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dns.go
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dns.go
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// Copyright (c) 2018 Zededa, Inc.
// SPDX-License-Identifier: Apache-2.0
package devicenetwork
import (
"fmt"
"net"
"os"
"path/filepath"
"strings"
"sync"
"time"
"github.com/lf-edge/eve/pkg/pillar/types"
"github.com/miekg/dns"
)
const (
// DhcpcdResolvConfDir : directory where dhcpcd stores resolv.conf
// files separately for every interface (named <interface>.dhcp).
DhcpcdResolvConfDir = "/run/dhcpcd/resolv.conf"
// WwanResolvConfDir : directory where wwan microservice stores resolv.conf
// files separately for every interface (named <interface>.dhcp).
WwanResolvConfDir = "/run/wwan/resolv.conf"
)
// ResolveConfDirs : directories where resolv.conf for an interface could be found.
var ResolveConfDirs = []string{DhcpcdResolvConfDir, WwanResolvConfDir}
const (
// DNSMaxParallelRequests is the maximum amount of parallel DNS requests
DNSMaxParallelRequests = 5
maxTTLSec int = 3600
dnsTimeout = 30 * time.Second
)
// DNSResponse represents a response from a DNS server (A Record)
type DNSResponse struct {
IP net.IP
TTL uint32
}
// IfnameToResolvConf : Look for a file created by dhcpcd
func IfnameToResolvConf(ifname string) string {
for _, d := range ResolveConfDirs {
filename := fmt.Sprintf("%s/%s.dhcp", d, ifname)
_, err := os.Stat(filename)
if err == nil {
return filename
}
}
return ""
}
// ResolvConfToIfname : Returns the name of the interface for which
// the given resolv.conf file was created.
func ResolvConfToIfname(resolvConf string) string {
ext := filepath.Ext(resolvConf)
if ext != ".dhcp" {
return ""
}
for _, d := range ResolveConfDirs {
if strings.HasPrefix(resolvConf, d) {
return strings.TrimSuffix(filepath.Base(resolvConf), ext)
}
}
return ""
}
// ResolveWithSrcIP resolves a domain with a given dns server and source Ip
func ResolveWithSrcIP(domain string, dnsServerIP net.IP, srcIP net.IP) ([]DNSResponse, error) {
var response []DNSResponse
sourceUDPAddr := net.UDPAddr{IP: srcIP}
dialer := net.Dialer{LocalAddr: &sourceUDPAddr}
dnsClient := dns.Client{Dialer: &dialer}
msg := dns.Msg{}
if domain[len(domain)-1] != '.' {
domain = domain + "."
}
msg.SetQuestion(domain, dns.TypeA)
dnsClient.Timeout = time.Duration(dnsTimeout)
reply, _, err := dnsClient.Exchange(&msg, net.JoinHostPort(dnsServerIP.String(), "53"))
if err != nil {
return response, fmt.Errorf("dns exchange failed: %v", err)
}
for _, answer := range reply.Answer {
if aRecord, ok := answer.(*dns.A); ok {
response = append(response, DNSResponse{
IP: aRecord.A,
TTL: aRecord.Header().Ttl,
})
}
}
return response, nil
}
// ResolveWithPortsLambda resolves a domain by using source IPs and dns servers from DeviceNetworkStatus
// As a resolver func ResolveWithSrcIP can be used
func ResolveWithPortsLambda(domain string,
dns types.DeviceNetworkStatus,
resolve func(string, net.IP, net.IP) ([]DNSResponse, error)) ([]DNSResponse, []error) {
quit := make(chan struct{})
work := make(chan struct{}, DNSMaxParallelRequests)
resolvedIPsChan := make(chan []DNSResponse)
countDNSRequests := 0
var errs []error
var errsMutex sync.Mutex
var wg sync.WaitGroup
for _, port := range dns.Ports {
if !port.IsL3Port || port.Cost > 0 {
continue
}
var srcIPs []net.IP
for _, addrInfo := range port.AddrInfoList {
if addrInfo.Addr.IsGlobalUnicast() {
srcIPs = append(srcIPs, addrInfo.Addr)
}
}
for _, dnsIP := range port.DNSServers {
for _, srcIP := range srcIPs {
wg.Add(1)
dnsIPCopy := make(net.IP, len(dnsIP))
copy(dnsIPCopy, dnsIP)
srcIPCopy := make(net.IP, len(srcIP))
copy(srcIPCopy, srcIP)
countDNSRequests++
go func(dnsIP, srcIP net.IP) {
select {
case work <- struct{}{}:
// if writable, means less than dnsMaxParallelRequests goroutines are currently running
}
select {
case <-quit:
// will return in case the quit chan has been closed,
// meaning another dns server already resolved the IP
return
default:
// do not wait for receiving a quit
}
response, err := resolve(domain, dnsIP, srcIP)
if err != nil {
errsMutex.Lock()
defer errsMutex.Unlock()
errs = append(errs, err)
}
if response != nil {
resolvedIPsChan <- response
}
<-work
wg.Done()
}(dnsIPCopy, srcIPCopy)
}
}
}
wgChan := make(chan struct{})
go func() {
wg.Wait()
close(wgChan)
}()
select {
case <-wgChan:
var responses []DNSResponse
if countDNSRequests == 0 {
// fallback in case no resolver is configured
ips, err := net.LookupIP(domain)
if err != nil {
return nil, append(errs, fmt.Errorf("fallback resolver failed: %+v", err))
}
for _, ip := range ips {
responses = append(responses, DNSResponse{
IP: ip,
TTL: uint32(maxTTLSec),
})
}
}
return responses, errs
case ip := <-resolvedIPsChan:
close(quit)
return ip, nil
}
}