[NETWORKCONTROL] Also cope with DNS files that have a size of 0.. (#833)

If the /etc/resolve.conf file (typeically the DNS file) does not exist or is empty, in debug, an
ASSERT fires in the DateElement since one triees to access an empty buffer.
While fixing this also found that there is already a Search for pattern method in the DataElement, so
start using it. Prune where you can prune ;-)

NetworkControl/NetworkControlImplementation.cpp

@@ -1315,66 +1315,40 @@ namespace Plugin
             if (file.IsValid() == false) {
                 SYSLOG(Logging::Notification, (_T("DNS functionality could NOT be updated [%s]"), _dnsFile.c_str()));
             } else {
-                string data((_T("#++SECTION: ")) + _service->Callsign() + '\n');
+                uint32_t offset = file.Size();
+		string startMarker((_T("#++SECTION: ")) + _service->Callsign() + '\n');
                 string endMarker((_T("#--SECTION: ")) + _service->Callsign() + '\n');
-                uint16_t start = 0;
-                uint16_t end = 0;
-                uint16_t offset = 1;
-                uint8_t index = 0;
-
-                do {
-                    index += offset - 1;
-                    offset = 0;
-
-                    // Find the first comparible character && check the remainder in the next step...
-                    while ((index < file.Size()) && (file[index] != data[offset])) {
-                        index++;
-                    }
-                    while ((index < file.Size()) && (offset < data.length()) && (file[index] == data[offset])) {
-                        index++;
-                        offset++;
-                    }
 
-                } while ((index < file.Size()) && (offset != data.length()));
+                if (offset > 0) {
+                    uint32_t start = static_cast<uint32_t>(file.Search(0, reinterpret_cast<const uint8_t*>(startMarker.c_str()), startMarker.length()));
 
-                start = index - offset;
-                offset = 1;
+                    if (start < file.Size()) {
+                        // We found a start marker, see if we have an end marker.
+                        uint32_t end = static_cast<uint32_t>(file.Search(start + startMarker.length(), reinterpret_cast<const uint8_t*>(endMarker.c_str()), endMarker.length()));
 
-                do {
-                    index += offset - 1;
-                    offset = 0;
+                        if (end < file.Size()) {
+                            end += endMarker.length();
+                            offset -= (end - start);
 
-                    // Find the first comparible character && check the remainder in the next step...
-                    while ((index < file.Size()) && (file[index] != endMarker[offset])) {
-                        index++;
-                    }
-                    while ((index < file.Size()) && (offset < endMarker.length()) && (file[index] == endMarker[offset])) {
-                        index++;
-                        offset++;
+                            if (offset > start) {
+                                // We found the beginning and the end of the section in this file, Wipe it.
+                                // move everything after de marker, over the marker sections.
+                                ::memcpy(&(file[start]), &file[end], static_cast<uint32_t>(file.Size()) - end);
+                            }
+                        }
                     }
-
-                } while ((index < file.Size()) && (offset != endMarker.length()));
-
-                end = ((index != 0) && (index == file.Size())) ? index - 1 : index;
-                uint16_t reduction = end - start;
-
-                if ((reduction != 0) && ((file.Size() - end) != 0)) {
-                    // move everything after de marker, over the marker sections.
-                    ::memcpy(&(file[start]), &file[end], static_cast<uint16_t>(file.Size()) - end);
                 }
 
-                offset = (static_cast<uint16_t>(file.Size()) - reduction);
-
                 NameServers servers;
                 DNS(servers);
 
                 for (const Core::NodeId& entry : servers) {
-                    data += string("nameserver ") + entry.HostAddress() + '\n';
+                    startMarker += string("nameserver ") + entry.HostAddress() + '\n';
                 }
 
-                data += endMarker;
-                file.Size(offset + data.length());
-                ::memcpy(&(file[offset]), data.c_str(), data.length());
+                startMarker += endMarker;
+                file.Size(offset + startMarker.length());
+                ::memcpy(&(file[offset]), startMarker.c_str(), startMarker.length());
                 file.Sync();
 
                 SYSLOG(Logging::Startup, (_T("DNS functionality updated [%s]"), _dnsFile.c_str()));