/**
* MCP Message Handler
*
* Handles incoming POST messages from MCP clients and routes them
* to the appropriate SSE transport based on session ID.
*/
import { FastifyRequest, FastifyReply } from 'fastify';
import { getTransport } from './sse';
import { logger } from '../../lib/logger';
// Create an MCP message-specific logger
const mcpMsgLogger = logger.child({ component: 'mcp-message' });
// Query parameters interface
interface McpMessageQuery {
sessionId?: string;
}
/**
* MCP message handler
*
* Routes incoming MCP protocol messages to the correct SSE transport.
* The sessionId is provided as a query parameter.
*/
export default async function mcpMessageHandler(
req: FastifyRequest<{ Querystring: McpMessageQuery }>,
reply: FastifyReply
): Promise<FastifyReply | void> {
const requestId = req.id || `mcp-${Date.now()}-${Math.random().toString(36).slice(2, 11)}`;
const sessionId = req.query.sessionId;
mcpMsgLogger.info('MCP message received', {
requestId,
sessionId: sessionId || 'missing',
hasBody: !!req.body,
});
// Validate session ID
if (!sessionId) {
mcpMsgLogger.warn('Missing session ID in MCP message', { requestId });
return reply.status(400).send({
error: 'Missing sessionId query parameter',
requestId,
});
}
// Find the transport for this session
const transport = getTransport(sessionId);
if (!transport) {
mcpMsgLogger.warn('Session not found for MCP message', {
requestId,
sessionId,
});
return reply.status(404).send({
error: 'Session not found. The SSE connection may have timed out or closed.',
requestId,
sessionId,
suggestion: 'Reconnect to /sse to establish a new session.',
});
}
// Route the message to the transport
try {
// The handlePostMessage method expects the raw Node.js request and response
await transport.handlePostMessage(req.raw, reply.raw);
mcpMsgLogger.debug('MCP message handled', {
requestId,
sessionId,
});
// Response is handled by the transport, don't send additional response
} catch (error) {
mcpMsgLogger.error('Failed to handle MCP message', {
requestId,
sessionId,
error: error instanceof Error ? error.message : 'Unknown error',
});
// Only send error if headers haven't been sent
if (!reply.raw.headersSent) {
return reply.status(500).send({
error: 'Failed to process MCP message',
requestId,
sessionId,
});
}
}
}
