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# Python/Twisted/Redis backed DNS server - resolves from NAME to IP addrs
# fallback to google or any other DNS server to resolv domains not present on Redis
# to set a new domain on redis, just issue a SET domain.tld ip_addr
# run with twistd -ny txredns.tac
# gleicon 2011

from twisted.names import dns, server, client, cache
from twisted.application import service, internet
from twisted.internet import defer
from twisted.python import log
import txredisapi

class RedisResolverBackend(client.Resolver):
    def __init__(self, redis, servers=None):
        self.redis = redis
        client.Resolver.__init__(self, servers=servers)
        self.ttl = 5
        
    @defer.inlineCallbacks
    def _get_ip_addr(self, hostname, timeout):
        ip = yield self.redis.get(hostname)
        log.msg('redis: %s'% ip)
        r = None
        if ip:
            defer.returnValue([(dns.RRHeader(hostname, dns.A, dns.IN, self.ttl, dns.Record_A(ip, self.ttl)),), (), ()])
        else:
            i = yield self._lookup(hostname, dns.IN, dns.A, timeout)
            defer.returnValue(i)
        
    def lookupAddress(self, name, timeout = None):
        return self._get_ip_addr(name, timeout)
       
def create_application():
    rd = txredisapi.lazyRedisConnectionPool()
    redisBackend = RedisResolverBackend(rd, servers=[('8.8.8.8', 53)])

    application = service.Application("txdnsredis")
    srv_collection = service.IServiceCollection(application)

    dnsFactory = server.DNSServerFactory(caches=[cache.CacheResolver()], clients=[redisBackend])

    internet.TCPServer(53, dnsFactory).setServiceParent(srv_collection)
    internet.UDPServer(53, dns.DNSDatagramProtocol(dnsFactory)).setServiceParent(srv_collection)
    return application

# .tac app
application = create_application()