modelcontextprotocol/java-sdk
Watch
1
0
Fork
You've already forked java-sdk
 0
Code Issues Pull requests Projects Releases Packages Wiki Activity Actions

Fix SSE event classification to follow spec for missing event field (#913)

Browse source 
Per the SSE specification (WHATWG HTML Living Standard 9.2.6), an event with no explicit event field MUST be dispatched as a message event. HttpClientStreamableHttpTransport previously used strict equality and silently dropped such frames in the reconnect/GET stream path, causing server-initiated notifications to never reach the handler. Extract classification into a package-private isMessageEvent helper and cover with parameterized unit tests.

Closes gh-885
This commit is contained in:
jiajingda 2026-08-07 23:48:03 +08:00 • committed by GitHub
commit f5aab36a2f
No known key found for this signature in database
GPG key ID: B5690EEEBB952194
1 changed files with 75 additions and 1 deletions
Download patch file Download diff file Expand all files Collapse all files

25
mcp-core/src/main/java/io/modelcontextprotocol/client/transport/HttpClientStreamableHttpTransport.java
View file

@ -114,6 +114,29 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
public static int BAD_REQUEST = 400;
/**
* Determines whether an SSE event should be treated as a "message" event carrying a
* JSON-RPC payload.
*
* <p>
* Per the <a href=
* "https://html.spec.whatwg.org/multipage/server-sent-events.html#event-stream-interpretation">
* SSE specification (WHATWG HTML Living Standard §9.2.6)</a>, an event with no
* explicit {@code event:} field MUST be dispatched as a {@code message} event by
* default. This method applies that rule by treating {@code null} or empty event
* names as equivalent to {@link #MESSAGE_EVENT_TYPE}.
*
* <p>
* This alignment ensures interoperability with MCP servers that emit bare
* {@code data:} frames without an accompanying {@code event:} line, which are valid
* per the SSE spec.
* @param eventName the SSE event name, which may be {@code null} or empty
* @return {@code true} if the event should be parsed as a JSON-RPC message
*/
static boolean isMessageEvent(String eventName) {
return eventName == null || eventName.isEmpty() || MESSAGE_EVENT_TYPE.equals(eventName);
}
private final McpJsonMapper jsonMapper;
private final URI baseUri;
@ -323,7 +346,7 @@ public class HttpClientStreamableHttpTransport implements McpClientTransport {
+ statusCode));
}
else if (statusCode >= 200 && statusCode < 300) {
if (MESSAGE_EVENT_TYPE.equals(sseResponseEvent.sseEvent().event())) {
if (isMessageEvent(sseResponseEvent.sseEvent().event())) {
String data = sseResponseEvent.sseEvent().data();
// Per 2025-11-25 spec (SEP-1699), servers may
// send SSE events