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// Copyright 2011 Miek Gieben. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// DNS server implementation.
package dns
import (
"github.com/miekg/radix"
"io"
"net"
"time"
)
type Handler interface {
ServeDNS(w ResponseWriter, r *Msg)
}
// A ResponseWriter interface is used by an DNS handler to
// construct an DNS response.
type ResponseWriter interface {
// RemoteAddr returns the net.Addr of the client that sent the current request.
RemoteAddr() net.Addr
// Write writes a reply back to the client.
Write(*Msg) error
// WriteBuf writes a raw buffer back to the client.
WriteBuf([]byte) error
// Close closes the connection.
Close() error
// TsigStatus returns the status of the Tsig.
TsigStatus() error
// TsigTimersOnly sets the tsig timers only boolean.
TsigTimersOnly(bool)
// Hijack lets the caller take over the connection.
// After a call to Hijack(), the DNS package will not do anything with the connection
Hijack()
}
type conn struct {
remoteAddr net.Addr // address of the client
handler Handler // request handler
request []byte // bytes read
_UDP *net.UDPConn // i/o connection if UDP was used
_TCP *net.TCPConn // i/o connection if TCP was used
tsigSecret map[string]string // the tsig secrets
}
type response struct {
conn *conn
hijacked bool // connection has been hijacked by handler
tsigStatus error
tsigTimersOnly bool
tsigRequestMAC string
}
// ServeMux is an DNS request multiplexer. It matches the
// zone name of each incoming request against a list of
// registered patterns add calls the handler for the pattern
// that most closely matches the zone name. ServeMux is DNSSEC aware, meaning
// that queries for the DS record are redirected to the parent zone (if that
// is also registered), otherwise the child gets the query.
type ServeMux struct {
m *radix.Radix
}
// NewServeMux allocates and returns a new ServeMux.
func NewServeMux() *ServeMux { return &ServeMux{m: radix.New()} }
// DefaultServeMux is the default ServeMux used by Serve.
var DefaultServeMux = NewServeMux()
// Authors is a list of authors that helped create or make Go DNS better.
var Authors = []string{"Miek Gieben", "Ask Bjørn Hansen", "Dave Cheney", "Dusty Wilson", "Peter van Dijk"}
// Version holds the current version.
var Version = "Go DNS"
// The HandlerFunc type is an adapter to allow the use of
// ordinary functions as DNS handlers. If f is a function
// with the appropriate signature, HandlerFunc(f) is a
// Handler object that calls f.
type HandlerFunc func(ResponseWriter, *Msg)
// ServerDNS calls f(w, r)
func (f HandlerFunc) ServeDNS(w ResponseWriter, r *Msg) {
f(w, r)
}
// FailedHandler returns a HandlerFunc
// returns SERVFAIL for every request it gets.
func HandleFailed(w ResponseWriter, r *Msg) {
m := new(Msg)
m.SetRcode(r, RcodeServerFailure)
// does not matter if this write fails
w.Write(m)
}
// AuthorHandler returns a HandlerFunc that returns the authors
// of Go DNS for 'authors.bind' or 'authors.server' queries in the
// CHAOS Class. Note with
//
// HandleFunc("authors.bind.", HandleAuthors)
//
// The handler is registered for all DNS classes, thereby potentially
// hijacking the authors.bind. zone in the IN class. If you need the
// authors.bind zone to exist in the IN class, you need to register
// some other handler, check the class in there and then call HandleAuthors.
func HandleAuthors(w ResponseWriter, r *Msg) {
if len(r.Question) != 1 {
HandleFailed(w, r)
return
}
if r.Question[0].Qtype != ClassCHAOS && r.Question[0].Qtype != TypeTXT {
HandleFailed(w, r)
return
}
if r.Question[0].Name != "authors.server." && r.Question[0].Name != "authors.bind." {
HandleFailed(w, r)
return
}
m := new(Msg)
m.SetReply(r)
for _, author := range Authors {
h := RR_Header{r.Question[0].Name, TypeTXT, ClassCHAOS, 0, 0}
m.Answer = append(m.Answer, &RR_TXT{h, []string{author}})
}
w.Write(m)
}
// VersionHandler returns a HandlerFunc that returns the version
// of Go DNS for 'version.bind' or 'version.server' queries in the
// CHAOS Class. Note with
//
// HandleFunc("version.bind.", HandleVersion)
//
// The handler is registered for all DNS classes, thereby potentially
// hijacking the version.bind. zone in the IN class. If you need the
// version.bind zone to exist in the IN class, you need to register
// some other handler, check the class in there and then call HandleVersion.
func HandleVersion(w ResponseWriter, r *Msg) {
if len(r.Question) != 1 {
HandleFailed(w, r)
return
}
if r.Question[0].Qtype != ClassCHAOS && r.Question[0].Qtype != TypeTXT {
HandleFailed(w, r)
return
}
if r.Question[0].Name != "version.server." && r.Question[0].Name != "version.bind." {
HandleFailed(w, r)
return
}
m := new(Msg)
m.SetReply(r)
h := RR_Header{r.Question[0].Name, TypeTXT, ClassCHAOS, 0, 0}
m.Answer = append(m.Answer, &RR_TXT{h, []string{Version}})
w.Write(m)
}
func authorHandler() Handler { return HandlerFunc(HandleAuthors) }
func failedHandler() Handler { return HandlerFunc(HandleFailed) }
func versionHandler() Handler { return HandlerFunc(HandleVersion) }
// Start a server on addresss and network speficied. Invoke handler
// for any incoming queries.
func ListenAndServe(addr string, network string, handler Handler) error {
server := &Server{Addr: addr, Net: network, Handler: handler}
return server.ListenAndServe()
}
func (mux *ServeMux) match(zone string, t uint16) Handler {
zone = toRadixName(zone)
if h, e := mux.m.Find(zone); e {
// If we got queried for a DS record, we must see if we
// if we also serve the parent. We then redirect the query to it.
if t != TypeDS {
return h.Value.(Handler)
}
if d := h.Up(); d != nil {
return d.Value.(Handler)
}
// No parent zone found, let the original handler take care of it
return h.Value.(Handler)
} else {
if h == nil {
return nil
}
return h.Value.(Handler)
}
panic("dns: not reached")
}
// Handle adds a handler to the ServeMux for pattern.
func (mux *ServeMux) Handle(pattern string, handler Handler) {
if pattern == "" {
panic("dns: invalid pattern " + pattern)
}
mux.m.Insert(toRadixName(Fqdn(pattern)), handler)
}
// Handle adds a handler to the ServeMux for pattern.
func (mux *ServeMux) HandleFunc(pattern string, handler func(ResponseWriter, *Msg)) {
mux.Handle(pattern, HandlerFunc(handler))
}
// HandleRemove deregistrars the handler specific for pattern from the ServeMux.
func (mux *ServeMux) HandleRemove(pattern string) {
if pattern == "" {
panic("dns: invalid pattern " + pattern)
}
// if its there, its gone
mux.m.Remove(toRadixName(Fqdn(pattern)))
}
// ServeDNS dispatches the request to the handler whose
// pattern most closely matches the request message. If DefaultServeMux
// is used the correct thing for DS queries is done: a possible parent
// is sought.
// If no handler is found a standard SERVFAIL message is returned
// If the request message does not have a single question in the
// question section a SERVFAIL is returned.
func (mux *ServeMux) ServeDNS(w ResponseWriter, request *Msg) {
var h Handler
if len(request.Question) != 1 {
h = failedHandler()
} else {
if h = mux.match(request.Question[0].Name, request.Question[0].Qtype); h == nil {
h = failedHandler()
}
}
h.ServeDNS(w, request)
}
// Handle registers the handler with the given pattern
// in the DefaultServeMux. The documentation for
// ServeMux explains how patterns are matched.
func Handle(pattern string, handler Handler) { DefaultServeMux.Handle(pattern, handler) }
// HandleRemove deregisters the handle with the given pattern
// in the DefaultServeMux.
func HandleRemove(pattern string) { DefaultServeMux.HandleRemove(pattern) }
// HandleFunc registers the handler function with the given pattern
// in the DefaultServeMux.
func HandleFunc(pattern string, handler func(ResponseWriter, *Msg)) {
DefaultServeMux.HandleFunc(pattern, handler)
}
// A Server defines parameters for running an DNS server.
type Server struct {
Addr string // address to listen on, ":dns" if empty
Net string // if "tcp" it will invoke a TCP listener, otherwise an UDP one
Handler Handler // handler to invoke, dns.DefaultServeMux if nil
UDPSize int // default buffer size to use to read incoming UDP messages
ReadTimeout time.Duration // the net.Conn.SetReadTimeout value for new connections
WriteTimeout time.Duration // the net.Conn.SetWriteTimeout value for new connections
TsigSecret map[string]string // secret(s) for Tsig map[<zonename>]<base64 secret>
}
// ListenAndServe starts a nameserver on the configured address in *Server.
func (srv *Server) ListenAndServe() error {
addr := srv.Addr
if addr == "" {
addr = ":domain"
}
switch srv.Net {
case "tcp", "tcp4", "tcp6":
a, e := net.ResolveTCPAddr(srv.Net, addr)
if e != nil {
return e
}
l, e := net.ListenTCP(srv.Net, a)
if e != nil {
return e
}
return srv.serveTCP(l)
case "udp", "udp4", "udp6":
a, e := net.ResolveUDPAddr(srv.Net, addr)
if e != nil {
return e
}
l, e := net.ListenUDP(srv.Net, a)
if e != nil {
return e
}
return srv.serveUDP(l)
}
return &Error{Err: "bad network"}
}
// serveTCP starts a TCP listener for the server.
// Each request is handled in a seperate goroutine.
func (srv *Server) serveTCP(l *net.TCPListener) error {
defer l.Close()
handler := srv.Handler
if handler == nil {
handler = DefaultServeMux
}
forever:
for {
rw, e := l.AcceptTCP()
if e != nil {
// don't bail out, but wait for a new request
continue
}
if srv.ReadTimeout != 0 {
rw.SetReadDeadline(time.Now().Add(srv.ReadTimeout))
}
if srv.WriteTimeout != 0 {
rw.SetWriteDeadline(time.Now().Add(srv.WriteTimeout))
}
l := make([]byte, 2)
n, err := rw.Read(l)
if err != nil || n != 2 {
continue
}
length, _ := unpackUint16(l, 0)
if length == 0 {
continue
}
m := make([]byte, int(length))
n, err = rw.Read(m[:int(length)])
if err != nil || n == 0 {
continue
}
i := n
for i < int(length) {
j, err := rw.Read(m[i:int(length)])
if err != nil {
continue forever
}
i += j
}
n = i
d := &conn{rw.RemoteAddr(), handler, m, nil, rw, srv.TsigSecret}
go d.serve()
}
panic("dns: not reached")
}
// serveUDP starts a UDP listener for the server.
// Each request is handled in a seperate goroutine.
func (srv *Server) serveUDP(l *net.UDPConn) error {
defer l.Close()
handler := srv.Handler
if handler == nil {
handler = DefaultServeMux
}
if srv.UDPSize == 0 {
srv.UDPSize = udpMsgSize
}
for {
if srv.ReadTimeout != 0 {
l.SetReadDeadline(time.Now().Add(srv.ReadTimeout))
}
if srv.WriteTimeout != 0 {
l.SetWriteDeadline(time.Now().Add(srv.WriteTimeout))
}
m := make([]byte, srv.UDPSize)
n, a, e := l.ReadFromUDP(m)
if e != nil || n == 0 {
// don't bail out, but wait for a new request
continue
}
m = m[:n]
d := &conn{a, handler, m, l, nil, srv.TsigSecret}
go d.serve()
}
panic("dns: not reached")
}
// Serve a new connection.
func (c *conn) serve() {
// for block to make it easy to break out to close the tcp connection
for {
// Request has been read in serveUDP or serveTCP
w := new(response)
w.conn = c
req := new(Msg)
if req.Unpack(c.request) != nil {
// Send a format error back
x := new(Msg)
x.SetRcodeFormatError(req)
w.Write(x)
break
}
w.tsigStatus = nil
if t := req.IsTsig(); t != nil {
secret := t.Hdr.Name
if _, ok := w.conn.tsigSecret[secret]; !ok {
w.tsigStatus = ErrKeyAlg
}
w.tsigStatus = TsigVerify(c.request, w.conn.tsigSecret[secret], "", false)
w.tsigTimersOnly = false
w.tsigRequestMAC = req.Extra[len(req.Extra)-1].(*RR_TSIG).MAC
}
c.handler.ServeDNS(w, req) // this does the writing back to the client
if w.hijacked {
// client takes care of the connection, i.e. calls Close()
return
}
break
}
// quite elaborate, but this was the original c.close() function
if c._TCP != nil {
switch {
case c._UDP != nil:
c._UDP.Close()
c._UDP = nil
case c._TCP != nil:
c._TCP.Close()
c._TCP = nil
}
}
}
// Write implements the ResponseWriter.Write method.
func (w *response) Write(m *Msg) (err error) {
var data []byte
if m == nil {
return &Error{Err: "nil message"}
}
if t := m.IsTsig(); t != nil {
data, w.tsigRequestMAC, err = TsigGenerate(m, w.conn.tsigSecret[t.Hdr.Name], w.tsigRequestMAC, w.tsigTimersOnly)
if err != nil {
return err
}
} else {
data, err = m.Pack()
if err != nil {
return err
}
}
return w.WriteBuf(data)
}
// WriteBuf implements the ResponseWriter.WriteBuf method.
func (w *response) WriteBuf(m []byte) (err error) {
if m == nil {
return &Error{Err: "nil message"}
}
switch {
case w.conn._UDP != nil:
_, err := w.conn._UDP.WriteTo(m, w.conn.remoteAddr)
if err != nil {
return err
}
case w.conn._TCP != nil:
if len(m) > MaxMsgSize {
return &Error{Err: "message too large"}
}
l := make([]byte, 2)
l[0], l[1] = packUint16(uint16(len(m)))
n, err := w.conn._TCP.Write(l)
if err != nil {
return err
}
if n != 2 {
return io.ErrShortWrite
}
n, err = w.conn._TCP.Write(m)
if err != nil {
return err
}
i := n
if i < len(m) {
j, err := w.conn._TCP.Write(m[i:len(m)])
if err != nil {
return err
}
i += j
}
n = i
}
return nil
}
// RemoteAddr implements the ResponseWriter.RemoteAddr method.
func (w *response) RemoteAddr() net.Addr { return w.conn.remoteAddr }
// TsigStatus implements the ResponseWriter.TsigStatus method.
func (w *response) TsigStatus() error { return w.tsigStatus }
// TsigTimersOnly implements the ResponseWriter.TsigTimersOnly method.
func (w *response) TsigTimersOnly(b bool) { w.tsigTimersOnly = b }
// Hijack implements the ResponseWriter.Hijack method.
func (w *response) Hijack() { w.hijacked = true }
// Close implements the ResponseWriter.Close method
func (w *response) Close() error {
if w.conn._UDP != nil {
e := w.conn._UDP.Close()
w.conn._UDP = nil
return e
}
if w.conn._TCP != nil {
e := w.conn._TCP.Close()
w.conn._TCP = nil
return e
}
// no-op
return nil
}
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