springcloud gateway 请求执行流程分析
一、示例
pom.xml
4.0.0
com.simplemall.micro.serv.base
base-serv
0.0.1-SNAPSHOT
com.simplemall.micro.serv.base.zuul
zuul-server
zuulServer
org.springframework.boot
spring-boot-starter-test
test
io.projectreactor.netty
reactor-netty
0.9.14.RELEASE
org.projectlombok
lombok
com.alibaba
fastjson
1.2.7
com.alibaba.cloud
spring-cloud-starter-alibaba-nacos-config
2.2.6.RELEASE
com.alibaba.cloud
spring-cloud-starter-alibaba-nacos-discovery
2.2.6.RELEASE
org.springframework.cloud
spring-cloud-starter-gateway
reactor-netty
io.projectreactor.netty
cn.dev33
sa-token-reactor-spring-boot-starter
1.28.0
cn.dev33
sa-token-dao-redis-jackson
1.28.0
org.apache.commons
commons-pool2
org.springframework.boot
spring-boot-maven-plugin
application.yml
server:
port: 9005
#eureka:
# client:
# service-url:
# defaultZone: http://127.0.0.1:9003/eureka/
sa-token:
token-name: authorization
is-concurrent: true
is-share: true
timeout: 3600
is-log: true
#spring.redis.database=0
#spring.redis.host=127.0.0.1
#spring.redis.port=6379
#spring.redis.timeout=10s
spring:
application:
name: gateway-server
# redis:
# database: 0
# host: 127.0.0.1
# port: 6379
# timeout: 10s
# lettuce:
# pool:
# max-active: 10
# max-wait: 200
# min-idle: 0
# max-idle: 8
# sleuth:
# sampler:
# probability: 1.0
zipkin:
base-url: http://127.0.0.1:9411
cloud:
nacos:
config:
server-addr: 127.0.0.1:8848
discovery:
server-addr: 127.0.0.1:8848
gateway:
enabled: true
httpclient:
connect-timeout: 1000
response-timeout: 3s
discovery:
locator:
enabled: true
routes:
- id: front-api
uri: lb://front-app1
predicates:
- Path=/app/**
filters:
- StripPrefix=1
- AddResponseHeader=X-Response-Default-Foo, Default-Bar
- id: nacosday
uri: lb://nacosday
predicates:
- Path=/nacosday/**
filters:
- StripPrefix=1
- AddResponseHeader=X-Response-Default-Foo, Default-BarsaTokenFilter
package com.simplemall.micro.serv.zuul.filter;
import cn.dev33.satoken.exception.BackResultException;
import cn.dev33.satoken.exception.SaTokenException;
import cn.dev33.satoken.exception.StopMatchException;
import cn.dev33.satoken.filter.SaFilterAuthStrategy;
import cn.dev33.satoken.filter.SaFilterErrorStrategy;
import cn.dev33.satoken.reactor.context.SaReactorHolder;
import cn.dev33.satoken.reactor.context.SaReactorSyncHolder;
import cn.dev33.satoken.router.SaRouter;
import cn.dev33.satoken.util.SaTokenConsts;
import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.core.Ordered;
import org.springframework.core.annotation.Order;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;
//import javax.servlet.*;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
@Order(SaTokenConsts.ASSEMBLY_ORDER)
public class SaReactorFilter implements GlobalFilter {
// ------------------------ 设置此过滤器 拦截 & 放行 的路由
/**
* 拦截路由
*/
private List includeList = new ArrayList<>();
/**
* 放行路由
*/
private List excludeList = new ArrayList<>();
/**
* 添加 [拦截路由]
* @param paths 路由
* @return 对象自身
*/
public SaReactorFilter addInclude(String... paths) {
includeList.addAll(Arrays.asList(paths));
return this;
}
/**
* 添加 [放行路由]
* @param paths 路由
* @return 对象自身
*/
public SaReactorFilter addExclude(String... paths) {
excludeList.addAll(Arrays.asList(paths));
return this;
}
/**
* 写入 [拦截路由] 集合
* @param pathList 路由集合
* @return 对象自身
*/
public SaReactorFilter setIncludeList(List pathList) {
includeList = pathList;
return this;
}
/**
* 写入 [放行路由] 集合
* @param pathList 路由集合
* @return 对象自身
*/
public SaReactorFilter setExcludeList(List pathList) {
excludeList = pathList;
return this;
}
/**
* 获取 [拦截路由] 集合
* @return see note
*/
public List getIncludeList() {
return includeList;
}
/**
* 获取 [放行路由] 集合
* @return see note
*/
public List getExcludeList() {
return excludeList;
}
// ------------------------ 钩子函数
/**
* 认证函数：每次请求执行
*/
public SaFilterAuthStrategy auth = r -> {};
/**
* 异常处理函数：每次[认证函数]发生异常时执行此函数
*/
public SaFilterErrorStrategy error = e -> {
throw new SaTokenException(e);
};
/**
* 前置函数：在每次[认证函数]之前执行
*/
public SaFilterAuthStrategy beforeAuth = r -> {};
/**
* 写入[认证函数]: 每次请求执行
* @param auth see note
* @return 对象自身
*/
public SaReactorFilter setAuth(SaFilterAuthStrategy auth) {
this.auth = auth;
return this;
}
/**
* 写入[异常处理函数]：每次[认证函数]发生异常时执行此函数
* @param error see note
* @return 对象自身
*/
public SaReactorFilter setError(SaFilterErrorStrategy error) {
this.error = error;
return this;
}
/**
* 写入[前置函数]：在每次[认证函数]之前执行
* @param beforeAuth see note
* @return 对象自身
*/
public SaReactorFilter setBeforeAuth(SaFilterAuthStrategy beforeAuth) {
this.beforeAuth = beforeAuth;
return this;
}
@Override
public Mono filter(ServerWebExchange exchange, GatewayFilterChain chain) {
// try {
// // 执行全局过滤器
// SaRouter.match(includeList).notMatch(excludeList).check(r -> {
// beforeAuth.run(null);
// auth.run(null);
// });
//
// } catch (StopMatchException e) {
//
// } catch (Throwable e) {
// e.printStackTrace();
// // 1. 获取异常处理策略结果
// String result = (e instanceof BackResultException) ? e.getMessage() : String.valueOf(error.run(e));
// return ErrorConvertor.errorResp(exchange.getResponse(), 500,result);
// }
//
// return chain.filter(exchange);
// 写入WebFilterChain对象
exchange.getAttributes().put(SaReactorHolder.CHAIN_KEY, chain);
// ---------- 全局认证处理
try {
// 写入全局上下文 (同步)
SaReactorSyncHolder.setContext(exchange);
// 执行全局过滤器
SaRouter.match(includeList).notMatch(excludeList).check(r -> {
beforeAuth.run(null);
auth.run(null);
});
} catch (StopMatchException e) {
} catch (Throwable e) {
e.printStackTrace();
// 1. 获取异常处理策略结果
String result = (e instanceof BackResultException) ? e.getMessage() : String.valueOf(error.run(e));
// 2. 写入输出流
if(exchange.getResponse().getHeaders().getFirst("Content-Type") == null) {
exchange.getResponse().getHeaders().set("Content-Type", "text/plain; charset=utf-8");
}
return exchange.getResponse().writeWith(Mono.just(exchange.getResponse().bufferFactory().wrap(result.getBytes())));
} finally {
// 清除上下文
SaReactorSyncHolder.clearContext();
}
// ---------- 执行
// 写入全局上下文 (同步)
SaReactorSyncHolder.setContext(exchange);
// 执行
return chain.filter(exchange).subscriberContext(ctx -> {
// 写入全局上下文 (异步)
ctx = ctx.put(SaReactorHolder.CONTEXT_KEY, exchange);
return ctx;
}).doFinally(r -> {
// 清除上下文
SaReactorSyncHolder.clearContext();
});
}
}
SaTokenFilterConfig
package com.simplemall.micro.serv.zuul.config;
import cn.dev33.satoken.context.SaHolder;
import cn.dev33.satoken.router.SaRouter;
import cn.dev33.satoken.stp.StpUtil;
import com.simplemall.micro.serv.zuul.filter.SaReactorFilter;
import com.simplemall.micro.serv.zuul.utils.AjaxJson;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
@Configuration
public class SaTokenFilterConfig {
@Bean
public SaReactorFilter createServletFilter(){
return new SaReactorFilter().addInclude("/**")
.addExclude("/favicon.ico")
.setAuth(r -> {
System.out.println("---------- 进入Sa-Token全局认证 -----------");
SaRouter.match("/**","/tb-acc/get", r2 -> StpUtil.checkLogin());
SaRouter.match("/tb-acc/getLoginInfo",r2 -> StpUtil.checkPermission("user-add"));
})
.setError(e -> {
System.out.println("---------- 进入Sa-Token异常处理 -----------");
return AjaxJson.getError(e.getMessage());
})
.setBeforeAuth(r -> {
SaHolder.getResponse()// 服务器名称
.setServer("sa-server")
// 是否可以在iframe显示视图： DENY=不可以 | SAMEORIGIN=同域下可以 | ALLOW-FROM uri=指定域名下可以
.setHeader("X-Frame-Options", "SAMEORIGIN")
// 是否启用浏览器默认XSS防护： 0=禁用 | 1=启用 | 1; mode=block 启用, 并在检查到XSS攻击时，停止渲染页面
.setHeader("X-XSS-Protection", "1; mode=block")
// 禁用浏览器内容嗅探
.setHeader("X-Content-Type-Options", "nosniff");
});
}
}
二、测试效果
1.在网关下启动nacosday这个微服务。
2.通过网关访问nacosday微服务。
http://localhost:9005/nacosday/tb-acc/get?id=4c5a2c38-2fc0-4977-a577-1625066ad8d3&device=pcm 网关日志
nacosday日志
3. 看到已经通过网关访问到服务层。
三、访问流程分析
1.总体流程
二、我们调试接口，跟踪代码。
1.看到总体流程为 netty.transport->reactor.netty->spring.web
HttpServerHandle
public void onStateChange(Connection connection, State newState) {
if (newState == HttpServerState.REQUEST_RECEIVED) {
try {
if (log.isDebugEnabled()) {
log.debug(format(connection.channel(), "Handler is being applied: {}"), handler);
}
HttpServerOperations ops = (HttpServerOperations) connection;
Mono.fromDirect(handler.apply(ops, ops))
.subscribe(ops.disposeSubscriber());
}
catch (Throwable t) {
log.error(format(connection.channel(), ""), t);
//"FutureReturnValueIgnored" this is deliberate
connection.channel()
.close();
}
}
}2.这里面重点为Mono.fromDirect(handler.apply(ops, ops)).subscribe(ops.disposeSubscriber());
这行代码包含了整个的请示路由，处理，是采用的webflux的响应式编程，由handler.apply(ops, ops)创建MONO的流程编排对象，然后subscribe来订阅此流程，才会真正触发流程的执行。
3.这里面进行响应式httpHandler适配器的应用，生成一个Mono流程对象。
ReactorHttpHandlerAdapter
@Override
public Mono apply(HttpServerRequest reactorRequest, HttpServerResponse reactorResponse) {
NettyDataBufferFactory bufferFactory = new NettyDataBufferFactory(reactorResponse.alloc());
try {
ReactorServerHttpRequest request = new ReactorServerHttpRequest(reactorRequest, bufferFactory);
ServerHttpResponse response = new ReactorServerHttpResponse(reactorResponse, bufferFactory);
if (request.getMethod() == HttpMethod.HEAD) {
response = new HttpHeadResponseDecorator(response);
}
return this.httpHandler.handle(request, response)
.doOnError(ex -> logger.trace(request.getLogPrefix() + "Failed to complete: " + ex.getMessage()))
.doOnSuccess(aVoid -> logger.trace(request.getLogPrefix() + "Handling completed"));
}
catch (URISyntaxException ex) {
if (logger.isDebugEnabled()) {
logger.debug("Failed to get request URI: " + ex.getMessage());
}
reactorResponse.status(HttpResponseStatus.BAD_REQUEST);
return Mono.empty();
}
} 4. 这里的httpHandler为WebServerManager.DelayedInitializationHttpHandler
5.接着这个代理delegate对象指向HttpWebHandlerAdapter
6.可以看到就是构造一个exchange对象，然后再继承又是代理处理。
这里面成功附加打印一个日志，失败时，进行出错显示统一处理，最后调用response设置完成。
HttpWebHandlerAdapter
@Override
public Mono handle(ServerHttpRequest request, ServerHttpResponse response) {
if (this.forwardedHeaderTransformer != null) {
request = this.forwardedHeaderTransformer.apply(request);
}
ServerWebExchange exchange = createExchange(request, response);
return getDelegate().handle(exchange)
.doOnSuccess(aVoid -> logResponse(exchange))
.onErrorResume(ex -> handleUnresolvedError(exchange, ex))
.then(Mono.defer(response::setComplete));
} 
7. 接下来的代理对象为ExceptionHandlingWebHandler，这个就是调用基类的处理函数，然后为这个Mono流程对象加上各种出错的异常处理器。
ExceptionHandlingWebHandler
@Override
public Mono handle(ServerWebExchange exchange) {
Mono completion;
try {
completion = super.handle(exchange);
}
catch (Throwable ex) {
completion = Mono.error(ex);
}
for (WebExceptionHandler handler : this.exceptionHandlers) {
completion = completion.onErrorResume(ex -> handler.handle(exchange, ex));
}
return completion;
} 
8. WebHandlerDecorator的代理对象为FilteringWebHandler
9.filterWebHandler就是调用chain的责任链模式调用。
FilteringWebHandler
@Override
public Mono handle(ServerWebExchange exchange) {
return this.chain.filter(exchange);
}
10.DefaultWebFilterChain.filter为生成一个懒加载的MONO对象。
DefaultWebFilterChain
@Override
public Mono filter(ServerWebExchange exchange) {
return Mono.defer(() ->
this.currentFilter != null && this.chain != null ?
invokeFilter(this.currentFilter, this.chain, exchange) :
this.handler.handle(exchange));
} 11.接着又回到第7步，我们看到前面的第10步并没有执行，必须要等待流程订阅时才执行。
12.然后又回到第一步，真正开始订阅流程，执行流程。
13.这里的ops就是HttpServerOperations，这个类实现了mono的自定义订阅类。
Mono的订阅方法为public abstract void subscribe(CoreSubscriber actual);
从上面可以看到ChannelOperations实现了CoreSubscriber接口，这里在 onSubscribe请求拉模式，拉取了 全量消息数据。
ChannelOperations
@Override
public final void onNext(Void aVoid) {
}
@Override
public final void onSubscribe(Subscription s) {
if (Operators.setOnce(OUTBOUND_CLOSE, this, s)) {
s.request(Long.MAX_VALUE);
}
}三、发送请求流程
1.现在我们开始真正触发流程。首先执行第二部分第10步，DefaultWebFilterChain.filter为生成一个懒加载的MONO对象。
2.首先经过WeightCalculatorWebFilter
WeightCalculatorWebFilter
@Override
public Mono filter(ServerWebExchange exchange, WebFilterChain chain) {
Map weights = getWeights(exchange);
for (String group : groupWeights.keySet()) {
GroupWeightConfig config = groupWeights.get(group);
if (config == null) {
if (log.isDebugEnabled()) {
log.debug("No GroupWeightConfig found for group: " + group);
}
continue; // nothing we can do, but this is odd
}
double r = this.random.nextDouble();
List ranges = config.ranges;
if (log.isTraceEnabled()) {
log.trace("Weight for group: " + group + ", ranges: " + ranges + ", r: "
+ r);
}
for (int i = 0; i < ranges.size() - 1; i++) {
if (r >= ranges.get(i) && r < ranges.get(i + 1)) {
String routeId = config.rangeIndexes.get(i);
weights.put(group, routeId);
break;
}
}
}
return chain.filter(exchange);
}
3.执行完上面的权重filter之后，又回DefaultWebFilterChain.filter的循环调用。
因为filter执行完了，执行handler.handle方法。
4.上面的handler为DispatcherHandler，这个类的handle方法，
4.1 这里面首先要对系统中所有内置的mappingHandle进行映射匹配，找到所有合适的handler
4.2 .next方法为取第一个handler
4.3 如果为空，则返回一个Mono.error
4.4 循环调用handler,返回结果
4.5 循环处理结果。
DispatcherHandler
@Override
public Mono handle(ServerWebExchange exchange) {
if (this.handlerMappings == null) {
return createNotFoundError();
}
return Flux.fromIterable(this.handlerMappings)
.concatMap(mapping -> mapping.getHandler(exchange))
.next()
.switchIfEmpty(createNotFoundError())
.flatMap(handler -> invokeHandler(exchange, handler))
.flatMap(result -> handleResult(exchange, result));
} 
HandlerMapping接口主要为根据exchange找到一个可用的Mono的handler对象。
Mono
5.RoutePredicateHandlerMapping负责路由查找，并更具路由断言判断路由是否可用
这里首先查找路由表，找到匹配的路由，然后将此路由设置到exchange的属性中，接着返回
FilteringWebHandler的MONO包装。
RoutePredicateHandlerMapping
@Override
protected Mono getHandlerInternal(ServerWebExchange exchange) {
// don't handle requests on management port if set and different than server port
if (this.managementPortType == DIFFERENT && this.managementPort != null
&& exchange.getRequest().getURI().getPort() == this.managementPort) {
return Mono.empty();
}
exchange.getAttributes().put(GATEWAY_HANDLER_MAPPER_ATTR, getSimpleName());
return lookupRoute(exchange)
// .log("route-predicate-handler-mapping", Level.FINER) //name this
.flatMap((Function>) r -> {
exchange.getAttributes().remove(GATEWAY_PREDICATE_ROUTE_ATTR);
if (logger.isDebugEnabled()) {
logger.debug(
"Mapping [" + getExchangeDesc(exchange) + "] to " + r);
}
exchange.getAttributes().put(GATEWAY_ROUTE_ATTR, r);
return Mono.just(webHandler);
}).switchIfEmpty(Mono.empty().then(Mono.fromRunnable(() -> {
exchange.getAttributes().remove(GATEWAY_PREDICATE_ROUTE_ATTR);
if (logger.isTraceEnabled()) {
logger.trace("No RouteDefinition found for ["
+ getExchangeDesc(exchange) + "]");
}
})));
} 
6.首先查找路由,我们来看下路由表信息
RoutePredicateHandlerMapping
protected Mono lookupRoute(ServerWebExchange exchange) {
return this.routeLocator.getRoutes()
// individually filter routes so that filterWhen error delaying is not a
// problem
.concatMap(route -> Mono.just(route).filterWhen(r -> {
// add the current route we are testing
exchange.getAttributes().put(GATEWAY_PREDICATE_ROUTE_ATTR, r.getId());
return r.getPredicate().apply(exchange);
})
// instead of immediately stopping main flux due to error, log and
// swallow it
.doOnError(e -> logger.error(
"Error applying predicate for route: " + route.getId(),
e))
.onErrorResume(e -> Mono.empty()))
// .defaultIfEmpty() put a static Route not found
// or .switchIfEmpty()
// .switchIfEmpty(Mono.empty().log("noroute"))
.next()
// TODO: error handling
.map(route -> {
if (logger.isDebugEnabled()) {
logger.debug("Route matched: " + route.getId());
}
validateRoute(route, exchange);
return route;
});
/*
* TODO: trace logging if (logger.isTraceEnabled()) {
* logger.trace("RouteDefinition did not match: " + routeDefinition.getId()); }
*/
} 然后通过filterWhen逐个路由进行匹配。匹配成功后返回了此路由
7.最终的handler返回的是一个 FilteringWebHandler
8.接着又回到第4.4步，开始执行handler。
看到SimpleHandlerAdapter能够支持FilteringWebHandler，接着调用其 webHandler
public class SimpleHandlerAdapter implements HandlerAdapter {
@Override
public Mono handle(ServerWebExchange exchange, Object handler) {
WebHandler webHandler = (WebHandler) handler;
Mono mono = webHandler.handle(exchange);
return mono.then(Mono.empty());
} 9.接着调用FilteringWebHandler.handler方法。 这里会构造13个filter,进行网关FILTER的责任链调用。
FilteringWebHandler
@Override
public Mono handle(ServerWebExchange exchange) {
Route route = exchange.getRequiredAttribute(GATEWAY_ROUTE_ATTR);
List gatewayFilters = route.getFilters();
List combined = new ArrayList<>(this.globalFilters);
combined.addAll(gatewayFilters);
// TODO: needed or cached?
AnnotationAwareOrderComparator.sort(combined);
if (logger.isDebugEnabled()) {
logger.debug("Sorted gatewayFilterFactories: " + combined);
}
return new DefaultGatewayFilterChain(combined).filter(exchange);
}
10. 默认网关的FILTER责任链调用，就是调用当前索引的filter.filter->在filter里面又再次调用chain.filter(这时filter索引会递增)->接着会调用到下一个filter，当所有filter调用完时，则完成。
private static class DefaultGatewayFilterChain implements GatewayFilterChain {
private final int index;
private final List filters;
@Override
public Mono filter(ServerWebExchange exchange) {
return Mono.defer(() -> {
if (this.index < filters.size()) {
GatewayFilter filter = filters.get(this.index);
DefaultGatewayFilterChain chain = new DefaultGatewayFilterChain(this,
this.index + 1);
return filter.filter(exchange, chain);
}
else {
return Mono.empty(); // complete
}
});
}
11.这里我们重点关注几个拼接URL和发起HTTP请求的FILTER
RewritePathGatewayFilterFactory：去掉/nacosday这种服务前缀。
@Override
public GatewayFilter apply(Config config) {
String replacement = config.replacement.replace("$\\", "$");
return new GatewayFilter() {
@Override
public Mono filter(ServerWebExchange exchange,
GatewayFilterChain chain) {
ServerHttpRequest req = exchange.getRequest();
addOriginalRequestUrl(exchange, req.getURI());
String path = req.getURI().getRawPath();
String newPath = path.replaceAll(config.regexp, replacement);
ServerHttpRequest request = req.mutate().path(newPath).build();
exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, request.getURI());
return chain.filter(exchange.mutate().request(request).build());
}
@Override
public String toString() {
return filterToStringCreator(RewritePathGatewayFilterFactory.this)
.append(config.getRegexp(), replacement).toString();
}
};
} 
通过正则去除之后，我们看下效果。
看到/nacosday的服务前缀已经从URL去掉。
12.RouteToRequestUrlFilter将URL协议进行改成，转换生成gatewayRequestUrl
，改lb：//nacosday协议。
RouteToRequestUrlFilter
@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();
URI mergedUrl = UriComponentsBuilder.fromUri(uri)
// .uri(routeUri)
.scheme(routeUri.getScheme()).host(routeUri.getHost())
.port(routeUri.getPort()).build(encoded).toUri();
exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, mergedUrl);
return chain.filter(exchange);
} 
13.LoadBalancerClientFilter为根据lb://nacosday的协议，通过负载均衡策略和服务注册中心，找到合适的后端服务实例，进行URL替换。
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);
if (log.isTraceEnabled()) {
log.trace("LoadBalancerClientFilter url before: " + url);
}
final ServiceInstance instance = choose(exchange);
if (instance == null) {
throw NotFoundException.create(properties.isUse404(),
"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 = instance.isSecure() ? "https" : "http";
if (schemePrefix != null) {
overrideScheme = url.getScheme();
}
URI requestUrl = loadBalancer.reconstructURI(
new DelegatingServiceInstance(instance, overrideScheme), uri);
if (log.isTraceEnabled()) {
log.trace("LoadBalancerClientFilter url chosen: " + requestUrl);
}
exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, requestUrl);
return chain.filter(exchange);
} 这里引用了RibbonLoadBalancerClient.choose来真正通过服务注册中心获取实例。
public ServiceInstance choose(String serviceId, Object hint) {
Server server = getServer(getLoadBalancer(serviceId), hint);
if (server == null) {
return null;
}
return new RibbonServer(serviceId, server, isSecure(server, serviceId),
serverIntrospector(serviceId).getMetadata(server));
}
看最后改写URL过程，可以看到已 经改为真实的URL.
14.NettyRoutingFilter为真正封装httpClient发起HTTP请求的filter.
这里为设置http header.创建httpClient,发起http请求。
@Override
@SuppressWarnings("Duplicates")
public Mono filter(ServerWebExchange exchange, GatewayFilterChain chain) {
URI requestUrl = exchange.getRequiredAttribute(GATEWAY_REQUEST_URL_ATTR);
String scheme = requestUrl.getScheme();
if (isAlreadyRouted(exchange) || (!"http".equalsIgnoreCase(scheme)
&& !"https".equalsIgnoreCase(scheme))) {
return chain.filter(exchange);
}
setAlreadyRouted(exchange);
ServerHttpRequest request = exchange.getRequest();
final HttpMethod method = HttpMethod.valueOf(request.getMethodValue());
final String url = requestUrl.toASCIIString();
HttpHeaders filtered = filterRequest(getHeadersFilters(), exchange);
final DefaultHttpHeaders httpHeaders = new DefaultHttpHeaders();
filtered.forEach(httpHeaders::set);
Route route = exchange.getAttribute(GATEWAY_ROUTE_ATTR);
Flux responseFlux = getHttpClient(route, exchange)
.headers(headers -> {
headers.add(httpHeaders);
// Will either be set below, or later by Netty
headers.remove(HttpHeaders.HOST);
if (preserveHost) {
String host = request.getHeaders().getFirst(HttpHeaders.HOST);
headers.add(HttpHeaders.HOST, host);
}
}).request(method).uri(url).send((req, nettyOutbound) -> {
if (log.isTraceEnabled()) {
nettyOutbound
.withConnection(connection -> log.trace("outbound route: "
+ connection.channel().id().asShortText()
+ ", inbound: " + exchange.getLogPrefix()));
}
return nettyOutbound.send(request.getBody().map(this::getByteBuf));
}).responseConnection((res, connection) -> {
exchange.getAttributes().put(CLIENT_RESPONSE_ATTR, res);
exchange.getAttributes().put(CLIENT_RESPONSE_CONN_ATTR, connection);
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()));
String contentTypeValue = headers.getFirst(HttpHeaders.CONTENT_TYPE);
if (StringUtils.hasLength(contentTypeValue)) {
exchange.getAttributes().put(ORIGINAL_RESPONSE_CONTENT_TYPE_ATTR,
contentTypeValue);
}
setResponseStatus(res, response);
// make sure headers filters run after setting status so it is
// available in response
HttpHeaders filteredResponseHeaders = HttpHeadersFilter.filter(
getHeadersFilters(), headers, exchange, Type.RESPONSE);
exchange.getAttributes().put(CLIENT_RESPONSE_HEADER_NAMES,
filteredResponseHeaders.keySet());
response.getHeaders().putAll(filteredResponseHeaders);
return Mono.just(res);
});
Duration responseTimeout = getResponseTimeout(route);
if (responseTimeout != null) {
responseFlux = responseFlux
.timeout(responseTimeout, Mono.error(new TimeoutException(
"Response took longer than timeout: " + responseTimeout)))
.onErrorMap(TimeoutException.class,
th -> new ResponseStatusException(HttpStatus.GATEWAY_TIMEOUT,
th.getMessage(), th));
}
return responseFlux.then(chain.filter(exchange));
} 
真正的通过netty发起请求
四、接收后端服务请求流程
1.
HttpClientConnect.HttpIOHandlerObserver.onStateChange(Connection connection, State newState)
@Override
public void onStateChange(Connection connection, State newState) {
if (newState == HttpClientState.RESPONSE_RECEIVED) {
sink.success(connection);
return;
}
if (newState == ConnectionObserver.State.CONFIGURED
&& HttpClientOperations.class == connection.getClass()) {
if (log.isDebugEnabled()) {
log.debug(format(connection.channel(), "Handler is being applied: {}"), handler);
}
Mono.defer(() -> Mono.fromDirect(handler.requestWithBody((HttpClientOperations) connection)))
.subscribe(connection.disposeSubscriber());
}
}
2.然后会回调到NettyRoutingFilter.filter中的匿名内部 receiver方法，从 这里可以看出，已经收到http的回应了。
3.将后端服务的结果，回写给客户端。
注意，在前面一步将connection写入CLIENT_RESPONSE_CONN_ATTR
exchange.getAttributes().put(CLIENT_RESPONSE_CONN_ATTR, connection);
在这一步读出来
Connection connection = exchange.getAttribute(CLIENT_RESPONSE_CONN_ATTR);
NettyWriteResponseFilter
@Override
public Mono filter(ServerWebExchange exchange, GatewayFilterChain chain) {
// NOTICE: nothing in "pre" filter stage as CLIENT_RESPONSE_CONN_ATTR is not added
// until the NettyRoutingFilter is run
// @formatter:off
return chain.filter(exchange)
.doOnError(throwable -> cleanup(exchange))
.then(Mono.defer(() -> {
Connection connection = exchange.getAttribute(CLIENT_RESPONSE_CONN_ATTR);
if (connection == null) {
return Mono.empty();
}
if (log.isTraceEnabled()) {
log.trace("NettyWriteResponseFilter start inbound: "
+ connection.channel().id().asShortText() + ", outbound: "
+ exchange.getLogPrefix());
}
ServerHttpResponse response = exchange.getResponse();
// TODO: needed?
final Flux body = connection
.inbound()
.receive()
.retain()
.map(byteBuf -> wrap(byteBuf, response));
MediaType contentType = null;
try {
contentType = response.getHeaders().getContentType();
}
catch (Exception e) {
if (log.isTraceEnabled()) {
log.trace("invalid media type", e);
}
}
return (isStreamingMediaType(contentType)
? response.writeAndFlushWith(body.map(Flux::just))
: response.writeWith(body));
})).doOnCancel(() -> cleanup(exchange));
// @formatter:on
} 最后不断读取与后端的connection数据，然后回写给客户端。
五、注意事项
1.如果配置了spring.cloud.gateway.discovery.locator.enabled为TRUE,则系统会自动扫描NACOS中所有的注册服务，然后自动为每个服务生成路由，这样会导致自定义的同名路由配置不会生效，RoutePredicateHandlerMapping在寻找路由时会先找到NACOS中的服务路由然后直接返回。
我们可以看到ReactiveCompositeDiscoveryClient_nacosday(第一个)的路由匹配策略和我们自定义(第3个)的是一样的 ，导致在寻找路由时，找到第一个就返回了，我们配置的相同匹配规则路由策略不会生效。
2.如果配置了spring.cloud.gateway.discovery.locator.enabled为FALSE,则不会将NACOS中注册的服务生成路由，不会冲突。
我们可以看到找到的路由是我们自定义配置的路由了。
3.还有一个注意事项，系统内置的过滤器前缀为左边，右边为实现的FILTER工厂类。
从下面可以看出filter的配置名称就是类名取前缀，去掉GatewayFilterFactory，AddRequestHeaderGatewayFilterFactory->AddRequestHeader
