Incorrect UnixResolverDnsServerAddressStreamProvider

[trustin]

Minimal yet complete reproducer code (or URL to code)

import static org.junit.Assert.assertNotNull;

import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStream;
import java.nio.charset.StandardCharsets;

import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.TemporaryFolder;

import io.netty.resolver.dns.UnixResolverDnsServerAddressStreamProvider;

public class ResolverTest {

    @Rule
    public final TemporaryFolder folder = new TemporaryFolder();

    @Test
    public void test() throws Exception {
        File f = folder.newFile();
        try (OutputStream out = new FileOutputStream(f)) {
            out.write(("domain linecorp.local\n" +
                       "nameserver 1.2.3.4\n" +
                       "nameserver 5.6.7.8\n").getBytes(StandardCharsets.UTF_8));
        }
        UnixResolverDnsServerAddressStreamProvider p =
                new UnixResolverDnsServerAddressStreamProvider(f, null);

        assertNotNull(p.nameServerAddressStream("somehost"));
    }
}

Expected behavior

UnixResolverDnsServerAddressStreamProvider.nameServerAddressStream() should not return null.

The expected behavior of DnsNameResolver is to try somehost. and then somehost.linecorp.local.

Actual behavior

Attempting to resolve a host will trigger a NPE:

java.lang.NullPointerException: nameServerAddrs
 at io.netty.util.internal.ObjectUtil.checkNotNull(ObjectUtil.java:31)
 at io.netty.resolver.dns.DnsNameResolverContext.<init>(DnsNameResolverContext.java:120)
 at io.netty.resolver.dns.DnsNameResolver$SingleResolverContext.<init>(DnsNameResolver.java:659)
 at io.netty.resolver.dns.DnsNameResolver.doResolveUncached(DnsNameResolver.java:653)
 at io.netty.resolver.dns.DnsNameResolver.doResolve(DnsNameResolver.java:590)
 at io.netty.resolver.dns.DnsNameResolver.doResolve(DnsNameResolver.java:523)
 at io.netty.resolver.SimpleNameResolver.resolve(SimpleNameResolver.java:63)
 at io.netty.resolver.dns.InflightNameResolver.resolve(InflightNameResolver.java:100)
 at io.netty.resolver.dns.InflightNameResolver.resolve(InflightNameResolver.java:66)
 at io.netty.resolver.dns.InflightNameResolver.resolve(InflightNameResolver.java:51)
 at io.netty.resolver.InetSocketAddressResolver.doResolve(InetSocketAddressResolver.java:57)
 at io.netty.resolver.InetSocketAddressResolver.doResolve(InetSocketAddressResolver.java:32)
 at io.netty.resolver.AbstractAddressResolver.resolve(AbstractAddressResolver.java:108)
 at io.netty.bootstrap.Bootstrap.doResolveAndConnect0(Bootstrap.java:208)
 at io.netty.bootstrap.Bootstrap.doResolveAndConnect(Bootstrap.java:170)
 at io.netty.bootstrap.Bootstrap.connect(Bootstrap.java:145)

Netty version

4.1.11

Workaround

Use DefaultDnsServerAddressStreamProvider.INSTANCE instead of DnsServerAddressStreamProviders.platformDefault().

[normanmaurer]

@trustin can you submit a pr with a fix ?

[trustin]

Can't promise it at the moment because of busyness... 😢

[Scottmitch]

The expected behavior of DnsNameResolver is to try somehost and then somehost.linecorp.local.

The behavior of modifying the hostname should be provided at a higher layer (e.g. DnsNameResolverContext.java). However UnixResolverDnsServerAddressStreamProvider default value when no match was found needs some work.

[Scottmitch]

See PR #6748