有谁理解spring cloud gateway如何实现异步的吗

lingli219 2021-06-24 18:59:11

以下这段代码来自NettyRoutingFilter这个类：

	@Override
	@SuppressWarnings("Duplicates")
	public Mono<Void> 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);

		boolean preserveHost = exchange.getAttributeOrDefault(PRESERVE_HOST_HEADER_ATTRIBUTE, false);
		Route route = exchange.getAttribute(GATEWAY_ROUTE_ATTR);

		Flux<HttpClientResponse> 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) -> {

			// 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);
			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);

			if (!filteredResponseHeaders.containsKey(HttpHeaders.TRANSFER_ENCODING)
					&& filteredResponseHeaders.containsKey(HttpHeaders.CONTENT_LENGTH)) {
				// It is not valid to have both the transfer-encoding header and
				// the content-length header.
				// Remove the transfer-encoding header in the response if the
				// content-length header is present.
				response.getHeaders().remove(HttpHeaders.TRANSFER_ENCODING);
			}

			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));
	}

是不是responseConnection后面括号内的处理逻辑相当于注册了一个回调，就是一旦请求返回结果，就会调用这段代码进行处理？

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