聊聊spring cloud gateway的LoadBalancerClientFilter-白红宇

聊聊spring cloud gateway的LoadBalancerClientFilter

阅读量：5961 次

发布时间：2019-06-19

本文共 8098 字，大约阅读时间需要 26 分钟。

序

本文主要研究一下spring cloud gateway的LoadBalancerClientFilter

GatewayLoadBalancerClientAutoConfiguration

spring-cloud-gateway-core-2.0.0.RELEASE-sources.jar!/org/springframework/cloud/gateway/config/GatewayLoadBalancerClientAutoConfiguration.java

@Configuration@ConditionalOnClass({LoadBalancerClient.class, RibbonAutoConfiguration.class, DispatcherHandler.class})@AutoConfigureAfter(RibbonAutoConfiguration.class)public class GatewayLoadBalancerClientAutoConfiguration {	// GlobalFilter beans	@Bean	@ConditionalOnBean(LoadBalancerClient.class)	public LoadBalancerClientFilter loadBalancerClientFilter(LoadBalancerClient client) {		return new LoadBalancerClientFilter(client);	}}

如果检测到有ribbon，则开启LoadBalancerClientFilter

LoadBalancerClientFilter

spring-cloud-gateway-core-2.0.0.RELEASE-sources.jar!/org/springframework/cloud/gateway/filter/LoadBalancerClientFilter.java

public class LoadBalancerClientFilter implements GlobalFilter, Ordered {	private static final Log log = LogFactory.getLog(LoadBalancerClientFilter.class);	public static final int LOAD_BALANCER_CLIENT_FILTER_ORDER = 10100;	private final LoadBalancerClient loadBalancer;	public LoadBalancerClientFilter(LoadBalancerClient loadBalancer) {		this.loadBalancer = loadBalancer;	}	@Override	public int getOrder() {		return LOAD_BALANCER_CLIENT_FILTER_ORDER;	}	@Override	public Mono
    
      filter(ServerWebExchange exchange, GatewayFilterChain chain) {		URI url = exchange.getAttribute(GATEWAY_REQUEST_URL_ATTR);		String schemePrefix = exchange.getAttribute(GATEWAY_SCHEME_PREFIX_ATTR);		if (url == null || (!"lb".equals(url.getScheme()) && !"lb".equals(schemePrefix))) {			return chain.filter(exchange);		}		//preserve the original url		addOriginalRequestUrl(exchange, url);		log.trace("LoadBalancerClientFilter url before: " + url);		final ServiceInstance instance = loadBalancer.choose(url.getHost());		if (instance == null) {			throw new NotFoundException("Unable to find instance for " + url.getHost());		}		URI uri = exchange.getRequest().getURI();		// if the `lb:
     
      ` mechanism was used, use `
      
       ` as the default,		// if the loadbalancer doesn't provide one.		String overrideScheme = null;		if (schemePrefix != null) {			overrideScheme = url.getScheme();		}		URI requestUrl = loadBalancer.reconstructURI(new DelegatingServiceInstance(instance, overrideScheme), uri);		log.trace("LoadBalancerClientFilter url chosen: " + requestUrl);		exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, requestUrl);		return chain.filter(exchange);	}    //......}

这里首先获取scheme，如果不是lb，则直接往下一个filter传递

之后通过loadBalancer.choose(url.getHost())来选取服务实例

最后构造好requestUrl，设置到GATEWAY_REQUEST_URL_ATTR属性中

GATEWAY_SCHEME_PREFIX_ATTR

spring-cloud-gateway-core-2.0.0.RELEASE-sources.jar!/org/springframework/cloud/gateway/filter/RouteToRequestUrlFilter.java GATEWAY_SCHEME_PREFIX_ATTR这个属性是在RouteToRequestUrlFilter里头设置进去的。

public class RouteToRequestUrlFilter implements GlobalFilter, Ordered {	private static final Log log = LogFactory.getLog(RouteToRequestUrlFilter.class);	public static final int ROUTE_TO_URL_FILTER_ORDER = 10000;	private static final String SCHEME_REGEX = "[a-zA-Z]([a-zA-Z]|\\d|\\+|\\.|-)*:.*";	static final Pattern schemePattern = Pattern.compile(SCHEME_REGEX);	@Override	public int getOrder() {		return ROUTE_TO_URL_FILTER_ORDER;	}	@Override	public Mono
    
      filter(ServerWebExchange exchange, GatewayFilterChain chain) {		Route route = exchange.getAttribute(GATEWAY_ROUTE_ATTR);		if (route == null) {			return chain.filter(exchange);		}		log.trace("RouteToRequestUrlFilter start");		URI uri = exchange.getRequest().getURI();		boolean encoded = containsEncodedParts(uri);		URI routeUri = route.getUri();		if (hasAnotherScheme(routeUri)) {			// this is a special url, save scheme to special attribute			// replace routeUri with schemeSpecificPart			exchange.getAttributes().put(GATEWAY_SCHEME_PREFIX_ATTR, routeUri.getScheme());			routeUri = URI.create(routeUri.getSchemeSpecificPart());		}		URI requestUrl = UriComponentsBuilder.fromUri(uri)				.uri(routeUri)				.build(encoded)				.toUri();		exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, requestUrl);		return chain.filter(exchange);	}	/* for testing */ static boolean hasAnotherScheme(URI uri) {		return schemePattern.matcher(uri.getSchemeSpecificPart()).matches() && uri.getHost() == null				&& uri.getRawPath() == null;	}}

GATEWAY_REQUEST_URL_ATTR

spring-cloud-gateway-core-2.0.0.RELEASE-sources.jar!/org/springframework/cloud/gateway/filter/NettyRoutingFilter.java

public class NettyRoutingFilter implements GlobalFilter, Ordered {	private final HttpClient httpClient;	private final ObjectProvider
    
     
      > headersFilters;	public NettyRoutingFilter(HttpClient httpClient,			ObjectProvider
      
       
        > headersFilters) {		this.httpClient = httpClient;		this.headersFilters = headersFilters;	}	@Override	public int getOrder() {		return Ordered.LOWEST_PRECEDENCE;	}	@Override	public Mono
        
          filter(ServerWebExchange exchange, GatewayFilterChain chain) {		URI requestUrl = exchange.getRequiredAttribute(GATEWAY_REQUEST_URL_ATTR);		String scheme = requestUrl.getScheme();		if (isAlreadyRouted(exchange) || (!"http".equals(scheme) && !"https".equals(scheme))) {			return chain.filter(exchange);		}		setAlreadyRouted(exchange);		ServerHttpRequest request = exchange.getRequest();		final HttpMethod method = HttpMethod.valueOf(request.getMethod().toString());		final String url = requestUrl.toString();		HttpHeaders filtered = filterRequest(this.headersFilters.getIfAvailable(),				exchange);		final DefaultHttpHeaders httpHeaders = new DefaultHttpHeaders();		filtered.forEach(httpHeaders::set);		String transferEncoding = request.getHeaders().getFirst(HttpHeaders.TRANSFER_ENCODING);		boolean chunkedTransfer = "chunked".equalsIgnoreCase(transferEncoding);		boolean preserveHost = exchange.getAttributeOrDefault(PRESERVE_HOST_HEADER_ATTRIBUTE, false);		return this.httpClient.request(method, url, req -> {			final HttpClientRequest proxyRequest = req.options(NettyPipeline.SendOptions::flushOnEach)					.headers(httpHeaders)					.chunkedTransfer(chunkedTransfer)					.failOnServerError(false)					.failOnClientError(false);			if (preserveHost) {				String host = request.getHeaders().getFirst(HttpHeaders.HOST);				proxyRequest.header(HttpHeaders.HOST, host);			}			return proxyRequest.sendHeaders() //I shouldn't need this					.send(request.getBody().map(dataBuffer ->							((NettyDataBuffer)dataBuffer).getNativeBuffer()));		}).doOnNext(res -> {			ServerHttpResponse response = exchange.getResponse();			// put headers and status so filters can modify the response			HttpHeaders headers = new HttpHeaders();			res.responseHeaders().forEach(entry -> headers.add(entry.getKey(), entry.getValue()));			exchange.getAttributes().put("original_response_content_type", headers.getContentType());			HttpHeaders filteredResponseHeaders = HttpHeadersFilter.filter(					this.headersFilters.getIfAvailable(), headers, exchange, Type.RESPONSE);						response.getHeaders().putAll(filteredResponseHeaders);			HttpStatus status = HttpStatus.resolve(res.status().code());			if (status != null) {				response.setStatusCode(status);			} else if (response instanceof AbstractServerHttpResponse) {				// https://jira.spring.io/browse/SPR-16748				((AbstractServerHttpResponse) response).setStatusCodeValue(res.status().code());			} else {				throw new IllegalStateException("Unable to set status code on response: " +res.status().code()+", "+response.getClass());			}			// Defer committing the response until all route filters have run			// Put client response as ServerWebExchange attribute and write response later NettyWriteResponseFilter			exchange.getAttributes().put(CLIENT_RESPONSE_ATTR, res);		}).then(chain.filter(exchange));	}}

在NettyRoutingFilter中根据GATEWAY_REQUEST_URL_ATTR属性读取requestUrl，然后进行相应请求。

小结

LoadBalancerClientFilter会作用在url以lb开头的路由，然后利用loadBalancer来获取服务实例，构造目标requestUrl，设置到GATEWAY_REQUEST_URL_ATTR属性中，供NettyRoutingFilter使用。

doc

转载于:https://my.oschina.net/go4it/blog/1833128

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