Make SASLMechanism.getAuthenticationText() return byte[]

every SASL Mechanism is designed as a byte array based protocol. XMPP
adds the constraint that the challenges and responses are send base64
encoded. It's therefore better API design to let getAuthenticationText()
return byte[] instead of String.

smack-core/src/main/java/org/jivesoftware/smack/sasl/SASLAnonymous.java

@@ -27,8 +27,10 @@ import javax.security.auth.callback.CallbackHandler;
  */
 public class SASLAnonymous extends SASLMechanism {
 
+    public static final String NAME = "ANONYMOUS";
+
     public String getName() {
-        return "ANONYMOUS";
+        return NAME;
     }
 
     @Override
@@ -43,8 +45,8 @@ public class SASLAnonymous extends SASLMechanism {
     }
 
     @Override
-    protected String getAuthenticationText() throws SmackException {
-        // TODO Auto-generated method stub
+    protected byte[] getAuthenticationText() throws SmackException {
+        // ANONYMOUS has no initial response, return null
         return null;
     }
 

smack-core/src/main/java/org/jivesoftware/smack/sasl/SASLMechanism.java

@@ -169,12 +169,28 @@ public abstract class SASLMechanism implements Comparable<SASLMechanism> {
     protected abstract void authenticateInternal(CallbackHandler cbh) throws SmackException;
 
     private final void authenticate() throws SmackException, NotConnectedException {
-        String authenticationText = getAuthenticationText();
+        byte[] authenticationBytes = getAuthenticationText();
+        String authenticationText;
+        if (authenticationBytes != null) {
+            authenticationText = StringUtils.encodeBase64(authenticationBytes);
+        } else {
+            // RFC6120 6.4.2 "If the initiating entity needs to send a zero-length initial response,
+            // it MUST transmit the response as a single equals sign character ("="), which
+            // indicates that the response is present but contains no data."
+            authenticationText = "=";
+        }
         // Send the authentication to the server
         connection.sendPacket(new AuthMechanism(getName(), authenticationText));
     }
 
-    protected abstract String getAuthenticationText() throws SmackException;
+    /**
+     * Should return the initial response of the SASL mechanism. The returned byte array will be
+     * send base64 encoded to the server. SASL mechanism are free to return <code>null</code> here.
+     * 
+     * @return the initial response or null
+     * @throws SmackException
+     */
+    protected abstract byte[] getAuthenticationText() throws SmackException;
 
     /**
      * The server is challenging the SASL mechanism for the stanza he just sent. Send a

smack-core/src/main/java/org/jivesoftware/smack/sasl/packet/SaslStanzas.java

@@ -37,8 +37,11 @@ public class SaslStanzas {
             if (mechanism == null) {
                 throw new NullPointerException("SASL mechanism shouldn't be null.");
             }
+            if (StringUtils.isNullOrEmpty(authenticationText)) {
+                throw new IllegalArgumentException("SASL authenticationText must not be null or empty (RFC6120 6.4.2)");
+            }
             this.mechanism = mechanism;
-            this.authenticationText = StringUtils.returnIfNotEmptyTrimmed(authenticationText);
+            this.authenticationText = authenticationText;
         }
 
         @Override

smack-sasl-javax/src/main/java/org/jivesoftware/smack/sasl/javax/SASLJavaXMechanism.java

@@ -33,7 +33,6 @@ import javax.security.sasl.SaslException;
 
 import org.jivesoftware.smack.SmackException;
 import org.jivesoftware.smack.sasl.SASLMechanism;
-import org.jivesoftware.smack.util.StringUtils;
 
 public abstract class SASLJavaXMechanism extends SASLMechanism {
 
@@ -107,19 +106,17 @@ public abstract class SASLJavaXMechanism extends SASLMechanism {
         }
     }
 
-    protected String getAuthenticationText() throws SmackException {
-        String authenticationText = null;
+    @Override
+    protected byte[] getAuthenticationText() throws SmackException {
         if (sc.hasInitialResponse()) {
-            byte[] response;
             try {
-                response = sc.evaluateChallenge(new byte[0]);
+                return sc.evaluateChallenge(new byte[0]);
             }
             catch (SaslException e) {
                 throw new SmackException(e);
             }
-            authenticationText = StringUtils.encodeBase64(response, false);
         }
-        return authenticationText;
+        return null;
     }
 
     @Override

smack-sasl-provided/src/main/java/org/jivesoftware/smack/sasl/provided/SASLDigestMD5Mechanism.java

@@ -62,7 +62,7 @@ public class SASLDigestMD5Mechanism extends SASLMechanism {
     }
 
     @Override
-    protected String getAuthenticationText() throws SmackException {
+    protected byte[] getAuthenticationText() throws SmackException {
         // DIGEST-MD5 has no initial response, return null
         return null;
     }