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dnsproxy.go
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dnsproxy.go
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// Package dnsproxy is responsible for the DNS proxy server that will redirect
// specified domains to the SNI proxy.
package dnsproxy
import (
"fmt"
"io"
"net"
"strings"
"github.com/AdguardTeam/dnsproxy/proxy"
"github.com/AdguardTeam/golibs/log"
"github.com/ameshkov/sniproxy/internal/filter"
"github.com/miekg/dns"
)
// defaultTTL is the default TTL for the rewritten records.
const defaultTTL = 60
// DNSProxy is a struct that manages the DNS proxy server. This server's
// purpose is to redirect queries to a specified SNI proxy.
type DNSProxy struct {
proxy *proxy.Proxy
redirectRules []string
redirectIPv4To net.IP
redirectIPv6To net.IP
dropRules []string
}
// type check
var _ io.Closer = (*DNSProxy)(nil)
// New creates a new instance of *DNSProxy.
func New(cfg *Config) (d *DNSProxy, err error) {
proxyConfig, err := createProxyConfig(cfg)
if err != nil {
return nil, fmt.Errorf("dnsproxy: invalid configuration: %w", err)
}
d = &DNSProxy{
redirectRules: cfg.RedirectRules,
redirectIPv4To: cfg.RedirectIPv4To,
redirectIPv6To: cfg.RedirectIPv6To,
dropRules: cfg.DropRules,
}
d.proxy = &proxy.Proxy{
Config: proxyConfig,
}
d.proxy.RequestHandler = d.requestHandler
return d, nil
}
// Start starts the DNSProxy server.
func (d *DNSProxy) Start() (err error) {
log.Info("dnsproxy: starting")
err = d.proxy.Start()
log.Info("dnsproxy: started successfully")
return err
}
// Close implements the [io.Closer] interface for DNSProxy.
func (d *DNSProxy) Close() (err error) {
log.Info("dnsproxy: stopping")
err = d.proxy.Stop()
log.Info("dnsproxy: stopped")
return err
}
// requestHandler is a [proxy.RequestHandler] implementation which purpose is
// to implement the actual redirection logic.
func (d *DNSProxy) requestHandler(p *proxy.Proxy, ctx *proxy.DNSContext) (err error) {
qName := strings.ToLower(ctx.Req.Question[0].Name)
qType := ctx.Req.Question[0].Qtype
log.Debug("dnsproxy: received DNS query %s %s", dns.Type(qType), qName)
if qType != dns.TypeA && qType != dns.TypeAAAA {
// Doing nothing with the request if it's not A/AAAA, we cannot
// rewrite them anyway.
return nil
}
domainName := strings.TrimSuffix(qName, ".")
if filter.MatchWildcards(domainName, d.dropRules) {
// Return empty response, effectively "dropping" the query.
ctx.Res = nil
log.Info("dnsproxy: dropping DNS query for %s %s", dns.Type(qType), qName)
return nil
}
if filter.MatchWildcards(domainName, d.redirectRules) {
d.rewrite(qName, qType, ctx)
return nil
}
return p.Resolve(ctx)
}
// rewrite rewrites the specified query and redirects the response to the
// configured IP addresses.
func (d *DNSProxy) rewrite(qName string, qType uint16, ctx *proxy.DNSContext) {
resp := &dns.Msg{}
resp.SetReply(ctx.Req)
log.Info("dnsproxy: rewriting DNS for %s %s", dns.Type(qType), qName)
hdr := dns.RR_Header{
Name: qName,
Rrtype: qType,
Class: dns.ClassINET,
Ttl: defaultTTL,
}
switch {
case qType == dns.TypeA && d.redirectIPv4To != nil:
resp.Answer = append(resp.Answer, &dns.A{
Hdr: hdr,
A: d.redirectIPv4To,
})
case qType == dns.TypeAAAA && d.redirectIPv6To != nil:
resp.Answer = append(resp.Answer, &dns.AAAA{
Hdr: hdr,
AAAA: d.redirectIPv6To,
})
}
ctx.Res = resp
}
// createProxyConfig creates DNS proxy configuration.
func createProxyConfig(cfg *Config) (proxyConfig proxy.Config, err error) {
upstreamCfg, err := proxy.ParseUpstreamsConfig([]string{cfg.Upstream}, nil)
if err != nil {
return proxyConfig, fmt.Errorf("failed to parse upstream %s: %w", cfg.Upstream, err)
}
ip := net.IP(cfg.ListenAddr.Addr().AsSlice())
udpPort := &net.UDPAddr{
IP: ip,
Port: int(cfg.ListenAddr.Port()),
}
tcpPort := &net.TCPAddr{
IP: ip,
Port: int(cfg.ListenAddr.Port()),
}
proxyConfig.UDPListenAddr = []*net.UDPAddr{udpPort}
proxyConfig.TCPListenAddr = []*net.TCPAddr{tcpPort}
proxyConfig.UpstreamConfig = upstreamCfg
return proxyConfig, nil
}