新增dnst隧道

This commit is contained in:
wenyifan
2026-07-04 13:01:21 +08:00
parent bf85966600
commit 74fef8838e
9 changed files with 906 additions and 0 deletions
+54
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@@ -0,0 +1,54 @@
package dns
import (
"context"
"net"
"time"
"github.com/quic-go/quic-go"
)
type quicSession struct {
session *quic.Conn
}
func (session *quicSession) GetConn() (*quicConn, error) {
ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
defer cancel()
stream, err := session.session.OpenStreamSync(ctx)
if err != nil {
return nil, err
}
return &quicConn{
Stream: stream,
laddr: session.session.LocalAddr(),
raddr: session.session.RemoteAddr(),
}, nil
}
func (session *quicSession) IsClosed() bool {
select {
case <-session.session.Context().Done():
return true
default:
return false
}
}
func (session *quicSession) Close() error {
return session.session.CloseWithError(quic.ApplicationErrorCode(0), "closed")
}
type quicConn struct {
*quic.Stream
laddr net.Addr
raddr net.Addr
}
func (c *quicConn) LocalAddr() net.Addr {
return c.laddr
}
func (c *quicConn) RemoteAddr() net.Addr {
return c.raddr
}
+153
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@@ -0,0 +1,153 @@
package dns
import (
"context"
"crypto/tls"
"errors"
"net"
"sync"
"github.com/go-gost/core/dialer"
"github.com/go-gost/core/logger"
md "github.com/go-gost/core/metadata"
dns_util "github.com/go-gost/x/internal/util/dns"
"github.com/go-gost/x/registry"
"github.com/quic-go/quic-go"
)
func init() {
registry.DialerRegistry().Register("dns", NewDialer)
registry.DialerRegistry().Register("dns-tunnel", NewDialer)
registry.DialerRegistry().Register("dnst", NewDialer)
}
type dnsDialer struct {
sessions map[string]*quicSession
sessionMutex sync.Mutex
logger logger.Logger
md metadata
options dialer.Options
}
func NewDialer(opts ...dialer.Option) dialer.Dialer {
options := dialer.Options{}
for _, opt := range opts {
opt(&options)
}
return &dnsDialer{
sessions: make(map[string]*quicSession),
logger: options.Logger,
options: options,
}
}
func (d *dnsDialer) Init(md md.Metadata) (err error) {
if err = d.parseMetadata(md); err != nil {
return
}
return nil
}
func (d *dnsDialer) Dial(ctx context.Context, addr string, opts ...dialer.DialOption) (conn net.Conn, err error) {
if _, _, err := net.SplitHostPort(addr); err != nil {
addr = net.JoinHostPort(addr, "0")
}
udpAddr, err := net.ResolveUDPAddr("udp", addr)
if err != nil {
return nil, err
}
d.sessionMutex.Lock()
session, ok := d.sessions[addr]
if session != nil && session.IsClosed() {
delete(d.sessions, addr)
ok = false
}
if !ok {
options := &dialer.DialOptions{}
for _, opt := range opts {
opt(options)
}
c, err := options.Dialer.Dial(ctx, "udp", "")
if err != nil {
d.sessionMutex.Unlock()
return nil, err
}
pc, ok := c.(net.PacketConn)
if !ok {
c.Close()
d.sessionMutex.Unlock()
return nil, errors.New("dns: wrong connection type")
}
pc = dns_util.ClientConn(
pc,
dns_util.DomainOption(d.md.domain),
dns_util.UDPSizeOption(d.md.udpSize),
)
session, err = d.initSession(ctx, udpAddr, pc)
if err != nil {
d.logger.Error(err)
pc.Close()
d.sessionMutex.Unlock()
return nil, err
}
d.sessions[addr] = session
}
d.sessionMutex.Unlock()
conn, err = session.GetConn()
if err != nil {
d.sessionMutex.Lock()
if d.sessions[addr] == session {
delete(d.sessions, addr)
}
session.Close()
d.sessionMutex.Unlock()
return nil, err
}
return
}
func (d *dnsDialer) initSession(ctx context.Context, addr net.Addr, conn net.PacketConn) (*quicSession, error) {
quicConfig := &quic.Config{
KeepAlivePeriod: d.md.keepAlivePeriod,
HandshakeIdleTimeout: d.md.handshakeTimeout,
MaxIdleTimeout: d.md.maxIdleTimeout,
Versions: []quic.Version{
quic.Version1,
quic.Version2,
},
MaxIncomingStreams: int64(d.md.maxStreams),
EnableDatagrams: d.md.enableDatagram,
}
tlsCfg := d.options.TLSConfig
if tlsCfg == nil {
tlsCfg = &tls.Config{}
} else {
tlsCfg = tlsCfg.Clone()
}
if len(tlsCfg.NextProtos) == 0 {
tlsCfg.NextProtos = []string{"h3", "quic/v1"}
}
session, err := quic.DialEarly(ctx, conn, addr, tlsCfg, quicConfig)
if err != nil {
return nil, err
}
return &quicSession{session: session}, nil
}
// Multiplex implements dialer.Multiplexer interface.
func (d *dnsDialer) Multiplex() bool {
return true
}
+48
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@@ -0,0 +1,48 @@
package dns
import (
"time"
mdata "github.com/go-gost/core/metadata"
mdutil "github.com/go-gost/x/metadata/util"
)
type metadata struct {
keepAlivePeriod time.Duration
maxIdleTimeout time.Duration
handshakeTimeout time.Duration
maxStreams int
enableDatagram bool
domain string
udpSize int
}
func (d *dnsDialer) parseMetadata(md mdata.Metadata) (err error) {
const (
keepAlive = "keepAlive"
keepAlivePeriod = "ttl"
handshakeTimeout = "handshakeTimeout"
maxIdleTimeout = "maxIdleTimeout"
maxStreams = "maxStreams"
domain = "domain"
udpSize = "udpSize"
)
if md == nil || !md.IsExists(keepAlive) || mdutil.GetBool(md, keepAlive) {
d.md.keepAlivePeriod = mdutil.GetDuration(md, keepAlivePeriod)
if d.md.keepAlivePeriod <= 0 {
d.md.keepAlivePeriod = 10 * time.Second
}
}
d.md.handshakeTimeout = mdutil.GetDuration(md, handshakeTimeout)
d.md.maxIdleTimeout = mdutil.GetDuration(md, maxIdleTimeout)
d.md.maxStreams = mdutil.GetInt(md, maxStreams)
d.md.enableDatagram = mdutil.GetBool(md, "quic.enableDatagram", "enableDatagram")
d.md.domain = mdutil.GetString(md, domain, "dns.domain")
d.md.udpSize = mdutil.GetInt(md, udpSize, "dns.udpSize")
return
}
+284
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@@ -0,0 +1,284 @@
package dns
import (
"errors"
"net"
"sync"
"sync/atomic"
"github.com/go-gost/core/common/bufpool"
mdns "github.com/miekg/dns"
)
const (
defaultDomain = "gost.local."
defaultUDPSize = 4096
readBufferSize = 65535
edns0PayloadOption uint16 = mdns.EDNS0LOCALSTART
)
var (
ErrInvalidPacket = errors.New("dns: invalid packet")
ErrShortBuffer = errors.New("dns: short buffer")
)
type options struct {
domain string
udpSize uint16
}
// Option configures a DNS packet wrapper.
type Option func(*options)
// DomainOption sets the DNS question name used by wrapped packets.
func DomainOption(domain string) Option {
return func(o *options) {
if domain != "" {
o.domain = mdns.Fqdn(domain)
}
}
}
// UDPSizeOption sets the EDNS0 UDP payload size advertised in wrapped packets.
func UDPSizeOption(size int) Option {
return func(o *options) {
if size > 0 && size <= readBufferSize {
o.udpSize = uint16(size)
}
}
}
func parseOptions(opts ...Option) options {
o := options{
domain: defaultDomain,
udpSize: defaultUDPSize,
}
for _, opt := range opts {
opt(&o)
}
return o
}
type clientConn struct {
net.PacketConn
id uint32
options options
}
// ClientConn wraps outbound payloads as DNS queries and unwraps DNS responses.
func ClientConn(conn net.PacketConn, opts ...Option) net.PacketConn {
return &clientConn{
PacketConn: conn,
options: parseOptions(opts...),
}
}
func (c *clientConn) ReadFrom(b []byte) (n int, addr net.Addr, err error) {
buf := bufpool.Get(readBufferSize)
defer bufpool.Put(buf)
for {
n, addr, err = c.PacketConn.ReadFrom(buf)
if err != nil {
return
}
m := mdns.Msg{}
if err = m.Unpack(buf[:n]); err != nil {
return 0, addr, err
}
if !m.Response {
continue
}
payload, ok := payloadFromMessage(&m)
if !ok {
continue
}
if len(b) < len(payload) {
return 0, addr, ErrShortBuffer
}
n = copy(b, payload)
return
}
}
func (c *clientConn) WriteTo(b []byte, addr net.Addr) (n int, err error) {
id := uint16(atomic.AddUint32(&c.id, 1))
wb, err := packQuery(id, c.options.domain, c.options.udpSize, b)
if err != nil {
return 0, err
}
_, err = c.PacketConn.WriteTo(wb, addr)
if err != nil {
return 0, err
}
return len(b), nil
}
type queryState struct {
id uint16
question []mdns.Question
}
type serverConn struct {
net.PacketConn
mu sync.RWMutex
queries map[string]queryState
options options
}
// ServerConn unwraps DNS queries as inbound payloads and wraps outbound
// payloads as DNS responses.
func ServerConn(conn net.PacketConn, opts ...Option) net.PacketConn {
return &serverConn{
PacketConn: conn,
queries: make(map[string]queryState),
options: parseOptions(opts...),
}
}
func (c *serverConn) ReadFrom(b []byte) (n int, addr net.Addr, err error) {
buf := bufpool.Get(readBufferSize)
defer bufpool.Put(buf)
for {
n, addr, err = c.PacketConn.ReadFrom(buf)
if err != nil {
return
}
m := mdns.Msg{}
if err = m.Unpack(buf[:n]); err != nil {
return 0, addr, err
}
if m.Response || !validQuestion(&m, c.options.domain) {
continue
}
payload, ok := payloadFromMessage(&m)
if !ok {
continue
}
if len(b) < len(payload) {
return 0, addr, ErrShortBuffer
}
c.storeQuery(addr, &m)
n = copy(b, payload)
return
}
}
func (c *serverConn) WriteTo(b []byte, addr net.Addr) (n int, err error) {
state := c.loadQuery(addr)
wb, err := packResponse(state.id, state.question, c.options.domain, c.options.udpSize, b)
if err != nil {
return 0, err
}
_, err = c.PacketConn.WriteTo(wb, addr)
if err != nil {
return 0, err
}
return len(b), nil
}
func (c *serverConn) storeQuery(addr net.Addr, m *mdns.Msg) {
if addr == nil {
return
}
state := queryState{
id: m.Id,
question: append([]mdns.Question(nil), m.Question...),
}
c.mu.Lock()
c.queries[addr.String()] = state
c.mu.Unlock()
}
func (c *serverConn) loadQuery(addr net.Addr) queryState {
if addr == nil {
return queryState{}
}
c.mu.RLock()
state := c.queries[addr.String()]
c.mu.RUnlock()
return state
}
func packQuery(id uint16, domain string, udpSize uint16, payload []byte) ([]byte, error) {
m := mdns.Msg{}
m.SetQuestion(domain, mdns.TypeNULL)
m.Id = id
m.RecursionDesired = false
addPayloadOpt(&m, udpSize, payload)
return m.Pack()
}
func packResponse(id uint16, question []mdns.Question, domain string, udpSize uint16, payload []byte) ([]byte, error) {
m := mdns.Msg{}
m.Id = id
m.Response = true
m.Authoritative = true
m.Rcode = mdns.RcodeSuccess
if len(question) > 0 {
m.Question = append([]mdns.Question(nil), question...)
} else {
m.SetQuestion(domain, mdns.TypeNULL)
m.Id = id
m.Response = true
m.Authoritative = true
}
addPayloadOpt(&m, udpSize, payload)
return m.Pack()
}
func addPayloadOpt(m *mdns.Msg, udpSize uint16, payload []byte) {
opt := &mdns.OPT{
Hdr: mdns.RR_Header{
Name: ".",
Rrtype: mdns.TypeOPT,
Class: udpSize,
},
Option: []mdns.EDNS0{
&mdns.EDNS0_LOCAL{
Code: edns0PayloadOption,
Data: append([]byte(nil), payload...),
},
},
}
m.Extra = append(m.Extra, opt)
}
func payloadFromMessage(m *mdns.Msg) ([]byte, bool) {
for _, rr := range m.Extra {
opt, ok := rr.(*mdns.OPT)
if !ok {
continue
}
for _, option := range opt.Option {
local, ok := option.(*mdns.EDNS0_LOCAL)
if !ok || local.Code != edns0PayloadOption {
continue
}
return append([]byte(nil), local.Data...), true
}
}
return nil, false
}
func validQuestion(m *mdns.Msg, domain string) bool {
if len(m.Question) == 0 {
return false
}
for _, q := range m.Question {
if q.Qtype == mdns.TypeNULL && mdns.CanonicalName(q.Name) == mdns.CanonicalName(domain) {
return true
}
}
return false
}
+61
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@@ -0,0 +1,61 @@
package dns
import (
"bytes"
"net"
"testing"
"time"
)
func TestPacketConnRoundTrip(t *testing.T) {
serverPC, err := net.ListenPacket("udp", "127.0.0.1:0")
if err != nil {
t.Fatal(err)
}
defer serverPC.Close()
clientPC, err := net.ListenPacket("udp", "127.0.0.1:0")
if err != nil {
t.Fatal(err)
}
defer clientPC.Close()
server := ServerConn(serverPC, DomainOption("tunnel.example."))
client := ClientConn(clientPC, DomainOption("tunnel.example."))
_ = server.SetDeadline(time.Now().Add(3 * time.Second))
_ = client.SetDeadline(time.Now().Add(3 * time.Second))
requestPayload := []byte("hello over dns")
if n, err := client.WriteTo(requestPayload, server.LocalAddr()); err != nil {
t.Fatal(err)
} else if n != len(requestPayload) {
t.Fatalf("client WriteTo wrote %d bytes, want %d", n, len(requestPayload))
}
buf := make([]byte, 1500)
n, clientAddr, err := server.ReadFrom(buf)
if err != nil {
t.Fatal(err)
}
if got := buf[:n]; !bytes.Equal(got, requestPayload) {
t.Fatalf("server ReadFrom got %q, want %q", got, requestPayload)
}
responsePayload := []byte("world over dns")
if n, err := server.WriteTo(responsePayload, clientAddr); err != nil {
t.Fatal(err)
} else if n != len(responsePayload) {
t.Fatalf("server WriteTo wrote %d bytes, want %d", n, len(responsePayload))
}
n, serverAddr, err := client.ReadFrom(buf)
if err != nil {
t.Fatal(err)
}
if serverAddr.String() != server.LocalAddr().String() {
t.Fatalf("response addr = %v, want %v", serverAddr, server.LocalAddr())
}
if got := buf[:n]; !bytes.Equal(got, responsePayload) {
t.Fatalf("client ReadFrom got %q, want %q", got, responsePayload)
}
}
+36
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@@ -27,11 +27,14 @@ import (
func init() {
registry.ListenerRegistry().Register("dns", NewListener)
registry.ListenerRegistry().Register("dns-tunnel", NewTunnelListener)
registry.ListenerRegistry().Register("dnst", NewTunnelListener)
}
type dnsListener struct {
addr net.Addr
server Server
tunnel listener.Listener
cqueue chan net.Conn
errChan chan error
logger logger.Logger
@@ -55,6 +58,29 @@ func (l *dnsListener) Init(md md.Metadata) (err error) {
return
}
if isTunnelMode(l.md.mode) {
tunnel := NewTunnelListener(
listener.AddrOption(l.options.Addr),
listener.RouterOption(l.options.Router),
listener.AutherOption(l.options.Auther),
listener.AuthOption(l.options.Auth),
listener.TLSConfigOption(l.options.TLSConfig),
listener.AdmissionOption(l.options.Admission),
listener.TrafficLimiterOption(l.options.TrafficLimiter),
listener.ConnLimiterOption(l.options.ConnLimiter),
listener.ServiceOption(l.options.Service),
listener.ProxyProtocolOption(l.options.ProxyProtocol),
listener.StatsOption(l.options.Stats),
listener.NetnsOption(l.options.Netns),
listener.LoggerOption(l.options.Logger),
)
if err = tunnel.Init(md); err != nil {
return
}
l.tunnel = tunnel
return nil
}
switch strings.ToLower(l.md.mode) {
case "tcp":
l.addr, err = net.ResolveTCPAddr("tcp", l.options.Addr)
@@ -230,6 +256,10 @@ func (l *dnsListener) Init(md md.Metadata) (err error) {
}
func (l *dnsListener) Accept() (conn net.Conn, err error) {
if l.tunnel != nil {
return l.tunnel.Accept()
}
var ok bool
select {
case conn = <-l.cqueue:
@@ -254,10 +284,16 @@ func (l *dnsListener) Accept() (conn net.Conn, err error) {
}
func (l *dnsListener) Close() error {
if l.tunnel != nil {
return l.tunnel.Close()
}
return l.server.Shutdown()
}
func (l *dnsListener) Addr() net.Addr {
if l.tunnel != nil {
return l.tunnel.Addr()
}
return l.addr
}
+10
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@@ -1,6 +1,7 @@
package dns
import (
"strings"
"time"
mdata "github.com/go-gost/core/metadata"
@@ -20,6 +21,15 @@ type metadata struct {
mptcp bool
}
func isTunnelMode(mode string) bool {
switch strings.ToLower(mode) {
case "tunnel", "quic", "packet":
return true
default:
return false
}
}
func (l *dnsListener) parseMetadata(md mdata.Metadata) (err error) {
const (
backlog = "backlog"
+205
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@@ -0,0 +1,205 @@
package dns
import (
"context"
"crypto/tls"
"net"
"strings"
"github.com/go-gost/core/limiter"
"github.com/go-gost/core/listener"
"github.com/go-gost/core/logger"
md "github.com/go-gost/core/metadata"
admission "github.com/go-gost/x/admission/wrapper"
xnet "github.com/go-gost/x/internal/net"
dns_util "github.com/go-gost/x/internal/util/dns"
traffic_limiter "github.com/go-gost/x/limiter/traffic"
limiter_wrapper "github.com/go-gost/x/limiter/traffic/wrapper"
metrics "github.com/go-gost/x/metrics/wrapper"
stats "github.com/go-gost/x/observer/stats/wrapper"
"github.com/quic-go/quic-go"
)
type dnsTunnelListener struct {
ln quic.EarlyListener
cqueue chan net.Conn
errChan chan error
logger logger.Logger
md tunnelMetadata
options listener.Options
}
func NewTunnelListener(opts ...listener.Option) listener.Listener {
options := listener.Options{}
for _, opt := range opts {
opt(&options)
}
return &dnsTunnelListener{
logger: options.Logger,
options: options,
}
}
func (l *dnsTunnelListener) Init(md md.Metadata) (err error) {
if err = l.parseMetadata(md); err != nil {
return
}
addr := l.options.Addr
if _, _, err := net.SplitHostPort(addr); err != nil {
addr = net.JoinHostPort(strings.Trim(addr, "[]"), "0")
}
network := "udp"
if xnet.IsIPv4(addr) {
network = "udp4"
}
laddr, err := net.ResolveUDPAddr(network, addr)
if err != nil {
return
}
lc := net.ListenConfig{}
var conn net.PacketConn
conn, err = lc.ListenPacket(context.Background(), network, laddr.String())
if err != nil {
return
}
conn = dns_util.ServerConn(
conn,
dns_util.DomainOption(l.md.domain),
dns_util.UDPSizeOption(l.md.udpSize),
)
conn = metrics.WrapPacketConn(l.options.Service, conn)
conn = stats.WrapPacketConn(conn, l.options.Stats)
conn = admission.WrapPacketConn(l.options.Admission, conn)
conn = limiter_wrapper.WrapPacketConn(
conn,
l.options.TrafficLimiter,
traffic_limiter.ServiceLimitKey,
limiter.ScopeOption(limiter.ScopeService),
limiter.ServiceOption(l.options.Service),
limiter.NetworkOption(conn.LocalAddr().Network()),
)
config := &quic.Config{
KeepAlivePeriod: l.md.keepAlivePeriod,
HandshakeIdleTimeout: l.md.handshakeTimeout,
MaxIdleTimeout: l.md.maxIdleTimeout,
Versions: []quic.Version{
quic.Version1,
quic.Version2,
},
MaxIncomingStreams: int64(l.md.maxStreams),
EnableDatagrams: l.md.enableDatagram,
}
tlsCfg := l.options.TLSConfig
if tlsCfg == nil {
tlsCfg = &tls.Config{}
} else {
tlsCfg = tlsCfg.Clone()
}
if len(tlsCfg.NextProtos) == 0 {
tlsCfg.NextProtos = []string{"h3", "quic/v1"}
}
ln, err := quic.ListenEarly(conn, tlsCfg, config)
if err != nil {
_ = conn.Close()
return
}
l.ln = *ln
l.cqueue = make(chan net.Conn, l.md.backlog)
l.errChan = make(chan error, 1)
go l.listenLoop()
return
}
func (l *dnsTunnelListener) Accept() (conn net.Conn, err error) {
var ok bool
select {
case conn = <-l.cqueue:
conn = limiter_wrapper.WrapConn(
conn,
l.options.TrafficLimiter,
conn.RemoteAddr().String(),
limiter.ScopeOption(limiter.ScopeConn),
limiter.ServiceOption(l.options.Service),
limiter.NetworkOption(conn.LocalAddr().Network()),
limiter.SrcOption(conn.RemoteAddr().String()),
)
case err, ok = <-l.errChan:
if !ok {
err = listener.ErrClosed
}
}
return
}
func (l *dnsTunnelListener) Close() error {
return l.ln.Close()
}
func (l *dnsTunnelListener) Addr() net.Addr {
return l.ln.Addr()
}
func (l *dnsTunnelListener) listenLoop() {
for {
ctx := context.Background()
session, err := l.ln.Accept(ctx)
if err != nil {
l.logger.Error("accept: ", err)
l.errChan <- err
close(l.errChan)
return
}
l.logger.Infof("new client session: %v", session.RemoteAddr())
go l.mux(ctx, session)
}
}
func (l *dnsTunnelListener) mux(ctx context.Context, session *quic.Conn) {
defer session.CloseWithError(0, "closed")
for {
stream, err := session.AcceptStream(ctx)
if err != nil {
l.logger.Error("accept stream: ", err)
return
}
conn := &dnsTunnelConn{
Stream: stream,
laddr: session.LocalAddr(),
raddr: session.RemoteAddr(),
}
select {
case l.cqueue <- conn:
case <-stream.Context().Done():
stream.Close()
default:
stream.Close()
l.logger.Warnf("connection queue is full, client %s discarded", session.RemoteAddr())
}
}
}
type dnsTunnelConn struct {
*quic.Stream
laddr net.Addr
raddr net.Addr
}
func (c *dnsTunnelConn) LocalAddr() net.Addr {
return c.laddr
}
func (c *dnsTunnelConn) RemoteAddr() net.Addr {
return c.raddr
}
+55
View File
@@ -0,0 +1,55 @@
package dns
import (
"time"
mdata "github.com/go-gost/core/metadata"
mdutil "github.com/go-gost/x/metadata/util"
)
type tunnelMetadata struct {
keepAlivePeriod time.Duration
handshakeTimeout time.Duration
maxIdleTimeout time.Duration
maxStreams int
enableDatagram bool
backlog int
domain string
udpSize int
}
func (l *dnsTunnelListener) parseMetadata(md mdata.Metadata) (err error) {
const (
keepAlive = "keepAlive"
keepAlivePeriod = "ttl"
handshakeTimeout = "handshakeTimeout"
maxIdleTimeout = "maxIdleTimeout"
maxStreams = "maxStreams"
backlog = "backlog"
domain = "domain"
udpSize = "udpSize"
)
l.md.backlog = mdutil.GetInt(md, backlog)
if l.md.backlog <= 0 {
l.md.backlog = defaultBacklog
}
if mdutil.GetBool(md, keepAlive) {
l.md.keepAlivePeriod = mdutil.GetDuration(md, keepAlivePeriod)
if l.md.keepAlivePeriod <= 0 {
l.md.keepAlivePeriod = 10 * time.Second
}
}
l.md.handshakeTimeout = mdutil.GetDuration(md, handshakeTimeout)
l.md.maxIdleTimeout = mdutil.GetDuration(md, maxIdleTimeout)
l.md.maxStreams = mdutil.GetInt(md, maxStreams)
l.md.enableDatagram = mdutil.GetBool(md, "quic.enableDatagram", "enableDatagram")
l.md.domain = mdutil.GetString(md, domain, "dns.domain")
l.md.udpSize = mdutil.GetInt(md, udpSize, "dns.udpSize")
return
}