Add McpApp, ProxyApp, middleware, context features, and sampling support#16
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Add patterns for: - Additional build directories (out/, cmake-build-*/) - IDE files (.vscode/, .idea/, swap files) - Compiled objects (*.o, *.obj, *.a, *.lib, *.so, *.dll) - Executables (*.exe, *.out) - CMake generated files - Package managers (vcpkg_installed/, _deps/) - OS files (.DS_Store, Thumbs.db)
Implement parameterized resource URIs like "weather://{city}/current":
- ResourceTemplate struct with uri_template, provider, and parsed info
- URI template parsing with RFC 6570 subset support:
- {var} - path parameter matching [^/?#]+
- {var*} - wildcard parameter matching .+
- {?a,b,c} - query parameters
- URL encoding/decoding utilities
- ResourceManager.register_template() and list_templates()
- ResourceManager.read() now matches templates if exact URI not found
- MCP handler support for resources/templates/list method
- Unit tests covering all template features
Implement app mounting feature for composing MCP servers: - Add McpApp class bundling Server + managers with mount support - Support mounting sub-apps with prefixes (tools: prefix_name, resources: scheme://prefix/path, prompts: prefix_name) - Implement aggregated listing (list_all_tools/resources/prompts) - Implement routing to dispatch calls to correct mounted app - Support nested mounting (multi-level composition) - Add MCP handler overload for McpApp - Add comprehensive unit tests (12 tests covering all scenarios) This mirrors Python fastmcp's mounting capability for server composition.
- ProxyApp class with client factory pattern for backend connections - Aggregation of local + remote tools/resources/prompts - Local-first routing: try local managers, fall back to remote - MCP handler support for ProxyApp - 9 unit tests covering all proxy functionality
- Add as_proxy parameter to mount() for proxy-based communication - Add InProcessMcpTransport for in-process MCP handler communication - Add list_all_tools_info() method for proper proxy tool metadata - Update aggregation (tools, resources, prompts) to include proxy mounts - Update routing (invoke_tool, read_resource, get_prompt) for proxy mounts - Add 9 proxy mode mounting tests covering tools, resources, prompts - Fix MCP handler to use list_all_tools_info() for proxy compatibility
- MiddlewareContext: Request context with method, message, source, type - Middleware base class with virtual hooks for each MCP operation - MiddlewarePipeline: Chains middleware with CallNext pattern - Built-in implementations: * LoggingMiddleware: Request/response logging with optional payload * TimingMiddleware: Execution time tracking with per-method stats * CachingMiddleware: Response caching with TTL and size limits * RateLimitingMiddleware: Token bucket rate limiting * ErrorHandlingMiddleware: Exception->MCP error conversion - Comprehensive test suite (11 tests)
Implements ArgTransform and TransformedTool for renaming, hiding, and modifying tool arguments with schema transformation support.
Enhances Context class with Python fastmcp parity: - State management (set_state/get_state with std::any) - Logging with levels (debug, info, warning, error) - Progress reporting with callback support - List change notifications - client_id and progress_token accessors
- Add test_e2e_tool_logging_to_notifications: verifies Context logging generates proper MCP notification JSON format - Add test_e2e_context_in_tool_handler: verifies Context factory pattern in tool handlers - Add SSE notification public API: send_notification() and broadcast_notification() methods in SseServerWrapper - Add integration test for Context → SSE API wiring verification
Tests cover tool registration, lookup, invocation, schema retrieval, and context argument exclusion. Mirrors Python test_tool_manager.py coverage.
Implement MCP sampling support for server-to-client LLM requests: - Add SamplingMessage, SamplingParams, SamplingResult types - Add sample() method with string and message vector overloads - Add sample_text() convenience method - Add has_sampling() check and set_sampling_callback() - Add 10 unit tests covering all sampling functionality This is the foundation for sampling; actual transport wiring will follow in subsequent commits.
Infrastructure for server-initiated requests to clients: - ServerSession class with send_request() and handle_response() - Request ID generation and promise/future correlation - Client capability tracking (sampling, elicitation, roots) - RequestTimeoutError and ClientError exception types - Static helpers: is_request(), is_response(), is_notification() - Thread-safe with mutex-protected pending request map - 10 unit tests including concurrent request handling
Connect ServerSession to SSE transport for bidirectional requests: - Create ServerSession for each new SSE connection - Wire send callback to push events to connection queue - Route incoming responses through ServerSession::handle_response() - Distinguish client requests (handle normally) from server responses - Add get_session() and connection_count() public methods - Make conns_mutex_ mutable to support const methods This enables server-initiated requests (sampling, elicitation) via SSE.
Wire Context.sample() to ServerSession for server-initiated sampling: - Add SessionAccessor type for retrieving ServerSession by session_id - make_mcp_handler_with_sampling() creates handler with sampling support - Inject session_id into request params._meta for handler access - Advertise sampling capability in initialize response - Convenience overload accepting SseServerWrapper for easy integration
Extract capabilities from initialize request params and store in ServerSession. This enables checking if client supports sampling/ elicitation/roots before attempting server-initiated requests.
Fixes CI format-check failures.
GCC 13.3 rejects `= {}` as default argument for aggregate structs even
with `= default` constructor. Use overloaded constructors instead.
- Change on_message to operator() for LoggingMiddleware, TimingMiddleware, and RateLimitingMiddleware to properly intercept all requests - Fix mounting.cpp test assertions: remove extra quotes from expected text - Fix test_middleware_pipeline.cpp: set ctx.type="" to test on_message fallback
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Summary
Major feature release combining multiple branches: