Disable MucMemoryLeakTest

Although it it not that unreliable, it causes false negatives once in
a while. This is because the standard Java SE API does not provide a
way to force a *full* garbage collection run, we need to resort to
unreliable hacks to trigger one.

The test itself is still useful to diagnose or refute alleged memory
leaks.

This commit also move the test from JUnit 4 to Junit 5.

smack-core/src/main/java/org/jivesoftware/smack/AbstractXMPPConnection.java

@@ -2012,7 +2012,7 @@ public abstract class AbstractXMPPConnection implements XMPPConnection {
             from = XmppStringUtils.completeJidFrom(localpart, to);
         }
         String id = getStreamId();
-        sendNonza(new StreamOpen(to, from, id));
+        sendNonza(new StreamOpen(to, from, id, config.getXmlLang(), StreamOpen.StreamContentNamespace.client));
     }
 
     public static final class SmackTlsContext {

smack-core/src/main/java/org/jivesoftware/smack/ConnectionConfiguration.java

@@ -24,6 +24,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.Set;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -118,6 +119,8 @@ public abstract class ConnectionConfiguration {
     private final String password;
     private final Resourcepart resource;
 
+    private final Locale language;
+
     /**
      * The optional SASL authorization identity (see RFC 6120 § 6.3.8).
      */
@@ -165,6 +168,8 @@ public abstract class ConnectionConfiguration {
         // Resource can be null, this means that the server must provide one
         resource = builder.resource;
 
+        language = builder.language;
+
         xmppServiceDomain = builder.xmppServiceDomain;
         if (xmppServiceDomain == null) {
             throw new IllegalArgumentException("Must define the XMPP domain");
@@ -476,6 +481,34 @@ public abstract class ConnectionConfiguration {
         return resource;
     }
 
+    /**
+     * Returns the stream language to use when connecting to the server.
+     *
+     * @return the stream language to use when connecting to the server.
+     */
+    public Locale getLanguage() {
+        return language;
+    }
+
+    /**
+     * Returns the xml:lang string of the stream language to use when connecting to the server.
+     *
+     * <p>If the developer sets the language to null, this will also return null, leading to
+     * the removal of the xml:lang tag from the stream. If a Locale("") is configured, this will
+     * return "", which can be used as an override.</p>
+     *
+     * @return the stream language to use when connecting to the server.
+     */
+    public String getXmlLang() {
+        // TODO: Change to Locale.toLanguageTag() once Smack's minimum Android API level is 21 or higher.
+        // This will need a workaround for new Locale("").getLanguageTag() returning "und". Expected
+        // behavior of this function:
+        //  - returns null if language is null
+        //  - returns "" if language.getLanguage() returns the empty string
+        //  - returns language.toLanguageTag() otherwise
+        return language != null ? language.toString().replace("_", "-") : null;
+    }
+
     /**
      * Returns the optional XMPP address to be requested as the SASL authorization identity.
      *
@@ -564,6 +597,7 @@ public abstract class ConnectionConfiguration {
         private CharSequence username;
         private String password;
         private Resourcepart resource;
+        private Locale language = Locale.getDefault();
         private boolean sendPresence = true;
         private ProxyInfo proxy;
         private CallbackHandler callbackHandler;
@@ -688,6 +722,19 @@ public abstract class ConnectionConfiguration {
             return getThis();
         }
 
+        /**
+         * Set the stream language.
+         *
+         * @param language the language to use.
+         * @return a reference to this builder.
+         * @see <a href="https://tools.ietf.org/html/rfc6120#section-4.7.4">RFC 6120 § 4.7.4</a>
+         * @see <a href="https://www.w3.org/TR/xml/#sec-lang-tag">XML 1.0 § 2.12 Language Identification</a>
+         */
+        public B setLanguage(Locale language) {
+            this.language = language;
+            return getThis();
+        }
+
         /**
          * Set the resource we are requesting from the server.
          *

smack-core/src/main/java/org/jivesoftware/smack/util/XmlStringBuilder.java

@@ -112,7 +112,7 @@ public class XmlStringBuilder implements Appendable, CharSequence, Element {
 
     public XmlStringBuilder element(String name, Enum<?> content) {
         assert content != null;
-        element(name, content.name());
+        element(name, content.toString());
         return this;
     }
 

smack-extensions/src/test/java/org/jivesoftware/smackx/muc/MucMemoryLeakTest.java

@@ -19,12 +19,14 @@ package org.jivesoftware.smackx.muc;
 import org.jivesoftware.smack.test.util.SmackTestSuite;
 import org.jivesoftware.smack.util.MemoryLeakTestUtil;
 
-import org.junit.Test;
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.Test;
 import org.jxmpp.stringprep.XmppStringprepException;
 
 public class MucMemoryLeakTest extends SmackTestSuite {
 
     @Test
+    @Disabled
     public void mucMemoryLeakTest() throws XmppStringprepException, IllegalArgumentException, InterruptedException {
         MemoryLeakTestUtil.noResourceLeakTest(c -> MultiUserChatManager.getInstanceFor(c));
     }