Hacktoberfest 2026: die Issues, die Maintainer für den Oktober markiert haben – offen und einsteigerfreundlich. Hacktoberfest-Issues durchsuchen

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

Offen Anfängerfreundlich
  • Stimmt etwas nicht?
#1,155 0 Kommentare 0 Reaktionen 0 zugewiesene Personen Auf GitHub ansehen

Maintainer antworten meist innerhalb von 3 Tagen

Dieses Issue hat noch niemand übernommen.

Bewertung

Schwierigkeit
2/5
Geschätzter Aufwand
1-3 Stunden
Anfängerfreundlichkeit
86/100
Issue-Typ
Bug
Klarheit
Klar beschrieben
Aktivitätsstatus
Aktiv
Tech-Stack
java
Bereich
api, backend

Rechercherichtung

Beginne in HttpServletStreamableServerTransportProvider#doGet und führe die bereitgestellte Reproduktion StreamableGetStreamHeadersTest.java gegen den Servlet-Transport aus. Als abgeschlossen gilt die Aufgabe, wenn die GET-Anfrage mit dem Status 200 und einem text/event-stream Content-Type abgeschlossen wird, bevor ein Event oder ein Keep-Alive-Ping gesendet wird.

Vom Indexierungsmodell aus dem Issue-Text verfasst.

Beschreibung

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();
	}

}
Vorherrschende Sprache
Java
Sterne
3.7k
Forks
1.1k
Ø Merge
2 T. 5 Std.
Gemergte PRs (30 T.)
4

Entwicklungsumgebung

Erste Schritte

  1. Lesen Sie das ganze Issue und danach den Beitragsleitfaden des Projekts.
  2. Schreiben Sie ins Issue, dass Sie es übernehmen — das erspart doppelte Arbeit.
  3. Forken Sie das Repository und arbeiten Sie in einem Branch.
  4. Öffnen Sie einen Pull Request, der die Issue-Nummer nennt.

Mehr aus modelcontextprotocol/java-sdk

Alle Issues in modelcontextprotocol/java-sdk

Ähnliche Issues

Weitere Issues zu Java

Neue Issues direkt in Ihr Postfach

Eine kurze Übersicht über anfängerfreundliche GitHub-Issues.