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Reject subscriptions/listen without notifications #1208

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9 changes: 6 additions & 3 deletions mcp-core/src/main/java/io/modelcontextprotocol/modern/server/SubscriptionsFeature.java
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Original file line number Diff line number Diff line change
Expand Up @@ -71,15 +71,18 @@ public Set<String> methods() {

@Override
public Mono<McpAsyncResponse<Result>> handle(McpRequestContext ctx, Object params) {
// The JSON creator fills a missing filter in, so check the raw params.
if (!(params instanceof Map<?, ?> map) || map.get("notifications") == null) {
return Mono.error(McpException.invalidParams("params.notifications is required"));
}
SubscriptionsListenRequest request;
try {
request = params == null ? null : this.jsonMapper.convertValue(params, SubscriptionsListenRequest.class);
request = this.jsonMapper.convertValue(params, SubscriptionsListenRequest.class);
}
catch (RuntimeException ex) {
return Mono.error(McpException.invalidParams("Malformed SubscriptionsListenRequest"));
}
SubscriptionFilter requested = request == null || request.notifications() == null ? SubscriptionFilter.EMPTY
: request.notifications();
SubscriptionFilter requested = request.notifications();
return Mono.just(McpAsyncResponse.streaming(notifier -> listen(ctx, intersect(requested), notifier)));
}

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35 changes: 35 additions & 0 deletions mcp-core/src/test/java/io/modelcontextprotocol/modern/server/SubscriptionsFeatureTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -211,6 +211,41 @@ void resourceSubscribeIsNotAdvertisedWithoutSubscriptions() {
assertThat(resourcesCapability(server)).containsEntry("subscribe", false);
}

@Test
void listenWithoutNotificationsIsRejectedAsInvalidParams() {
McpServer server = toolsServer(new McpChangeFeed());
JSONRPCRequest request = new JSONRPCRequest("subscriptions/listen", 1, Map.of("_meta", meta()));

assertThat(server.handle(McpTransportContext.EMPTY, request).block()).isInstanceOfSatisfying(
McpTransportResponse.Error.class,
error -> assertThat(error.response().error().code()).isEqualTo(McpSchema.ErrorCodes.INVALID_PARAMS));
}

@Test
void listenWithNullNotificationsIsRejectedAsInvalidParams() {
McpServer server = toolsServer(new McpChangeFeed());
Map<String, Object> params = new HashMap<>();
params.put("_meta", meta());
params.put("notifications", null);
JSONRPCRequest request = new JSONRPCRequest("subscriptions/listen", 1, params);

assertThat(server.handle(McpTransportContext.EMPTY, request).block()).isInstanceOfSatisfying(
McpTransportResponse.Error.class,
error -> assertThat(error.response().error().code()).isEqualTo(McpSchema.ErrorCodes.INVALID_PARAMS));
}

@Test
void listenWithEmptyNotificationsIsAccepted() {
McpServer server = toolsServer(new McpChangeFeed());
Map<String, Object> params = new HashMap<>();
params.put("_meta", meta());
params.put("notifications", Map.of());
JSONRPCRequest request = new JSONRPCRequest("subscriptions/listen", 1, params);

assertThat(server.handle(McpTransportContext.EMPTY, request).block())
.isInstanceOf(McpTransportResponse.Streaming.class);
}

private static McpServer resourcesServer(boolean supportsSubscribe, McpChangePublisher publisher) {
McpAsyncResourceRepository repository = new McpAsyncResourceRepository() {
@Override
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14 changes: 14 additions & 0 deletions ...modelcontextprotocol/modern/server/transport/HttpServletMcpTransportIntegrationTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -6,6 +6,7 @@

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.Socket;
Expand Down Expand Up @@ -260,6 +261,19 @@ void unknownToolIsInvalidParams() throws Exception {
assertThat(errorCode(response)).isEqualTo(ErrorCodes.INVALID_PARAMS);
}

@Test
void listenWithoutNotificationsIsInvalidParams() throws Exception {
HttpRequest request = post("subscriptions/listen", Map.of("_meta", meta())).build();
HttpResponse<InputStream> response = HttpClient.newHttpClient()
.send(request, HttpResponse.BodyHandlers.ofInputStream());

try (InputStream body = response.body()) {
assertThat(response.statusCode()).isEqualTo(400);
assertThat(new String(body.readAllBytes(), StandardCharsets.UTF_8))
.contains("\"code\":" + ErrorCodes.INVALID_PARAMS);
}
}

@Test
void streamingBodyExceptionIsAnsweredInStream() throws Exception {
HttpResponse<String> response = callTool("fails-streaming");
Expand Down