control/controlclient: use dnscache.Resolver for Noise client

This passes the *dnscache.Resolver down from the Direct client into the
Noise client and from there into the controlhttp client. This retains
the Resolver so that it can share state across calls instead of creating
a new resolver.

Updates #4845
Updates #6110

Signed-off-by: Andrew Dunham <andrew@du.nham.ca>
Change-Id: Ia5d6af1870f3b5b5d7dd5685d775dcf300aec7af

control/controlclient/noise.go

@@ -19,6 +19,7 @@ import (
 	"golang.org/x/net/http2"
 	"tailscale.com/control/controlbase"
 	"tailscale.com/control/controlhttp"
+	"tailscale.com/net/dnscache"
 	"tailscale.com/net/netmon"
 	"tailscale.com/net/tsdial"
 	"tailscale.com/tailcfg"
@@ -158,6 +159,7 @@ type NoiseClient struct {
 	sfDial singleflight.Group[struct{}, *noiseConn]
 
 	dialer       *tsdial.Dialer
+	dnsCache     *dnscache.Resolver
 	privKey      key.MachinePrivate
 	serverPubKey key.MachinePublic
 	host         string // the host part of serverURL
@@ -179,13 +181,39 @@ type NoiseClient struct {
 	connPool map[int]*noiseConn // active connections not yet closed; see noiseConn.Close
 }
 
+// NoiseOpts contains options for the NewNoiseClient function. All fields are
+// required unless otherwise specified.
+type NoiseOpts struct {
+	// PrivKey is this node's private key.
+	PrivKey key.MachinePrivate
+	// ServerPubKey is the public key of the server.
+	ServerPubKey key.MachinePublic
+	// ServerURL is the URL of the server to connect to.
+	ServerURL string
+	// Dialer's SystemDial function is used to connect to the server.
+	Dialer *tsdial.Dialer
+	// DNSCache is the caching Resolver to use to connect to the server.
+	//
+	// This field can be nil.
+	DNSCache *dnscache.Resolver
+	// Logf is the log function to use. This field can be nil.
+	Logf logger.Logf
+	// NetMon is the network monitor that, if set, will be used to get the
+	// network interface state. This field can be nil; if so, the current
+	// state will be looked up dynamically.
+	NetMon *netmon.Monitor
+	// DialPlan, if set, is a function that should return an explicit plan
+	// on how to connect to the server.
+	DialPlan func() *tailcfg.ControlDialPlan
+}
+
 // NewNoiseClient returns a new noiseClient for the provided server and machine key.
 // serverURL is of the form https://<host>:<port> (no trailing slash).
 //
 // netMon may be nil, if non-nil it's used to do faster interface lookups.
 // dialPlan may be nil
-func NewNoiseClient(privKey key.MachinePrivate, serverPubKey key.MachinePublic, serverURL string, dialer *tsdial.Dialer, logf logger.Logf, netMon *netmon.Monitor, dialPlan func() *tailcfg.ControlDialPlan) (*NoiseClient, error) {
-	u, err := url.Parse(serverURL)
+func NewNoiseClient(opts NoiseOpts) (*NoiseClient, error) {
+	u, err := url.Parse(opts.ServerURL)
 	if err != nil {
 		return nil, err
 	}
@@ -205,16 +233,18 @@ func NewNoiseClient(privKey key.MachinePrivate, serverPubKey key.MachinePublic,
 		httpPort = "80"
 		httpsPort = "443"
 	}
+
 	np := &NoiseClient{
-		serverPubKey: serverPubKey,
-		privKey:      privKey,
+		serverPubKey: opts.ServerPubKey,
+		privKey:      opts.PrivKey,
 		host:         u.Hostname(),
 		httpPort:     httpPort,
 		httpsPort:    httpsPort,
-		dialer:       dialer,
-		dialPlan:     dialPlan,
-		logf:         logf,
-		netMon:       netMon,
+		dialer:       opts.Dialer,
+		dnsCache:     opts.DNSCache,
+		dialPlan:     opts.DialPlan,
+		logf:         opts.Logf,
+		netMon:       opts.NetMon,
 	}
 
 	// Create the HTTP/2 Transport using a net/http.Transport
@@ -373,6 +403,7 @@ func (nc *NoiseClient) dial() (*noiseConn, error) {
 		ControlKey:      nc.serverPubKey,
 		ProtocolVersion: uint16(tailcfg.CurrentCapabilityVersion),
 		Dialer:          nc.dialer.SystemDial,
+		DNSCache:        nc.dnsCache,
 		DialPlan:        dialPlan,
 		Logf:            nc.logf,
 		NetMon:          nc.netMon,