HTTPDNS:Best practices for using HTTPDNS with Apache HttpClient in Java

1. Background

Both Apache HttpClient 4.x and 5.x support HTTPDNS integration through the DnsResolver interface.

2. Implement a custom DnsResolver

import org.apache.hc.client5.http.DnsResolver;
import com.alibaba.sdk.java.httpdns.HttpDnsClient;
import com.alibaba.sdk.java.httpdns.HTTPDNSResult;
import com.alibaba.sdk.java.httpdns.RequestIpType;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.List;

public class HttpDnsResolver implements DnsResolver {
    
    private final HttpDnsClient httpDnsClient;
    
    public HttpDnsResolver(HttpDnsClient httpDnsClient) {
        this.httpDnsClient = httpDnsClient;
    }

    @Override
    public String resolveCanonicalHostname(String host) {
        return host;
    }

    @Override
    public InetAddress[] resolve(String host) throws UnknownHostException {
        HTTPDNSResult result = httpDnsClient.getHttpDnsResultForHostSyncNonBlocking(host, RequestIpType.both);

        List<InetAddress> addresses = new ArrayList<>();
        try {
            if (result != null && result.getIps() != null) {
                for (String ip : result.getIps()) {
                    addresses.add(InetAddress.getByName(ip));
                }
            }
            if (result != null && result.getIpv6s() != null) {
                for (String ip : result.getIpv6s()) {
                    addresses.add(InetAddress.getByName(ip));
                }
            }
        } catch (UnknownHostException e) {
            // Ignore the failure to parse a single IP address.
        }
        
        if (!addresses.isEmpty()) {
            return addresses.toArray(new InetAddress[0]);
        }
        
        // Degrade to the system DNS.
        return InetAddress.getAllByName(host);
    }
}

import org.apache.http.conn.DnsResolver;
import com.alibaba.sdk.java.httpdns.HttpDnsClient;
import com.alibaba.sdk.java.httpdns.HTTPDNSResult;
import com.alibaba.sdk.java.httpdns.RequestIpType;

import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.List;

public class HttpDnsResolver4 implements DnsResolver {
    
    private final HttpDnsClient httpDnsClient;
    
    public HttpDnsResolver4(HttpDnsClient httpDnsClient) {
        this.httpDnsClient = httpDnsClient;
    }

    @Override
    public InetAddress[] resolve(String host) throws UnknownHostException {
        HTTPDNSResult result = httpDnsClient.getHttpDnsResultForHostSyncNonBlocking(host, RequestIpType.both);

        List<InetAddress> addresses = new ArrayList<>();
        try {
            if (result != null && result.getIps() != null) {
                for (String ip : result.getIps()) {
                    addresses.add(InetAddress.getByName(ip));
                }
            }
            if (result != null && result.getIpv6s() != null) {
                for (String ip : result.getIpv6s()) {
                    addresses.add(InetAddress.getByName(ip));
                }
            }
        } catch (UnknownHostException e) {
            // Ignore the failure to parse a single IP address.
        }
        
        if (!addresses.isEmpty()) {
            return addresses.toArray(new InetAddress[0]);
        }
        
        // Degrade to the system DNS.
        return InetAddress.getAllByName(host);
    }
}

3. Configure HttpClient

import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.HttpClients;
import org.apache.hc.client5.http.impl.io.PoolingHttpClientConnectionManagerBuilder;
import org.apache.hc.client5.http.io.HttpClientConnectionManager;

HttpDnsClient httpDnsClient = HttpDnsClient.getClient(accountId);

HttpClientConnectionManager connectionManager = PoolingHttpClientConnectionManagerBuilder.create()
    .setDnsResolver(new HttpDnsResolver(httpDnsClient))
    .build();

CloseableHttpClient httpClient = HttpClients.custom()
    .setConnectionManager(connectionManager)
    .build();

import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

HttpDnsClient httpDnsClient = HttpDnsClient.getClient(accountId);

CloseableHttpClient httpClient = HttpClients.custom()
    .setDnsResolver(new HttpDnsResolver4(httpDnsClient))
    .build();

4. Summary

Advantages of this approach:

• Simple integration: Requires only a DnsResolver implementation.

• High versatility: Works with HTTPS, SNI, and cookies without additional certificate validation or domain verification.

• Version compatibility: Supports both HttpClient 4.x and 5.x.