tailcfg, ipn, controlclient: add MapResponse.ClientVersion, plumb to IPN bus

Updates #6480

Change-Id: I6321071425cd091148d8140d1eb24dd536bb7984
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/backend.go

@@ -95,6 +95,10 @@ type Notify struct {
 	// macOS Network Extension.
 	LocalTCPPort *uint16 `json:",omitempty"`
 
+	// ClientVersion, if non-nil, describes whether a client version update
+	// is available.
+	ClientVersion *tailcfg.ClientVersion `json:",omitempty"`
+
 	// type is mirrored in xcode/Shared/IPN.swift
 }
 

ipn/ipnlocal/local.go

@@ -1271,6 +1271,7 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 		LinkMonitor:          b.e.GetLinkMonitor(),
 		Pinger:               b,
 		PopBrowserURL:        b.tellClientToBrowseToURL,
+		OnClientVersion:      b.onClientVersion,
 		Dialer:               b.Dialer(),
 		Status:               b.setClientStatus,
 		C2NHandler:           http.HandlerFunc(b.handleC2N),
@@ -1836,6 +1837,21 @@ func (b *LocalBackend) tellClientToBrowseToURL(url string) {
 	}
 }
 
+// onClientVersion is called on MapResponse updates when a MapResponse contains
+// a non-nil ClientVersion message.
+func (b *LocalBackend) onClientVersion(v *tailcfg.ClientVersion) {
+	switch runtime.GOOS {
+	case "darwin", "ios":
+		// These auto-update well enough, and we haven't converted the
+		// ClientVersion types to Swift yet, so don't send them in ipn.Notify
+		// messages.
+	default:
+		// But everything else is a Go client and can deal with this field, even
+		// if they ignore it.
+		b.send(ipn.Notify{ClientVersion: v})
+	}
+}
+
 // For testing lazy machine key generation.
 var panicOnMachineKeyGeneration = envknob.RegisterBool("TS_DEBUG_PANIC_MACHINE_KEY")