/**
* Metrics Request Handler (SMELL-001 God Object Refactor)
*
* Handles GET /metrics endpoint - Prometheus metrics exposition format.
*
* Responsibilities:
* - Fetch metrics from MetricsExporter
* - Return Prometheus text format
* - Handle errors gracefully
*
* Complexity: LOW (30 lines, 1 dependency, simple logic)
*
* WHY separate handler?
* - Single Responsibility Principle: Only concerned with metrics endpoint
* - Easy to test: Mock MetricsExporter, verify response format
* - Easy to modify: Change metrics format without touching other endpoints
*
* @see https://github.com/aberemia24/code-executor-MCP/issues/42
*/
import type { IncomingMessage, ServerResponse } from 'http';
import type { IRequestHandler } from './request-handler.interface.js';
import type { MetricsExporter } from '../../observability/metrics-exporter.js';
import { normalizeError } from '../../utils/utils.js';
/**
* Handles GET /metrics - Prometheus Metrics Endpoint
*
* Returns Prometheus exposition format metrics for monitoring:
* - Cache metrics (hits/misses)
* - HTTP metrics (requests, duration)
* - Circuit breaker metrics (state)
* - Connection pool metrics (active connections, queue depth)
*
* SECURITY: Authentication validated by MCPProxyServer before routing.
* Metrics endpoints expose operational data that can be used for
* reconnaissance attacks (cache patterns, usage rates, resource limits).
*/
export class MetricsRequestHandler implements IRequestHandler {
/**
* Create metrics request handler
*
* @param metricsExporter - Prometheus metrics exporter
*/
constructor(private metricsExporter: MetricsExporter) {}
/**
* Handle GET /metrics request
*
* @param req - HTTP request
* @param res - HTTP response
* @param authToken - Pre-validated auth token (for audit logging)
*/
async handle(
_req: IncomingMessage,
res: ServerResponse,
_authToken: string
): Promise<void> {
try {
// Fetch Prometheus metrics from exporter
const metrics = await this.metricsExporter.getMetrics();
// Return Prometheus text format
res.writeHead(200, { 'Content-Type': 'text/plain; version=0.0.4' });
res.end(metrics);
} catch (error) {
// Error handling: Return 500 with JSON error
res.writeHead(500, { 'Content-Type': 'application/json' });
res.end(
JSON.stringify({
error: normalizeError(error, 'Metrics request failed').message,
})
);
}
}
}
