426 lines
11 KiB
Go
426 lines
11 KiB
Go
// Copyright 2011 Miek Gieben. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// DNS server implementation.
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package dns
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import (
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"github.com/miekg/radix"
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"io"
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"net"
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"time"
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)
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type Handler interface {
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ServeDNS(w ResponseWriter, r *Msg)
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}
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// A ResponseWriter interface is used by an DNS handler to
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// construct an DNS response.
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type ResponseWriter interface {
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// RemoteAddr returns the net.Addr of the client that sent the current request.
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RemoteAddr() net.Addr
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// TsigStatus returns the status of the Tsig.
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TsigStatus() error
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// Write writes a reply back to the client.
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Write(*Msg) error
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// WriteBuf writes a raw buffer back to the client.
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WriteBuf([]byte) error
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}
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type conn struct {
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remoteAddr net.Addr // address of the client
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handler Handler // request handler
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request []byte // bytes read
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_UDP *net.UDPConn // i/o connection if UDP was used
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_TCP *net.TCPConn // i/o connection if TCP was used
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hijacked bool // connection has been hijacked by hander TODO(mg)
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tsigSecret map[string]string // the tsig secrets
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}
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type response struct {
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conn *conn
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req *Msg
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tsigStatus error
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tsigTimersOnly bool
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tsigRequestMAC string
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}
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// ServeMux is an DNS request multiplexer. It matches the
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// zone name of each incoming request against a list of
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// registered patterns add calls the handler for the pattern
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// that most closely matches the zone name. ServeMux is DNSSEC aware, meaning
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// that queries for the DS record are redirected to the parent zone (if that
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// is also registered), otherwise the child gets the query.
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type ServeMux struct {
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m *radix.Radix
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}
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// NewServeMux allocates and returns a new ServeMux.
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func NewServeMux() *ServeMux { return &ServeMux{m: radix.New()} }
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// DefaultServeMux is the default ServeMux used by Serve.
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var DefaultServeMux = NewServeMux()
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// The HandlerFunc type is an adapter to allow the use of
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// ordinary functions as DNS handlers. If f is a function
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// with the appropriate signature, HandlerFunc(f) is a
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// Handler object that calls f.
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type HandlerFunc func(ResponseWriter, *Msg)
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// ServerDNS calls f(w, r)
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func (f HandlerFunc) ServeDNS(w ResponseWriter, r *Msg) {
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f(w, r)
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}
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// Failed is a helper handler that returns an answer with
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// RCODE = servfail for every request.
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func Failed(w ResponseWriter, r *Msg) {
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m := new(Msg)
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m.SetRcode(r, RcodeServerFailure)
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w.Write(m)
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}
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// FailedHandler returns HandlerFunc with Failed.
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func FailedHandler() Handler { return HandlerFunc(Failed) }
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// Start a server on addresss and network speficied. Invoke handler
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// for any incoming queries.
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func ListenAndServe(addr string, network string, handler Handler) error {
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server := &Server{Addr: addr, Net: network, Handler: handler}
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return server.ListenAndServe()
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}
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func (mux *ServeMux) match(zone string, t uint16) Handler {
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zone = toRadixName(zone)
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if h := mux.m.Find(zone); h != nil && h.Value != nil {
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// If we got queried for a DS record, we must see if we
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// if we also serve the parent. We then redirect it.
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if t == TypeDS {
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if d := h.Up(); d != nil {
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return d.Value.(Handler)
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}
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}
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return h.Value.(Handler)
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}
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// Best matching one.
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if h := mux.m.Predecessor(zone); h != nil && h.Value != nil {
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return h.Value.(Handler)
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}
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return nil
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}
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// Handle adds a handler to the ServeMux for pattern.
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func (mux *ServeMux) Handle(pattern string, handler Handler) {
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if pattern == "" {
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panic("dns: invalid pattern " + pattern)
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}
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mux.m.Insert(toRadixName(Fqdn(pattern)), handler)
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}
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// Handle adds a handler to the ServeMux for pattern.
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func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Msg)) {
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mux.Handle(pattern, HandlerFunc(handler))
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}
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// HandleRemove deregistrars the handler specific for pattern from the ServeMux.
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func (mux *ServeMux) HandleRemove(pattern string) {
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if pattern == "" {
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panic("dns: invalid pattern " + pattern)
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}
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// if its there, its gone
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mux.m.Remove(toRadixName(Fqdn(pattern)))
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}
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// ServeDNS dispatches the request to the handler whose
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// pattern most closely matches the request message. For DS queries
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// a parent zone is sought.
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// If no handler is found a standard SERVFAIL message is returned
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func (mux *ServeMux) ServeDNS(w ResponseWriter, request *Msg) {
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var h Handler
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if len(request.Question) != 1 {
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h = FailedHandler()
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} else {
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if h = mux.match(request.Question[0].Name, request.Question[0].Qtype); h == nil {
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h = FailedHandler()
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}
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}
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h.ServeDNS(w, request)
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}
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// Handle registers the handler with the given pattern
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// in the DefaultServeMux. The documentation for
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// ServeMux explains how patterns are matched.
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func Handle(pattern string, handler Handler) { DefaultServeMux.Handle(pattern, handler) }
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// HandleRemove deregisters the handle with the given pattern
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// in the DefaultServeMux.
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func HandleRemove(pattern string) { DefaultServeMux.HandleRemove(pattern) }
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// HandleFunc registers the handler function with the given pattern
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// in the DefaultServeMux.
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func HandleFunc(pattern string, handler func(ResponseWriter, *Msg)) {
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DefaultServeMux.HandleFunc(pattern, handler)
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}
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// A Server defines parameters for running an DNS server.
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type Server struct {
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Addr string // address to listen on, ":dns" if empty
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Net string // if "tcp" it will invoke a TCP listener, otherwise an UDP one
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Handler Handler // handler to invoke, dns.DefaultServeMux if nil
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UDPSize int // default buffer size to use to read incoming UDP messages
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ReadTimeout time.Duration // the net.Conn.SetReadTimeout value for new connections
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WriteTimeout time.Duration // the net.Conn.SetWriteTimeout value for new connections
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TsigSecret map[string]string // secret(s) for Tsig map[<zonename>]<base64 secret>
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}
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// ListenAndServe starts a nameserver on the configured address in *Server.
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func (srv *Server) ListenAndServe() error {
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addr := srv.Addr
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if addr == "" {
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addr = ":domain"
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}
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switch srv.Net {
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case "tcp", "tcp4", "tcp6":
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a, e := net.ResolveTCPAddr(srv.Net, addr)
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if e != nil {
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return e
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}
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l, e := net.ListenTCP(srv.Net, a)
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if e != nil {
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return e
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}
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return srv.ServeTCP(l)
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case "udp", "udp4", "udp6":
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a, e := net.ResolveUDPAddr(srv.Net, addr)
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if e != nil {
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return e
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}
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l, e := net.ListenUDP(srv.Net, a)
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if e != nil {
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return e
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}
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return srv.ServeUDP(l)
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}
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return &Error{Err: "bad network"}
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}
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// ServeTCP starts a TCP listener for the server.
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// Each request is handled in a seperate goroutine.
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func (srv *Server) ServeTCP(l *net.TCPListener) error {
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defer l.Close()
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handler := srv.Handler
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if handler == nil {
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handler = DefaultServeMux
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}
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forever:
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for {
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rw, e := l.AcceptTCP()
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if e != nil {
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return e
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}
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if srv.ReadTimeout != 0 {
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rw.SetReadDeadline(time.Now().Add(srv.ReadTimeout))
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}
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if srv.WriteTimeout != 0 {
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rw.SetWriteDeadline(time.Now().Add(srv.WriteTimeout))
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}
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l := make([]byte, 2)
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n, err := rw.Read(l)
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if err != nil || n != 2 {
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continue
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}
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length, _ := unpackUint16(l, 0)
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if length == 0 {
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continue
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}
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m := make([]byte, int(length))
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n, err = rw.Read(m[:int(length)])
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if err != nil || n == 0 {
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continue
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}
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i := n
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for i < int(length) {
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j, err := rw.Read(m[i:int(length)])
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if err != nil {
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continue forever
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}
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i += j
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}
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n = i
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d, err := newConn(rw, nil, rw.RemoteAddr(), m, handler, srv.TsigSecret)
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if err != nil {
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continue
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}
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go d.serve()
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}
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panic("dns: not reached")
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}
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// ServeUDP starts a UDP listener for the server.
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// Each request is handled in a seperate goroutine.
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func (srv *Server) ServeUDP(l *net.UDPConn) error {
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defer l.Close()
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handler := srv.Handler
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if handler == nil {
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handler = DefaultServeMux
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}
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if srv.UDPSize == 0 {
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srv.UDPSize = udpMsgSize
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}
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for {
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m := make([]byte, srv.UDPSize)
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n, a, e := l.ReadFromUDP(m)
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if e != nil || n == 0 {
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return e
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}
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m = m[:n]
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if srv.ReadTimeout != 0 {
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l.SetReadDeadline(time.Now().Add(srv.ReadTimeout))
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}
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if srv.WriteTimeout != 0 {
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l.SetWriteDeadline(time.Now().Add(srv.WriteTimeout))
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}
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d, err := newConn(nil, l, a, m, handler, srv.TsigSecret)
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if err != nil {
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continue
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}
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go d.serve()
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}
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panic("dns: not reached")
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}
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func newConn(t *net.TCPConn, u *net.UDPConn, a net.Addr, buf []byte, handler Handler, tsig map[string]string) (*conn, error) {
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c := new(conn)
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c.handler = handler
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c._TCP = t
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c._UDP = u
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c.remoteAddr = a
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c.request = buf
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c.tsigSecret = tsig
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return c, nil
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}
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// Close the connection.
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func (c *conn) close() {
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switch {
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case c._UDP != nil:
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c._UDP.Close()
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c._UDP = nil
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case c._TCP != nil:
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c._TCP.Close()
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c._TCP = nil
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}
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}
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// Serve a new connection.
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func (c *conn) serve() {
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// for block to make it easy to break out to close the tcp connection
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for {
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// Request has been read in ServeUDP or ServeTCP
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w := new(response)
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w.conn = c
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req := new(Msg)
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if !req.Unpack(c.request) {
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// Send a format error back
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x := new(Msg)
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x.SetRcodeFormatError(req)
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w.Write(x)
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break
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}
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w.tsigStatus = nil
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if t := req.IsTsig(); t != nil {
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secret := t.Hdr.Name
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if _, ok := w.conn.tsigSecret[secret]; !ok {
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w.tsigStatus = ErrKeyAlg
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}
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w.tsigStatus = TsigVerify(c.request, w.conn.tsigSecret[secret], "", false)
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w.tsigTimersOnly = false // Will this ever be true?
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w.tsigRequestMAC = req.Extra[len(req.Extra)-1].(*RR_TSIG).MAC
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}
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w.req = req
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c.handler.ServeDNS(w, w.req) // this does the writing back to the client
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if c.hijacked {
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return
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}
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break
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}
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if c._TCP != nil {
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c.close() // Listen and Serve is closed then
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}
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}
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// Write implements the ResponseWriter.Write method.
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func (w *response) Write(m *Msg) (err error) {
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var (
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data []byte
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ok bool
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)
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if m == nil {
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return &Error{Err: "nil message"}
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}
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if t := m.IsTsig(); t != nil {
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data, w.tsigRequestMAC, err = TsigGenerate(m, w.conn.tsigSecret[t.Hdr.Name], w.tsigRequestMAC, w.tsigTimersOnly)
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if err != nil {
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return err
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}
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} else {
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data, ok = m.Pack()
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if !ok {
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return ErrPack
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}
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}
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return w.WriteBuf(data)
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}
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// WriteBuf implements the ResponseWriter.WriteBuf method.
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func (w *response) WriteBuf(m []byte) (err error) {
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if m == nil {
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return &Error{Err: "nil message"}
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}
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switch {
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case w.conn._UDP != nil:
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_, err := w.conn._UDP.WriteTo(m, w.conn.remoteAddr)
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if err != nil {
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return err
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}
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case w.conn._TCP != nil:
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if len(m) > MaxMsgSize {
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return ErrBuf
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}
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l := make([]byte, 2)
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l[0], l[1] = packUint16(uint16(len(m)))
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n, err := w.conn._TCP.Write(l)
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if err != nil {
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return err
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}
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if n != 2 {
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return io.ErrShortWrite
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}
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n, err = w.conn._TCP.Write(m)
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if err != nil {
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return err
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}
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i := n
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if i < len(m) {
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j, err := w.conn._TCP.Write(m[i:len(m)])
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if err != nil {
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return err
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}
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i += j
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}
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n = i
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}
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return nil
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}
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// RemoteAddr implements the ResponseWriter.RemoteAddr method.
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func (w *response) RemoteAddr() net.Addr { return w.conn.remoteAddr }
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// TsigStatus implements the ResponseWriter.TsigStatus method.
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func (w *response) TsigStatus() error { return w.tsigStatus }
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