Normalize IDN hostnames to punycode before DNS resolution to prevent …

…UnknownHostException during connection.

httpclient5/src/main/java/org/apache/hc/client5/http/SystemDefaultDnsResolver.java

@@ -26,6 +26,7 @@
  */
 package org.apache.hc.client5.http;
 
+import java.net.IDN;
 import java.net.InetAddress;
 import java.net.UnknownHostException;
 
@@ -44,8 +45,9 @@ public class SystemDefaultDnsResolver implements DnsResolver {
     @Override
     public InetAddress[] resolve(final String host) throws UnknownHostException {
         try {
+            final String normalizedHost = IDN.toASCII(host);
             // Try resolving using the default resolver
-            return InetAddress.getAllByName(host);
+            return InetAddress.getAllByName(normalizedHost);
         } catch (final UnknownHostException e) {
             // If default resolver fails, try stripping the IPv6 zone ID and resolving again
             String strippedHost = null;