src/main/java/com/googlesource/gerrit/plugins/metricsreporters/GerritPrometheusExporter.java

// Copyright (C) 2018 The Android Open Source Project
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package com.googlesource.gerrit.plugins.metricsreporters;

import com.codahale.metrics.MetricRegistry;
import com.google.inject.Inject;
import com.google.inject.Singleton;
import io.prometheus.client.CollectorRegistry;
import io.prometheus.client.dropwizard.DropwizardExports;
import io.prometheus.client.exporter.MetricsServlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletResponse;

@SuppressWarnings("serial")
@Singleton
public class GerritPrometheusExporter extends MetricsServlet {
  CapabilityChecker capabilityChecker;

  @Inject
  public GerritPrometheusExporter(MetricRegistry registry,
      CapabilityChecker capabilityChecker) {
    this.capabilityChecker = capabilityChecker;

    // Hook the Dropwizard registry into the Prometheus registry
    // via the DropwizardExports collector.
    CollectorRegistry.defaultRegistry.register(new DropwizardExports(registry));
  }

  @Override
  public void service(ServletRequest req, ServletResponse res)
      throws ServletException, IOException {
    if (capabilityChecker.canViewMetrics()) {
      super.service(req, res);
    } else {
      HttpServletResponse httpResponse = (HttpServletResponse) res;
      httpResponse.sendError(HttpServletResponse.SC_FORBIDDEN,
          "Forbidden access");
	  }
  }
};