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feat: Add protocol version negotiation

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Implement protocol version negotiation between MCP client and server to ensure
compatibility and graceful version handling.
The server will now suggest the latest supported version when an
unsupported version is requested, while the client will verify
version compatibility during initialization.

- Support multiple protocol versions in both client and server
- Negotiate compatible version during initialization
- Fall back to latest version when unsupported version requested
- Add comprehensive test coverage for version negotiation

Resolves #71

Signed-off-by: Christian Tzolov <christian.tzolov@broadcom.com>
This commit is contained in:
Christian Tzolov 2025-01-24 12:59:30 +01:00 • committed by Christian Tzolov
commit a424b36653
4 changed files with 370 additions and 13 deletions
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8
mcp/src/test/java/org/springframework/ai/mcp/MockMcpTransport.java
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@ -32,7 +32,10 @@ import org.springframework.ai.mcp.spec.McpSchema.JSONRPCNotification;
import org.springframework.ai.mcp.spec.McpSchema.JSONRPCRequest;
import org.springframework.ai.mcp.spec.ServerMcpTransport;
@SuppressWarnings("unused")
/**
* A mock implementation of the {@link ClientMcpTransport} and {@link ServerMcpTransport}
* interfaces.
*/
public class MockMcpTransport implements ClientMcpTransport, ServerMcpTransport {
private final AtomicInteger inboundMessageCount = new AtomicInteger(0);
@ -91,6 +94,7 @@ public class MockMcpTransport implements ClientMcpTransport, ServerMcpTransport
connected = false;
outgoing.tryEmitComplete();
inbound.tryEmitComplete();
// Wait for all subscribers to complete
return Mono.empty();
});
}
@ -100,4 +104,4 @@ public class MockMcpTransport implements ClientMcpTransport, ServerMcpTransport
return new ObjectMapper().convertValue(data, typeRef);
}
}
}

1
mcp/src/test/java/org/springframework/ai/mcp/client/McpAsyncClientResponseHandlerTests.java
View file

@ -20,7 +20,6 @@ import java.time.Duration;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;
import java.util.function.Consumer;
import java.util.function.Function;
import com.fasterxml.jackson.core.JsonProcessingException;

170
mcp/src/test/java/org/springframework/ai/mcp/client/McpClientProtocolVersionTests.java Normal file
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@ -0,0 +1,170 @@
/*
* Copyright 2024-2024 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.ai.mcp.client;
import java.time.Duration;
import java.util.List;
import org.junit.jupiter.api.Test;
import reactor.core.publisher.Mono;
import reactor.test.StepVerifier;
import org.springframework.ai.mcp.MockMcpTransport;
import org.springframework.ai.mcp.spec.McpError;
import org.springframework.ai.mcp.spec.McpSchema;
import org.springframework.ai.mcp.spec.McpSchema.InitializeResult;
import static org.assertj.core.api.Assertions.assertThat;
/**
* Tests for MCP protocol version negotiation and compatibility.
*/
class McpClientProtocolVersionTests {
private static final Duration REQUEST_TIMEOUT = Duration.ofSeconds(30);
private static final McpSchema.Implementation CLIENT_INFO = new McpSchema.Implementation("test-client", "1.0.0");
@Test
void shouldUseLatestVersionByDefault() {
MockMcpTransport transport = new MockMcpTransport();
McpAsyncClient client = McpClient.async(transport)
.clientInfo(CLIENT_INFO)
.requestTimeout(REQUEST_TIMEOUT)
.build();
try {
Mono<InitializeResult> initializeResultMono = client.initialize();
StepVerifier.create(initializeResultMono).then(() -> {
McpSchema.JSONRPCRequest request = transport.getLastSentMessageAsRequest();
assertThat(request.params()).isInstanceOf(McpSchema.InitializeRequest.class);
McpSchema.InitializeRequest initRequest = (McpSchema.InitializeRequest) request.params();
assertThat(initRequest.protocolVersion()).isEqualTo(McpSchema.LATEST_PROTOCOL_VERSION);
transport.simulateIncomingMessage(new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(),
new McpSchema.InitializeResult(McpSchema.LATEST_PROTOCOL_VERSION, null,
new McpSchema.Implementation("test-server", "1.0.0"), null),
null));
}).assertNext(result -> {
assertThat(result.protocolVersion()).isEqualTo(McpSchema.LATEST_PROTOCOL_VERSION);
}).verifyComplete();
}
finally {
// Ensure cleanup happens even if test fails
StepVerifier.create(client.closeGracefully()).verifyComplete();
}
}
@Test
void shouldNegotiateSpecificVersion() {
String oldVersion = "0.1.0";
MockMcpTransport transport = new MockMcpTransport();
McpAsyncClient client = McpClient.async(transport)
.clientInfo(CLIENT_INFO)
.requestTimeout(REQUEST_TIMEOUT)
.build();
client.setProtocolVersions(List.of(oldVersion, McpSchema.LATEST_PROTOCOL_VERSION));
try {
Mono<InitializeResult> initializeResultMono = client.initialize();
StepVerifier.create(initializeResultMono).then(() -> {
McpSchema.JSONRPCRequest request = transport.getLastSentMessageAsRequest();
assertThat(request.params()).isInstanceOf(McpSchema.InitializeRequest.class);
McpSchema.InitializeRequest initRequest = (McpSchema.InitializeRequest) request.params();
assertThat(initRequest.protocolVersion()).isIn(List.of(oldVersion, McpSchema.LATEST_PROTOCOL_VERSION));
transport.simulateIncomingMessage(new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(),
new McpSchema.InitializeResult(oldVersion, null,
new McpSchema.Implementation("test-server", "1.0.0"), null),
null));
}).assertNext(result -> {
assertThat(result.protocolVersion()).isEqualTo(oldVersion);
}).verifyComplete();
}
finally {
StepVerifier.create(client.closeGracefully()).verifyComplete();
}
}
@Test
void shouldFailForUnsupportedVersion() {
String unsupportedVersion = "999.999.999";
MockMcpTransport transport = new MockMcpTransport();
McpAsyncClient client = McpClient.async(transport)
.clientInfo(CLIENT_INFO)
.requestTimeout(REQUEST_TIMEOUT)
.build();
try {
Mono<InitializeResult> initializeResultMono = client.initialize();
StepVerifier.create(initializeResultMono).then(() -> {
McpSchema.JSONRPCRequest request = transport.getLastSentMessageAsRequest();
assertThat(request.params()).isInstanceOf(McpSchema.InitializeRequest.class);
transport.simulateIncomingMessage(new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(),
new McpSchema.InitializeResult(unsupportedVersion, null,
new McpSchema.Implementation("test-server", "1.0.0"), null),
null));
}).expectError(McpError.class).verify();
}
finally {
StepVerifier.create(client.closeGracefully()).verifyComplete();
}
}
@Test
void shouldUseHighestVersionWhenMultipleSupported() {
String oldVersion = "0.1.0";
String middleVersion = "0.2.0";
String latestVersion = McpSchema.LATEST_PROTOCOL_VERSION;
MockMcpTransport transport = new MockMcpTransport();
McpAsyncClient client = McpClient.async(transport)
.clientInfo(CLIENT_INFO)
.requestTimeout(REQUEST_TIMEOUT)
.build();
client.setProtocolVersions(List.of(oldVersion, middleVersion, latestVersion));
try {
Mono<InitializeResult> initializeResultMono = client.initialize();
StepVerifier.create(initializeResultMono).then(() -> {
McpSchema.JSONRPCRequest request = transport.getLastSentMessageAsRequest();
McpSchema.InitializeRequest initRequest = (McpSchema.InitializeRequest) request.params();
assertThat(initRequest.protocolVersion()).isEqualTo(latestVersion);
transport.simulateIncomingMessage(new McpSchema.JSONRPCResponse(McpSchema.JSONRPC_VERSION, request.id(),
new McpSchema.InitializeResult(latestVersion, null,
new McpSchema.Implementation("test-server", "1.0.0"), null),
null));
}).assertNext(result -> {
assertThat(result.protocolVersion()).isEqualTo(latestVersion);
}).verifyComplete();
}
finally {
StepVerifier.create(client.closeGracefully()).verifyComplete();
}
}
}

132
mcp/src/test/java/org/springframework/ai/mcp/server/McpServerProtocolVersionTests.java Normal file
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@ -0,0 +1,132 @@
/*
* Copyright 2024-2024 the original author or authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.springframework.ai.mcp.server;
import java.util.List;
import java.util.UUID;
import org.junit.jupiter.api.Test;
import org.springframework.ai.mcp.MockMcpTransport;
import org.springframework.ai.mcp.spec.McpSchema;
import static org.assertj.core.api.Assertions.assertThat;
/**
* Tests for MCP server protocol version negotiation and compatibility.
*/
class McpServerProtocolVersionTests {
private static final McpSchema.Implementation SERVER_INFO = new McpSchema.Implementation("test-server", "1.0.0");
private static final McpSchema.Implementation CLIENT_INFO = new McpSchema.Implementation("test-client", "1.0.0");
private McpSchema.JSONRPCRequest jsonRpcInitializeRequest(String requestId, String protocolVersion) {
return new McpSchema.JSONRPCRequest(McpSchema.JSONRPC_VERSION, McpSchema.METHOD_INITIALIZE, requestId,
new McpSchema.InitializeRequest(protocolVersion, null, CLIENT_INFO));
}
@Test
void shouldUseLatestVersionByDefault() {
MockMcpTransport transport = new MockMcpTransport();
McpAsyncServer server = McpServer.async(transport).serverInfo(SERVER_INFO).build();
String requestId = UUID.randomUUID().toString();
transport.simulateIncomingMessage(jsonRpcInitializeRequest(requestId, McpSchema.LATEST_PROTOCOL_VERSION));
McpSchema.JSONRPCMessage response = transport.getLastSentMessage();
assertThat(response).isInstanceOf(McpSchema.JSONRPCResponse.class);
McpSchema.JSONRPCResponse jsonResponse = (McpSchema.JSONRPCResponse) response;
assertThat(jsonResponse.id()).isEqualTo(requestId);
assertThat(jsonResponse.result()).isInstanceOf(McpSchema.InitializeResult.class);
McpSchema.InitializeResult result = (McpSchema.InitializeResult) jsonResponse.result();
assertThat(result.protocolVersion()).isEqualTo(McpSchema.LATEST_PROTOCOL_VERSION);
server.closeGracefully().subscribe();
}
@Test
void shouldNegotiateSpecificVersion() {
String oldVersion = "0.1.0";
MockMcpTransport transport = new MockMcpTransport();
McpAsyncServer server = McpServer.async(transport).serverInfo(SERVER_INFO).build();
server.setProtocolVersions(List.of(oldVersion, McpSchema.LATEST_PROTOCOL_VERSION));
String requestId = UUID.randomUUID().toString();
transport.simulateIncomingMessage(jsonRpcInitializeRequest(requestId, oldVersion));
McpSchema.JSONRPCMessage response = transport.getLastSentMessage();
assertThat(response).isInstanceOf(McpSchema.JSONRPCResponse.class);
McpSchema.JSONRPCResponse jsonResponse = (McpSchema.JSONRPCResponse) response;
assertThat(jsonResponse.id()).isEqualTo(requestId);
assertThat(jsonResponse.result()).isInstanceOf(McpSchema.InitializeResult.class);
McpSchema.InitializeResult result = (McpSchema.InitializeResult) jsonResponse.result();
assertThat(result.protocolVersion()).isEqualTo(oldVersion);
server.closeGracefully().subscribe();
}
@Test
void shouldSuggestLatestVersionForUnsupportedVersion() {
String unsupportedVersion = "999.999.999";
MockMcpTransport transport = new MockMcpTransport();
McpAsyncServer server = McpServer.async(transport).serverInfo(SERVER_INFO).build();
String requestId = UUID.randomUUID().toString();
transport.simulateIncomingMessage(jsonRpcInitializeRequest(requestId, unsupportedVersion));
McpSchema.JSONRPCMessage response = transport.getLastSentMessage();
assertThat(response).isInstanceOf(McpSchema.JSONRPCResponse.class);
McpSchema.JSONRPCResponse jsonResponse = (McpSchema.JSONRPCResponse) response;
assertThat(jsonResponse.id()).isEqualTo(requestId);
assertThat(jsonResponse.result()).isInstanceOf(McpSchema.InitializeResult.class);
McpSchema.InitializeResult result = (McpSchema.InitializeResult) jsonResponse.result();
assertThat(result.protocolVersion()).isEqualTo(McpSchema.LATEST_PROTOCOL_VERSION);
server.closeGracefully().subscribe();
}
@Test
void shouldUseHighestVersionWhenMultipleSupported() {
String oldVersion = "0.1.0";
String middleVersion = "0.2.0";
String latestVersion = McpSchema.LATEST_PROTOCOL_VERSION;
MockMcpTransport transport = new MockMcpTransport();
McpAsyncServer server = McpServer.async(transport).serverInfo(SERVER_INFO).build();
server.setProtocolVersions(List.of(oldVersion, middleVersion, latestVersion));
String requestId = UUID.randomUUID().toString();
transport.simulateIncomingMessage(jsonRpcInitializeRequest(requestId, latestVersion));
McpSchema.JSONRPCMessage response = transport.getLastSentMessage();
assertThat(response).isInstanceOf(McpSchema.JSONRPCResponse.class);
McpSchema.JSONRPCResponse jsonResponse = (McpSchema.JSONRPCResponse) response;
assertThat(jsonResponse.id()).isEqualTo(requestId);
assertThat(jsonResponse.result()).isInstanceOf(McpSchema.InitializeResult.class);
McpSchema.InitializeResult result = (McpSchema.InitializeResult) jsonResponse.result();
assertThat(result.protocolVersion()).isEqualTo(latestVersion);
server.closeGracefully().subscribe();
}
}