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