聊聊spring cloud的PreserveHostHeaderGatewayFilter

序

本文主要研究下spring cloud gateway的PreserveHostHeaderGatewayFilter

GatewayAutoConfiguration

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/config/GatewayAutoConfiguration.java

@Configuration
@ConditionalOnProperty(name = "spring.cloud.gateway.enabled", matchIfMissing = true)
@EnableConfigurationProperties
@AutoConfigureBefore(HttpHandlerAutoConfiguration.class)
@AutoConfigureAfter({GatewayLoadBalancerClientAutoConfiguration.class, GatewayClassPathWarningAutoConfiguration.class})
@ConditionalOnClass(DispatcherHandler.class)
public class GatewayAutoConfiguration {
    //......
	@Bean
	public PreserveHostHeaderGatewayFilterFactory preserveHostHeaderGatewayFilterFactory() {
		return new PreserveHostHeaderGatewayFilterFactory();
	}
    //......
}

PreserveHostHeaderGatewayFilterFactory

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/config/GatewayAutoConfiguration.java

public class PreserveHostHeaderGatewayFilterFactory extends AbstractGatewayFilterFactory {

	public GatewayFilter apply() {
		return apply(o -> {});
	}

    public GatewayFilter apply(Object config) {
		return (exchange, chain) -> {
			exchange.getAttributes().put(PRESERVE_HOST_HEADER_ATTRIBUTE, true);
			return chain.filter(exchange);
		};
	}
}

这个filter超级简单，就往exchange添加PRESERVE_HOST_HEADER_ATTRIBUTE，设置为true

NettyRoutingFilter

spring-cloud-gateway-core-2.0.0.RC2-sources.jar!/org/springframework/cloud/gateway/filter/NettyRoutingFilter.java

public class NettyRoutingFilter implements GlobalFilter, Ordered {

	private final HttpClient httpClient;
	private final ObjectProvider<List<HttpHeadersFilter>> headersFilters;

	public NettyRoutingFilter(HttpClient httpClient,
			ObjectProvider<List<HttpHeadersFilter>> headersFilters) {
		this.httpClient = httpClient;
		this.headersFilters = headersFilters;
	}

	@Override
	public int getOrder() {
		return Ordered.LOWEST_PRECEDENCE;
	}

	@Override
	public Mono<Void> 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()));

			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));
	}
}

这里从读取PRESERVE_HOST_HEADER_ATTRIBUTE属性，没有则默认false。若是为true，则proxyRequest.header(HttpHeaders.HOST, host)，传递host头部。

小结

PreserveHostHeaderGatewayFilter就是在gateway转发请求的时候把原始请求的host头部带上，转发给目标服务。默认该filter是启用的。

doc

• 112.6 PreserveHostHeader GatewayFilter Factory