diff --git a/derp/derphttp/derphttp_client.go b/derp/derphttp/derphttp_client.go
index 2d1a821d7..cfe6d0225 100644
--- a/derp/derphttp/derphttp_client.go
+++ b/derp/derphttp/derphttp_client.go
@@ -26,6 +26,7 @@ import (
"time"
"tailscale.com/derp"
+ "tailscale.com/net/dnscache"
"tailscale.com/types/key"
"tailscale.com/types/logger"
)
@@ -37,7 +38,8 @@ import (
// Send/Recv will completely re-establish the connection (unless Close
// has been called).
type Client struct {
- TLSConfig *tls.Config // for sever connection, optional, nil means default
+ TLSConfig *tls.Config // for sever connection, optional, nil means default
+ DNSCache *dnscache.Resolver // optional; if nil, no caching
privateKey key.Private
logf logger.Logf
@@ -137,11 +139,23 @@ func (c *Client) connect(ctx context.Context, caller string) (client *derp.Clien
}
}()
+ host := c.url.Hostname()
+ hostOrIP := host
+
var d net.Dialer
- log.Printf("Dialing: %q", net.JoinHostPort(c.url.Hostname(), urlPort(c.url)))
- tcpConn, err = d.DialContext(ctx, "tcp", net.JoinHostPort(c.url.Hostname(), urlPort(c.url)))
+ log.Printf("Dialing: %q", net.JoinHostPort(host, urlPort(c.url)))
+
+ if c.DNSCache != nil {
+ ip, err := c.DNSCache.LookupIP(ctx, host)
+ if err != nil {
+ return nil, err
+ }
+ hostOrIP = ip.String()
+ }
+
+ tcpConn, err = d.DialContext(ctx, "tcp", net.JoinHostPort(hostOrIP, urlPort(c.url)))
if err != nil {
- return nil, err
+ return nil, fmt.Errorf("Dial of %q: %v", host, err)
}
// Now that we have a TCP connection, force close it.
diff --git a/net/dnscache/dnscache.go b/net/dnscache/dnscache.go
new file mode 100644
index 000000000..b435e5aaa
--- /dev/null
+++ b/net/dnscache/dnscache.go
@@ -0,0 +1,151 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// 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
+
+import (
+ "context"
+ "fmt"
+ "net"
+ "sync"
+ "time"
+
+ "golang.org/x/sync/singleflight"
+)
+
+var single = &Resolver{
+ Forward: &net.Resolver{PreferGo: true},
+}
+
+// Get returns a caching Resolver singleton.
+func Get() *Resolver { return single }
+
+const fixedTTL = 10 * time.Minute
+
+// Resolver is a minimal DNS caching resolver.
+//
+// The TTL is always fixed for now. It's not intended for general use.
+// Cache entries are never cleaned up so it's intended that this is
+// only used with a fixed set of hostnames.
+type Resolver struct {
+ // Forward is the resolver to use to populate the cache.
+ // If nil, net.DefaultResolver is used.
+ Forward *net.Resolver
+
+ sf singleflight.Group
+
+ mu sync.Mutex
+ ipCache map[string]ipCacheEntry
+}
+
+type ipCacheEntry struct {
+ ip net.IP
+ expires time.Time
+}
+
+func (r *Resolver) fwd() *net.Resolver {
+ if r.Forward != nil {
+ return r.Forward
+ }
+ return net.DefaultResolver
+}
+
+// LookupIP returns the first IPv4 address found, otherwise the first IPv6 address.
+func (r *Resolver) LookupIP(ctx context.Context, host string) (net.IP, error) {
+ if ip := net.ParseIP(host); ip != nil {
+ if ip4 := ip.To4(); ip4 != nil {
+ return ip4, nil
+ }
+ return ip, nil
+ }
+
+ if ip, ok := r.lookupIPCache(host); ok {
+ return ip, nil
+ }
+
+ ch := r.sf.DoChan(host, func() (interface{}, error) {
+ ip, err := r.lookupIP(host)
+ if err != nil {
+ return nil, err
+ }
+ return ip, nil
+ })
+ select {
+ case res := <-ch:
+ if res.Err != nil {
+ return nil, res.Err
+ }
+ return res.Val.(net.IP), nil
+ case <-ctx.Done():
+ return nil, ctx.Err()
+ }
+}
+
+func (r *Resolver) lookupIPCache(host string) (ip net.IP, ok bool) {
+ r.mu.Lock()
+ defer r.mu.Unlock()
+ if ent, ok := r.ipCache[host]; ok && ent.expires.After(time.Now()) {
+ return ent.ip, true
+ }
+ return nil, false
+}
+
+func (r *Resolver) lookupIP(host string) (net.IP, error) {
+ if ip, ok := r.lookupIPCache(host); ok {
+ return ip, nil
+ }
+
+ ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+ defer cancel()
+ ips, err := r.fwd().LookupIPAddr(ctx, host)
+ if err != nil {
+ return nil, err
+ }
+ if len(ips) == 0 {
+ return nil, fmt.Errorf("no IPs for %q found", host)
+ }
+
+ for _, ipa := range ips {
+ if ip4 := ipa.IP.To4(); ip4 != nil {
+ return r.addIPCache(host, ip4, fixedTTL), nil
+ }
+ }
+ return r.addIPCache(host, ips[0].IP, fixedTTL), nil
+}
+
+func (r *Resolver) addIPCache(host string, ip net.IP, d time.Duration) net.IP {
+ if isPrivateIP(ip) {
+ // Don't cache obviously wrong entries from captive portals.
+ // TODO: use DoH or DoT for the forwarding resolver?
+ return ip
+ }
+
+ r.mu.Lock()
+ defer r.mu.Unlock()
+ if r.ipCache == nil {
+ r.ipCache = make(map[string]ipCacheEntry)
+ }
+ r.ipCache[host] = ipCacheEntry{ip: ip, expires: time.Now().Add(d)}
+ return ip
+}
+
+func mustCIDR(s string) *net.IPNet {
+ _, ipNet, err := net.ParseCIDR("100.64.0.0/10")
+ if err != nil {
+ panic(err)
+ }
+ return ipNet
+}
+
+func isPrivateIP(ip net.IP) bool {
+ return private1.Contains(ip) || private2.Contains(ip) || private3.Contains(ip)
+}
+
+var (
+ private1 = mustCIDR("10.0.0.0/8")
+ private2 = mustCIDR("172.16.0.0/12")
+ private3 = mustCIDR("192.168.0.0/16")
+)
diff --git a/netcheck/netcheck.go b/netcheck/netcheck.go
index 34d57f450..3bd314d71 100644
--- a/netcheck/netcheck.go
+++ b/netcheck/netcheck.go
@@ -17,6 +17,7 @@ import (
"golang.org/x/sync/errgroup"
"tailscale.com/interfaces"
+ "tailscale.com/net/dnscache"
"tailscale.com/stun"
"tailscale.com/stunner"
"tailscale.com/types/logger"
@@ -181,6 +182,7 @@ func GetReport(ctx context.Context, logf logger.Logf) (*Report, error) {
Endpoint: add,
Servers: stunServers,
Logf: logf,
+ DNSCache: dnscache.Get(),
}
grp.Go(func() error { return s4.Run(ctx) })
go reader(s4, pc4, unlimited)
@@ -190,6 +192,7 @@ func GetReport(ctx context.Context, logf logger.Logf) (*Report, error) {
Endpoint: addHair,
Servers: stunServers,
Logf: logf,
+ DNSCache: dnscache.Get(),
}
grp.Go(func() error { return s4Hair.Run(ctx) })
go reader(s4Hair, pc4Hair, 2)
@@ -201,6 +204,7 @@ func GetReport(ctx context.Context, logf logger.Logf) (*Report, error) {
Servers: stunServers6,
Logf: logf,
OnlyIPv6: true,
+ DNSCache: dnscache.Get(),
}
grp.Go(func() error { return s6.Run(ctx) })
go reader(s6, pc6, unlimited)
diff --git a/stunner/stunner.go b/stunner/stunner.go
index 6d2c0e4e4..54fa1360c 100644
--- a/stunner/stunner.go
+++ b/stunner/stunner.go
@@ -12,6 +12,7 @@ import (
"sync"
"time"
+ "tailscale.com/net/dnscache"
"tailscale.com/stun"
)
@@ -38,9 +39,9 @@ type Stunner struct {
Servers []string // STUN servers to contact
- // Resolver optionally specifies a resolver to use for DNS lookups.
- // If nil, net.DefaultResolver is used.
- Resolver *net.Resolver
+ // DNSCache optionally specifies a DNSCache to use.
+ // If nil, a DNS cache is not used.
+ DNSCache *dnscache.Resolver
// Logf optionally specifies a log function. If nil, logging is disabled.
Logf func(format string, args ...interface{})
@@ -118,9 +119,6 @@ func (s *Stunner) Receive(p []byte, fromAddr *net.UDPAddr) {
}
func (s *Stunner) resolver() *net.Resolver {
- if s.Resolver != nil {
- return s.Resolver
- }
return net.DefaultResolver
}
@@ -192,9 +190,18 @@ func (s *Stunner) sendSTUN(ctx context.Context, server string) error {
}
addr := &net.UDPAddr{Port: addrPort}
- ipAddrs, err := s.resolver().LookupIPAddr(ctx, host)
- if err != nil {
- return fmt.Errorf("lookup ip addr: %v", err)
+ var ipAddrs []net.IPAddr
+ if s.DNSCache != nil {
+ ip, err := s.DNSCache.LookupIP(ctx, host)
+ if err != nil {
+ return fmt.Errorf("lookup ip addr: %v", err)
+ }
+ ipAddrs = []net.IPAddr{{IP: ip}}
+ } else {
+ ipAddrs, err = s.resolver().LookupIPAddr(ctx, host)
+ if err != nil {
+ return fmt.Errorf("lookup ip addr: %v", err)
+ }
}
for _, ipAddr := range ipAddrs {
ip4 := ipAddr.IP.To4()
diff --git a/wgengine/magicsock/magicsock.go b/wgengine/magicsock/magicsock.go
index 20fe7073e..b54b0774d 100644
--- a/wgengine/magicsock/magicsock.go
+++ b/wgengine/magicsock/magicsock.go
@@ -31,6 +31,7 @@ import (
"tailscale.com/derp"
"tailscale.com/derp/derphttp"
"tailscale.com/interfaces"
+ "tailscale.com/net/dnscache"
"tailscale.com/netcheck"
"tailscale.com/stun"
"tailscale.com/stunner"
@@ -638,6 +639,7 @@ func (c *Conn) derpWriteChanOfAddr(addr *net.UDPAddr) chan<- derpWriteRequest {
c.logf("derphttp.NewClient: port %d, host %q invalid? err: %v", addr.Port, host, err)
return nil
}
+ dc.DNSCache = dnscache.Get()
dc.TLSConfig = c.derpTLSConfig
ctx, cancel := context.WithCancel(context.Background())