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fw-daemon/dns.go

69 lines
1.4 KiB

package main
import (
"net"
"strings"
"sync"
"github.com/subgraph/fw-daemon/nfqueue"
)
type dnsCache struct {
ipMap map[string]string
lock sync.Mutex
done chan struct{}
}
func NewDnsCache() *dnsCache {
return &dnsCache{
ipMap: make(map[string]string),
done: make(chan struct{}),
}
}
func (dc *dnsCache) processDNS(pkt *nfqueue.Packet) {
dns := &dnsMsg{}
if !dns.Unpack(pkt.Payload) {
log.Warning("Failed to Unpack DNS message")
return
}
if !dns.response {
return
}
if len(dns.question) != 1 {
log.Warning("Length of DNS Question section is not 1 as expected: %d", len(dns.question))
return
}
q := dns.question[0]
if q.Qtype == dnsTypeA {
dc.processRecordA(q.Name, dns.answer)
return
}
log.Info("Unhandled DNS message: %v", dns)
}
func (dc *dnsCache) processRecordA(name string, answers []dnsRR) {
dc.lock.Lock()
defer dc.lock.Unlock()
for _, rr := range answers {
switch rec := rr.(type) {
case *dnsRR_A:
ip := net.IPv4(byte(rec.A>>24), byte(rec.A>>16), byte(rec.A>>8), byte(rec.A)).String()
if strings.HasSuffix(name, ".") {
name = name[:len(name)-1]
}
dc.ipMap[ip] = name
log.Info("Adding %s: %s", name, ip)
default:
log.Warning("Unexpected RR type in answer section of A response: %v", rec)
}
}
}
func (dc *dnsCache) Lookup(ip net.IP) string {
dc.lock.Lock()
defer dc.lock.Unlock()
return dc.ipMap[ip.String()]
}