feature/featuretags: add a catch-all "Debug" feature flag

Saves 168 KB.

Updates #12614

Change-Id: Iaab3ae3efc6ddc7da39629ef13e5ec44976952ba
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/c2n.go

@@ -15,6 +15,8 @@ import (
 	"time"
 
 	"tailscale.com/control/controlclient"
+	"tailscale.com/feature"
+	"tailscale.com/feature/buildfeatures"
 	"tailscale.com/ipn"
 	"tailscale.com/net/sockstats"
 	"tailscale.com/tailcfg"
@@ -130,6 +132,10 @@ func handleC2NLogtailFlush(b *LocalBackend, w http.ResponseWriter, r *http.Reque
 }
 
 func handleC2NDebugNetMap(b *LocalBackend, w http.ResponseWriter, r *http.Request) {
+	if !buildfeatures.HasDebug {
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
+		return
+	}
 	ctx := r.Context()
 	if r.Method != httpm.POST && r.Method != httpm.GET {
 		http.Error(w, "method not allowed", http.StatusMethodNotAllowed)
@@ -190,20 +196,36 @@ func handleC2NDebugNetMap(b *LocalBackend, w http.ResponseWriter, r *http.Reques
 }
 
 func handleC2NDebugGoroutines(_ *LocalBackend, w http.ResponseWriter, r *http.Request) {
+	if !buildfeatures.HasDebug {
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
+		return
+	}
 	w.Header().Set("Content-Type", "text/plain")
 	w.Write(goroutines.ScrubbedGoroutineDump(true))
 }
 
 func handleC2NDebugPrefs(b *LocalBackend, w http.ResponseWriter, r *http.Request) {
+	if !buildfeatures.HasDebug {
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
+		return
+	}
 	writeJSON(w, b.Prefs())
 }
 
 func handleC2NDebugMetrics(_ *LocalBackend, w http.ResponseWriter, r *http.Request) {
+	if !buildfeatures.HasDebug {
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
+		return
+	}
 	w.Header().Set("Content-Type", "text/plain")
 	clientmetric.WritePrometheusExpositionFormat(w)
 }
 
 func handleC2NDebugComponentLogging(b *LocalBackend, w http.ResponseWriter, r *http.Request) {
+	if !buildfeatures.HasDebug {
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
+		return
+	}
 	component := r.FormValue("component")
 	secs, _ := strconv.Atoi(r.FormValue("secs"))
 	if secs == 0 {

ipn/ipnlocal/local.go

@@ -557,12 +557,14 @@ func NewLocalBackend(logf logger.Logf, logID logid.PublicID, sys *tsd.System, lo
 		b.logf("[unexpected] failed to wire up PeerAPI port for engine %T", e)
 	}
 
-	for _, component := range ipn.DebuggableComponents {
-		key := componentStateKey(component)
-		if ut, err := ipn.ReadStoreInt(pm.Store(), key); err == nil {
-			if until := time.Unix(ut, 0); until.After(b.clock.Now()) {
-				// conditional to avoid log spam at start when off
-				b.SetComponentDebugLogging(component, until)
+	if buildfeatures.HasDebug {
+		for _, component := range ipn.DebuggableComponents {
+			key := componentStateKey(component)
+			if ut, err := ipn.ReadStoreInt(pm.Store(), key); err == nil {
+				if until := time.Unix(ut, 0); until.After(b.clock.Now()) {
+					// conditional to avoid log spam at start when off
+					b.SetComponentDebugLogging(component, until)
+				}
 			}
 		}
 	}
@@ -666,6 +668,9 @@ func componentStateKey(component string) ipn.StateKey {
 //   - magicsock
 //   - sockstats
 func (b *LocalBackend) SetComponentDebugLogging(component string, until time.Time) error {
+	if !buildfeatures.HasDebug {
+		return feature.ErrUnavailable
+	}
 	b.mu.Lock()
 	defer b.mu.Unlock()
 
@@ -790,6 +795,9 @@ func (b *LocalBackend) QueryDNS(name string, queryType dnsmessage.Type) (res []b
 // enabled until, or the zero time if component's time is not currently
 // enabled.
 func (b *LocalBackend) GetComponentDebugLogging(component string) time.Time {
+	if !buildfeatures.HasDebug {
+		return time.Time{}
+	}
 	b.mu.Lock()
 	defer b.mu.Unlock()