/
server.go
357 lines (302 loc) · 10.2 KB
/
server.go
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// Package dnsserver implements all the interfaces from Caddy, so that CoreDNS can be a servertype plugin.
package dnsserver
import (
"context"
"fmt"
"net"
"runtime"
"strings"
"sync"
"time"
"github.com/coredns/caddy"
"github.com/coredns/coredns/plugin"
"github.com/coredns/coredns/plugin/metrics/vars"
"github.com/coredns/coredns/plugin/pkg/edns"
"github.com/coredns/coredns/plugin/pkg/log"
"github.com/coredns/coredns/plugin/pkg/rcode"
"github.com/coredns/coredns/plugin/pkg/reuseport"
"github.com/coredns/coredns/plugin/pkg/trace"
"github.com/coredns/coredns/plugin/pkg/transport"
"github.com/coredns/coredns/request"
"github.com/miekg/dns"
ot "github.com/opentracing/opentracing-go"
)
// Server represents an instance of a server, which serves
// DNS requests at a particular address (host and port). A
// server is capable of serving numerous zones on
// the same address and the listener may be stopped for
// graceful termination (POSIX only).
type Server struct {
Addr string // Address we listen on
server [2]*dns.Server // 0 is a net.Listener, 1 is a net.PacketConn (a *UDPConn) in our case.
m sync.Mutex // protects the servers
zones map[string]*Config // zones keyed by their address
dnsWg sync.WaitGroup // used to wait on outstanding connections
graceTimeout time.Duration // the maximum duration of a graceful shutdown
trace trace.Trace // the trace plugin for the server
debug bool // disable recover()
classChaos bool // allow non-INET class queries
}
// NewServer returns a new CoreDNS server and compiles all plugins in to it. By default CH class
// queries are blocked unless queries from enableChaos are loaded.
func NewServer(addr string, group []*Config) (*Server, error) {
s := &Server{
Addr: addr,
zones: make(map[string]*Config),
graceTimeout: 5 * time.Second,
}
// We have to bound our wg with one increment
// to prevent a "race condition" that is hard-coded
// into sync.WaitGroup.Wait() - basically, an add
// with a positive delta must be guaranteed to
// occur before Wait() is called on the wg.
// In a way, this kind of acts as a safety barrier.
s.dnsWg.Add(1)
for _, site := range group {
if site.Debug {
s.debug = true
log.D.Set()
}
// set the config per zone
s.zones[site.Zone] = site
// compile custom plugin for everything
var stack plugin.Handler
for i := len(site.Plugin) - 1; i >= 0; i-- {
stack = site.Plugin[i](stack)
// register the *handler* also
site.registerHandler(stack)
if s.trace == nil && stack.Name() == "trace" {
// we have to stash away the plugin, not the
// Tracer object, because the Tracer won't be initialized yet
if t, ok := stack.(trace.Trace); ok {
s.trace = t
}
}
// Unblock CH class queries when any of these plugins are loaded.
if _, ok := EnableChaos[stack.Name()]; ok {
s.classChaos = true
}
}
site.pluginChain = stack
}
if !s.debug {
// When reloading we need to explicitly disable debug logging if it is now disabled.
log.D.Clear()
}
return s, nil
}
// Compile-time check to ensure Server implements the caddy.GracefulServer interface
var _ caddy.GracefulServer = &Server{}
// Serve starts the server with an existing listener. It blocks until the server stops.
// This implements caddy.TCPServer interface.
func (s *Server) Serve(l net.Listener) error {
s.m.Lock()
s.server[tcp] = &dns.Server{Listener: l, Net: "tcp", Handler: dns.HandlerFunc(func(w dns.ResponseWriter, r *dns.Msg) {
ctx := context.WithValue(context.Background(), Key{}, s)
ctx = context.WithValue(ctx, LoopKey{}, 0)
s.ServeDNS(ctx, w, r)
})}
s.m.Unlock()
return s.server[tcp].ActivateAndServe()
}
// ServePacket starts the server with an existing packetconn. It blocks until the server stops.
// This implements caddy.UDPServer interface.
func (s *Server) ServePacket(p net.PacketConn) error {
s.m.Lock()
s.server[udp] = &dns.Server{PacketConn: p, Net: "udp", Handler: dns.HandlerFunc(func(w dns.ResponseWriter, r *dns.Msg) {
ctx := context.WithValue(context.Background(), Key{}, s)
ctx = context.WithValue(ctx, LoopKey{}, 0)
s.ServeDNS(ctx, w, r)
})}
s.m.Unlock()
return s.server[udp].ActivateAndServe()
}
// Listen implements caddy.TCPServer interface.
func (s *Server) Listen() (net.Listener, error) {
l, err := reuseport.Listen("tcp", s.Addr[len(transport.DNS+"://"):])
if err != nil {
return nil, err
}
return l, nil
}
// WrapListener Listen implements caddy.GracefulServer interface.
func (s *Server) WrapListener(ln net.Listener) net.Listener {
return ln
}
// ListenPacket implements caddy.UDPServer interface.
func (s *Server) ListenPacket() (net.PacketConn, error) {
p, err := reuseport.ListenPacket("udp", s.Addr[len(transport.DNS+"://"):])
if err != nil {
return nil, err
}
return p, nil
}
// Stop stops the server. It blocks until the server is
// totally stopped. On POSIX systems, it will wait for
// connections to close (up to a max timeout of a few
// seconds); on Windows it will close the listener
// immediately.
// This implements Caddy.Stopper interface.
func (s *Server) Stop() (err error) {
if runtime.GOOS != "windows" {
// force connections to close after timeout
done := make(chan struct{})
go func() {
s.dnsWg.Done() // decrement our initial increment used as a barrier
s.dnsWg.Wait()
close(done)
}()
// Wait for remaining connections to finish or
// force them all to close after timeout
select {
case <-time.After(s.graceTimeout):
case <-done:
}
}
// Close the listener now; this stops the server without delay
s.m.Lock()
for _, s1 := range s.server {
// We might not have started and initialized the full set of servers
if s1 != nil {
err = s1.Shutdown()
}
}
s.m.Unlock()
return
}
// Address together with Stop() implement caddy.GracefulServer.
func (s *Server) Address() string { return s.Addr }
// ServeDNS is the entry point for every request to the address that
// is bound to. It acts as a multiplexer for the requests zonename as
// defined in the request so that the correct zone
// (configuration and plugin stack) will handle the request.
func (s *Server) ServeDNS(ctx context.Context, w dns.ResponseWriter, r *dns.Msg) {
// The default dns.Mux checks the question section size, but we have our
// own mux here. Check if we have a question section. If not drop them here.
if r == nil || len(r.Question) == 0 {
errorAndMetricsFunc(s.Addr, w, r, dns.RcodeServerFailure)
return
}
if !s.debug {
defer func() {
// In case the user doesn't enable error plugin, we still
// need to make sure that we stay alive up here
if rec := recover(); rec != nil {
log.Errorf("Recovered from panic in server: %q", s.Addr)
vars.Panic.Inc()
errorAndMetricsFunc(s.Addr, w, r, dns.RcodeServerFailure)
}
}()
}
if !s.classChaos && r.Question[0].Qclass != dns.ClassINET {
errorAndMetricsFunc(s.Addr, w, r, dns.RcodeRefused)
return
}
if m, err := edns.Version(r); err != nil { // Wrong EDNS version, return at once.
w.WriteMsg(m)
return
}
// Wrap the response writer in a ScrubWriter so we automatically make the reply fit in the client's buffer.
w = request.NewScrubWriter(r, w)
q := strings.ToLower(r.Question[0].Name)
var (
off int
end bool
dshandler *Config
)
for {
if h, ok := s.zones[q[off:]]; ok {
if h.pluginChain == nil { // zone defined, but has not got any plugins
errorAndMetricsFunc(s.Addr, w, r, dns.RcodeRefused)
return
}
if r.Question[0].Qtype != dns.TypeDS {
rcode, _ := h.pluginChain.ServeDNS(ctx, w, r)
if !plugin.ClientWrite(rcode) {
errorFunc(s.Addr, w, r, rcode)
}
return
}
// The type is DS, keep the handler, but keep on searching as maybe we are serving
// the parent as well and the DS should be routed to it - this will probably *misroute* DS
// queries to a possibly grand parent, but there is no way for us to know at this point
// if there is an actual delegation from grandparent -> parent -> zone.
// In all fairness: direct DS queries should not be needed.
dshandler = h
}
off, end = dns.NextLabel(q, off)
if end {
break
}
}
if r.Question[0].Qtype == dns.TypeDS && dshandler != nil && dshandler.pluginChain != nil {
// DS request, and we found a zone, use the handler for the query.
rcode, _ := dshandler.pluginChain.ServeDNS(ctx, w, r)
if !plugin.ClientWrite(rcode) {
errorFunc(s.Addr, w, r, rcode)
}
return
}
// Wildcard match, if we have found nothing try the root zone as a last resort.
if h, ok := s.zones["."]; ok && h.pluginChain != nil {
rcode, _ := h.pluginChain.ServeDNS(ctx, w, r)
if !plugin.ClientWrite(rcode) {
errorFunc(s.Addr, w, r, rcode)
}
return
}
// Still here? Error out with REFUSED.
errorAndMetricsFunc(s.Addr, w, r, dns.RcodeRefused)
}
// OnStartupComplete lists the sites served by this server
// and any relevant information, assuming Quiet is false.
func (s *Server) OnStartupComplete() {
if Quiet {
return
}
out := startUpZones("", s.Addr, s.zones)
if out != "" {
fmt.Print(out)
}
}
// Tracer returns the tracer in the server if defined.
func (s *Server) Tracer() ot.Tracer {
if s.trace == nil {
return nil
}
return s.trace.Tracer()
}
// errorFunc responds to an DNS request with an error.
func errorFunc(server string, w dns.ResponseWriter, r *dns.Msg, rc int) {
state := request.Request{W: w, Req: r}
answer := new(dns.Msg)
answer.SetRcode(r, rc)
state.SizeAndDo(answer)
w.WriteMsg(answer)
}
func errorAndMetricsFunc(server string, w dns.ResponseWriter, r *dns.Msg, rc int) {
state := request.Request{W: w, Req: r}
answer := new(dns.Msg)
answer.SetRcode(r, rc)
state.SizeAndDo(answer)
vars.Report(server, state, vars.Dropped, rcode.ToString(rc), answer.Len(), time.Now())
w.WriteMsg(answer)
}
const (
tcp = 0
udp = 1
)
type (
// Key is the context key for the current server added to the context.
Key struct{}
// LoopKey is the context key to detect server wide loops.
LoopKey struct{}
)
// EnableChaos is a map with plugin names for which we should open CH class queries as we block these by default.
var EnableChaos = map[string]struct{}{
"chaos": {},
"forward": {},
"proxy": {},
}
// Quiet mode will not show any informative output on initialization.
var Quiet bool