Remote MCP Support: HTTP and SSE Transports

This PR adds direct HTTP and Server-Sent Events (SSE) transport support to Netdata's Model Context Protocol (MCP) implementation, enabling AI assistants to connect directly to Netdata without requiring the nd-mcp bridge. It also allows the dev preview api key to be given to http authorization bearer header.

Summary

Netdata's MCP server now supports three transport mechanisms:

• WebSocket (existing): via /mcp endpoint
• HTTP Streamable (new): chunked JSON-RPC over HTTP via /mcp endpoint
• SSE (new): Server-Sent Events via /mcp?transport=sse or detected via Accept: text/event-stream header

This enables modern MCP clients like npx @modelcontextprotocol/remote-mcp to connect directly to Netdata's HTTP endpoints, while maintaining backward compatibility with stdio-based clients through the existing bridge.

Key Changes

Core MCP Architecture:

• Refactored JSON-RPC handling into separate mcp-jsonrpc.c module for transport-agnostic message processing
• Removed request ID tracking (mcp-request-id.c) - now handled individually by each transport adapter
• Added HTTP response tracking in web_client for MCP session management

New Transport Adapters:

• mcp-http.c: Implements chunked HTTP transport with proper content negotiation
• mcp-sse.c: Implements Server-Sent Events with event-based message framing
• Refactored mcp-websocket.c to use common JSON-RPC module

Enhanced Test Client:

• Added support for testing all three transports (WebSocket, HTTP, SSE)
• Improved SSE parsing with proper event-data handling
• Added bearer token authentication support
• Better error handling and transport selection

Documentation Updates:

• Comprehensive transport comparison and usage guide in docs/learn/mcp.md
• Updated src/web/mcp/README.md with direct connection examples
• Added protocol analysis documents for HTTP/SSE transports
• Updated TODO list reflecting completed Phase 1/2 tasks

Technical Details

Transport Selection:
The /mcp endpoint automatically selects the transport based on:

1. Query parameter: ?transport=sse forces SSE
2. Accept header: Accept: text/event-stream triggers SSE
3. Default: HTTP streamable (chunked JSON)

Message Framing:

• HTTP: Chunked transfer encoding with JSON-RPC messages
• SSE: Event stream with event: message and data: fields
• WebSocket: JSON-RPC over WebSocket frames (unchanged)

Session Management:
Each transport adapter maintains its own request tracking and session state, enabling proper message correlation and response routing.

Benefits

1. Simpler Deployment: Many AI clients can now connect directly without bridge setup
2. Broader Compatibility: Standard HTTP/SSE enables integration with more MCP clients
3. Better Performance: Direct connection eliminates bridge overhead
4. Backward Compatible: Existing WebSocket and stdio/bridge configurations continue to work

Testing

The MCP test client (src/web/mcp/mcp-test-client/index.html) now supports all three transports and can be used to verify functionality:

• WebSocket: ws://localhost:19999/mcp
• HTTP: http://localhost:19999/mcp
• SSE: http://localhost:19999/mcp?transport=sse

Migration Path

• No breaking changes: Existing configurations using nd-mcp bridge continue to work
• New option: Clients supporting HTTP/SSE can now connect directly
• Recommended: Use direct HTTP/SSE for new deployments; keep bridge for stdio-only clients