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fix: improve streamable HTTP session reinitialization #469

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fix: improve streamable HTTP session reinitialization #469

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7b8a36e
fix: improve streamable HTTP session reinitialization
tzolov Aug 7, 2025
4482c4d
refactor: improve error handling with standard Java exceptions
tzolov Aug 8, 2025
ddd4241
fix broken tests
tzolov Aug 8, 2025
18f1c4d
increase some test timeouts to 15 sec
tzolov Aug 8, 2025
7094a94
temp disable (Web|Http)ClientStreamableHttpTransportErrorHandlingTest
tzolov Aug 9, 2025
675b13a
re-enable the *ClientStreamableHttpTransportErrorHandlingTest
tzolov Aug 10, 2025
e0135a6
improve HttpClientStreamableHttpTransportErrorHandlingTest
tzolov Aug 10, 2025
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33 changes: 22 additions & 11 deletions .../main/java/io/modelcontextprotocol/client/transport/WebClientStreamableHttpTransport.java
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Original file line number Diff line number Diff line change
Expand Up @@ -31,6 +31,7 @@
import io.modelcontextprotocol.spec.McpClientTransport;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpTransportException;
import io.modelcontextprotocol.spec.McpTransportSession;
import io.modelcontextprotocol.spec.McpTransportSessionNotFoundException;
import io.modelcontextprotocol.spec.McpTransportStream;
Expand Down Expand Up @@ -70,6 +71,8 @@
*/
public class WebClientStreamableHttpTransport implements McpClientTransport {

private static final String MISSING_SESSION_ID = "[missing_session_id]";

private static final Logger logger = LoggerFactory.getLogger(WebClientStreamableHttpTransport.class);

private static final String MCP_PROTOCOL_VERSION = ProtocolVersions.MCP_2025_03_26;
Expand Down Expand Up @@ -221,8 +224,13 @@ else if (isNotAllowed(response)) {
return Flux.empty();
}
else if (isNotFound(response)) {
String sessionIdRepresentation = sessionIdOrPlaceholder(transportSession);
return mcpSessionNotFoundError(sessionIdRepresentation);
if (transportSession.sessionId().isPresent()) {
String sessionIdRepresentation = sessionIdOrPlaceholder(transportSession);
return mcpSessionNotFoundError(sessionIdRepresentation);
}
else {
return this.extractError(response, MISSING_SESSION_ID);
}
}
else {
return response.<McpSchema.JSONRPCMessage>createError().doOnError(e -> {
Expand Down Expand Up @@ -318,10 +326,10 @@ else if (mediaType.isCompatibleWith(MediaType.APPLICATION_JSON)) {
}
}
else {
if (isNotFound(response)) {
if (isNotFound(response) && !sessionRepresentation.equals(MISSING_SESSION_ID)) {
return mcpSessionNotFoundError(sessionRepresentation);
}
return extractError(response, sessionRepresentation);
return this.extractError(response, sessionRepresentation);
}
})
.flatMap(jsonRpcMessage -> this.handler.get().apply(Mono.just(jsonRpcMessage)))
Expand Down Expand Up @@ -362,10 +370,10 @@ private Flux<McpSchema.JSONRPCMessage> extractError(ClientResponse response, Str
McpSchema.JSONRPCResponse.class);
jsonRpcError = jsonRpcResponse.error();
toPropagate = jsonRpcError != null ? new McpError(jsonRpcError)
: new McpError("Can't parse the jsonResponse " + jsonRpcResponse);
: new McpTransportException("Can't parse the jsonResponse " + jsonRpcResponse);
}
catch (IOException ex) {
toPropagate = new RuntimeException("Sending request failed", e);
toPropagate = new McpTransportException("Sending request failed, " + e.getMessage(), e);
logger.debug("Received content together with {} HTTP code response: {}", response.statusCode(), body);
}

Expand All @@ -374,7 +382,11 @@ private Flux<McpSchema.JSONRPCMessage> extractError(ClientResponse response, Str
// invalidate the session
// https://github.com/modelcontextprotocol/typescript-sdk/issues/389
if (responseException.getStatusCode().isSameCodeAs(HttpStatus.BAD_REQUEST)) {
return Mono.error(new McpTransportSessionNotFoundException(sessionRepresentation, toPropagate));
if (!sessionRepresentation.equals(MISSING_SESSION_ID)) {
return Mono.error(new McpTransportSessionNotFoundException(sessionRepresentation, toPropagate));
}
return Mono.error(new McpTransportException("Received 400 BAD REQUEST for session "
+ sessionRepresentation + ". " + toPropagate.getMessage(), toPropagate));
}
return Mono.error(toPropagate);
}).flux();
Expand Down Expand Up @@ -403,7 +415,7 @@ private static boolean isEventStream(ClientResponse response) {
}

private static String sessionIdOrPlaceholder(McpTransportSession<?> transportSession) {
return transportSession.sessionId().orElse("[missing_session_id]");
return transportSession.sessionId().orElse(MISSING_SESSION_ID);
}

private Flux<McpSchema.JSONRPCMessage> directResponseFlux(McpSchema.JSONRPCMessage sentMessage,
Expand All @@ -421,8 +433,7 @@ private Flux<McpSchema.JSONRPCMessage> directResponseFlux(McpSchema.JSONRPCMessa
}
}
catch (IOException e) {
// TODO: this should be a McpTransportError
s.error(e);
s.error(new McpTransportException(e));
}
}).flatMapIterable(Function.identity());
}
Expand All @@ -449,7 +460,7 @@ private Tuple2<Optional<String>, Iterable<McpSchema.JSONRPCMessage>> parse(Serve
return Tuples.of(Optional.ofNullable(event.id()), List.of(message));
}
catch (IOException ioException) {
throw new McpError("Error parsing JSON-RPC message: " + event.data());
throw new McpTransportException("Error parsing JSON-RPC message: " + event.data(), ioException);
}
}
else {
Expand Down
5 changes: 1 addition & 4 deletions ...lux/src/main/java/io/modelcontextprotocol/client/transport/WebFluxSseClientTransport.java
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Original file line number Diff line number Diff line change
Expand Up @@ -14,7 +14,6 @@

import io.modelcontextprotocol.spec.HttpHeaders;
import io.modelcontextprotocol.spec.McpClientTransport;
import io.modelcontextprotocol.spec.McpError;
import io.modelcontextprotocol.spec.McpSchema;
import io.modelcontextprotocol.spec.McpSchema.JSONRPCMessage;
import io.modelcontextprotocol.spec.ProtocolVersions;
Expand Down Expand Up @@ -197,8 +196,6 @@ public List<String> protocolVersions() {
* @param handler a function that processes incoming JSON-RPC messages and returns
* responses
* @return a Mono that completes when the connection is fully established
* @throws McpError if there's an error processing SSE events or if an unrecognized
* event type is received
*/
@Override
public Mono<Void> connect(Function<Mono<JSONRPCMessage>, Mono<JSONRPCMessage>> handler) {
Expand All @@ -215,7 +212,7 @@ public Mono<Void> connect(Function<Mono<JSONRPCMessage>, Mono<JSONRPCMessage>> h
else {
// TODO: clarify with the spec if multiple events can be
// received
s.error(new McpError("Failed to handle SSE endpoint event"));
s.error(new RuntimeException("Failed to handle SSE endpoint event"));
}
}
else if (MESSAGE_EVENT_TYPE.equals(event.event())) {
Expand Down
2 changes: 2 additions & 0 deletions .../mcp-spring-webflux/src/test/java/io/modelcontextprotocol/WebFluxSseIntegrationTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@

import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Timeout;
import org.springframework.http.server.reactive.HttpHandler;
import org.springframework.http.server.reactive.ReactorHttpHandlerAdapter;
import org.springframework.web.reactive.function.client.WebClient;
Expand All @@ -26,6 +27,7 @@
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

@Timeout(15)
class WebFluxSseIntegrationTests extends AbstractMcpClientServerIntegrationTests {

private static final int PORT = TestUtil.findAvailablePort();
Expand Down
2 changes: 2 additions & 0 deletions ...pring-webflux/src/test/java/io/modelcontextprotocol/WebFluxStatelessIntegrationTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@

import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Timeout;
import org.springframework.http.server.reactive.HttpHandler;
import org.springframework.http.server.reactive.ReactorHttpHandlerAdapter;
import org.springframework.web.reactive.function.client.WebClient;
Expand All @@ -26,6 +27,7 @@
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

@Timeout(15)
class WebFluxStatelessIntegrationTests extends AbstractStatelessIntegrationTests {

private static final int PORT = TestUtil.findAvailablePort();
Expand Down
2 changes: 2 additions & 0 deletions ...ring-webflux/src/test/java/io/modelcontextprotocol/WebFluxStreamableIntegrationTests.java
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Original file line number Diff line number Diff line change
Expand Up @@ -8,6 +8,7 @@

import org.junit.jupiter.api.AfterEach;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Timeout;
import org.springframework.http.server.reactive.HttpHandler;
import org.springframework.http.server.reactive.ReactorHttpHandlerAdapter;
import org.springframework.web.reactive.function.client.WebClient;
Expand All @@ -26,6 +27,7 @@
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

@Timeout(15)
class WebFluxStreamableIntegrationTests extends AbstractMcpClientServerIntegrationTests {

private static final int PORT = TestUtil.findAvailablePort();
Expand Down
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