code: /*
   * Licensed to the Apache Software Foundation (ASF) under one or more
   * contributor license agreements.  See the NOTICE file distributed with
   * this work for additional information regarding copyright ownership.
   * The ASF licenses this file to You 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 org.apache.skywalking.oap.server.telemetry.prometheus.httpserver;
  
  import com.google.common.util.concurrent.ThreadFactoryBuilder;
  import io.netty.bootstrap.ServerBootstrap;
  import io.netty.channel.EventLoopGroup;
  import io.netty.channel.nio.NioEventLoopGroup;
  import io.netty.channel.socket.nio.NioServerSocketChannel;
  import io.netty.handler.logging.LogLevel;
  import io.netty.handler.logging.LoggingHandler;
  import java.util.Optional;
  import java.util.concurrent.ThreadFactory;
  import lombok.RequiredArgsConstructor;
  import lombok.extern.slf4j.Slf4j;
  import org.apache.skywalking.oap.server.library.server.ssl.HTTPDynamicSslContext;
  import org.apache.skywalking.oap.server.telemetry.prometheus.PrometheusConfig;
  
  /**
   * An HTTP server that sends back the content of the received HTTP request
   * in a pretty plaintext form.
   */
  @RequiredArgsConstructor
  @Slf4j
  public final class HttpServer {
  
      private final PrometheusConfig config;
  
      public void start() throws InterruptedException {
          // Configure SSL.
          final HTTPDynamicSslContext sslCtx;
          if (config.isSslEnabled()) {
              sslCtx = HTTPDynamicSslContext.forServer(config.getSslKeyPath(), config.getSslCertChainPath());
          } else {
              sslCtx = null;
          }
  
          // Configure the server.
          ThreadFactory tf = new ThreadFactoryBuilder().setDaemon(true).build();
          EventLoopGroup bossGroup = new NioEventLoopGroup(1, tf);
          EventLoopGroup workerGroup = new NioEventLoopGroup(0, tf);
          ServerBootstrap b = new ServerBootstrap();
          b.group(bossGroup, workerGroup)
              .channel(NioServerSocketChannel.class)
              .handler(new LoggingHandler(LogLevel.INFO))
              .childHandler(new HttpServerInitializer(sslCtx));
  
          b.bind(config.getHost(), config.getPort()).sync();
          Optional.ofNullable(sslCtx).ifPresent(HTTPDynamicSslContext::start);
  
          log.info("Prometheus exporter endpoint:" +
              (config.isSslEnabled() ? "https" : "http") + "://" + config.getHost() + ":" + config.getPort() + '/');
      }
  }
  