/*
    * Copyright 2013 The Netty Project
    *
    * The Netty Project 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:
    *
    * https://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 io.netty.handler.codec.http.cors;
  
  import io.netty.buffer.Unpooled;
  import io.netty.channel.ChannelDuplexHandler;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPromise;
  import io.netty.handler.codec.http.DefaultFullHttpResponse;
  import io.netty.handler.codec.http.HttpContent;
  import io.netty.handler.codec.http.HttpHeaderNames;
  import io.netty.handler.codec.http.HttpHeaderValues;
  import io.netty.handler.codec.http.HttpHeaders;
  import io.netty.handler.codec.http.DefaultHttpHeadersFactory;
  import io.netty.handler.codec.http.HttpRequest;
  import io.netty.handler.codec.http.HttpResponse;
  import io.netty.handler.codec.http.HttpUtil;
  import io.netty.util.ReferenceCountUtil;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import java.util.Collections;
  import java.util.List;
  
  import static io.netty.handler.codec.http.HttpMethod.OPTIONS;
  import static io.netty.handler.codec.http.HttpResponseStatus.FORBIDDEN;
  import static io.netty.handler.codec.http.HttpResponseStatus.OK;
  import static io.netty.util.ReferenceCountUtil.release;
  import static io.netty.util.internal.ObjectUtil.checkNonEmpty;
  import static io.netty.util.internal.ObjectUtil.checkNotNull;
  
  /**
   * Handles <a href="https://www.w3.org/TR/cors/">Cross Origin Resource Sharing</a> (CORS) requests.
   * <p>
   * This handler can be configured using one or more {@link CorsConfig}, please
   * refer to this class for details about the configuration options available.
   * <p>
   * If CORS support is enabled for at least one {@link CorsConfig}, every response written
   * by this handler will carry {@code Vary: Origin}, including responses to requests without
   * {@code Origin} header or with an origin that is not allowed.
   */
  public class CorsHandler extends ChannelDuplexHandler {
  
      private static final InternalLogger logger = InternalLoggerFactory.getInstance(CorsHandler.class);
      private static final String ANY_ORIGIN = "*";
      private static final String NULL_ORIGIN = "null";
      private CorsConfig config;
  
      private HttpRequest request;
      private final List<CorsConfig> configList;
      private final boolean isShortCircuit;
      private final boolean varyOnOrigin;
      private boolean consumeContent;
  
      /**
       * Creates a new instance with a single {@link CorsConfig}.
       */
      public CorsHandler(final CorsConfig config) {
          this(Collections.singletonList(checkNotNull(config, "config")), config.isShortCircuit());
      }
  
      /**
       * Creates a new instance with the specified config list. If more than one
       * config matches a certain origin, the first in the List will be used.
       *
       * @param configList     List of {@link CorsConfig}
       * @param isShortCircuit Same as {@link CorsConfig#isShortCircuit} but applicable to all supplied configs.
       */
      public CorsHandler(final List<CorsConfig> configList, boolean isShortCircuit) {
          checkNonEmpty(configList, "configList");
          this.configList = configList;
          this.isShortCircuit = isShortCircuit;
          this.varyOnOrigin = isCorsSupportEnabled();
      }
  
      private boolean isCorsSupportEnabled() {
          for (CorsConfig config : configList) {
              if (config.isCorsSupportEnabled()) {
                  return true;
              }
          }
          return false;
      }
  
     @Override
     public void channelRead(final ChannelHandlerContext ctx, final Object msg) throws Exception {
         if (msg instanceof HttpRequest) {
             request = (HttpRequest) msg;
             final String origin = request.headers().get(HttpHeaderNames.ORIGIN);
             config = getForOrigin(origin);
             if (isPreflightRequest(request)) {
                 handlePreflight(ctx, request);
                 // Enable consumeContent so that all following HttpContent
                 // for this request will be released and not propagated downstream.
                 consumeContent = true;
                 return;
             }
             if (isShortCircuit && !(origin == null || config != null)) {
                 forbidden(ctx, request);
                 consumeContent = true;
                 return;
             }
 
             // This request is forwarded, stop discarding
             consumeContent = false;
             ctx.fireChannelRead(msg);
             return;
         }
 
         if (consumeContent && (msg instanceof HttpContent)) {
             ReferenceCountUtil.release(msg);
             return;
         }
 
         ctx.fireChannelRead(msg);
     }
 
     private void handlePreflight(final ChannelHandlerContext ctx, final HttpRequest request) {
         final HttpResponse response = new DefaultFullHttpResponse(
                 request.protocolVersion(),
                 OK,
                 Unpooled.buffer(0),
                 DefaultHttpHeadersFactory.headersFactory().withCombiningHeaders(true),
                 DefaultHttpHeadersFactory.trailersFactory().withCombiningHeaders(true));
         if (setOrigin(response)) {
             setAllowMethods(response);
             setAllowHeaders(response);
             setAllowCredentials(response);
             setMaxAge(response);
             setPreflightHeaders(response);
             setAllowPrivateNetwork(response);
         }
         if (!response.headers().contains(HttpHeaderNames.CONTENT_LENGTH)) {
             response.headers().set(HttpHeaderNames.CONTENT_LENGTH, HttpHeaderValues.ZERO);
         }
         release(request);
         respond(ctx, request, response);
     }
 
     /**
      * This is a non CORS specification feature which enables the setting of preflight
      * response headers that might be required by intermediaries.
      *
      * @param response the HttpResponse to which the preflight response headers should be added.
      */
     private void setPreflightHeaders(final HttpResponse response) {
         response.headers().add(config.preflightResponseHeaders());
     }
 
     private CorsConfig getForOrigin(String requestOrigin) {
         for (CorsConfig corsConfig : configList) {
             if (corsConfig.isAnyOriginSupported()) {
                 return corsConfig;
             }
             if (corsConfig.origins().contains(requestOrigin)) {
                 return corsConfig;
             }
             if (corsConfig.isNullOriginAllowed() && NULL_ORIGIN.equals(requestOrigin)) {
                 return corsConfig;
             }
         }
         return null;
     }
 
     private boolean setOrigin(final HttpResponse response) {
         final String origin = request.headers().get(HttpHeaderNames.ORIGIN);
         if (origin != null && config != null) {
             if (NULL_ORIGIN.equals(origin) && config.isNullOriginAllowed()) {
                 setNullOrigin(response);
                 setVaryHeader(response);
                 return true;
             }
             if (config.isAnyOriginSupported()) {
                 if (config.isCredentialsAllowed()) {
                     echoRequestOrigin(response);
                     setVaryHeader(response);
                 } else {
                     setAnyOrigin(response);
                 }
                 return true;
             }
             if (config.origins().contains(origin)) {
                 setOrigin(response, origin);
                 setVaryHeader(response);
                 return true;
             }
             logger.debug("Request origin [{}]] was not among the configured origins [{}]", origin, config.origins());
         }
         return false;
     }
 
     private void echoRequestOrigin(final HttpResponse response) {
         setOrigin(response, request.headers().get(HttpHeaderNames.ORIGIN));
     }
 
     private static void setVaryHeader(final HttpResponse response) {
         if (!response.headers().containsValue(HttpHeaderNames.VARY, HttpHeaderNames.ORIGIN, true)) {
             response.headers().add(HttpHeaderNames.VARY, HttpHeaderNames.ORIGIN);
         }
     }
 
     private static void setAnyOrigin(final HttpResponse response) {
         setOrigin(response, ANY_ORIGIN);
     }
 
     private static void setNullOrigin(final HttpResponse response) {
         setOrigin(response, NULL_ORIGIN);
     }
 
     private static void setOrigin(final HttpResponse response, final String origin) {
         response.headers().set(HttpHeaderNames.ACCESS_CONTROL_ALLOW_ORIGIN, origin);
     }
 
     private void setAllowCredentials(final HttpResponse response) {
         if (config.isCredentialsAllowed()
                 && !response.headers().get(HttpHeaderNames.ACCESS_CONTROL_ALLOW_ORIGIN).equals(ANY_ORIGIN)) {
             response.headers().set(HttpHeaderNames.ACCESS_CONTROL_ALLOW_CREDENTIALS, "true");
         }
     }
 
     private static boolean isPreflightRequest(final HttpRequest request) {
         final HttpHeaders headers = request.headers();
         return OPTIONS.equals(request.method()) &&
                 headers.contains(HttpHeaderNames.ORIGIN) &&
                 headers.contains(HttpHeaderNames.ACCESS_CONTROL_REQUEST_METHOD);
     }
 
     private void setExposeHeaders(final HttpResponse response) {
         if (!config.exposedHeaders().isEmpty()) {
             response.headers().set(HttpHeaderNames.ACCESS_CONTROL_EXPOSE_HEADERS, config.exposedHeaders());
         }
     }
 
     private void setAllowMethods(final HttpResponse response) {
         response.headers().set(HttpHeaderNames.ACCESS_CONTROL_ALLOW_METHODS, config.allowedRequestMethods());
     }
 
     private void setAllowHeaders(final HttpResponse response) {
         response.headers().set(HttpHeaderNames.ACCESS_CONTROL_ALLOW_HEADERS, config.allowedRequestHeaders());
     }
 
     private void setMaxAge(final HttpResponse response) {
         response.headers().set(HttpHeaderNames.ACCESS_CONTROL_MAX_AGE, config.maxAge());
     }
 
     private void setAllowPrivateNetwork(final HttpResponse response) {
         if (request.headers().contains(HttpHeaderNames.ACCESS_CONTROL_REQUEST_PRIVATE_NETWORK)) {
             if (config.isPrivateNetworkAllowed()) {
                 response.headers().set(HttpHeaderNames.ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK, "true");
             } else {
                 response.headers().set(HttpHeaderNames.ACCESS_CONTROL_ALLOW_PRIVATE_NETWORK, "false");
             }
         }
     }
 
     @Override
     public void write(final ChannelHandlerContext ctx, final Object msg, final ChannelPromise promise)
             throws Exception {
         if (msg instanceof HttpResponse) {
             final HttpResponse response = (HttpResponse) msg;
             if (config != null && config.isCorsSupportEnabled() && setOrigin(response)) {
                 setAllowCredentials(response);
                 setExposeHeaders(response);
             }
             if (varyOnOrigin) {
                 setVaryHeader(response);
             }
         }
         ctx.write(msg, promise);
     }
 
     private static void forbidden(final ChannelHandlerContext ctx, final HttpRequest request) {
         HttpResponse response = new DefaultFullHttpResponse(
                 request.protocolVersion(), FORBIDDEN, ctx.alloc().buffer(0));
         response.headers().set(HttpHeaderNames.CONTENT_LENGTH, HttpHeaderValues.ZERO);
         release(request);
         respond(ctx, request, response);
     }
 
     private static void respond(
             final ChannelHandlerContext ctx,
             final HttpRequest request,
             final HttpResponse response) {
 
         final boolean keepAlive = HttpUtil.isKeepAlive(request);
 
         HttpUtil.setKeepAlive(response, keepAlive);
 
         final ChannelFuture future = ctx.writeAndFlush(response);
         if (!keepAlive) {
             future.addListener(ChannelFutureListener.CLOSE);
         }
     }
 }