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svcbmsg.go
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svcbmsg.go
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package dnsforward
import (
"encoding/base64"
"net"
"strconv"
"github.com/AdguardTeam/golibs/log"
"github.com/AdguardTeam/urlfilter/rules"
"github.com/miekg/dns"
)
// genAnswerHTTPS returns a properly initialized HTTPS resource record.
//
// See the comment on genAnswerSVCB for a list of current restrictions on
// parameter values.
func (s *Server) genAnswerHTTPS(req *dns.Msg, svcb *rules.DNSSVCB) (ans *dns.HTTPS) {
ans = &dns.HTTPS{
SVCB: *s.genAnswerSVCB(req, svcb),
}
ans.Hdr.Rrtype = dns.TypeHTTPS
return ans
}
// strToSVCBKey is the string-to-svcb-key mapping.
//
// See https://github.com/miekg/dns/blob/23c4faca9d32b0abbb6e179aa1aadc45ac53a916/svcb.go#L27.
//
// TODO(a.garipov): Propose exporting this API or something similar in the
// github.com/miekg/dns module.
var strToSVCBKey = map[string]dns.SVCBKey{
"alpn": dns.SVCB_ALPN,
"echconfig": dns.SVCB_ECHCONFIG,
"ipv4hint": dns.SVCB_IPV4HINT,
"ipv6hint": dns.SVCB_IPV6HINT,
"mandatory": dns.SVCB_MANDATORY,
"no-default-alpn": dns.SVCB_NO_DEFAULT_ALPN,
"port": dns.SVCB_PORT,
}
// svcbKeyHandler is a handler for one SVCB parameter key.
type svcbKeyHandler func(valStr string) (val dns.SVCBKeyValue)
// svcbKeyHandlers are the supported SVCB parameters handlers.
var svcbKeyHandlers = map[string]svcbKeyHandler{
"alpn": func(valStr string) (val dns.SVCBKeyValue) {
return &dns.SVCBAlpn{
Alpn: []string{valStr},
}
},
"echconfig": func(valStr string) (val dns.SVCBKeyValue) {
ech, err := base64.StdEncoding.DecodeString(valStr)
if err != nil {
log.Debug("can't parse svcb/https echconfig: %s; ignoring", err)
return nil
}
return &dns.SVCBECHConfig{
ECH: ech,
}
},
"ipv4hint": func(valStr string) (val dns.SVCBKeyValue) {
ip := net.ParseIP(valStr)
if ip4 := ip.To4(); ip == nil || ip4 == nil {
log.Debug("can't parse svcb/https ipv4 hint %q; ignoring", valStr)
return nil
}
return &dns.SVCBIPv4Hint{
Hint: []net.IP{ip},
}
},
"ipv6hint": func(valStr string) (val dns.SVCBKeyValue) {
ip := net.ParseIP(valStr)
if ip == nil {
log.Debug("can't parse svcb/https ipv6 hint %q; ignoring", valStr)
return nil
}
return &dns.SVCBIPv6Hint{
Hint: []net.IP{ip},
}
},
"mandatory": func(valStr string) (val dns.SVCBKeyValue) {
code, ok := strToSVCBKey[valStr]
if !ok {
log.Debug("unknown svcb/https mandatory key %q, ignoring", valStr)
return nil
}
return &dns.SVCBMandatory{
Code: []dns.SVCBKey{code},
}
},
"no-default-alpn": func(_ string) (val dns.SVCBKeyValue) {
return &dns.SVCBNoDefaultAlpn{}
},
"port": func(valStr string) (val dns.SVCBKeyValue) {
port64, err := strconv.ParseUint(valStr, 10, 16)
if err != nil {
log.Debug("can't parse svcb/https port: %s; ignoring", err)
return nil
}
return &dns.SVCBPort{
Port: uint16(port64),
}
},
}
// genAnswerSVCB returns a properly initialized SVCB resource record.
//
// Currently, there are several restrictions on how the parameters are parsed.
// Firstly, the parsing of non-contiguous values isn't supported. Secondly, the
// parsing of value-lists is not supported either.
//
// ipv4hint=127.0.0.1 // Supported.
// ipv4hint="127.0.0.1" // Unsupported.
// ipv4hint=127.0.0.1,127.0.0.2 // Unsupported.
// ipv4hint="127.0.0.1,127.0.0.2" // Unsupported.
//
// TODO(a.garipov): Support all of these.
func (s *Server) genAnswerSVCB(req *dns.Msg, svcb *rules.DNSSVCB) (ans *dns.SVCB) {
ans = &dns.SVCB{
Hdr: s.hdr(req, dns.TypeSVCB),
Priority: svcb.Priority,
Target: dns.Fqdn(svcb.Target),
}
if len(svcb.Params) == 0 {
return ans
}
values := make([]dns.SVCBKeyValue, 0, len(svcb.Params))
for k, valStr := range svcb.Params {
handler, ok := svcbKeyHandlers[k]
if !ok {
log.Debug("unknown svcb/https key %q, ignoring", k)
continue
}
val := handler(valStr)
if val == nil {
continue
}
values = append(values, val)
}
if len(values) > 0 {
ans.Value = values
}
return ans
}