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fix:avoid streamable listening sse duplicate creation #524

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fix:avoid streamable listening sse duplicate creation #524

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3dac307
avoid streamable listening sse duplicate creation
taobaorun Aug 28, 2025
c7cbe98
Listening stream already exists for this session and will be closed t…
taobaorun Aug 31, 2025
e87387b
Atomically close the existing listening stream and switch to the new …
taobaorun Sep 1, 2025
4b30e0a
fix listening sse stream close blocking
taobaorun Sep 3, 2025
90ecbb4
resolve conflicts
taobaorun Sep 3, 2025
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15 changes: 11 additions & 4 deletions ...va/io/modelcontextprotocol/server/transport/WebFluxStreamableServerTransportProvider.java
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Original file line number Diff line number Diff line change
Expand Up @@ -200,9 +200,16 @@ private Mono<ServerResponse> handleGet(ServerRequest request) {
.body(Flux.<ServerSentEvent<?>>create(sink -> {
WebFluxStreamableMcpSessionTransport sessionTransport = new WebFluxStreamableMcpSessionTransport(
sink);
McpStreamableServerSession.McpStreamableServerSessionStream listeningStream = session
.listeningStream(sessionTransport);
sink.onDispose(listeningStream::close);
session.listeningStream(sessionTransport)
.doOnNext(serverSessionStream -> sink
.onDispose(() -> serverSessionStream.closeGracefully().subscribe(v -> {
}, error -> logger.warn("Failed to close listening stream gracefully", error))))
.doOnError(error -> {
logger.error("Failed to create listening stream", error);
sink.error(error);
})
.subscribe(serverSessionStream -> logger.debug("Listening stream created successfully"),
sink::error);
// TODO Clarify why the outer context is not present in the
// Flux.create sink?
}).contextWrite(ctx -> ctx.put(McpTransportContext.KEY, transportContext)), ServerSentEvent.class);
Expand Down Expand Up @@ -491,4 +498,4 @@ public WebFluxStreamableServerTransportProvider build() {

}

}
}
13 changes: 8 additions & 5 deletions ...ava/io/modelcontextprotocol/server/transport/WebMvcStreamableServerTransportProvider.java
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Original file line number Diff line number Diff line change
Expand Up @@ -10,6 +10,7 @@
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.locks.ReentrantLock;

import io.modelcontextprotocol.spec.McpStreamableServerSession.McpStreamableServerSessionStream;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.http.HttpStatus;
Expand Down Expand Up @@ -288,13 +289,15 @@ private ServerResponse handleGet(ServerRequest request) {
}
else {
// Establish new listening stream
McpStreamableServerSession.McpStreamableServerSessionStream listeningStream = session
Mono<McpStreamableServerSession.McpStreamableServerSessionStream> listeningStream = session
.listeningStream(sessionTransport);

sseBuilder.onComplete(() -> {
listeningStream.subscribe(serverSessionStream -> sseBuilder.onComplete(() -> {
logger.debug("SSE connection completed for session: {}", sessionId);
listeningStream.close();
});
serverSessionStream.close();
}), error -> {
sseBuilder.error(error);
logger.error("Failed to create listening stream", error);
}, () -> logger.debug("Listening stream created successfully"));
}
}, Duration.ZERO);
}
Expand Down
56 changes: 30 additions & 26 deletions ...o/modelcontextprotocol/server/transport/HttpServletStreamableServerTransportProvider.java
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Original file line number Diff line number Diff line change
Expand Up @@ -13,6 +13,7 @@
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.locks.ReentrantLock;

import io.modelcontextprotocol.spec.McpStreamableServerSession.McpStreamableServerSessionStream;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

Expand Down Expand Up @@ -315,33 +316,36 @@ protected void doGet(HttpServletRequest request, HttpServletResponse response)
}
else {
// Establish new listening stream
McpStreamableServerSession.McpStreamableServerSessionStream listeningStream = session
.listeningStream(sessionTransport);

asyncContext.addListener(new jakarta.servlet.AsyncListener() {
@Override
public void onComplete(jakarta.servlet.AsyncEvent event) throws IOException {
logger.debug("SSE connection completed for session: {}", sessionId);
listeningStream.close();
}

@Override
public void onTimeout(jakarta.servlet.AsyncEvent event) throws IOException {
logger.debug("SSE connection timed out for session: {}", sessionId);
listeningStream.close();
}
session.listeningStream(sessionTransport)
.doOnNext(serverSessionStream -> asyncContext.addListener(new jakarta.servlet.AsyncListener() {
@Override
public void onComplete(jakarta.servlet.AsyncEvent event) throws IOException {
logger.debug("SSE connection completed for session: {}", sessionId);
serverSessionStream.close();
}

@Override
public void onTimeout(jakarta.servlet.AsyncEvent event) throws IOException {
logger.debug("SSE connection timed out for session: {}", sessionId);
serverSessionStream.close();
}

@Override
public void onError(jakarta.servlet.AsyncEvent event) throws IOException {
logger.debug("SSE connection error for session: {}", sessionId);
serverSessionStream.close();
}

@Override
public void onStartAsync(jakarta.servlet.AsyncEvent event) throws IOException {
// No action needed
}
}))
.doOnError(error -> {
logger.error("Failed to create listening stream", error);
})
.subscribe(serverSessionStream -> logger.debug("Listening stream created successfully"));

@Override
public void onError(jakarta.servlet.AsyncEvent event) throws IOException {
logger.debug("SSE connection error for session: {}", sessionId);
listeningStream.close();
}

@Override
public void onStartAsync(jakarta.servlet.AsyncEvent event) throws IOException {
// No action needed
}
});
}
}
catch (Exception e) {
Expand Down
12 changes: 9 additions & 3 deletions mcp/src/main/java/io/modelcontextprotocol/spec/McpStreamableServerSession.java
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Original file line number Diff line number Diff line change
Expand Up @@ -136,10 +136,16 @@ public Mono<Void> delete() {
* @param transport The dedicated SSE transport stream
* @return a stream representation
*/
public McpStreamableServerSessionStream listeningStream(McpStreamableServerTransport transport) {
public Mono<McpStreamableServerSessionStream> listeningStream(McpStreamableServerTransport transport) {
McpStreamableServerSessionStream listeningStream = new McpStreamableServerSessionStream(transport);
this.listeningStreamRef.set(listeningStream);
return listeningStream;
McpLoggableSession oldStream = this.listeningStreamRef.getAndSet(listeningStream);
if (oldStream != null) {
logger.debug(
"Listening stream already exists for this session:{} and will be closed to make way for the new listening SSE stream",
this.id);
return oldStream.closeGracefully().thenReturn(listeningStream);
}
return Mono.just(listeningStream);
}

// TODO: keep track of history by keeping a map from eventId to stream and then
Expand Down