Preserve the host name of address when parsing /etc/hosts file

Motivation:

When an InetNameResolver resolves a name, it is expected to reserve the
requested host name in the resolved InetAddress.

DefaultHostsFileEntriesResolver does not preserve the host name. For
example, resolving 'localhost' will return an InetAddress whose address
is '127.0.0.1', but its getHostString() will not return 'localhost' but
just '127.0.0.1'.

Modifications:

Fix the construction of parsed InetAddresses in HostsFileParser

Result:

Host name is preserved in the resolved InetAddress

resolver/src/main/java/io/netty/resolver/HostsFileParser.java

@@ -31,6 +31,7 @@
 import java.util.List;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.regex.Pattern;
 
 import static io.netty.util.internal.ObjectUtil.*;
 
@@ -43,6 +44,8 @@ public final class HostsFileParser {
     private static final String WINDOWS_HOSTS_FILE_RELATIVE_PATH = "\\system32\\drivers\\etc\\hosts";
     private static final String X_PLATFORMS_HOSTS_FILE_PATH = "/etc/hosts";
 
+    private static final Pattern WHITESPACES = Pattern.compile("[ \t]+");
+
     private static final InternalLogger logger = InternalLoggerFactory.getInstance(HostsFileParser.class);
 
     private static File locateHostsFile() {
@@ -126,7 +129,7 @@ public static Map<String, InetAddress> parse(Reader reader) throws IOException {
 
                 // split
                 List<String> lineParts = new ArrayList<String>();
-                for (String s: line.split("[ \t]+")) {
+                for (String s: WHITESPACES.split(line)) {
                     if (!s.isEmpty()) {
                         lineParts.add(s);
                     }
@@ -145,21 +148,23 @@ public static Map<String, InetAddress> parse(Reader reader) throws IOException {
                     continue;
                 }
 
-                InetAddress inetAddress = InetAddress.getByAddress(ipBytes);
-
                 // loop over hostname and aliases
                 for (int i = 1; i < lineParts.size(); i ++) {
                     String hostname = lineParts.get(i);
                     if (!entries.containsKey(hostname)) {
                         // trying to map a host to multiple IPs is wrong
                         // only the first entry is honored
-                        entries.put(hostname, inetAddress);
+                        entries.put(hostname, InetAddress.getByAddress(hostname, ipBytes));
                     }
                 }
             }
             return entries;
         } finally {
-            buff.close();
+            try {
+                buff.close();
+            } catch (IOException e) {
+                logger.warn("Failed to close a reader", e);
+            }
         }
     }