Spring RestTemplate & AsyncRestTemplate with Netty4 hangs forever

Question

Very simple setup:

pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>demo-rest-client</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>demo-rest-client</name>
    <description>Demo project for Spring Boot</description>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.1.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
        <java.version>1.8</java.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-all</artifactId>
            <version>4.1.5.Final</version>
        </dependency>
        <dependency>
            <groupId>io.netty</groupId>
            <artifactId>netty-buffer</artifactId>
            <version>4.1.5.Final</version>
        </dependency>
        <dependency>
            <groupId>com.squareup.okhttp3</groupId>
            <artifactId>okhttp</artifactId>
            <version>3.4.1</version>
        </dependency>
        <dependency>
            <groupId>io.github.openfeign</groupId>
            <artifactId>feign-core</artifactId>
            <version>9.3.1</version>
        </dependency>
        <dependency>
            <groupId>io.github.openfeign</groupId>
            <artifactId>feign-hystrix</artifactId>
            <version>9.3.1</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

And a test case to demonstrate different usages of AsyncRestTemplate:

SampleTests.java

package com.example;

import com.netflix.hystrix.HystrixCommand;
import com.netflix.hystrix.HystrixCommandProperties;
import feign.RequestLine;
import feign.hystrix.HystrixFeign;
import feign.hystrix.SetterFactory;
import org.junit.Test;
import org.springframework.http.ResponseEntity;
import org.springframework.http.client.Netty4ClientHttpRequestFactory;
import org.springframework.http.client.OkHttp3ClientHttpRequestFactory;
import org.springframework.util.concurrent.ListenableFuture;
import org.springframework.web.client.AsyncRestTemplate;
import org.springframework.web.client.RestTemplate;

public class SampleTests {

    private static final String URL = "https://api.github.com/users/octocat";
    private static final int DEFAULT_SLEEP_MILLIS = 20;
    private static final int DEFAULT_TIMEOUT = 10000;

    @Test(timeout = DEFAULT_TIMEOUT)
    public void syncRestNetty() throws Exception {
        RestTemplate restTemplate = new RestTemplate(new Netty4ClientHttpRequestFactory());
        ResponseEntity<String> response = restTemplate.getForEntity(URL, String.class);
        System.out.println("response = " + response);
    }

    @Test(timeout = DEFAULT_TIMEOUT)
    public void asyncRestNetty() throws Exception {
        AsyncRestTemplate restTemplate = new AsyncRestTemplate(new Netty4ClientHttpRequestFactory());
        ListenableFuture<ResponseEntity<String>> listenableFuture = restTemplate.getForEntity(URL, String.class);
        listenableFuture.addCallback(result -> System.out.println("result = " + result), Throwable::printStackTrace);
        while (!listenableFuture.isDone()) {
            Thread.sleep(DEFAULT_SLEEP_MILLIS);
        }
        System.out.println("the end");
    }

    @Test
    public void asyncRestOkHttp() throws Exception {
        AsyncRestTemplate restTemplate = new AsyncRestTemplate(new OkHttp3ClientHttpRequestFactory());
        ListenableFuture<ResponseEntity<String>> listenableFuture = restTemplate.getForEntity(URL, String.class);
        listenableFuture.addCallback(result -> System.out.println("result = " + result), Throwable::printStackTrace);
        while (!listenableFuture.isDone()) {
            Thread.sleep(DEFAULT_SLEEP_MILLIS);
        }
        System.out.println("the end");
    }

    @Test
    public void asyncRestHystrixFeign() throws Exception {
        GitHub gitHub = HystrixFeign.builder()
                .setterFactory((target, method) -> new SetterFactory.Default().create(target, method).andCommandPropertiesDefaults(HystrixCommandProperties.defaultSetter().withExecutionTimeoutInMilliseconds(10000)))
                .target(GitHub.class, "https://api.github.com");
        HystrixCommand<String> command = gitHub.octocatAsync();
        command.toObservable().subscribe(result -> System.out.println("result = " + result), Throwable::printStackTrace);
        while (!command.isExecutionComplete()) {
            Thread.sleep(DEFAULT_SLEEP_MILLIS);
        }
        System.out.println("command.getExecutionTimeInMilliseconds() = " + command.getExecutionTimeInMilliseconds());
        System.out.println("the end");
    }

    interface GitHub {
        @RequestLine("GET /users/octocat")
        HystrixCommand<String> octocatAsync();
    }
}

When trying to run the tests which use Netty they just hang forever. (To see this please remove the JUnit timeout constraint). But if I run the exact same code with other clients everything works as expected.

I have tried different versions of Spring Boot and Netty but did not succeed. And from the logs everything looks ok.

What am I missing here?

EDIT: Opened a ticket https://jira.spring.io/browse/SPR-14744 as suggested on Spring Gitter

EDIT-2: Answer from Brian Clozel helped me find the issue which is related to Netty not realizing the server sent an empty response (a particular case with Github API and plain http) so I am marking it as accepted.

Answer 1

Can you try to configure your request factory with a Netty Sslcontext?

Netty4ClientHttpRequestFactory nettyFactory = new Netty4ClientHttpRequestFactory();
nettyFactory.setSslContext(SslContextBuilder.forClient().build());
AsyncRestTemplate restTemplate = new AsyncRestTemplate(nettyFactory);

Without that context, the client is trying to send plaintext requests to the https endpoint; in that case, you're probably getting an HTTP 400 response.

In your example code, the throwable should be an instance of HttpClientErrorException, and you could get that information by logging the response status or its body with exception.getResponseBodyAsString().