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fix: server pendingResponses leak #718

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fix: server pendingResponses leak #718

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28 changes: 17 additions & 11 deletions mcp-core/src/main/java/io/modelcontextprotocol/spec/McpServerSession.java
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Original file line number Diff line number Diff line change
Expand Up @@ -4,26 +4,26 @@

package io.modelcontextprotocol.spec;

import java.time.Duration;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;

import io.modelcontextprotocol.common.McpTransportContext;
import io.modelcontextprotocol.json.TypeRef;
import io.modelcontextprotocol.server.McpAsyncServerExchange;
import io.modelcontextprotocol.server.McpInitRequestHandler;
import io.modelcontextprotocol.server.McpNotificationHandler;
import io.modelcontextprotocol.server.McpRequestHandler;
import io.modelcontextprotocol.json.TypeRef;
import io.modelcontextprotocol.util.Assert;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import reactor.core.publisher.Mono;
import reactor.core.publisher.MonoSink;
import reactor.core.publisher.Sinks;

import java.time.Duration;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.concurrent.atomic.AtomicLong;
import java.util.concurrent.atomic.AtomicReference;

/**
* Represents a Model Context Protocol (MCP) session on the server side. It manages
* bidirectional JSON-RPC communication with the client.
Expand All @@ -36,7 +36,9 @@ public class McpServerSession implements McpLoggableSession {

private final String id;

/** Duration to wait for request responses before timing out */
/**
* Duration to wait for request responses before timing out
*/
private final Duration requestTimeout;

private final AtomicLong requestCounter = new AtomicLong(0);
Expand Down Expand Up @@ -165,6 +167,8 @@ public <T> Mono<T> sendRequest(String method, Object requestParams, TypeRef<T> t
this.pendingResponses.remove(requestId);
sink.error(error);
});
// remove pending response when sink is disposed(e.g. timeout)
sink.onDispose(() -> this.pendingResponses.remove(requestId));
}).timeout(requestTimeout).handle((jsonRpcResponse, sink) -> {
if (jsonRpcResponse.error() != null) {
sink.error(new McpError(jsonRpcResponse.error()));
Expand Down Expand Up @@ -345,13 +349,15 @@ private MethodNotFoundError getMethodNotFoundError(String method) {

@Override
public Mono<Void> closeGracefully() {
// TODO: clear pendingResponses and emit errors?
this.pendingResponses.values().forEach(sink -> sink.error(new RuntimeException("Session closed")));
this.pendingResponses.clear();
return this.transport.closeGracefully();
}

@Override
public void close() {
// TODO: clear pendingResponses and emit errors?
this.pendingResponses.values().forEach(sink -> sink.error(new RuntimeException("Session closed")));
this.pendingResponses.clear();
this.transport.close();
}

Expand Down