add isSocketAddressEmpty

java/jni/ZT_jniutils.cpp

@@ -531,3 +531,28 @@ jbyteArray newByteArray(JNIEnv *env, size_t count) {
 
     return byteArrayObj;
 }
+
+bool isSocketAddressEmpty(const sockaddr_storage addr) {
+
+    //
+    // was:
+    // struct sockaddr_storage nullAddress = {0};
+    //
+    // but was getting this warning:
+    // warning: suggest braces around initialization of subobject
+    //
+    // when building ZeroTierOne
+    //
+    sockaddr_storage emptyAddress; //NOLINT
+
+    //
+    // It is possible to assume knowledge about internals of sockaddr_storage and construct
+    // correct 0-initializer, but it is simpler to just treat sockaddr_storage as opaque and
+    // use memset here to fill with 0
+    //
+    // This is also done in InetAddress.hpp for InetAddress
+    //
+    memset(&emptyAddress, 0, sizeof(sockaddr_storage));
+
+    return (memcmp(&addr, &emptyAddress, sizeof(sockaddr_storage)) == 0); //NOLINT
+}

java/jni/ZT_jniutils.h

@@ -160,4 +160,6 @@ jbyteArray newByteArray(JNIEnv *env, const unsigned char *bytes, size_t count);
 
 jbyteArray newByteArray(JNIEnv *env, size_t count);
 
+bool isSocketAddressEmpty(const sockaddr_storage addr);
+
 #endif // ZT_jniutils_h_