/*
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    * 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.
   * ====================================================================
   *
   * This software consists of voluntary contributions made by many
   * individuals on behalf of the Apache Software Foundation.  For more
   * information on the Apache Software Foundation, please see
   * <http://www.apache.org/>.
   *
   */
  
  package org.apache.hc.client5.http.impl.classic;
  
  import java.io.IOException;
  
  import org.apache.hc.client5.http.AuthenticationStrategy;
  import org.apache.hc.client5.http.HttpRoute;
  import org.apache.hc.client5.http.RouteTracker;
  import org.apache.hc.client5.http.auth.AuthExchange;
  import org.apache.hc.client5.http.auth.ChallengeType;
  import org.apache.hc.client5.http.classic.ExecChain;
  import org.apache.hc.client5.http.classic.ExecChainHandler;
  import org.apache.hc.client5.http.classic.ExecRuntime;
  import org.apache.hc.client5.http.config.RequestConfig;
  import org.apache.hc.client5.http.impl.TunnelRefusedException;
  import org.apache.hc.client5.http.impl.auth.HttpAuthenticator;
  import org.apache.hc.client5.http.impl.routing.BasicRouteDirector;
  import org.apache.hc.client5.http.protocol.HttpClientContext;
  import org.apache.hc.client5.http.routing.HttpRouteDirector;
  import org.apache.hc.core5.annotation.Contract;
  import org.apache.hc.core5.annotation.Internal;
  import org.apache.hc.core5.annotation.ThreadingBehavior;
  import org.apache.hc.core5.http.ClassicHttpRequest;
  import org.apache.hc.core5.http.ClassicHttpResponse;
  import org.apache.hc.core5.http.ConnectionReuseStrategy;
  import org.apache.hc.core5.http.HttpEntity;
  import org.apache.hc.core5.http.HttpException;
  import org.apache.hc.core5.http.HttpHeaders;
  import org.apache.hc.core5.http.HttpHost;
  import org.apache.hc.core5.http.HttpRequest;
  import org.apache.hc.core5.http.HttpStatus;
  import org.apache.hc.core5.http.HttpVersion;
  import org.apache.hc.core5.http.io.entity.EntityUtils;
  import org.apache.hc.core5.http.message.BasicClassicHttpRequest;
  import org.apache.hc.core5.http.message.StatusLine;
  import org.apache.hc.core5.http.protocol.HttpProcessor;
  import org.apache.hc.core5.util.Args;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Request execution handler in the classic request execution chain
   * that is responsible for establishing connection to the target
   * origin server as specified by the current connection route.
   *
   * @since 5.0
   */
  @Contract(threading = ThreadingBehavior.STATELESS)
  @Internal
  public final class ConnectExec implements ExecChainHandler {
  
      private static final Logger LOG = LoggerFactory.getLogger(ConnectExec.class);
  
      private final ConnectionReuseStrategy reuseStrategy;
      private final HttpProcessor proxyHttpProcessor;
      private final AuthenticationStrategy proxyAuthStrategy;
      private final HttpAuthenticator authenticator;
      private final HttpRouteDirector routeDirector;
  
      public ConnectExec(
              final ConnectionReuseStrategy reuseStrategy,
              final HttpProcessor proxyHttpProcessor,
              final AuthenticationStrategy proxyAuthStrategy) {
          Args.notNull(reuseStrategy, "Connection reuse strategy");
          Args.notNull(proxyHttpProcessor, "Proxy HTTP processor");
          Args.notNull(proxyAuthStrategy, "Proxy authentication strategy");
          this.reuseStrategy      = reuseStrategy;
          this.proxyHttpProcessor = proxyHttpProcessor;
          this.proxyAuthStrategy  = proxyAuthStrategy;
          this.authenticator      = new HttpAuthenticator(LOG);
          this.routeDirector      = new BasicRouteDirector();
      }
  
     @Override
     public ClassicHttpResponse execute(
             final ClassicHttpRequest request,
             final ExecChain.Scope scope,
             final ExecChain chain) throws IOException, HttpException {
         Args.notNull(request, "HTTP request");
         Args.notNull(scope, "Scope");
 
         final String exchangeId = scope.exchangeId;
         final HttpRoute route = scope.route;
         final HttpClientContext context = scope.clientContext;
         final ExecRuntime execRuntime = scope.execRuntime;
 
         if (!execRuntime.isEndpointAcquired()) {
             final Object userToken = context.getUserToken();
             if (LOG.isDebugEnabled()) {
                 LOG.debug("{}: acquiring connection with route {}", exchangeId, route);
             }
             execRuntime.acquireEndpoint(exchangeId, route, userToken, context);
         }
         try {
             if (!execRuntime.isEndpointConnected()) {
                 if (LOG.isDebugEnabled()) {
                     LOG.debug("{}: opening connection {}", exchangeId, route);
                 }
 
                 final RouteTracker/RouteTracker.html#RouteTracker">RouteTracker tracker = new RouteTracker(route);
                 int step;
                 do {
                     final HttpRoute fact = tracker.toRoute();
                     step = this.routeDirector.nextStep(route, fact);
 
                     switch (step) {
 
                         case HttpRouteDirector.CONNECT_TARGET:
                             execRuntime.connectEndpoint(context);
                             tracker.connectTarget(route.isSecure());
                             break;
                         case HttpRouteDirector.CONNECT_PROXY:
                             execRuntime.connectEndpoint(context);
                             final HttpHost proxy  = route.getProxyHost();
                             tracker.connectProxy(proxy, route.isSecure() && !route.isTunnelled());
                             break;
                         case HttpRouteDirector.TUNNEL_TARGET: {
                             final boolean secure = createTunnelToTarget(exchangeId, route, request, execRuntime, context);
                             if (LOG.isDebugEnabled()) {
                                 LOG.debug("{}: tunnel to target created.", exchangeId);
                             }
                             tracker.tunnelTarget(secure);
                         }   break;
 
                         case HttpRouteDirector.TUNNEL_PROXY: {
                             // The most simple example for this case is a proxy chain
                             // of two proxies, where P1 must be tunnelled to P2.
                             // route: Source -> P1 -> P2 -> Target (3 hops)
                             // fact:  Source -> P1 -> Target       (2 hops)
                             final int hop = fact.getHopCount()-1; // the hop to establish
                             final boolean secure = createTunnelToProxy(route, hop, context);
                             if (LOG.isDebugEnabled()) {
                                 LOG.debug("{}: tunnel to proxy created.", exchangeId);
                             }
                             tracker.tunnelProxy(route.getHopTarget(hop), secure);
                         }   break;
 
                         case HttpRouteDirector.LAYER_PROTOCOL:
                             execRuntime.upgradeTls(context);
                             tracker.layerProtocol(route.isSecure());
                             break;
 
                         case HttpRouteDirector.UNREACHABLE:
                             throw new HttpException("Unable to establish route: " +
                                     "planned = " + route + "; current = " + fact);
                         case HttpRouteDirector.COMPLETE:
                             break;
                         default:
                             throw new IllegalStateException("Unknown step indicator "
                                     + step + " from RouteDirector.");
                     }
 
                 } while (step > HttpRouteDirector.COMPLETE);
             }
             return chain.proceed(request, scope);
 
         } catch (final IOException | HttpException | RuntimeException ex) {
             execRuntime.discardEndpoint();
             throw ex;
         }
     }
 
     /**
      * Creates a tunnel to the target server.
      * The connection must be established to the (last) proxy.
      * A CONNECT request for tunnelling through the proxy will
      * be created and sent, the response received and checked.
      * This method does <i>not</i> processChallenge the connection with
      * information about the tunnel, that is left to the caller.
      */
     private boolean createTunnelToTarget(
             final String exchangeId,
             final HttpRoute route,
             final HttpRequest request,
             final ExecRuntime execRuntime,
             final HttpClientContext context) throws HttpException, IOException {
 
         final RequestConfig config = context.getRequestConfig();
 
         final HttpHost target = route.getTargetHost();
         final HttpHost proxy = route.getProxyHost();
         final AuthExchange proxyAuthExchange = context.getAuthExchange(proxy);
         ClassicHttpResponse response = null;
 
         final String authority = target.toHostString();
         final ClassicHttpRequest connect = new BasicClassicHttpRequest("CONNECT", target, authority);
         connect.setVersion(HttpVersion.HTTP_1_1);
 
         this.proxyHttpProcessor.process(connect, null, context);
 
         while (response == null) {
             connect.removeHeaders(HttpHeaders.PROXY_AUTHORIZATION);
             this.authenticator.addAuthResponse(proxy, ChallengeType.PROXY, connect, proxyAuthExchange, context);
 
             response = execRuntime.execute(exchangeId, connect, context);
             this.proxyHttpProcessor.process(response, response.getEntity(), context);
 
             final int status = response.getCode();
             if (status < HttpStatus.SC_SUCCESS) {
                 throw new HttpException("Unexpected response to CONNECT request: " + new StatusLine(response));
             }
 
             if (config.isAuthenticationEnabled()) {
                 if (this.authenticator.isChallenged(proxy, ChallengeType.PROXY, response,
                         proxyAuthExchange, context)) {
                     if (this.authenticator.updateAuthState(proxy, ChallengeType.PROXY, response,
                             this.proxyAuthStrategy, proxyAuthExchange, context)) {
                         // Retry request
                         if (this.reuseStrategy.keepAlive(request, response, context)) {
                             if (LOG.isDebugEnabled()) {
                                 LOG.debug("{}: connection kept alive", exchangeId);
                             }
                             // Consume response content
                             final HttpEntity entity = response.getEntity();
                             EntityUtils.consume(entity);
                         } else {
                             execRuntime.disconnectEndpoint();
                         }
                         response = null;
                     }
                 }
             }
         }
 
         final int status = response.getCode();
         if (status >= HttpStatus.SC_REDIRECTION) {
 
             // Buffer response content
             final HttpEntity entity = response.getEntity();
             final String responseMessage = entity != null ? EntityUtils.toString(entity) : null;
             execRuntime.disconnectEndpoint();
             throw new TunnelRefusedException("CONNECT refused by proxy: " + new StatusLine(response), responseMessage);
         }
 
         // How to decide on security of the tunnelled connection?
         // The socket factory knows only about the segment to the proxy.
         // Even if that is secure, the hop to the target may be insecure.
         // Leave it to derived classes, consider insecure by default here.
         return false;
     }
 
     /**
      * Creates a tunnel to an intermediate proxy.
      * This method is <i>not</i> implemented in this class.
      * It just throws an exception here.
      */
     private boolean createTunnelToProxy(
             final HttpRoute route,
             final int hop,
             final HttpClientContext context) throws HttpException {
 
         // Have a look at createTunnelToTarget and replicate the parts
         // you need in a custom derived class. If your proxies don't require
         // authentication, it is not too hard. But for the stock version of
         // HttpClient, we cannot make such simplifying assumptions and would
         // have to include proxy authentication code. The HttpComponents team
         // is currently not in a position to support rarely used code of this
         // complexity. Feel free to submit patches that refactor the code in
         // createTunnelToTarget to facilitate re-use for proxy tunnelling.
 
         throw new HttpException("Proxy chains are not supported.");
     }
 
 }