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net/dnscache: cache all IPs per hostname

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Not yet used in the dialer, but plumbed around.

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick 2021-07-26 11:58:28 -07:00 committed by Brad Fitzpatrick
parent 7428ecfebd
commit e299300b48
2 changed files with 43 additions and 34 deletions
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2
derp/derphttp/derphttp_client.go
View File

@ -370,7 +370,7 @@ func (c *Client) dialURL(ctx context.Context) (net.Conn, error) {
dialer := netns.NewDialer()
if c.DNSCache != nil {
ip, _, err := c.DNSCache.LookupIP(ctx, host)
ip, _, _, err := c.DNSCache.LookupIP(ctx, host)
if err == nil {
hostOrIP = ip.String()
}

75
net/dnscache/dnscache.go
View File

@ -2,6 +2,8 @@
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// TODO(bradfitz): update this code to use netaddr more
// Package dnscache contains a minimal DNS cache that makes a bunch of
// assumptions that are only valid for us. Not recommended for general use.
package dnscache
@ -78,8 +80,9 @@ type Resolver struct {
}
type ipCacheEntry struct {
ip net.IP // either v4 or v6
ip6 net.IP // nil if no v4 or no v6
ip net.IP // either v4 or v6
ip6 net.IP // nil if no v4 or no v6
allIPs []net.IPAddr // 1+ v4 and/or v6
expires time.Time
}
@ -105,81 +108,82 @@ var debug, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_DNS_CACHE"))
//
// If err is nil, ip will be non-nil. The v6 address may be nil even
// with a nil error.
func (r *Resolver) LookupIP(ctx context.Context, host string) (ip, v6 net.IP, err error) {
func (r *Resolver) LookupIP(ctx context.Context, host string) (ip, v6 net.IP, allIPs []net.IPAddr, err error) {
if ip := net.ParseIP(host); ip != nil {
if ip4 := ip.To4(); ip4 != nil {
return ip4, nil, nil
return ip4, nil, []net.IPAddr{{IP: ip4}}, nil
}
if debug {
log.Printf("dnscache: %q is an IP", host)
}
return ip, nil, nil
return ip, nil, []net.IPAddr{{IP: ip}}, nil
}
if ip, ip6, ok := r.lookupIPCache(host); ok {
if ip, ip6, allIPs, ok := r.lookupIPCache(host); ok {
if debug {
log.Printf("dnscache: %q = %v (cached)", host, ip)
}
return ip, ip6, nil
return ip, ip6, allIPs, nil
}
type ipPair struct {
type ipRes struct {
ip, ip6 net.IP
allIPs []net.IPAddr
}
ch := r.sf.DoChan(host, func() (interface{}, error) {
ip, ip6, err := r.lookupIP(host)
ip, ip6, allIPs, err := r.lookupIP(host)
if err != nil {
return nil, err
}
return ipPair{ip, ip6}, nil
return ipRes{ip, ip6, allIPs}, nil
})
select {
case res := <-ch:
if res.Err != nil {
if r.UseLastGood {
if ip, ip6, ok := r.lookupIPCacheExpired(host); ok {
if ip, ip6, allIPs, ok := r.lookupIPCacheExpired(host); ok {
if debug {
log.Printf("dnscache: %q using %v after error", host, ip)
}
return ip, ip6, nil
return ip, ip6, allIPs, nil
}
}
if debug {
log.Printf("dnscache: error resolving %q: %v", host, res.Err)
}
return nil, nil, res.Err
return nil, nil, nil, res.Err
}
pair := res.Val.(ipPair)
return pair.ip, pair.ip6, nil
r := res.Val.(ipRes)
return r.ip, r.ip6, r.allIPs, nil
case <-ctx.Done():
if debug {
log.Printf("dnscache: context done while resolving %q: %v", host, ctx.Err())
}
return nil, nil, ctx.Err()
return nil, nil, nil, ctx.Err()
}
}
func (r *Resolver) lookupIPCache(host string) (ip, ip6 net.IP, ok bool) {
func (r *Resolver) lookupIPCache(host string) (ip, ip6 net.IP, allIPs []net.IPAddr, ok bool) {
r.mu.Lock()
defer r.mu.Unlock()
if ent, ok := r.ipCache[host]; ok && ent.expires.After(time.Now()) {
return ent.ip, ent.ip6, true
return ent.ip, ent.ip6, ent.allIPs, true
}
return nil, nil, false
return nil, nil, nil, false
}
func (r *Resolver) lookupIPCacheExpired(host string) (ip, ip6 net.IP, ok bool) {
func (r *Resolver) lookupIPCacheExpired(host string) (ip, ip6 net.IP, allIPs []net.IPAddr, ok bool) {
r.mu.Lock()
defer r.mu.Unlock()
if ent, ok := r.ipCache[host]; ok {
return ent.ip, ent.ip6, true
return ent.ip, ent.ip6, ent.allIPs, true
}
return nil, nil, false
return nil, nil, nil, false
}
func (r *Resolver) lookupTimeoutForHost(host string) time.Duration {
if r.UseLastGood {
if _, _, ok := r.lookupIPCacheExpired(host); ok {
if _, _, _, ok := r.lookupIPCacheExpired(host); ok {
// If we have some previous good value for this host,
// don't give this DNS lookup much time. If we're in a
// situation where the user's DNS server is unreachable
@ -194,12 +198,12 @@ func (r *Resolver) lookupTimeoutForHost(host string) time.Duration {
return 10 * time.Second
}
func (r *Resolver) lookupIP(host string) (ip, ip6 net.IP, err error) {
if ip, ip6, ok := r.lookupIPCache(host); ok {
func (r *Resolver) lookupIP(host string) (ip, ip6 net.IP, allIPs []net.IPAddr, err error) {
if ip, ip6, allIPs, ok := r.lookupIPCache(host); ok {
if debug {
log.Printf("dnscache: %q found in cache as %v", host, ip)
}
return ip, ip6, nil
return ip, ip6, allIPs, nil
}
ctx, cancel := context.WithTimeout(context.Background(), r.lookupTimeoutForHost(host))
@ -218,10 +222,10 @@ func (r *Resolver) lookupIP(host string) (ip, ip6 net.IP, err error) {
}
}
if err != nil {
return nil, nil, err
return nil, nil, nil, err
}
if len(ips) == 0 {
return nil, nil, fmt.Errorf("no IPs for %q found", host)
return nil, nil, nil, fmt.Errorf("no IPs for %q found", host)
}
have4 := false
@ -240,11 +244,11 @@ func (r *Resolver) lookupIP(host string) (ip, ip6 net.IP, err error) {
}
}
}
r.addIPCache(host, ip, ip6, r.ttl())
return ip, ip6, nil
r.addIPCache(host, ip, ip6, ips, r.ttl())
return ip, ip6, ips, nil
}
func (r *Resolver) addIPCache(host string, ip, ip6 net.IP, d time.Duration) {
func (r *Resolver) addIPCache(host string, ip, ip6 net.IP, allIPs []net.IPAddr, d time.Duration) {
if isPrivateIP(ip) {
// Don't cache obviously wrong entries from captive portals.
// TODO: use DoH or DoT for the forwarding resolver?
@ -263,7 +267,12 @@ func (r *Resolver) addIPCache(host string, ip, ip6 net.IP, d time.Duration) {
if r.ipCache == nil {
r.ipCache = make(map[string]ipCacheEntry)
}
r.ipCache[host] = ipCacheEntry{ip: ip, ip6: ip6, expires: time.Now().Add(d)}
r.ipCache[host] = ipCacheEntry{
ip: ip,
ip6: ip6,
allIPs: allIPs,
expires: time.Now().Add(d),
}
}
func mustCIDR(s string) *net.IPNet {
@ -315,7 +324,7 @@ func Dialer(fwd DialContextFunc, dnsCache *Resolver) DialContextFunc {
}
}()
ip, ip6, err := dnsCache.LookupIP(ctx, host)
ip, ip6, _, err := dnsCache.LookupIP(ctx, host)
if err != nil {
return nil, fmt.Errorf("failed to resolve %q: %w", host, err)
}