Merge branch '4.0'

Also slightly improve OfflineMessageManager.getMessages()

Conflicts:
	build.gradle
	smack-extensions/src/main/java/org/jivesoftware/smackx/offline/OfflineMessageManager.java

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

@@ -20,6 +20,7 @@ package org.jivesoftware.smack;
 import org.jivesoftware.smack.packet.Session;
 import org.jivesoftware.smack.proxy.ProxyInfo;
 import org.jivesoftware.smack.util.DNSUtil;
+import org.jivesoftware.smack.util.StringUtils;
 import org.jivesoftware.smack.util.dns.HostAddress;
 import org.jxmpp.util.XmppStringUtils;
 
@@ -191,6 +192,9 @@ public class ConnectionConfiguration implements Cloneable {
     }
 
     protected void init(String serviceName, ProxyInfo proxy) {
+        if (StringUtils.isEmpty(serviceName)) {
+            throw new IllegalArgumentException("serviceName must not be the empty String");
+        }
         this.serviceName = serviceName;
         this.proxy = proxy;
 
@@ -645,6 +649,9 @@ public class ConnectionConfiguration implements Cloneable {
     }
 
     private void initHostAddresses(String host, int port) {
+        if (StringUtils.isEmpty(host)) {
+            throw new IllegalArgumentException("host must not be the empty String");
+        }
         hostAddresses = new ArrayList<HostAddress>(1);
         HostAddress hostAddress;
         hostAddress = new HostAddress(host, port);

smack-core/src/main/java/org/jivesoftware/smack/compression/Java7ZlibInputOutputStream.java

@@ -48,6 +48,9 @@ public class Java7ZlibInputOutputStream extends XMPPInputOutputStream {
     private final static boolean supported;
     private final static int compressionLevel = Deflater.DEFAULT_COMPRESSION;
 
+    private static final int SYNC_FLUSH_INT = 2;
+    private static final int FULL_FLUSH_INT = 3;
+
     static {
         Method m = null;
         try {
@@ -100,25 +103,23 @@ public class Java7ZlibInputOutputStream extends XMPPInputOutputStream {
 
     @Override
     public OutputStream getOutputStream(OutputStream outputStream) {
+        final int flushMethodInt;
+        if (flushMethod == FlushMethod.SYNC_FLUSH) {
+            flushMethodInt = SYNC_FLUSH_INT;
+        } else {
+            flushMethodInt = FULL_FLUSH_INT;
+        }
         return new DeflaterOutputStream(outputStream, new Deflater(compressionLevel)) {
             public void flush() throws IOException {
                 if (!supported) {
                     super.flush();
                     return;
                 }
-                int count = 0;
-                if (!def.needsInput()) {
-                    do {
-                        count = def.deflate(buf, 0, buf.length);
-                        out.write(buf, 0, count);
-                    } while (count > 0);
-                    out.flush();
-                }
                 try {
-                    do {
-                        count = (Integer) method.invoke(def, buf, 0, buf.length, 2);
+                    int count;
+                    while ((count = (Integer) method.invoke(def, buf, 0, buf.length, flushMethodInt)) != 0) {
                         out.write(buf, 0, count);
-                    } while (count > 0);
+                    }
                 } catch (IllegalArgumentException e) {
                     throw new IOException("Can't flush");
                 } catch (IllegalAccessException e) {

smack-core/src/main/java/org/jivesoftware/smack/compression/XMPPInputOutputStream.java

@@ -20,6 +20,21 @@ import java.io.InputStream;
 import java.io.OutputStream;
 
 public abstract class XMPPInputOutputStream {
+
+    protected static FlushMethod flushMethod;
+
+    /**
+     * Set the used flushed method when compressing data. The default is full flush which may not
+     * achieve the best compression ratio, but provides better security against certain attacks.
+     * Only use sync flush if you fully understand the implications.
+     * 
+     * @see <a href="https://blog.thijsalkema.de/blog/2014/08/07/https-attacks-and-xmpp-2-crime-and-breach/">Attacks against XMPP when using compression</a>
+     * @param flushMethod
+     */
+    public static void setFlushMethod(FlushMethod flushMethod) {
+        XMPPInputOutputStream.flushMethod = flushMethod;
+    }
+
     protected String compressionMethod;
 
     public String getCompressionMethod() {
@@ -31,4 +46,9 @@ public abstract class XMPPInputOutputStream {
     public abstract InputStream getInputStream(InputStream inputStream) throws Exception;
 
     public abstract OutputStream getOutputStream(OutputStream outputStream) throws Exception;
+
+    public enum FlushMethod {
+        FULL_FLUSH,
+        SYNC_FLUSH,
+    }
 }

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

@@ -279,13 +279,23 @@ public class StringUtils {
     }
 
     /**
-     * Returns true if the given CharSequence is not null or empty.
+     * Returns true if the given CharSequence is null or empty.
      *
      * @param cs
-     * @return true if the given CharSequence is not null or empty
+     * @return true if the given CharSequence is null or empty
      */
     public static boolean isNullOrEmpty(CharSequence cs) {
-        return cs == null || cs.length() == 0;
+        return cs == null || isEmpty(cs);
+    }
+
+    /**
+     * Returns true if the given CharSequence is empty
+     * 
+     * @param cs
+     * @return true if the given CharSequence is empty
+     */
+    public static boolean isEmpty(CharSequence cs) {
+        return cs.length() == 0;
     }
 
     public static String collectionToString(Collection<String> collection) {