为什么WebClient在这个网络流量应用程序中被阻塞？

Question

我正在开发一个web流量应用程序，它公开一个WebClient调用的http端点，然后修改WebClient调用的响应体，然后返回到客户端。当我启用封锁线时，我发现它阻塞了，我正在试图找出原因。

下面是我可以想出的用于重新创建行为的最简单的代码版本。我还在这里放置了一个工作项目：https://github.com/aztosca/web-client-test。注入的WebClient.Builder是他们推荐使用的Spring的预配置实例。

我认为阻塞狗抱怨是因为事件循环线程被阻塞了。我认为使用WebClient可以防止这种情况发生，并确保在适当的线程上发生任何阻塞，但在这里发生了一些我还不明白的事情(我是网络流量新手)。

有人能帮我理解一下为什么这会阻塞线程而不应该阻止它吗？并建议如何修复它？

• netty: 4.1.58
• 弹簧-启动: 2.4.2
• 春季: 5.3.3

@SpringBootApplication
public class WebClientTestApplication {

    public static void main(String[] args) {
        BlockHound.install();
        SpringApplication.run(WebClientTestApplication.class, args);
    }
    
    static String endpoint  =  "http://postman-echo.com/get?name=value";

    @Bean
    public RouterFunction<ServerResponse> testWebClient(WebClient.Builder webClientBuilder) {
        
        WebClient webClient = webClientBuilder.build();
        
        HandlerFunction<ServerResponse> testHandler = new HandlerFunction<>() { 
            @Override
            public Mono<ServerResponse> handle(ServerRequest request) {

                Mono<String> stringMono = webClient.get().uri(endpoint)
                        .retrieve().bodyToMono(String.class)
                        .flatMap(body -> Mono.just("Modify the response " + body));

                return ServerResponse.ok().contentType(MediaType.TEXT_PLAIN)
                        .body(stringMono, String.class); 
            }
        };
        return RouterFunctions.route(GET("/test-web-client").and(
                accept(MediaType.TEXT_PLAIN)),testHandler::handle);  
    }
}

这就是在上面的代码中使用http://postman-echo.com/get?name=value时所发生的情况。

Caused by: reactor.blockhound.BlockingOperationError: Blocking call! java.io.FileInputStream#readBytes
    at java.base/java.io.FileInputStream.readBytes(FileInputStream.java) ~[na:na]
    at java.base/java.io.FileInputStream.read(FileInputStream.java:279) ~[na:na]
    at java.base/sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284) ~[na:na]
    at java.base/sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326) ~[na:na]
    at java.base/sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178) ~[na:na]
    at java.base/java.io.InputStreamReader.read(InputStreamReader.java:185) ~[na:na]
    at java.base/java.io.BufferedReader.fill(BufferedReader.java:161) ~[na:na]
    at java.base/java.io.BufferedReader.readLine(BufferedReader.java:326) ~[na:na]
    at java.base/java.io.BufferedReader.readLine(BufferedReader.java:392) ~[na:na]
    at io.netty.resolver.dns.UnixResolverDnsServerAddressStreamProvider.parseEtcResolverSearchDomains(UnixResolverDnsServerAddressStreamProvider.java:373) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.resolver.dns.UnixResolverDnsServerAddressStreamProvider.parseEtcResolverSearchDomains(UnixResolverDnsServerAddressStreamProvider.java:354) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.resolver.dns.DnsNameResolver.<clinit>(DnsNameResolver.java:137) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
    at io.netty.resolver.dns.DnsNameResolverBuilder.<init>(DnsNameResolverBuilder.java:49) ~[netty-resolver-dns-4.1.58.Final.jar:4.1.58.Final]
    at reactor.netty.transport.NameResolverProvider.newNameResolverGroup(NameResolverProvider.java:405) ~[reactor-netty-core-1.0.3.jar:1.0.3]
    ......

如果您修改端点以使用https：https://postman-echo.com/get?name=value，则会发生这种情况。

Caused by: reactor.blockhound.BlockingOperationError: Blocking call! java.io.FileInputStream#readBytes
    at java.base/java.io.FileInputStream.readBytes(FileInputStream.java) ~[na:na]
    at java.base/java.io.FileInputStream.read(FileInputStream.java:279) ~[na:na]
    at java.base/java.io.BufferedInputStream.fill(BufferedInputStream.java:252) ~[na:na]
    at java.base/java.io.BufferedInputStream.read(BufferedInputStream.java:271) ~[na:na]
    at java.base/sun.security.util.DerValue.init(DerValue.java:388) ~[na:na]
    at java.base/sun.security.util.DerValue.<init>(DerValue.java:331) ~[na:na]
    at java.base/sun.security.util.DerValue.<init>(DerValue.java:344) ~[na:na]
    at java.base/sun.security.pkcs12.PKCS12KeyStore.engineLoad(PKCS12KeyStore.java:1993) ~[na:na]
    at java.base/sun.security.util.KeyStoreDelegator.engineLoad(KeyStoreDelegator.java:222) ~[na:na]
    at java.base/java.security.KeyStore.load(KeyStore.java:1479) ~[na:na]
    at java.base/sun.security.ssl.TrustStoreManager$TrustAnchorManager.loadKeyStore(TrustStoreManager.java:365) ~[na:na]
    ......

Answer 1

据报道，这似乎是一种问题。

修正是合并，它将在4.1.59.Final版本中发布，到编写时它还没有发布，但它是一个计划中的里程碑。