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/*
*
* Copyright 2017 gRPC authors.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
*/
package naming
import (
"context"
"errors"
"fmt"
"net"
"strconv"
"time"
"google.golang.org/grpc/grpclog"
)
const (
defaultPort = "443"
defaultFreq = time.Minute * 30
)
var (
errMissingAddr = errors.New("missing address")
errWatcherClose = errors.New("watcher has been closed")
lookupHost = net.DefaultResolver.LookupHost
lookupSRV = net.DefaultResolver.LookupSRV
)
// NewDNSResolverWithFreq creates a DNS Resolver that can resolve DNS names, and
// create watchers that poll the DNS server using the frequency set by freq.
func NewDNSResolverWithFreq(freq time.Duration) (Resolver, error) {
return &dnsResolver{freq: freq}, nil
}
// NewDNSResolver creates a DNS Resolver that can resolve DNS names, and create
// watchers that poll the DNS server using the default frequency defined by defaultFreq.
func NewDNSResolver() (Resolver, error) {
return NewDNSResolverWithFreq(defaultFreq)
}
// dnsResolver handles name resolution for names following the DNS scheme
type dnsResolver struct {
// frequency of polling the DNS server that the watchers created by this resolver will use.
freq time.Duration
}
// formatIP returns ok = false if addr is not a valid textual representation of an IP address.
// If addr is an IPv4 address, return the addr and ok = true.
// If addr is an IPv6 address, return the addr enclosed in square brackets and ok = true.
func formatIP(addr string) (addrIP string, ok bool) {
ip := net.ParseIP(addr)
if ip == nil {
return "", false
}
if ip.To4() != nil {
return addr, true
}
return "[" + addr + "]", true
}
// parseTarget takes the user input target string, returns formatted host and port info.
// If target doesn't specify a port, set the port to be the defaultPort.
// If target is in IPv6 format and host-name is enclosed in sqarue brackets, brackets
// are strippd when setting the host.
// examples:
// target: "www.google.com" returns host: "www.google.com", port: "443"
// target: "ipv4-host:80" returns host: "ipv4-host", port: "80"
// target: "[ipv6-host]" returns host: "ipv6-host", port: "443"
// target: ":80" returns host: "localhost", port: "80"
// target: ":" returns host: "localhost", port: "443"
func parseTarget(target string) (host, port string, err error) {
if target == "" {
return "", "", errMissingAddr
}
if ip := net.ParseIP(target); ip != nil {
// target is an IPv4 or IPv6(without brackets) address
return target, defaultPort, nil
}
if host, port, err := net.SplitHostPort(target); err == nil {
// target has port, i.e ipv4-host:port, [ipv6-host]:port, host-name:port
if host == "" {
// Keep consistent with net.Dial(): If the host is empty, as in ":80", the local system is assumed.
host = "localhost"
}
if port == "" {
// If the port field is empty(target ends with colon), e.g. "[::1]:", defaultPort is used.
port = defaultPort
}
return host, port, nil
}
if host, port, err := net.SplitHostPort(target + ":" + defaultPort); err == nil {
// target doesn't have port
return host, port, nil
}
return "", "", fmt.Errorf("invalid target address %v", target)
}
// Resolve creates a watcher that watches the name resolution of the target.
func (r *dnsResolver) Resolve(target string) (Watcher, error) {
host, port, err := parseTarget(target)
if err != nil {
return nil, err
}
if net.ParseIP(host) != nil {
ipWatcher := &ipWatcher{
updateChan: make(chan *Update, 1),
}
host, _ = formatIP(host)
ipWatcher.updateChan <- &Update{Op: Add, Addr: host + ":" + port}
return ipWatcher, nil
}
ctx, cancel := context.WithCancel(context.Background())
return &dnsWatcher{
r: r,
host: host,
port: port,
ctx: ctx,
cancel: cancel,
t: time.NewTimer(0),
}, nil
}
// dnsWatcher watches for the name resolution update for a specific target
type dnsWatcher struct {
r *dnsResolver
host string
port string
// The latest resolved address set
curAddrs map[string]*Update
ctx context.Context
cancel context.CancelFunc
t *time.Timer
}
// ipWatcher watches for the name resolution update for an IP address.
type ipWatcher struct {
updateChan chan *Update
}
// Next returns the address resolution Update for the target. For IP address,
// the resolution is itself, thus polling name server is unnecessary. Therefore,
// Next() will return an Update the first time it is called, and will be blocked
// for all following calls as no Update exists until watcher is closed.
func (i *ipWatcher) Next() ([]*Update, error) {
u, ok := <-i.updateChan
if !ok {
return nil, errWatcherClose
}
return []*Update{u}, nil
}
// Close closes the ipWatcher.
func (i *ipWatcher) Close() {
close(i.updateChan)
}
// AddressType indicates the address type returned by name resolution.
type AddressType uint8
const (
// Backend indicates the server is a backend server.
Backend AddressType = iota
// GRPCLB indicates the server is a grpclb load balancer.
GRPCLB
)
// AddrMetadataGRPCLB contains the information the name resolver for grpclb should provide. The
// name resolver used by the grpclb balancer is required to provide this type of metadata in
// its address updates.
type AddrMetadataGRPCLB struct {
// AddrType is the type of server (grpc load balancer or backend).
AddrType AddressType
// ServerName is the name of the grpc load balancer. Used for authentication.
ServerName string
}
// compileUpdate compares the old resolved addresses and newly resolved addresses,
// and generates an update list
func (w *dnsWatcher) compileUpdate(newAddrs map[string]*Update) []*Update {
var res []*Update
for a, u := range w.curAddrs {
if _, ok := newAddrs[a]; !ok {
u.Op = Delete
res = append(res, u)
}
}
for a, u := range newAddrs {
if _, ok := w.curAddrs[a]; !ok {
res = append(res, u)
}
}
return res
}
func (w *dnsWatcher) lookupSRV() map[string]*Update {
newAddrs := make(map[string]*Update)
_, srvs, err := lookupSRV(w.ctx, "grpclb", "tcp", w.host)
if err != nil {
grpclog.Infof("grpc: failed dns SRV record lookup due to %v.\n", err)
return nil
}
for _, s := range srvs {
lbAddrs, err := lookupHost(w.ctx, s.Target)
if err != nil {
grpclog.Warningf("grpc: failed load banlacer address dns lookup due to %v.\n", err)
continue
}
for _, a := range lbAddrs {
a, ok := formatIP(a)
if !ok {
grpclog.Errorf("grpc: failed IP parsing due to %v.\n", err)
continue
}
addr := a + ":" + strconv.Itoa(int(s.Port))
newAddrs[addr] = &Update{Addr: addr,
Metadata: AddrMetadataGRPCLB{AddrType: GRPCLB, ServerName: s.Target}}
}
}
return newAddrs
}
func (w *dnsWatcher) lookupHost() map[string]*Update {
newAddrs := make(map[string]*Update)
addrs, err := lookupHost(w.ctx, w.host)
if err != nil {
grpclog.Warningf("grpc: failed dns A record lookup due to %v.\n", err)
return nil
}
for _, a := range addrs {
a, ok := formatIP(a)
if !ok {
grpclog.Errorf("grpc: failed IP parsing due to %v.\n", err)
continue
}
addr := a + ":" + w.port
newAddrs[addr] = &Update{Addr: addr}
}
return newAddrs
}
func (w *dnsWatcher) lookup() []*Update {
newAddrs := w.lookupSRV()
if newAddrs == nil {
// If failed to get any balancer address (either no corresponding SRV for the
// target, or caused by failure during resolution/parsing of the balancer target),
// return any A record info available.
newAddrs = w.lookupHost()
}
result := w.compileUpdate(newAddrs)
w.curAddrs = newAddrs
return result
}
// Next returns the resolved address update(delta) for the target. If there's no
// change, it will sleep for 30 mins and try to resolve again after that.
func (w *dnsWatcher) Next() ([]*Update, error) {
for {
select {
case <-w.ctx.Done():
return nil, errWatcherClose
case <-w.t.C:
}
result := w.lookup()
// Next lookup should happen after an interval defined by w.r.freq.
w.t.Reset(w.r.freq)
if len(result) > 0 {
return result, nil
}
}
}
func (w *dnsWatcher) Close() {
w.cancel()
}