fix: align ip version preference for the wrapped emulator (#1052)

* fix: align ip version preference for the wrapped  emulator

When the  emulator wrapper is started with -Djava.net.preferIPv6Addresses=true on a machine that defaults to ipv4,
the golang emulator and the java client will pick different ip stacks and not be able to connect. This change will
use java to resolve the localhost's ip address and push it down to the golang emulator

* remove debug

* whitespace

Author: igorbernstein2

google-cloud-bigtable-emulator/src/main/java/com/google/cloud/bigtable/emulator/v2/Emulator.java

@@ -25,10 +25,13 @@
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
+import java.net.InetAddress;
 import java.net.ServerSocket;
 import java.net.Socket;
+import java.net.UnknownHostException;
 import java.nio.file.Path;
 import java.util.Locale;
+import java.util.Optional;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.TimeoutException;
 import java.util.logging.Level;
@@ -98,10 +101,24 @@ public synchronized void start() throws IOException, TimeoutException, Interrupt
     }
     this.port = getAvailablePort();
 
+    // Try to align the localhost address across java & golang emulator
+    // This should fix issues on systems that default to ipv4 but the jvm is started with
+    // -Djava.net.preferIPv6Addresses=true
+    Optional<String> localhostAddress = Optional.empty();
+    try {
+      localhostAddress = Optional.of(InetAddress.getByName(null).getHostAddress());
+    } catch (UnknownHostException e) {
+    }
+
     // Workaround https://bugs.openjdk.java.net/browse/JDK-8068370
     for (int attemptsLeft = 3; process == null; attemptsLeft--) {
       try {
-        process = Runtime.getRuntime().exec(String.format("%s -port %d", executable, port));
+        String cmd = executable.toString();
+        if (localhostAddress.isPresent()) {
+          cmd += String.format(" -host [%s]", localhostAddress.get());
+        }
+        cmd += String.format(" -port %d", port);
+        process = Runtime.getRuntime().exec(cmd);
       } catch (IOException e) {
         if (attemptsLeft > 0) {
           Thread.sleep(1000);