SpringCloud Finchley Gateway 缓存请求Body和Form表单的实现

在接入Spring-Cloud-Gateway时，可能有需求进行缓存Json-Body数据或者Form-Urlencoded数据的情况。

由于Spring-Cloud-Gateway是以WebFlux为基础的响应式架构设计，所以在原有Zuul基础上迁移过来的过程中，传统的编程思路，并不适合于Reactor Stream的开发。

网络上有许多缓存案例，但是在测试过程中出现各种Bug问题，在缓存Body时，需要考虑整体的响应式操作，才能更合理的缓存数据

下面提供缓存Json-Body数据或者Form-Urlencoded数据的具体实现方案，该方案经测试，满足各方面需求，以及避免了网络上其他缓存方案所出现的问题

定义一个GatewayContext类，用于存储请求中缓存的数据

import lombok.Getter;
import lombok.Setter;
import lombok.ToString;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;

@Getter
@Setter
@ToString
public class GatewayContext {

  public static final String CACHE_GATEWAY_CONTEXT = "cacheGatewayContext";

  /**
   * cache json body
   */
  private String cacheBody;
  /**
   * cache formdata
   */
  private MultiValueMap<String, String> formData;
  /**
   * cache reqeust path
   */
  private String path;
}

实现GlobalFilter和Ordered接口用于缓存请求数据

1 . 该示例只支持缓存下面3种MediaType

• APPLICATION_JSON--Json数据
• APPLICATION_JSON_UTF8--Json数据
• APPLICATION_FORM_URLENCODED--FormData表单数据

2 . 经验总结:

• 在缓存Body时,不能够在Filter内部直接进行缓存，需要按照响应式的处理方式，在异步操作路途上进行缓存Body，由于Body只能读取一次，所以要读取完成后要重新封装新的request和exchange才能保证请求正常传递到下游
• 在缓存FormData时，FormData也只能读取一次，所以在读取完毕后，需要重新封装request和exchange,这里要注意，如果对FormData内容进行了修改，则必须重新定义Header中的content-length已保证传输数据的大小一致

import com.choice.cloud.architect.usergate.option.FilterOrderEnum;
import com.choice.cloud.architect.usergate.support.GatewayContext;
import io.netty.buffer.ByteBufAllocator;
import lombok.extern.slf4j.Slf4j;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.core.Ordered;
import org.springframework.core.io.ByteArrayResource;
import org.springframework.core.io.buffer.DataBuffer;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.core.io.buffer.NettyDataBufferFactory;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.codec.HttpMessageReader;
import org.springframework.http.server.reactive.ServerHttpRequest;
import org.springframework.http.server.reactive.ServerHttpRequestDecorator;
import org.springframework.util.MultiValueMap;
import org.springframework.web.reactive.function.server.HandlerStrategies;
import org.springframework.web.reactive.function.server.ServerRequest;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Flux;
import reactor.core.publisher.Mono;

import java.io.UnsupportedEncodingException;
import java.net.URLEncoder;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.List;
import java.util.Map;

@Slf4j
public class GatewayContextFilter implements GlobalFilter, Ordered {

  /**
   * default HttpMessageReader
   */
  private static final List<HttpMessageReader<?>> messageReaders = HandlerStrategies.withDefaults().messageReaders();

  @Override
  public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
    /**
     * save request path and serviceId into gateway context
     */
    ServerHttpRequest request = exchange.getRequest();
    String path = request.getPath().pathWithinApplication().value();
    GatewayContext gatewayContext = new GatewayContext();
    gatewayContext.getAllRequestData().addAll(request.getQueryParams());
    gatewayContext.setPath(path);
    /**
     * save gateway context into exchange
     */
    exchange.getAttributes().put(GatewayContext.CACHE_GATEWAY_CONTEXT,gatewayContext);
    HttpHeaders headers = request.getHeaders();
    MediaType contentType = headers.getContentType();
    long contentLength = headers.getContentLength();
    if(contentLength>0){
      if(MediaType.APPLICATION_JSON.equals(contentType) || MediaType.APPLICATION_JSON_UTF8.equals(contentType)){
        return readBody(exchange, chain,gatewayContext);
      }
      if(MediaType.APPLICATION_FORM_URLENCODED.equals(contentType)){
        return readFormData(exchange, chain,gatewayContext);
      }
    }
    log.debug("[GatewayContext]ContentType:{},Gateway context is set with {}",contentType, gatewayContext);
    return chain.filter(exchange);

  }

  @Override
  public int getOrder() {
    return Integer.MIN_VALUE;
  }

  /**
   * ReadFormData
   * @param exchange
   * @param chain
   * @return
   */
  private Mono<Void> readFormData(ServerWebExchange exchange,GatewayFilterChain chain,GatewayContext gatewayContext){
    HttpHeaders headers = exchange.getRequest().getHeaders();
    return exchange.getFormData()
        .doOnNext(multiValueMap -> {
          gatewayContext.setFormData(multiValueMap);
          log.debug("[GatewayContext]Read FormData:{}",multiValueMap);
        })
        .then(Mono.defer(() -> {
          Charset charset = headers.getContentType().getCharset();
          charset = charset == null? StandardCharsets.UTF_8:charset;
          String charsetName = charset.name();
          MultiValueMap<String, String> formData = gatewayContext.getFormData();
          /**
           * formData is empty just return
           */
          if(null == formData || formData.isEmpty()){
            return chain.filter(exchange);
          }
          StringBuilder formDataBodyBuilder = new StringBuilder();
          String entryKey;
          List<String> entryValue;
          try {
            /**
             * remove system param ,repackage form data
             */
            for (Map.Entry<String, List<String>> entry : formData.entrySet()) {
              entryKey = entry.getKey();
              entryValue = entry.getValue();
              if (entryValue.size() > 1) {
                for(String value : entryValue){
                  formDataBodyBuilder.append(entryKey).append("=").append(URLEncoder.encode(value, charsetName)).append("&");
                }
              } else {
                formDataBodyBuilder.append(entryKey).append("=").append(URLEncoder.encode(entryValue.get(0), charsetName)).append("&");
              }
            }
          }catch (UnsupportedEncodingException e){
            //ignore URLEncode Exception
          }
          /**
           * substring with the last char '&'
           */
          String formDataBodyString = "";
          if(formDataBodyBuilder.length()>0){
            formDataBodyString = formDataBodyBuilder.substring(0, formDataBodyBuilder.length() - 1);
          }
          /**
           * get data bytes
           */
          byte[] bodyBytes = formDataBodyString.getBytes(charset);
          int contentLength = bodyBytes.length;
          ServerHttpRequestDecorator decorator = new ServerHttpRequestDecorator(
              exchange.getRequest()) {
            /**
             * change content-length
             * @return
             */
            @Override
            public HttpHeaders getHeaders() {
              HttpHeaders httpHeaders = new HttpHeaders();
              httpHeaders.putAll(super.getHeaders());
              if (contentLength > 0) {
                httpHeaders.setContentLength(contentLength);
              } else {
                httpHeaders.set(HttpHeaders.TRANSFER_ENCODING, "chunked");
              }
              return httpHeaders;
            }

            /**
             * read bytes to Flux<Databuffer>
             * @return
             */
            @Override
            public Flux<DataBuffer> getBody() {
              return DataBufferUtils.read(new ByteArrayResource(bodyBytes),new NettyDataBufferFactory(ByteBufAllocator.DEFAULT),contentLength);
            }
          };
          ServerWebExchange mutateExchange = exchange.mutate().request(decorator).build();
          log.debug("[GatewayContext]Rewrite Form Data :{}",formDataBodyString);
          return chain.filter(mutateExchange);
        }));
  }

  /**
   * ReadJsonBody
   * @param exchange
   * @param chain
   * @return
   */
  private Mono<Void> readBody(ServerWebExchange exchange,GatewayFilterChain chain,GatewayContext gatewayContext){
    /**
     * join the body
     */
    return DataBufferUtils.join(exchange.getRequest().getBody())
        .flatMap(dataBuffer -> {
          /**
           * read the body Flux<Databuffer>
           */
          DataBufferUtils.retain(dataBuffer);
          Flux<DataBuffer> cachedFlux = Flux.defer(() -> Flux.just(dataBuffer.slice(0, dataBuffer.readableByteCount())));
          /**
           * repackage ServerHttpRequest
           */
          ServerHttpRequest mutatedRequest = new ServerHttpRequestDecorator(exchange.getRequest()) {
            @Override
            public Flux<DataBuffer> getBody() {
              return cachedFlux;
            }
          };
          /**
           * mutate exchage with new ServerHttpRequest
           */
          ServerWebExchange mutatedExchange = exchange.mutate().request(mutatedRequest).build();
          /**
           * read body string with default messageReaders
           */
          return ServerRequest.create(mutatedExchange, messageReaders)
              .bodyToMono(String.class)
              .doOnNext(objectValue -> {
                gatewayContext.setCacheBody(objectValue);
                log.debug("[GatewayContext]Read JsonBody:{}",objectValue);
              }).then(chain.filter(mutatedExchange));
        });
  }

}

在后续Filter中，可以直接从ServerExchange中获取GatewayContext，就可以获取到缓存的数据，如果需要缓存其他数据，则可以根据自己的需求，添加到GatewayContext中即可

代码如下:

GatewayContext gatewayContext = exchange.getAttribute(GatewayContext.CACHE_GATEWAY_CONTEXT);

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