Enable -Werror and add XmppHostnameVerifier

We now treat warnings as errors (-Werror).

In order to do so, it was necessary to remove Java7HostnameVerifier
since it depended on internal properietary API. XmppHostnameVerifier
take the place of it.

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

@@ -0,0 +1,59 @@
+/**
+ *
+ * Copyright 2015 Florian Schmaus
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.jivesoftware.smack.util;
+
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class IpAddressUtil {
+
+    private static final Pattern IPV4_PATTERN = Pattern.compile("^(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})\\.(\\d{1,3})$");
+
+    public static boolean isIPv4LiteralAddress(String string) {
+        Matcher matcher = IPV4_PATTERN.matcher(string);
+        if (!matcher.matches()) {
+            return false;
+        }
+
+        for (int i = 0; i < 3; i++) {
+            String ipSegment = matcher.group(i);
+            int ipSegmentInt;
+            try {
+                ipSegmentInt = Integer.valueOf(ipSegment);
+            } catch (NumberFormatException e) {
+                throw new AssertionError(e);
+            }
+            if (ipSegmentInt > 255) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    public static boolean isIPv6LiteralAddress(final String string) {
+        final String[] octets = string.split(":");
+        if (octets.length != 8) {
+            return false;
+        }
+        // TODO handle compressed zeros and validate octets
+        return true;
+    }
+
+    public static boolean isIpAddress(String string) {
+        return isIPv4LiteralAddress(string) || isIPv6LiteralAddress(string);
+    }
+}