SpringCloud Finchley Gateway 缓存请求Body和Form表单

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
  APPLICATION_JSON_UTF8
  APPLICATION_FORM_URLENCODED
  

• 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

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