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pool.go
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pool.go
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package resolver
import (
"context"
"fmt"
"github.com/miekg/dns"
"slices"
"sync"
"sync/atomic"
"time"
)
type NameserverPoolStatus uint8
const (
PoolEmpty NameserverPoolStatus = iota
PoolExpired
PoolHasHostnamesButNoIpAddresses
PrimedButNeedsEnhancing
PoolPrimed
)
type nameserverPool struct {
hostsWithoutAddresses []string
ipv4 []exchanger
ipv4Next atomic.Uint32
ipv6 []exchanger
ipv6Next atomic.Uint32
updating sync.RWMutex
enriched sync.Once
expires time.Time
}
func (pool *nameserverPool) hasIPv4() bool {
return pool.countIPv4() > 0
}
func (pool *nameserverPool) hasIPv6() bool {
return pool.countIPv6() > 0
}
func (pool *nameserverPool) countIPv4() int {
pool.updating.RLock()
c := len(pool.ipv4)
pool.updating.RUnlock()
return c
}
func (pool *nameserverPool) countIPv6() int {
pool.updating.RLock()
c := len(pool.ipv6)
pool.updating.RUnlock()
return c
}
func (pool *nameserverPool) getIPv4() exchanger {
pool.updating.RLock()
defer pool.updating.RUnlock()
if pool.hasIPv4() {
// Increments to the next server each time.
// There's a race condition here, but the outcome isn't "important" enough to warrant locking.
ipv4Next := pool.ipv4Next.Load() % uint32(len(pool.ipv4))
pool.ipv4Next.Store(ipv4Next + 1)
return pool.ipv4[ipv4Next]
}
return nil
}
func (pool *nameserverPool) getIPv6() exchanger {
pool.updating.RLock()
defer pool.updating.RUnlock()
if pool.hasIPv6() {
// Increments to the next server each time.
// There's a race condition here, but the outcome isn't "important" enough to warrant locking.
ipv6Next := pool.ipv6Next.Load() % uint32(len(pool.ipv6))
pool.ipv6Next.Store(ipv6Next + 1)
return pool.ipv6[ipv6Next]
}
return nil
}
//---
func (pool *nameserverPool) expired() bool {
pool.updating.RLock()
b := !pool.expires.IsZero() && pool.expires.Before(time.Now())
pool.updating.RUnlock()
return b
}
func (pool *nameserverPool) status() NameserverPoolStatus {
pool.updating.RLock()
defer pool.updating.RUnlock()
ipv4Count := pool.countIPv4()
ipv6Count := pool.countIPv6()
if ipv4Count == 0 && ipv6Count == 0 && len(pool.hostsWithoutAddresses) == 0 {
return PoolEmpty
}
total := ipv4Count
if IPv6Available() {
total = total + ipv6Count
}
if total == 0 {
return PoolHasHostnamesButNoIpAddresses
}
// If there are unknown addresses, and we have less than x IPs, then we want to enrich.
if total < DesireNumberOfNameserversPerZone && len(pool.hostsWithoutAddresses) > 0 {
return PrimedButNeedsEnhancing
}
return PoolPrimed
}
func newNameserverPool(nameservers []*dns.NS, extra []dns.RR) *nameserverPool {
pool := &nameserverPool{}
var ttl = MaxTTLAllowed
pool.hostsWithoutAddresses = make([]string, 0, len(nameservers))
for _, rr := range nameservers {
hostname := canonicalName(rr.Ns)
if hostname == "b.gtld-servers.net." {
// I don't like this server.
continue
}
ttl = min(rr.Header().Ttl, ttl)
//---
a, aaaa, minTtlSeen := findAddressesForHostname(hostname, extra)
if len(a) == 0 && len(aaaa) == 0 {
pool.hostsWithoutAddresses = append(pool.hostsWithoutAddresses, hostname)
continue
}
//---
ttl = min(minTtlSeen, ttl)
for _, addr := range a {
pool.ipv4 = append(pool.ipv4, &nameserver{
hostname: addr.Header().Name,
addr: addr.A.String(),
})
}
for _, addr := range aaaa {
pool.ipv6 = append(pool.ipv6, &nameserver{
hostname: addr.Header().Name,
addr: addr.AAAA.String(),
})
}
}
pool.hostsWithoutAddresses = slices.Clip(pool.hostsWithoutAddresses)
pool.expires = time.Now().Add(time.Duration(ttl) * time.Second)
return pool
}
func findAddressesForHostname(hostname string, records []dns.RR) ([]*dns.A, []*dns.AAAA, uint32) {
a := make([]*dns.A, 0, len(records))
aaaa := make([]*dns.AAAA, 0, len(records))
var ttl = MaxTTLAllowed
for _, rr := range records {
if canonicalName(rr.Header().Name) != hostname {
continue
}
switch addr := rr.(type) {
case *dns.A:
a = append(a, addr)
ttl = min(rr.Header().Ttl, ttl)
case *dns.AAAA:
aaaa = append(aaaa, addr)
ttl = min(rr.Header().Ttl, ttl)
}
}
return a, aaaa, ttl
}
func (pool *nameserverPool) enrich(records []dns.RR) {
if len(records) == 0 {
return
}
pool.updating.Lock()
defer pool.updating.Unlock()
var ttl = MaxTTLAllowed
hostnamesStillWithoutAddresses := make([]string, 0, len(pool.hostsWithoutAddresses))
for _, hostname := range pool.hostsWithoutAddresses {
a, aaaa, minTtlSeen := findAddressesForHostname(hostname, records)
if len(a) == 0 && len(aaaa) == 0 {
hostnamesStillWithoutAddresses = append(hostnamesStillWithoutAddresses, hostname)
continue
}
//---
ttl = min(minTtlSeen, ttl)
for _, addr := range a {
pool.ipv4 = append(pool.ipv4, &nameserver{
hostname: addr.Header().Name,
addr: addr.A.String(),
})
}
for _, addr := range aaaa {
pool.ipv6 = append(pool.ipv6, &nameserver{
hostname: addr.Header().Name,
addr: addr.AAAA.String(),
})
}
}
if !pool.expires.IsZero() {
expires := time.Now().Add(time.Duration(ttl) * time.Second)
if expires.Before(pool.expires) {
pool.expires = expires
}
}
pool.hostsWithoutAddresses = slices.Clip(hostnamesStillWithoutAddresses)
}
func (pool *nameserverPool) exchange(ctx context.Context, m *dns.Msg) Response {
response := Response{}
switch pool.status() {
case PoolPrimed:
case PrimedButNeedsEnhancing:
default:
response.Err = fmt.Errorf("server pool not setup")
return response
}
if pool.hasIPv6() && IPv6Available() {
server := pool.getIPv6()
response = server.exchange(ctx, m)
} else {
server := pool.getIPv4()
response = server.exchange(ctx, m)
}
if response.Empty() || response.Error() || response.Truncated() {
// If there was an issue, we give it one more try.
// If we have more than one nameserver, this will try a different one.
if pool.hasIPv4() {
server := pool.getIPv4()
response = server.exchange(ctx, m)
} else {
server := pool.getIPv6()
response = server.exchange(ctx, m)
}
}
if response.Empty() && !response.Error() {
// If we get an empty response without an error, we'll add an error.
response.Err = fmt.Errorf("no nameserver setup for %s", m.Question[0].Name)
}
return response
}