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package resolver
import (
"fmt"
"math/rand"
"net"
"time"
"linum/internal/cache"
"linum/internal/dns"
)
const (
maxDelegations = 30
maxCNAME = 10
maxDepth = 20
queryTimeout = 2 * time.Second
)
type Recursive struct {
hints []NS
cache *cache.Cache
}
func NewRecursive(hintsPath string) (*Recursive, error) {
hints, err := LoadHints(hintsPath)
if err != nil {
return nil, fmt.Errorf("load hints: %w", err)
}
return &Recursive{
hints: hints,
cache: cache.New(),
}, nil
}
func (r *Recursive) Resolve(query *dns.Msg) (*dns.Msg, error) {
if len(query.Question) == 0 {
return nil, fmt.Errorf("no question")
}
q := query.Question[0]
resp, err := r.resolve(q.Name, q.Type, q.Class, query.Header.ID, 0)
if err != nil {
return nil, err
}
resp.Header.SetQR(true)
resp.Header.SetRA(true)
return resp, nil
}
func (r *Recursive) resolve(qname dns.Name, qtype, qclass uint16, id uint16, depth int) (*dns.Msg, error) {
if depth > maxDepth {
return nil, fmt.Errorf("max depth exceeded")
}
if cached, ok := r.cache.Get(qname, qtype, qclass); ok {
resp := *cached
resp.Header.ID = id
return &resp, nil
}
resp, err := r.followDelegations(qname, qtype, qclass, id, depth)
if err != nil {
return nil, err
}
if resp.Header.Rcode() == dns.RcodeNoError || resp.Header.Rcode() == dns.RcodeNxDomain {
ttl := minTTL(resp)
r.cache.Set(qname, qtype, qclass, resp, ttl)
}
if resp.Header.Rcode() == dns.RcodeNoError && len(resp.Answer) > 0 {
for _, rr := range resp.Answer {
if rr.Type == dns.TypeCNAME {
if cname, ok := rr.Data.(*dns.CNAME); ok {
targetResp, err := r.resolve(cname.Cname, qtype, qclass, id, depth+1)
if err != nil {
return resp, nil
}
merged := *resp
merged.Answer = append(merged.Answer, targetResp.Answer...)
return &merged, nil
}
}
}
}
return resp, nil
}
func (r *Recursive) followDelegations(qname dns.Name, qtype, qclass, id uint16, depth int) (*dns.Msg, error) {
nsList := make([]NS, len(r.hints))
copy(nsList, r.hints)
rand.Shuffle(len(nsList), func(i, j int) {
nsList[i], nsList[j] = nsList[j], nsList[i]
})
for delegations := 0; delegations < maxDelegations; delegations++ {
resp, err := r.queryNSList(nsList, qname, qtype, qclass, id, depth)
if err != nil {
return nil, err
}
if len(resp.Answer) > 0 {
return resp, nil
}
if resp.Header.Rcode() == dns.RcodeNxDomain {
return resp, nil
}
if len(resp.Ns) > 0 {
newNS := extractDelegation(resp)
if len(newNS) > 0 {
nsList = newNS
rand.Shuffle(len(nsList), func(i, j int) {
nsList[i], nsList[j] = nsList[j], nsList[i]
})
continue
}
}
return resp, nil
}
return nil, fmt.Errorf("max delegations exceeded")
}
func (r *Recursive) queryNSList(nsList []NS, qname dns.Name, qtype, qclass, id uint16, depth int) (*dns.Msg, error) {
var lastErr error
for _, ns := range nsList {
addr := ns.Addr
if addr == "" {
nsName, err := dns.NewName(ns.Name)
if err != nil {
lastErr = err
continue
}
ip, err := r.resolveNS(nsName, id, depth)
if err != nil {
lastErr = err
continue
}
addr = ip
}
resp, err := r.query(addr, qname, qtype, qclass, id)
if err != nil {
lastErr = err
continue
}
return resp, nil
}
return nil, fmt.Errorf("all NS failed: %w", lastErr)
}
func (r *Recursive) query(server string, qname dns.Name, qtype, qclass, id uint16) (*dns.Msg, error) {
q := &dns.Msg{
Header: dns.Header{ID: id},
Question: []dns.Question{{Name: qname, Type: qtype, Class: qclass}},
}
wire, err := dns.Pack(q)
if err != nil {
return nil, err
}
conn, err := net.DialTimeout("udp", net.JoinHostPort(server, "53"), queryTimeout)
if err != nil {
return nil, err
}
defer conn.Close()
conn.SetDeadline(time.Now().Add(queryTimeout))
if _, err := conn.Write(wire); err != nil {
return nil, err
}
buf := make([]byte, 4096)
n, err := conn.Read(buf)
if err != nil {
return nil, err
}
return dns.Unpack(buf[:n])
}
func (r *Recursive) resolveNS(name dns.Name, id uint16, depth int) (string, error) {
resp, err := r.resolve(name, dns.TypeA, dns.ClassIN, id, depth+1)
if err != nil {
return "", err
}
for _, rr := range resp.Answer {
if a, ok := rr.Data.(*dns.A); ok {
return a.Addr.String(), nil
}
}
return "", fmt.Errorf("no A record for %s", name.String())
}
func extractDelegation(resp *dns.Msg) []NS {
var nsList []NS
glue := make(map[string]string)
for _, rr := range resp.Extra {
if rr.Type == dns.TypeA {
if a, ok := rr.Data.(*dns.A); ok {
glue[rr.Name.String()] = a.Addr.String()
}
}
}
for _, rr := range resp.Ns {
if rr.Type == dns.TypeNS {
if ns, ok := rr.Data.(*dns.NS); ok {
nsList = append(nsList, NS{
Name: ns.Ns.String(),
Addr: glue[ns.Ns.String()],
})
}
}
}
return nsList
}
func minTTL(resp *dns.Msg) uint32 {
min := uint32(300)
for _, rr := range resp.Answer {
if rr.TTL < min {
min = rr.TTL
}
}
for _, rr := range resp.Ns {
if rr.TTL < min {
min = rr.TTL
}
}
return min
}
|
