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.exception;
  
  import java.util.List;
  
  import com.alibaba.csp.sentinel.adapter.gateway.sc.callback.GatewayCallbackManager;
  import com.alibaba.csp.sentinel.slots.block.BlockException;
  import com.alibaba.csp.sentinel.util.function.Supplier;
  
  import org.springframework.http.codec.HttpMessageWriter;
  import org.springframework.http.codec.ServerCodecConfigurer;
  import org.springframework.web.reactive.function.server.ServerResponse;
  import org.springframework.web.reactive.result.view.ViewResolver;
  import org.springframework.web.server.ServerWebExchange;
  import org.springframework.web.server.WebExceptionHandler;
  import reactor.core.publisher.Mono;
  
  /**
   * @author Eric Zhao
   * @since 1.6.0
   */
  public class SentinelGatewayBlockExceptionHandler implements WebExceptionHandler {
  
      private List<ViewResolver> viewResolvers;
      private List<HttpMessageWriter<?>> messageWriters;
  
      public SentinelGatewayBlockExceptionHandler(List<ViewResolver> viewResolvers, ServerCodecConfigurer serverCodecConfigurer) {
          this.viewResolvers = viewResolvers;
          this.messageWriters = serverCodecConfigurer.getWriters();
      }
  
      private Mono<Void> writeResponse(ServerResponse response, ServerWebExchange exchange) {
          return response.writeTo(exchange, contextSupplier.get());
      }
  
      @Override
      public Mono<Void> handle(ServerWebExchange exchange, Throwable ex) {
          if (exchange.getResponse().isCommitted()) {
              return Mono.error(ex);
          }
          // This exception handler only handles rejection by Sentinel.
          if (!BlockException.isBlockException(ex)) {
              return Mono.error(ex);
          }
          return handleBlockedRequest(exchange, ex)
              .flatMap(response -> writeResponse(response, exchange));
      }
  
      private Mono<ServerResponse> handleBlockedRequest(ServerWebExchange exchange, Throwable throwable) {
          return GatewayCallbackManager.getBlockHandler().handleRequest(exchange, throwable);
      }
  
      private final Supplier<ServerResponse.Context> contextSupplier = () -> new ServerResponse.Context() {
          @Override
          public List<HttpMessageWriter<?>> messageWriters() {
              return SentinelGatewayBlockExceptionHandler.this.messageWriters;
          }
  
          @Override
          public List<ViewResolver> viewResolvers() {
              return SentinelGatewayBlockExceptionHandler.this.viewResolvers;
          }
      };
  }
  