all: generate discovery key, plumb it around

Not actually used yet.

Updates #483

wgengine/magicsock/magicsock.go

@@ -84,6 +84,8 @@ type Conn struct {
 	lastEndpoints         []string
 	peerSet               map[key.Public]struct{}
 
+	discoPrivate key.Private
+
 	// addrsByUDP is a map of every remote ip:port to a priority
 	// list of endpoint addresses for a peer.
 	// The priority list is provided by wgengine configuration.
@@ -476,6 +478,14 @@ func (c *Conn) SetNetInfoCallback(fn func(*tailcfg.NetInfo)) {
 	}
 }
 
+// SetDiscoPrivateKey sets the discovery key.
+func (c *Conn) SetDiscoPrivateKey(k key.Private) {
+	c.mu.Lock()
+	defer c.mu.Unlock()
+	c.discoPrivate = k
+	c.logf("magicsock: disco key set; public: %x", k.Public())
+}
+
 // c.mu must NOT be held.
 func (c *Conn) setNearestDERP(derpNum int) (wantDERP bool) {
 	c.mu.Lock()

wgengine/userspace.go

@@ -830,6 +830,10 @@ func (e *userspaceEngine) SetDERPMap(dm *tailcfg.DERPMap) {
 	e.magicConn.SetDERPMap(dm)
 }
 
+func (e *userspaceEngine) SetDiscoPrivateKey(k key.Private) {
+	e.magicConn.SetDiscoPrivateKey(k)
+}
+
 func (e *userspaceEngine) UpdateStatus(sb *ipnstate.StatusBuilder) {
 	st, err := e.getStatus()
 	if err != nil {

wgengine/watchdog.go

@@ -13,6 +13,7 @@ import (
 	"github.com/tailscale/wireguard-go/wgcfg"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/tailcfg"
+	"tailscale.com/types/key"
 	"tailscale.com/wgengine/filter"
 	"tailscale.com/wgengine/router"
 	"tailscale.com/wgengine/tsdns"
@@ -96,6 +97,9 @@ func (e *watchdogEngine) LinkChange(isExpensive bool) {
 func (e *watchdogEngine) SetDERPMap(m *tailcfg.DERPMap) {
 	e.watchdog("SetDERPMap", func() { e.wrap.SetDERPMap(m) })
 }
+func (e *watchdogEngine) SetDiscoPrivateKey(k key.Private) {
+	e.watchdog("SetDiscoPrivateKey", func() { e.wrap.SetDiscoPrivateKey(k) })
+}
 func (e *watchdogEngine) Close() {
 	e.watchdog("Close", e.wrap.Close)
 }

wgengine/wgengine.go

@@ -11,6 +11,7 @@ import (
 	"github.com/tailscale/wireguard-go/wgcfg"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/tailcfg"
+	"tailscale.com/types/key"
 	"tailscale.com/wgengine/filter"
 	"tailscale.com/wgengine/router"
 	"tailscale.com/wgengine/tsdns"
@@ -56,6 +57,7 @@ type Engine interface {
 	//
 	// This is called whenever the tailcontrol (control plane)
 	// sends an updated network map.
+
 	//
 	// The returned error is ErrNoChanges if no changes were made.
 	Reconfig(*wgcfg.Config, *router.Config) error
@@ -108,6 +110,10 @@ type Engine interface {
 	// new NetInfo summary is available.
 	SetNetInfoCallback(NetInfoCallback)
 
+	// SetDiscoPrivateKey sets the private key used for path discovery
+	// messages.
+	SetDiscoPrivateKey(key.Private)
+
 	// UpdateStatus populates the network state using the provided
 	// status builder.
 	UpdateStatus(*ipnstate.StatusBuilder)