implementation of DNS relay
functions:
- forwarding
- blocking
- cache
first the program reads a list of cache urls from file url ip-address
when comes a request, it will check whether the requested url is in cache
- if so it will check whether the ip-address is
0.0.0.0- if so, the request will be block
- else return the cached ip-address
- otherwise, it will forward the request to remote server
8.8.8.8(default)
(optional)
--remoteDNS (ip address of remote DNS)
--dnsListPath (path of cache file format needed (plz see dns-local.txt)