replayed on
// the candidate before retiring the authoritative old transport.
Expand Down Expand Up @@ -1771,12 +1775,13 @@ impl McpConnection {
if !resources.is_empty() {
filter.resource_subscriptions = Some(resources.iter().cloned().collect());
}
let controller = subscriptions::SubscriptionController::start(
self.peer(),
filter,
self.sink.clone(),
)
.await?;
if subscription_filter_is_empty(&filter) {
return Ok(());
}
let mut sink = self.sink.clone();
sink.active = self.inner.lock().await.service().active.clone();
let controller =
subscriptions::SubscriptionController::start(self.peer(), filter, sink).await?;
*subscriptions = Some(controller);
}
Ok(())
Expand Down Expand Up @@ -1813,6 +1818,18 @@ impl McpConnection {
if let Some(controller) = self.subscriptions.lock().await.as_ref() {
return controller.subscribe_resource(uri).await;
}
if self.modern() {
// Resource-only servers have no catalog stream to extend. Start a
// modern stream with the explicit URI, never a legacy subscribe RPC.
let mut filter = self.subscription_filter();
filter.resource_subscriptions = Some(vec![uri]);
let mut sink = self.sink.clone();
sink.active = self.inner.lock().await.service().active.clone();
let controller =
subscriptions::SubscriptionController::start(self.peer(), filter, sink).await?;
*self.subscriptions.lock().await = Some(controller);
return Ok(());
}
self.peer()
.subscribe(rmcp_model::SubscribeRequestParams::new(uri.clone()))
.await
Expand All @@ -1836,6 +1853,10 @@ impl McpConnection {
if let Some(controller) = self.subscriptions.lock().await.as_ref() {
return controller.unsubscribe_resource(uri).await;
}
if self.modern() {
// No modern controller means no resource subscription exists.
return Ok(());
}
self.peer()
.unsubscribe(rmcp_model::UnsubscribeRequestParams::new(uri.clone()))
.await
Expand Down Expand Up @@ -2185,12 +2206,34 @@ impl McpConnection {

fn filter_for_capabilities(capabilities: &McpServerCapabilities) -> McpSubscriptionFilter {
let mut filter = McpSubscriptionFilter::default();
filter.tools_list_changed = capabilities.tools.as_ref().map(|_| true);
filter.resources_list_changed = capabilities.resources.as_ref().map(|_| true);
filter.prompts_list_changed = capabilities.prompts.as_ref().map(|_| true);
filter.tools_list_changed = capabilities
.tools
.as_ref()
.and_then(|c| c.list_changed)
.filter(|enabled| *enabled);
filter.resources_list_changed = capabilities
.resources
.as_ref()
.and_then(|c| c.list_changed)
.filter(|enabled| *enabled);
filter.prompts_list_changed = capabilities
.prompts
.as_ref()
.and_then(|c| c.list_changed)
.filter(|enabled| *enabled);
filter
}

fn subscription_filter_is_empty(filter: &McpSubscriptionFilter) -> bool {
filter.tools_list_changed != Some(true)
&& filter.resources_list_changed != Some(true)
&& filter.prompts_list_changed != Some(true)
&& filter
.resource_subscriptions
.as_ref()
.is_none_or(Vec::is_empty)
}

fn client_lifecycle() -> ClientLifecycleMode {
ClientLifecycleMode::Auto {
// Auto must retry discovery at a mutually supported version before an
Expand Down
122 changes: 122 additions & 0 deletions crates/agentkit-mcp/tests/modern_http.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -148,13 +148,38 @@ async fn rpc(
} else {
capabilities.build()
};
let capabilities = match token {
"Bearer caps-missing" => json!({}),
"Bearer caps-empty" => json!({"tools":{},"resources":{},"prompts":{}}),
"Bearer caps-false" => {
json!({"tools":{"listChanged":false},"resources":{"listChanged":false},"prompts":{"listChanged":false}})
}
"Bearer caps-resource" => json!({"resources":{"subscribe":true}}),
"Bearer caps-mixed" => {
json!({"tools":{"listChanged":true},"resources":{"listChanged":false},"prompts":{}})
}
"Bearer caps-true" => {
json!({"tools":{"listChanged":true},"resources":{"listChanged":true},"prompts":{"listChanged":true}})
}
_ => serde_json::to_value(capabilities).unwrap(),
};
let capabilities = serde_json::from_value(capabilities).unwrap();
serde_json::to_value(DiscoverResult::new(
vec![ProtocolVersion::V_2026_07_28],
capabilities,
))
.unwrap()
}
"subscriptions/listen" => {
if matches!(
token,
"Bearer caps-missing" | "Bearer caps-empty" | "Bearer caps-false"
) {
return Json(json!({"jsonrpc":"2.0", "id":id, "error":{
"code":-32601, "message":"subscriptions not supported"
}}))
.into_response();
}
let (frames, receiver) = mpsc::unbounded_channel();
let filter = message["params"]["notifications"].clone();
if token != "Bearer hold" && !state.hold_ack.load(Ordering::SeqCst) {
Expand Down Expand Up @@ -736,3 +761,100 @@ async fn auto_http_no_common_version_does_not_initialize() {
})
.await;
}

#[tokio::test]
async fn advertised_catalog_flags_gate_listen_on_connect_discover_and_reconnect() {
bounded(async {
for profile in ["missing", "empty", "false", "mixed", "true"] {
let mut fixture = Fixture::start().await;
let token = format!("caps-{profile}");
if let McpTransportBinding::StreamableHttp(binding) = &mut fixture.config.transport {
*binding = binding.clone().with_bearer_token(&token);
}
let connection = McpConnection::connect(&fixture.config).await.unwrap();
let expected = match profile {
"mixed" => Some(json!({"toolsListChanged":true})),
"true" => Some(json!({"toolsListChanged":true,"resourcesListChanged":true,"promptsListChanged":true})),
_ => None,
};
let initial = if let Some(filter) = &expected {
let stream = fixture.listen().await;
assert_eq!(&stream.filter, filter);
Some(stream)
} else {
assert!(connection.subscription_status().await.is_none());
None
};
connection.discover().await.unwrap();
connection.discover().await.unwrap();
connection.resolve_auth(auth(&token)).await.unwrap();
connection.discover().await.unwrap();
let replacement = if let Some(filter) = &expected {
let stream = fixture.listen().await;
assert_eq!(&stream.filter, filter);
Some(stream)
} else {
None
};
let requests = fixture.requests.lock().await;
assert_eq!(requests.iter().filter(|(_, r)| r["method"] == "subscriptions/listen").count(), if expected.is_some() { 2 } else { 0 }, "{profile}");
drop(requests);
connection.close().await.unwrap();
drop((initial, replacement));
}
}).await;
}

#[tokio::test]
async fn resource_only_server_starts_modern_stream_lazily_and_replays_on_reconnect() {
bounded(async {
let mut fixture = Fixture::start().await;
if let McpTransportBinding::StreamableHttp(binding) = &mut fixture.config.transport {
*binding = binding.clone().with_bearer_token("caps-resource");
}
let connection = McpConnection::connect(&fixture.config).await.unwrap();
connection.discover().await.unwrap();
connection
.unsubscribe_resource("memo:absent")
.await
.unwrap();
assert!(connection.subscription_status().await.is_none());
assert!(
!fixture
.requests
.lock()
.await
.iter()
.any(|(_, r)| r["method"] == "subscriptions/listen")
);
// Reconnect before the first stream exists: lazy startup must use the
// replacement transport's active notification sink.
connection.resolve_auth(auth("caps-resource")).await.unwrap();
let mut events = connection.subscribe_events();
connection.subscribe_resource("memo:one").await.unwrap();
let initial = fixture.listen().await;
assert_eq!(
initial.filter,
json!({"resourceSubscriptions":["memo:one"]})
);
initial.notify("notifications/resources/updated", json!({"uri":"memo:one"}));
assert!(matches!(events.recv().await.unwrap(), McpServerEvent::ResourceUpdated(params) if params.uri == "memo:one"));
connection
.resolve_auth(auth("caps-resource"))
.await
.unwrap();
let replacement = fixture.listen().await;
assert_eq!(
replacement.filter,
json!({"resourceSubscriptions":["memo:one"]})
);
connection.unsubscribe_resource("memo:one").await.unwrap();
assert!(!fixture.requests.lock().await.iter().any(|(_, r)| matches!(
r["method"].as_str(),
Some("resources/subscribe" | "resources/unsubscribe")
)));
connection.close().await.unwrap();
drop((initial, replacement));
})
.await;
}