content: /*
   * Copyright 1999-2019 Alibaba Group Holding Ltd.
   *
   * 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.alibaba.csp.sentinel.adapter.gateway.sc.callback;
  
  import java.util.List;
  
  import org.springframework.http.HttpStatus;
  import org.springframework.http.InvalidMediaTypeException;
  import org.springframework.http.MediaType;
  import org.springframework.util.MimeTypeUtils;
  
  import org.springframework.web.reactive.function.server.ServerResponse;
  import org.springframework.web.server.ServerWebExchange;
  import reactor.core.publisher.Mono;
  
  
  /**
   * The default implementation of {@link BlockRequestHandler}.
   * Compatible with Spring WebFlux v6x and Spring Cloud Gateway.
   *
   * @author uuuyuqi
   */
  public class DefaultBlockRequestHandler implements BlockRequestHandler {
  
      private static final String DEFAULT_BLOCK_MSG_PREFIX = "Blocked by Sentinel: ";
  
      @Override
      public Mono<ServerResponse> handleRequest(ServerWebExchange exchange, Throwable ex) {
          if (acceptsHtml(exchange)) {
              return htmlErrorResponse(ex);
          }
          // JSON result by default.
          return ServerResponse.status(HttpStatus.TOO_MANY_REQUESTS)
              .contentType(MediaType.APPLICATION_JSON)
              .bodyValue(buildErrorResult(ex));
      }
  
      private Mono<ServerResponse> htmlErrorResponse(Throwable ex) {
          return ServerResponse.status(HttpStatus.TOO_MANY_REQUESTS)
              .contentType(MediaType.TEXT_PLAIN)
              .bodyValue(DEFAULT_BLOCK_MSG_PREFIX + ex.getClass().getSimpleName());
      }
  
      private ErrorResult buildErrorResult(Throwable ex) {
          return new ErrorResult(HttpStatus.TOO_MANY_REQUESTS.value(),
              DEFAULT_BLOCK_MSG_PREFIX + ex.getClass().getSimpleName());
      }
  
      /**
       * Reference from {@code DefaultErrorWebExceptionHandler} of Spring Boot.
       */
      private boolean acceptsHtml(ServerWebExchange exchange) {
          try {
              List<MediaType> acceptedMediaTypes = exchange.getRequest().getHeaders().getAccept();
              acceptedMediaTypes.remove(MediaType.ALL);
              MimeTypeUtils.sortBySpecificity(acceptedMediaTypes);
              return acceptedMediaTypes.stream()
                  .anyMatch(MediaType.TEXT_HTML::isCompatibleWith);
          } catch (InvalidMediaTypeException ex) {
              return false;
          }
      }
  
      private static class ErrorResult {
          private final int code;
          private final String message;
  
          ErrorResult(int code, String message) {
              this.code = code;
              this.message = message;
          }
  
          public int getCode() {
              return code;
          }
  
          public String getMessage() {
              return message;
          }
      }
  }
  