Hacktoberfest 2026 : les issues que les mainteneurs ont marquées pour octobre, ouvertes et accessibles aux débutants. Parcourir les issues Hacktoberfest

HttpServletStreamableServerTransportProvider: GET stream sends no status or headers until the first event

Ouverte Adaptée aux débutants
  • Quelque chose ne va pas ?
#1,155 0 commentaires 0 réactions 0 personnes assignées Voir sur GitHub

Les mainteneurs répondent en général sous 3 jours

Personne n'a encore pris cette issue.

Évaluation

Difficulté
2/5
Temps estimé
1-3 heures
Accessibilité débutants
86/100
Type d'issue
Bug
Clarté
Clairement spécifiée
Activité
Active
Stack technique
java
Domaine
api, backend

Piste de recherche

Commencez dans HttpServletStreamableServerTransportProvider#doGet et exécutez la reproduction fournie StreamableGetStreamHeadersTest.java avec le transport servlet. C’est terminé lorsque la requête GET se termine avec le statut 200 et un Content-Type text/event-stream avant l’envoi de tout événement ou ping keep-alive.

Rédigé par le modèle d'indexation à partir du texte de l'issue.

Description

Bug description
After initialize, a GET to the MCP endpoint with Accept: text/event-stream gets no status line and no headers. doGet sets the SSE headers and starts async but doesn't flush, so nothing is sent until the server writes its first event to the stream. If the server has nothing to send, the client never gets a response.

Clients that wait for headers time out. Node's fetch (undici) gives up after its default headersTimeout of 300 s with UND_ERR_HEADERS_TIMEOUT. mcp-remote then retries twice and stops ("Maximum reconnection attempts (2) exceeded"). After that the server has no stream to the client, and server-initiated requests fail with Stream unavailable for session ... (see also #1061).

With keepAliveInterval set, the first ping sends the headers, but only after one interval.

The spec says the server must either return Content-Type: text/event-stream for this GET or return 405 (Streamable HTTP, 2025-11-25).

Environment

  • Where it was seen: mcp-core 1.1.1, Spring Boot 4.0.5 (embedded Tomcat), Java 25.0.3, macOS 27.0.1. Client: Claude Desktop through mcp-remote 0.14.3, protocol 2025-11-25.
  • Reproduced with the test below: mcp-core 1.1.1 and 2.0.1, tomcat-embed-core 11.0.22, JDK 26.0.1, macOS 14.7.4. The doGet code is the same on main (1cf7903).
  • No keep-alive configured.

Steps to reproduce

  1. POST initialize and note the Mcp-Session-Id.
  2. POST notifications/initialized. You get 202.
  3. GET the endpoint with Accept: text/event-stream and the session ID.
curl -sN --max-time 20 -D - http://127.0.0.1:8080/mcp -H 'Accept: text/event-stream' -H "Mcp-Session-Id: $SID"

Actual: 0 bytes received in 20 s.

Expected behavior
200 with Content-Type: text/event-stream sent as soon as the GET stream opens, before any event is ready.

Minimal Complete Reproducible example
Dependencies: io.modelcontextprotocol.sdk:mcp, org.apache.tomcat.embed:tomcat-embed-core:11.0.22, org.junit.jupiter:junit-jupiter. The test fails with java.util.concurrent.TimeoutException on 1.1.1 and 2.0.1. If .keepAliveInterval(Duration.ofSeconds(1)) is added to the builder, it passes: the headers arrive with the first ping.

StreamableGetStreamHeadersTest.java 
package repro;

import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertTrue;

import java.io.InputStream;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import java.nio.file.Files;
import java.util.concurrent.TimeUnit;

import org.apache.catalina.Context;
import org.apache.catalina.startup.Tomcat;
import org.junit.jupiter.api.Test;

import io.modelcontextprotocol.server.McpAsyncServer;
import io.modelcontextprotocol.server.McpServer;
import io.modelcontextprotocol.server.transport.HttpServletStreamableServerTransportProvider;

class StreamableGetStreamHeadersTest {

	@Test
	void getStreamSendsHeadersBeforeFirstEvent() throws Exception {
		HttpServletStreamableServerTransportProvider transport = HttpServletStreamableServerTransportProvider.builder()
			.build();
		McpAsyncServer server = McpServer.async(transport).serverInfo("repro", "1").build();

		Tomcat tomcat = new Tomcat();
		tomcat.setBaseDir(Files.createTempDirectory("tomcat").toString());
		tomcat.setPort(0);
		Context context = tomcat.addContext("", null);
		Tomcat.addServlet(context, "mcp", transport).setAsyncSupported(true);
		context.addServletMappingDecoded("/*", "mcp");
		tomcat.start();

		try {
			URI endpoint = URI.create("http://127.0.0.1:" + tomcat.getConnector().getLocalPort() + "/mcp");
			HttpClient client = HttpClient.newHttpClient();

			String sessionId = client.send(post(endpoint, null, """
					{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2025-11-25",\
					"capabilities":{},"clientInfo":{"name":"repro","version":"1"}}}"""),
					HttpResponse.BodyHandlers.discarding())
				.headers()
				.firstValue("Mcp-Session-Id")
				.orElseThrow();
			assertEquals(202, client.send(post(endpoint, sessionId, """
					{"jsonrpc":"2.0","method":"notifications/initialized"}"""),
					HttpResponse.BodyHandlers.discarding())
				.statusCode());

			HttpRequest get = HttpRequest.newBuilder(endpoint)
				.header("Accept", "text/event-stream")
				.header("Mcp-Session-Id", sessionId)
				.GET()
				.build();

			// Completes once the status line and headers arrive. Fails with TimeoutException.
			HttpResponse<InputStream> response = client.sendAsync(get, HttpResponse.BodyHandlers.ofInputStream())
				.get(5, TimeUnit.SECONDS);

			assertEquals(200, response.statusCode());
			assertTrue(response.headers().firstValue("Content-Type").orElse("").startsWith("text/event-stream"));
			response.body().close();
		}
		finally {
			server.closeGracefully().block();
			tomcat.stop();
			tomcat.destroy();
		}
	}

	private static HttpRequest post(URI endpoint, String sessionId, String body) {
		HttpRequest.Builder builder = HttpRequest.newBuilder(endpoint)
			.header("Accept", "application/json, text/event-stream")
			.header("Content-Type", "application/json")
			.POST(HttpRequest.BodyPublishers.ofString(body));
		if (sessionId != null) {
			builder.header("Mcp-Session-Id", sessionId);
		}
		return builder.build();
	}

}
Langage dominant
Java
Étoiles
3.7k
Forks
1.1k
Merge moyen
2 j 5 h
PR mergées (30 j)
4

Préparer son environnement

Par où commencer

  1. Lisez l'issue en entier, puis le guide de contribution du projet.
  2. Signalez en commentaire que vous la prenez — cela évite que deux personnes fassent le même travail.
  3. Forkez le dépôt et travaillez sur une branche.
  4. Ouvrez une pull request qui référence le numéro de l'issue.

Autres issues de modelcontextprotocol/java-sdk

Toutes les issues de modelcontextprotocol/java-sdk

Issues similaires

Plus d'issues Java

Recevez les nouvelles issues par e-mail

Un résumé court des issues GitHub adaptées aux débutants.