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package server
import (
"codeberg.org/miekg/dns"
"codeberg.org/miekg/dns/rdata"
"context"
"errors"
"io"
"linum/internal/blocklist"
"linum/internal/cache"
"linum/internal/resolver"
"log/slog"
"net"
"net/netip"
"runtime/debug"
"time"
)
func (s *Server) handleQuery(ctx context.Context, w dns.ResponseWriter, req *dns.Msg) {
defer func() {
if r := recover(); r != nil {
slog.Error("panic in query handler", "recover", r, "stack", string(debug.Stack()))
m := new(dns.Msg)
m.Response = true
m.Rcode = dns.RcodeServerFailure
if req != nil {
m.ID = req.ID
m.Question = req.Question
}
io.Copy(w, m)
}
}()
clientIP := parseClientIP(w.RemoteAddr())
if !s.isAllowed(clientIP) {
slog.Warn("query denied by ACL", "client", clientIP)
s.writeRefused(w, req)
return
}
if !s.rateLimit(clientIP.String()) {
slog.Warn("query rate limited", "client", clientIP)
s.writeRefused(w, req)
return
}
if len(req.Question) == 0 {
m := new(dns.Msg)
m.Rcode = dns.RcodeFormatError
m.Response = true
m.ID = req.ID
m.Question = req.Question
io.Copy(w, m)
return
}
q := req.Question[0]
qname := q.Header().Name
qtype := dns.RRToType(q)
qclass := q.Header().Class
if s.blocklist != nil && s.blocklist.IsBlocked(qname) {
resp := s.blockedResponse(req)
resp.ID = req.ID
io.Copy(w, resp)
slog.Info("query served", "qname", qname, "qtype",
dns.TypeToString[qtype], "rcode", dns.RcodeToString[resp.Rcode],
"blocked", true)
return
}
if s.cache != nil {
key := cache.Key{Name: qname, Qtype: qtype, Class: qclass}
if packed, ok := s.cache.Get(key); ok {
packed[0] = byte(req.ID >> 8)
packed[1] = byte(req.ID)
io.Copy(w, &dns.Msg{Data: packed})
slog.Debug("query served", "qname", qname, "qtype",
dns.TypeToString[qtype], "cached", true)
return
}
}
resp, blocked := s.buildResponse(req)
resp.ID = req.ID
resp.Data = nil
if _, err := io.Copy(w, resp); err != nil {
slog.Error("write failed", "err", err, "qname", qname)
return
}
slog.Info("query served", "qname", qname, "qtype", dns.TypeToString[qtype],
"rcode", dns.RcodeToString[resp.Rcode], "blocked", blocked)
}
func (s *Server) buildResponse(req *dns.Msg) (*dns.Msg, bool) {
if len(req.Question) == 0 {
m := new(dns.Msg)
m.Rcode = dns.RcodeFormatError
m.Response = true
m.ID = req.ID
m.Question = req.Question
return m, false
}
q := req.Question[0]
qname := q.Header().Name
qtype := dns.RRToType(q)
qclass := q.Header().Class
ctx, cancel := context.WithTimeout(s.baseCtx, 10*time.Second)
defer cancel()
reply, err := s.resolver.Lookup(ctx, qname, qtype)
if err != nil {
rcode := dns.RcodeServerFailure
if errors.Is(err, resolver.ErrUnsupportedType) {
rcode = dns.RcodeNotImplemented
}
slog.Error("resolution failed",
"err", err,
"qname", qname,
"qtype", dns.TypeToString[qtype],
)
m := new(dns.Msg)
m.Rcode = uint16(rcode)
m.Response = true
m.ID = req.ID
m.Question = req.Question
return m, false
}
reply.ID = req.ID
if s.cache != nil && reply.Rcode != dns.RcodeServerFailure {
key := cache.Key{Name: qname, Qtype: qtype, Class: qclass}
s.cache.Set(key, reply, 0)
}
return reply, false
}
func (s *Server) blockedResponse(req *dns.Msg) *dns.Msg {
m := new(dns.Msg)
m.Response = true
m.ID = req.ID
m.Opcode = req.Opcode
m.RecursionDesired = req.RecursionDesired
m.Question = req.Question
m.Authoritative = true
if s.blocklist.Response() == blocklist.ResponseNXDOMAIN {
m.Rcode = dns.RcodeNameError
return m
}
q := req.Question[0]
qname := q.Header().Name
qtype := dns.RRToType(q)
switch qtype {
case dns.TypeA:
m.Answer = append(m.Answer, &dns.A{
Hdr: dns.Header{Name: qname, Class: dns.ClassINET, TTL: 60},
A: rdata.A{Addr: netip.AddrFrom4([4]byte{})},
})
case dns.TypeAAAA:
m.Answer = append(m.Answer, &dns.AAAA{
Hdr: dns.Header{Name: qname, Class: dns.ClassINET, TTL: 60},
AAAA: rdata.AAAA{Addr: netip.IPv6Unspecified()},
})
}
return m
}
func parseClientIP(addr net.Addr) net.IP {
switch a := addr.(type) {
case *net.UDPAddr:
return a.IP
case *net.TCPAddr:
return a.IP
}
host, _, _ := net.SplitHostPort(addr.String())
return net.ParseIP(host)
}
func parseHTTPClientIP(addr string) net.IP {
host, _, err := net.SplitHostPort(addr)
if err != nil {
return net.ParseIP(addr)
}
return net.ParseIP(host)
}
func (s *Server) isAllowed(ip net.IP) bool {
if ip == nil {
return false
}
if ip4 := ip.To4(); ip4 != nil {
ip = ip4
}
for _, n := range s.aclNets {
if n.Contains(ip) {
return true
}
}
return false
}
func (s *Server) rateLimit(ip string) bool {
if s.rateLimiter == nil {
return true
}
return s.rateLimiter.allow(ip)
}
func (s *Server) writeRefused(w dns.ResponseWriter, req *dns.Msg) {
resp := new(dns.Msg)
resp.Response = true
resp.ID = req.ID
resp.Question = req.Question
resp.Rcode = dns.RcodeRefused
io.Copy(w, resp)
}
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