v0.12.0

Release Notes

❗ Breaking Changes

• Re-purposed McpTransportContext to reuse in server and client packages and made immutable - more details below
• Updated (Async|Sync)HttpRequestCustomizer class signatures as part of transport context implementation
• Users relying on template resources in resources/list should migrate to using resources/templates/list

🚀 New Features

Transport Context Support (#522)

• Added McpTransportContext to MCP Clients - Provides a unified API for reading context in which MCP Client requests are issued, regardless of sync/async implementation
• Enhanced HttpRequestCustomizer support - Context is now available to both McpAsyncHttpRequestCustomizer and McpSyncHttpRequestCustomizer
• Improved thread-local handling - Addresses limitations with thread local usage in request customizers
• Breaking Change: Updated signatures for (Async|Sync)HttpRequestCustomizer classes
• Breaking Change: McpTransportContext io.modelcontextprotocol.server -> io.modelcontextprotocol.common package change, void put(String key, Object value), and McpTransportContext copy() method removal.
• Breaking Change: DefaultMcpTransportContext class made package private and changed package to io.modelcontextprotocol.common
• Changed McpTransportContext usage patterns - it is now immutable and can be created via a static factory method McpTransportContext create(Map<String, Object> metadata)

🐛 Bug Fixes

Resource Listing Compliance (#528)

• Fixed resource template filtering - Template resources containing {} parameters are now properly excluded from standard resources/list responses
• MCP Specification compliance - Ensures proper separation between regular resources (resources/list) and resource templates (resources/templates/list)
• Issue: Fixes #319 where template resources were incorrectly appearing in both endpoints

Test Stability Improvements (#535)

• Fixed flaky test - Resolved intermittent failures in HttpClientStreamableHttpTransportErrorHandlingTest

🔧 Testing & Infrastructure Improvements

Resource Cleanup & Test Reliability (#537)

• Enhanced resource management - Added try-finally blocks to guarantee server cleanup on test completion
• Synchronous shutdown - Implemented closeGracefully().block() for proper synchronous shutdown
• Resource leak prevention - Added try-with-resources for client lifecycle management
• Reduced test flakiness - Prevents resource leaks that could cause test instability

Test Performance Optimization (#531)

• Significant performance boost - Static container reuse across all client and transport tests
• ~10x speed improvement - Containerized MCP server is now shared within test classes rather than recreated per test

Docker Infrastructure Updates (#536)

• Updated test dependencies - Upgraded mcp-everything-server Docker image from v2 to v3 across all integration tests

Comprehensive Context Testing (#529)

• Expanded test coverage - Added integration tests for transport context propagation between MCP clients and servers
• Multi-environment testing - Coverage for both Spring WebFlux and WebMVC environments
• Transport type coverage - Tests across stateless, streamable, and SSE transport types
• Context validation - Verifies proper flow of authentication tokens, correlation IDs, and metadata through HTTP headers

📋 Technical Details

Compatibility

• All changes maintain backward compatibility except for the noted breaking changes
• Spring WebFlux and WebMVC environments fully supported
• Docker image updates require no user action

🧪 Testing

• 103 async server tests passing
• Comprehensive integration test coverage added
• Resource cleanup and lifecycle management improved
• Test execution time significantly reduced through container optimization

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Contributors:

• Christian Tzolov (@tzolov)
• Daniel Garnier-Moiroux (@Kehrlann)
• Richie Caputo (@arcaputo3)

Full Changelog: v0.11.0...v0.12.0