tailcfg, control/controlclient: add method to exit client from control plane

Change-Id: Ic28ef283ba63396b68fab86bfb0a8ee8f432474c
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

control/controlclient/direct.go

@@ -765,6 +765,10 @@ func (c *Direct) sendMapRequest(ctx context.Context, maxPolls int, cb func(*netm
 		// being conservative here, if Debug not present set to False
 		controlknobs.SetDisableUPnP(hasDebug && resp.Debug.DisableUPnP.EqualBool(true))
 		if hasDebug {
+			if code := resp.Debug.Exit; code != nil {
+				c.logf("exiting process with status %v per controlplane", *code)
+				os.Exit(*code)
+			}
 			if resp.Debug.LogHeapPprof {
 				go logheap.LogHeap(resp.Debug.LogHeapURL)
 			}

tailcfg/tailcfg.go

@@ -48,7 +48,8 @@ import (
 //    22: 2021-06-16: added MapResponse.DNSConfig.ExtraRecords
 //    23: 2021-08-25: DNSConfig.Routes values may be empty (for ExtraRecords support in 1.14.1+)
 //    24: 2021-09-18: MapResponse.Health from control to node; node shows in "tailscale status"
-const CurrentMapRequestVersion = 24
+//    25: 2021-11-01: MapResponse.Debug.Exit
+const CurrentMapRequestVersion = 25
 
 type StableID string
 
@@ -1119,12 +1120,16 @@ type Debug struct {
 	// fixed port.
 	RandomizeClientPort bool `json:",omitempty"`
 
-	/// DisableUPnP is whether the client will attempt to perform a UPnP portmapping.
+	// DisableUPnP is whether the client will attempt to perform a UPnP portmapping.
 	// By default, we want to enable it to see if it works on more clients.
 	//
 	// If UPnP catastrophically fails for people, this should be set to True to kill
 	// new attempts at UPnP connections.
 	DisableUPnP opt.Bool `json:",omitempty"`
+
+	// Exit optionally specifies that the client should os.Exit
+	// with this code.
+	Exit *int `json:",omitempty"`
 }
 
 func appendKey(base []byte, prefix string, k [32]byte) []byte {

version/version.go

@@ -14,7 +14,7 @@ import (
 // Long is a full version number for this build, of the form
 // "x.y.z-commithash", or "date.yyyymmdd" if no actual version was
 // provided.
-var Long = "date.20211022"
+var Long = "date.20211101"
 
 // Short is a short version number for this build, of the form
 // "x.y.z", or "date.yyyymmdd" if no actual version was provided.