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>

client/local/local.go

@@ -31,6 +31,8 @@ import (
 	"tailscale.com/client/tailscale/apitype"
 	"tailscale.com/drive"
 	"tailscale.com/envknob"
+	"tailscale.com/feature"
+	"tailscale.com/feature/buildfeatures"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnstate"
 	"tailscale.com/net/netutil"
@@ -608,6 +610,9 @@ func (lc *Client) SetDevStoreKeyValue(ctx context.Context, key, value string) er
 // the provided duration. If the duration is in the past, the debug logging
 // is disabled.
 func (lc *Client) SetComponentDebugLogging(ctx context.Context, component string, d time.Duration) error {
+	if !buildfeatures.HasDebug {
+		return feature.ErrUnavailable
+	}
 	body, err := lc.send(ctx, "POST",
 		fmt.Sprintf("/localapi/v0/component-debug-logging?component=%s&secs=%d",
 			url.QueryEscape(component), int64(d.Seconds())), 200, nil)
@@ -862,6 +867,9 @@ func (lc *Client) EditPrefs(ctx context.Context, mp *ipn.MaskedPrefs) (*ipn.Pref
 // GetDNSOSConfig returns the system DNS configuration for the current device.
 // That is, it returns the DNS configuration that the system would use if Tailscale weren't being used.
 func (lc *Client) GetDNSOSConfig(ctx context.Context) (*apitype.DNSOSConfig, error) {
+	if !buildfeatures.HasDNS {
+		return nil, feature.ErrUnavailable
+	}
 	body, err := lc.get200(ctx, "/localapi/v0/dns-osconfig")
 	if err != nil {
 		return nil, err
@@ -877,6 +885,9 @@ func (lc *Client) GetDNSOSConfig(ctx context.Context) (*apitype.DNSOSConfig, err
 // It returns the raw DNS response bytes and the resolvers that were used to answer the query
 // (often just one, but can be more if we raced multiple resolvers).
 func (lc *Client) QueryDNS(ctx context.Context, name string, queryType string) (bytes []byte, resolvers []*dnstype.Resolver, err error) {
+	if !buildfeatures.HasDNS {
+		return nil, nil, feature.ErrUnavailable
+	}
 	body, err := lc.get200(ctx, fmt.Sprintf("/localapi/v0/dns-query?name=%s&type=%s", url.QueryEscape(name), queryType))
 	if err != nil {
 		return nil, nil, err

cmd/tailscaled/depaware-min.txt

@@ -106,7 +106,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/net/portmapper/portmappertype                  from tailscale.com/net/netcheck+
         tailscale.com/net/sockopts                                   from tailscale.com/wgengine/magicsock
         tailscale.com/net/sockstats                                  from tailscale.com/control/controlclient+
-        tailscale.com/net/stun                                       from tailscale.com/ipn/localapi+
+        tailscale.com/net/stun                                       from tailscale.com/net/netcheck+
         tailscale.com/net/tlsdial                                    from tailscale.com/control/controlclient+
         tailscale.com/net/tlsdial/blockblame                         from tailscale.com/net/tlsdial
         tailscale.com/net/tsaddr                                     from tailscale.com/ipn+
@@ -141,7 +141,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext
         tailscale.com/types/netlogtype                               from tailscale.com/net/connstats
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+
-        tailscale.com/types/nettype                                  from tailscale.com/ipn/localapi+
+        tailscale.com/types/nettype                                  from tailscale.com/net/batching+
         tailscale.com/types/opt                                      from tailscale.com/control/controlknobs+
         tailscale.com/types/persist                                  from tailscale.com/control/controlclient+
         tailscale.com/types/preftype                                 from tailscale.com/ipn+

cmd/tailscaled/depaware-minbox.txt

@@ -129,7 +129,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/net/portmapper/portmappertype                  from tailscale.com/net/netcheck+
         tailscale.com/net/sockopts                                   from tailscale.com/wgengine/magicsock
         tailscale.com/net/sockstats                                  from tailscale.com/control/controlclient+
-        tailscale.com/net/stun                                       from tailscale.com/ipn/localapi+
+        tailscale.com/net/stun                                       from tailscale.com/net/netcheck+
         tailscale.com/net/tlsdial                                    from tailscale.com/control/controlclient+
         tailscale.com/net/tlsdial/blockblame                         from tailscale.com/net/tlsdial
         tailscale.com/net/tsaddr                                     from tailscale.com/ipn+
@@ -166,7 +166,7 @@ tailscale.com/cmd/tailscaled dependencies: (generated by github.com/tailscale/de
         tailscale.com/types/mapx                                     from tailscale.com/ipn/ipnext
         tailscale.com/types/netlogtype                               from tailscale.com/net/connstats
         tailscale.com/types/netmap                                   from tailscale.com/control/controlclient+
-        tailscale.com/types/nettype                                  from tailscale.com/ipn/localapi+
+        tailscale.com/types/nettype                                  from tailscale.com/net/batching+
         tailscale.com/types/opt                                      from tailscale.com/control/controlknobs+
         tailscale.com/types/persist                                  from tailscale.com/control/controlclient+
         tailscale.com/types/preftype                                 from tailscale.com/ipn+

control/controlclient/direct.go

@@ -1193,7 +1193,7 @@ func (c *Direct) handleDebugMessage(ctx context.Context, debug *tailcfg.Debug) e
 		c.logf("exiting process with status %v per controlplane", *code)
 		os.Exit(*code)
 	}
-	if debug.DisableLogTail {
+	if buildfeatures.HasLogTail && debug.DisableLogTail {
 		logtail.Disable()
 		envknob.SetNoLogsNoSupport()
 	}

feature/buildfeatures/feature_debug_disabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build ts_omit_debug
+
+package buildfeatures
+
+// HasDebug is whether the binary was built with support for modular feature "various debug support, for things that don't have or need their own more specific feature".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_debug" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasDebug = false

feature/buildfeatures/feature_debug_enabled.go

@@ -0,0 +1,13 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// Code generated by gen.go; DO NOT EDIT.
+
+//go:build !ts_omit_debug
+
+package buildfeatures
+
+// HasDebug is whether the binary was built with support for modular feature "various debug support, for things that don't have or need their own more specific feature".
+// Specifically, it's whether the binary was NOT built with the "ts_omit_debug" build tag.
+// It's a const so it can be used for dead code elimination.
+const HasDebug = true

feature/featuretags/featuretags.go

@@ -97,6 +97,7 @@ var Features = map[FeatureTag]FeatureMeta{
 	"clientupdate":  {"ClientUpdate", "Client auto-update support", nil},
 	"completion":    {"Completion", "CLI shell completion", nil},
 	"dbus":          {"DBus", "Linux DBus support", nil},
+	"debug":         {"Debug", "various debug support, for things that don't have or need their own more specific feature", nil},
 	"debugeventbus": {"DebugEventBus", "eventbus debug support", nil},
 	"debugportmapper": {
 		Sym:  "DebugPortMapper",

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 {
+	if buildfeatures.HasDebug {
-		key := componentStateKey(component)
+		for _, component := range ipn.DebuggableComponents {
-		if ut, err := ipn.ReadStoreInt(pm.Store(), key); err == nil {
+			key := componentStateKey(component)
-			if until := time.Unix(ut, 0); until.After(b.clock.Now()) {
+			if ut, err := ipn.ReadStoreInt(pm.Store(), key); err == nil {
-				// conditional to avoid log spam at start when off
+				if until := time.Unix(ut, 0); until.After(b.clock.Now()) {
-				b.SetComponentDebugLogging(component, until)
+					// 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()
 

ipn/localapi/debug.go

@@ -0,0 +1,465 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+//go:build !ts_omit_debug
+
+package localapi
+
+import (
+	"context"
+	"encoding/json"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/netip"
+	"reflect"
+	"slices"
+	"strconv"
+	"sync"
+	"time"
+
+	"tailscale.com/feature"
+	"tailscale.com/feature/buildfeatures"
+	"tailscale.com/ipn"
+	"tailscale.com/types/logger"
+	"tailscale.com/util/eventbus"
+	"tailscale.com/util/httpm"
+)
+
+func init() {
+	Register("component-debug-logging", (*Handler).serveComponentDebugLogging)
+	Register("debug", (*Handler).serveDebug)
+	Register("dev-set-state-store", (*Handler).serveDevSetStateStore)
+	Register("debug-bus-events", (*Handler).serveDebugBusEvents)
+	Register("debug-bus-graph", (*Handler).serveEventBusGraph)
+	Register("debug-derp-region", (*Handler).serveDebugDERPRegion)
+	Register("debug-dial-types", (*Handler).serveDebugDialTypes)
+	Register("debug-log", (*Handler).serveDebugLog)
+	Register("debug-packet-filter-matches", (*Handler).serveDebugPacketFilterMatches)
+	Register("debug-packet-filter-rules", (*Handler).serveDebugPacketFilterRules)
+	Register("debug-peer-endpoint-changes", (*Handler).serveDebugPeerEndpointChanges)
+}
+
+func (h *Handler) serveDebugPeerEndpointChanges(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitRead {
+		http.Error(w, "status access denied", http.StatusForbidden)
+		return
+	}
+
+	ipStr := r.FormValue("ip")
+	if ipStr == "" {
+		http.Error(w, "missing 'ip' parameter", http.StatusBadRequest)
+		return
+	}
+	ip, err := netip.ParseAddr(ipStr)
+	if err != nil {
+		http.Error(w, "invalid IP", http.StatusBadRequest)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+	chs, err := h.b.GetPeerEndpointChanges(r.Context(), ip)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	e := json.NewEncoder(w)
+	e.SetIndent("", "\t")
+	e.Encode(chs)
+}
+
+func (h *Handler) serveComponentDebugLogging(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitWrite {
+		http.Error(w, "debug access denied", http.StatusForbidden)
+		return
+	}
+	component := r.FormValue("component")
+	secs, _ := strconv.Atoi(r.FormValue("secs"))
+	err := h.b.SetComponentDebugLogging(component, h.clock.Now().Add(time.Duration(secs)*time.Second))
+	var res struct {
+		Error string
+	}
+	if err != nil {
+		res.Error = err.Error()
+	}
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(res)
+}
+
+func (h *Handler) serveDebugDialTypes(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitWrite {
+		http.Error(w, "debug-dial-types access denied", http.StatusForbidden)
+		return
+	}
+	if r.Method != httpm.POST {
+		http.Error(w, "only POST allowed", http.StatusMethodNotAllowed)
+		return
+	}
+
+	ip := r.FormValue("ip")
+	port := r.FormValue("port")
+	network := r.FormValue("network")
+
+	addr := ip + ":" + port
+	if _, err := netip.ParseAddrPort(addr); err != nil {
+		w.WriteHeader(http.StatusBadRequest)
+		fmt.Fprintf(w, "invalid address %q: %v", addr, err)
+		return
+	}
+
+	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
+	defer cancel()
+
+	var bareDialer net.Dialer
+
+	dialer := h.b.Dialer()
+
+	var peerDialer net.Dialer
+	peerDialer.Control = dialer.PeerDialControlFunc()
+
+	// Kick off a dial with each available dialer in parallel.
+	dialers := []struct {
+		name string
+		dial func(context.Context, string, string) (net.Conn, error)
+	}{
+		{"SystemDial", dialer.SystemDial},
+		{"UserDial", dialer.UserDial},
+		{"PeerDial", peerDialer.DialContext},
+		{"BareDial", bareDialer.DialContext},
+	}
+	type result struct {
+		name string
+		conn net.Conn
+		err  error
+	}
+	results := make(chan result, len(dialers))
+
+	var wg sync.WaitGroup
+	for _, dialer := range dialers {
+		dialer := dialer // loop capture
+
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			conn, err := dialer.dial(ctx, network, addr)
+			results <- result{dialer.name, conn, err}
+		}()
+	}
+
+	wg.Wait()
+	for range len(dialers) {
+		res := <-results
+		fmt.Fprintf(w, "[%s] connected=%v err=%v\n", res.name, res.conn != nil, res.err)
+		if res.conn != nil {
+			res.conn.Close()
+		}
+	}
+}
+
+func (h *Handler) serveDebug(w http.ResponseWriter, r *http.Request) {
+	if !buildfeatures.HasDebug {
+		http.Error(w, "debug not supported in this build", http.StatusNotImplemented)
+		return
+	}
+	if !h.PermitWrite {
+		http.Error(w, "debug access denied", http.StatusForbidden)
+		return
+	}
+	if r.Method != httpm.POST {
+		http.Error(w, "POST required", http.StatusMethodNotAllowed)
+		return
+	}
+	// The action is normally in a POST form parameter, but
+	// some actions (like "notify") want a full JSON body, so
+	// permit some to have their action in a header.
+	var action string
+	switch v := r.Header.Get("Debug-Action"); v {
+	case "notify":
+		action = v
+	default:
+		action = r.FormValue("action")
+	}
+	var err error
+	switch action {
+	case "derp-set-homeless":
+		h.b.MagicConn().SetHomeless(true)
+	case "derp-unset-homeless":
+		h.b.MagicConn().SetHomeless(false)
+	case "rebind":
+		err = h.b.DebugRebind()
+	case "restun":
+		err = h.b.DebugReSTUN()
+	case "notify":
+		var n ipn.Notify
+		err = json.NewDecoder(r.Body).Decode(&n)
+		if err != nil {
+			break
+		}
+		h.b.DebugNotify(n)
+	case "notify-last-netmap":
+		h.b.DebugNotifyLastNetMap()
+	case "break-tcp-conns":
+		err = h.b.DebugBreakTCPConns()
+	case "break-derp-conns":
+		err = h.b.DebugBreakDERPConns()
+	case "force-netmap-update":
+		h.b.DebugForceNetmapUpdate()
+	case "control-knobs":
+		k := h.b.ControlKnobs()
+		w.Header().Set("Content-Type", "application/json")
+		err = json.NewEncoder(w).Encode(k.AsDebugJSON())
+		if err == nil {
+			return
+		}
+	case "pick-new-derp":
+		err = h.b.DebugPickNewDERP()
+	case "force-prefer-derp":
+		var n int
+		err = json.NewDecoder(r.Body).Decode(&n)
+		if err != nil {
+			break
+		}
+		h.b.DebugForcePreferDERP(n)
+	case "peer-relay-servers":
+		servers := h.b.DebugPeerRelayServers().Slice()
+		slices.SortFunc(servers, func(a, b netip.Addr) int {
+			return a.Compare(b)
+		})
+		err = json.NewEncoder(w).Encode(servers)
+		if err == nil {
+			return
+		}
+	case "":
+		err = fmt.Errorf("missing parameter 'action'")
+	default:
+		err = fmt.Errorf("unknown action %q", action)
+	}
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusBadRequest)
+		return
+	}
+	w.Header().Set("Content-Type", "text/plain")
+	io.WriteString(w, "done\n")
+}
+
+func (h *Handler) serveDevSetStateStore(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitWrite {
+		http.Error(w, "debug access denied", http.StatusForbidden)
+		return
+	}
+	if r.Method != httpm.POST {
+		http.Error(w, "POST required", http.StatusMethodNotAllowed)
+		return
+	}
+	if err := h.b.SetDevStateStore(r.FormValue("key"), r.FormValue("value")); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+	w.Header().Set("Content-Type", "text/plain")
+	io.WriteString(w, "done\n")
+}
+
+func (h *Handler) serveDebugPacketFilterRules(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitWrite {
+		http.Error(w, "debug access denied", http.StatusForbidden)
+		return
+	}
+	nm := h.b.NetMap()
+	if nm == nil {
+		http.Error(w, "no netmap", http.StatusNotFound)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+
+	enc := json.NewEncoder(w)
+	enc.SetIndent("", "\t")
+	enc.Encode(nm.PacketFilterRules)
+}
+
+func (h *Handler) serveDebugPacketFilterMatches(w http.ResponseWriter, r *http.Request) {
+	if !h.PermitWrite {
+		http.Error(w, "debug access denied", http.StatusForbidden)
+		return
+	}
+	nm := h.b.NetMap()
+	if nm == nil {
+		http.Error(w, "no netmap", http.StatusNotFound)
+		return
+	}
+	w.Header().Set("Content-Type", "application/json")
+
+	enc := json.NewEncoder(w)
+	enc.SetIndent("", "\t")
+	enc.Encode(nm.PacketFilter)
+}
+
+// debugEventError provides the JSON encoding of internal errors from event processing.
+type debugEventError struct {
+	Error string
+}
+
+// serveDebugBusEvents taps into the tailscaled/utils/eventbus and streams
+// events to the client.
+func (h *Handler) serveDebugBusEvents(w http.ResponseWriter, r *http.Request) {
+	// Require write access (~root) as the logs could contain something
+	// sensitive.
+	if !h.PermitWrite {
+		http.Error(w, "event bus access denied", http.StatusForbidden)
+		return
+	}
+	if r.Method != httpm.GET {
+		http.Error(w, "GET required", http.StatusMethodNotAllowed)
+		return
+	}
+
+	bus, ok := h.LocalBackend().Sys().Bus.GetOK()
+	if !ok {
+		http.Error(w, "event bus not running", http.StatusNoContent)
+		return
+	}
+
+	f, ok := w.(http.Flusher)
+	if !ok {
+		http.Error(w, "streaming unsupported", http.StatusInternalServerError)
+		return
+	}
+
+	io.WriteString(w, `{"Event":"[event listener connected]\n"}`+"\n")
+	f.Flush()
+
+	mon := bus.Debugger().WatchBus()
+	defer mon.Close()
+
+	i := 0
+	for {
+		select {
+		case <-r.Context().Done():
+			fmt.Fprintf(w, `{"Event":"[event listener closed]\n"}`)
+			return
+		case <-mon.Done():
+			return
+		case event := <-mon.Events():
+			data := eventbus.DebugEvent{
+				Count: i,
+				Type:  reflect.TypeOf(event.Event).String(),
+				Event: event.Event,
+				From:  event.From.Name(),
+			}
+			for _, client := range event.To {
+				data.To = append(data.To, client.Name())
+			}
+
+			if msg, err := json.Marshal(data); err != nil {
+				data.Event = debugEventError{Error: fmt.Sprintf(
+					"failed to marshal JSON for %T", event.Event,
+				)}
+				if errMsg, err := json.Marshal(data); err != nil {
+					fmt.Fprintf(w,
+						`{"Count": %d, "Event":"[ERROR] failed to marshal JSON for %T\n"}`,
+						i, event.Event)
+				} else {
+					w.Write(errMsg)
+				}
+			} else {
+				w.Write(msg)
+			}
+			f.Flush()
+			i++
+		}
+	}
+}
+
+// serveEventBusGraph taps into the event bus and dumps out the active graph of
+// publishers and subscribers. It does not represent anything about the messages
+// exchanged.
+func (h *Handler) serveEventBusGraph(w http.ResponseWriter, r *http.Request) {
+	if r.Method != httpm.GET {
+		http.Error(w, "GET required", http.StatusMethodNotAllowed)
+		return
+	}
+
+	bus, ok := h.LocalBackend().Sys().Bus.GetOK()
+	if !ok {
+		http.Error(w, "event bus not running", http.StatusPreconditionFailed)
+		return
+	}
+
+	debugger := bus.Debugger()
+	clients := debugger.Clients()
+
+	graph := map[string]eventbus.DebugTopic{}
+
+	for _, client := range clients {
+		for _, pub := range debugger.PublishTypes(client) {
+			topic, ok := graph[pub.Name()]
+			if !ok {
+				topic = eventbus.DebugTopic{Name: pub.Name()}
+			}
+			topic.Publisher = client.Name()
+			graph[pub.Name()] = topic
+		}
+		for _, sub := range debugger.SubscribeTypes(client) {
+			topic, ok := graph[sub.Name()]
+			if !ok {
+				topic = eventbus.DebugTopic{Name: sub.Name()}
+			}
+			topic.Subscribers = append(topic.Subscribers, client.Name())
+			graph[sub.Name()] = topic
+		}
+	}
+
+	// The top level map is not really needed for the client, convert to a list.
+	topics := eventbus.DebugTopics{}
+	for _, v := range graph {
+		topics.Topics = append(topics.Topics, v)
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	json.NewEncoder(w).Encode(topics)
+}
+
+func (h *Handler) serveDebugLog(w http.ResponseWriter, r *http.Request) {
+	if !buildfeatures.HasLogTail {
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
+		return
+	}
+	if !h.PermitRead {
+		http.Error(w, "debug-log access denied", http.StatusForbidden)
+		return
+	}
+	if r.Method != httpm.POST {
+		http.Error(w, "only POST allowed", http.StatusMethodNotAllowed)
+		return
+	}
+	defer h.b.TryFlushLogs() // kick off upload after we're done logging
+
+	type logRequestJSON struct {
+		Lines  []string
+		Prefix string
+	}
+
+	var logRequest logRequestJSON
+	if err := json.NewDecoder(r.Body).Decode(&logRequest); err != nil {
+		http.Error(w, "invalid JSON body", http.StatusBadRequest)
+		return
+	}
+
+	prefix := logRequest.Prefix
+	if prefix == "" {
+		prefix = "debug-log"
+	}
+	logf := logger.WithPrefix(h.logf, prefix+": ")
+
+	// We can write logs too fast for logtail to handle, even when
+	// opting-out of rate limits. Limit ourselves to at most one message
+	// per 20ms and a burst of 60 log lines, which should be fast enough to
+	// not block for too long but slow enough that we can upload all lines.
+	logf = logger.SlowLoggerWithClock(r.Context(), logf, 20*time.Millisecond, 60, h.clock.Now)
+
+	for _, line := range logRequest.Lines {
+		logf("%s", line)
+	}
+
+	w.WriteHeader(http.StatusNoContent)
+}

ipn/localapi/debugderp.go

@@ -1,6 +1,8 @@
 // Copyright (c) Tailscale Inc & AUTHORS
 // SPDX-License-Identifier: BSD-3-Clause
 
+//go:build !ts_omit_debug
+
 package localapi
 
 import (

ipn/localapi/localapi.go

@@ -7,7 +7,6 @@ package localapi
 import (
 	"bytes"
 	"cmp"
-	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -16,7 +15,6 @@ import (
 	"net/http"
 	"net/netip"
 	"net/url"
-	"reflect"
 	"runtime"
 	"slices"
 	"strconv"
@@ -80,18 +78,7 @@ var handler = map[string]LocalAPIHandler{
 	"check-prefs":                  (*Handler).serveCheckPrefs,
 	"check-reverse-path-filtering": (*Handler).serveCheckReversePathFiltering,
 	"check-udp-gro-forwarding":     (*Handler).serveCheckUDPGROForwarding,
-	"component-debug-logging":      (*Handler).serveComponentDebugLogging,
-	"debug":                        (*Handler).serveDebug,
-	"debug-bus-events":             (*Handler).serveDebugBusEvents,
-	"debug-bus-graph":              (*Handler).serveEventBusGraph,
-	"debug-derp-region":            (*Handler).serveDebugDERPRegion,
-	"debug-dial-types":             (*Handler).serveDebugDialTypes,
-	"debug-log":                    (*Handler).serveDebugLog,
-	"debug-packet-filter-matches":  (*Handler).serveDebugPacketFilterMatches,
-	"debug-packet-filter-rules":    (*Handler).serveDebugPacketFilterRules,
-	"debug-peer-endpoint-changes":  (*Handler).serveDebugPeerEndpointChanges,
 	"derpmap":                      (*Handler).serveDERPMap,
-	"dev-set-state-store":          (*Handler).serveDevSetStateStore,
 	"dial":                         (*Handler).serveDial,
 	"disconnect-control":           (*Handler).disconnectControl,
 	"dns-osconfig":                 (*Handler).serveDNSOSConfig,
@@ -638,352 +625,6 @@ func (h *Handler) serveUserMetrics(w http.ResponseWriter, r *http.Request) {
 	h.b.UserMetricsRegistry().Handler(w, r)
 }
 
-func (h *Handler) serveDebug(w http.ResponseWriter, r *http.Request) {
-	if !h.PermitWrite {
-		http.Error(w, "debug access denied", http.StatusForbidden)
-		return
-	}
-	if r.Method != httpm.POST {
-		http.Error(w, "POST required", http.StatusMethodNotAllowed)
-		return
-	}
-	// The action is normally in a POST form parameter, but
-	// some actions (like "notify") want a full JSON body, so
-	// permit some to have their action in a header.
-	var action string
-	switch v := r.Header.Get("Debug-Action"); v {
-	case "notify":
-		action = v
-	default:
-		action = r.FormValue("action")
-	}
-	var err error
-	switch action {
-	case "derp-set-homeless":
-		h.b.MagicConn().SetHomeless(true)
-	case "derp-unset-homeless":
-		h.b.MagicConn().SetHomeless(false)
-	case "rebind":
-		err = h.b.DebugRebind()
-	case "restun":
-		err = h.b.DebugReSTUN()
-	case "notify":
-		var n ipn.Notify
-		err = json.NewDecoder(r.Body).Decode(&n)
-		if err != nil {
-			break
-		}
-		h.b.DebugNotify(n)
-	case "notify-last-netmap":
-		h.b.DebugNotifyLastNetMap()
-	case "break-tcp-conns":
-		err = h.b.DebugBreakTCPConns()
-	case "break-derp-conns":
-		err = h.b.DebugBreakDERPConns()
-	case "force-netmap-update":
-		h.b.DebugForceNetmapUpdate()
-	case "control-knobs":
-		k := h.b.ControlKnobs()
-		w.Header().Set("Content-Type", "application/json")
-		err = json.NewEncoder(w).Encode(k.AsDebugJSON())
-		if err == nil {
-			return
-		}
-	case "pick-new-derp":
-		err = h.b.DebugPickNewDERP()
-	case "force-prefer-derp":
-		var n int
-		err = json.NewDecoder(r.Body).Decode(&n)
-		if err != nil {
-			break
-		}
-		h.b.DebugForcePreferDERP(n)
-	case "peer-relay-servers":
-		servers := h.b.DebugPeerRelayServers().Slice()
-		slices.SortFunc(servers, func(a, b netip.Addr) int {
-			return a.Compare(b)
-		})
-		err = json.NewEncoder(w).Encode(servers)
-		if err == nil {
-			return
-		}
-	case "":
-		err = fmt.Errorf("missing parameter 'action'")
-	default:
-		err = fmt.Errorf("unknown action %q", action)
-	}
-	if err != nil {
-		http.Error(w, err.Error(), http.StatusBadRequest)
-		return
-	}
-	w.Header().Set("Content-Type", "text/plain")
-	io.WriteString(w, "done\n")
-}
-
-func (h *Handler) serveDevSetStateStore(w http.ResponseWriter, r *http.Request) {
-	if !h.PermitWrite {
-		http.Error(w, "debug access denied", http.StatusForbidden)
-		return
-	}
-	if r.Method != httpm.POST {
-		http.Error(w, "POST required", http.StatusMethodNotAllowed)
-		return
-	}
-	if err := h.b.SetDevStateStore(r.FormValue("key"), r.FormValue("value")); err != nil {
-		http.Error(w, err.Error(), http.StatusInternalServerError)
-		return
-	}
-	w.Header().Set("Content-Type", "text/plain")
-	io.WriteString(w, "done\n")
-}
-
-func (h *Handler) serveDebugPacketFilterRules(w http.ResponseWriter, r *http.Request) {
-	if !h.PermitWrite {
-		http.Error(w, "debug access denied", http.StatusForbidden)
-		return
-	}
-	nm := h.b.NetMap()
-	if nm == nil {
-		http.Error(w, "no netmap", http.StatusNotFound)
-		return
-	}
-	w.Header().Set("Content-Type", "application/json")
-
-	enc := json.NewEncoder(w)
-	enc.SetIndent("", "\t")
-	enc.Encode(nm.PacketFilterRules)
-}
-
-func (h *Handler) serveDebugPacketFilterMatches(w http.ResponseWriter, r *http.Request) {
-	if !h.PermitWrite {
-		http.Error(w, "debug access denied", http.StatusForbidden)
-		return
-	}
-	nm := h.b.NetMap()
-	if nm == nil {
-		http.Error(w, "no netmap", http.StatusNotFound)
-		return
-	}
-	w.Header().Set("Content-Type", "application/json")
-
-	enc := json.NewEncoder(w)
-	enc.SetIndent("", "\t")
-	enc.Encode(nm.PacketFilter)
-}
-
-// EventError provides the JSON encoding of internal errors from event processing.
-type EventError struct {
-	Error string
-}
-
-// serveDebugBusEvents taps into the tailscaled/utils/eventbus and streams
-// events to the client.
-func (h *Handler) serveDebugBusEvents(w http.ResponseWriter, r *http.Request) {
-	// Require write access (~root) as the logs could contain something
-	// sensitive.
-	if !h.PermitWrite {
-		http.Error(w, "event bus access denied", http.StatusForbidden)
-		return
-	}
-	if r.Method != httpm.GET {
-		http.Error(w, "GET required", http.StatusMethodNotAllowed)
-		return
-	}
-
-	bus, ok := h.LocalBackend().Sys().Bus.GetOK()
-	if !ok {
-		http.Error(w, "event bus not running", http.StatusNoContent)
-		return
-	}
-
-	f, ok := w.(http.Flusher)
-	if !ok {
-		http.Error(w, "streaming unsupported", http.StatusInternalServerError)
-		return
-	}
-
-	io.WriteString(w, `{"Event":"[event listener connected]\n"}`+"\n")
-	f.Flush()
-
-	mon := bus.Debugger().WatchBus()
-	defer mon.Close()
-
-	i := 0
-	for {
-		select {
-		case <-r.Context().Done():
-			fmt.Fprintf(w, `{"Event":"[event listener closed]\n"}`)
-			return
-		case <-mon.Done():
-			return
-		case event := <-mon.Events():
-			data := eventbus.DebugEvent{
-				Count: i,
-				Type:  reflect.TypeOf(event.Event).String(),
-				Event: event.Event,
-				From:  event.From.Name(),
-			}
-			for _, client := range event.To {
-				data.To = append(data.To, client.Name())
-			}
-
-			if msg, err := json.Marshal(data); err != nil {
-				data.Event = EventError{Error: fmt.Sprintf(
-					"failed to marshal JSON for %T", event.Event,
-				)}
-				if errMsg, err := json.Marshal(data); err != nil {
-					fmt.Fprintf(w,
-						`{"Count": %d, "Event":"[ERROR] failed to marshal JSON for %T\n"}`,
-						i, event.Event)
-				} else {
-					w.Write(errMsg)
-				}
-			} else {
-				w.Write(msg)
-			}
-			f.Flush()
-			i++
-		}
-	}
-}
-
-// serveEventBusGraph taps into the event bus and dumps out the active graph of
-// publishers and subscribers. It does not represent anything about the messages
-// exchanged.
-func (h *Handler) serveEventBusGraph(w http.ResponseWriter, r *http.Request) {
-	if r.Method != httpm.GET {
-		http.Error(w, "GET required", http.StatusMethodNotAllowed)
-		return
-	}
-
-	bus, ok := h.LocalBackend().Sys().Bus.GetOK()
-	if !ok {
-		http.Error(w, "event bus not running", http.StatusPreconditionFailed)
-		return
-	}
-
-	debugger := bus.Debugger()
-	clients := debugger.Clients()
-
-	graph := map[string]eventbus.DebugTopic{}
-
-	for _, client := range clients {
-		for _, pub := range debugger.PublishTypes(client) {
-			topic, ok := graph[pub.Name()]
-			if !ok {
-				topic = eventbus.DebugTopic{Name: pub.Name()}
-			}
-			topic.Publisher = client.Name()
-			graph[pub.Name()] = topic
-		}
-		for _, sub := range debugger.SubscribeTypes(client) {
-			topic, ok := graph[sub.Name()]
-			if !ok {
-				topic = eventbus.DebugTopic{Name: sub.Name()}
-			}
-			topic.Subscribers = append(topic.Subscribers, client.Name())
-			graph[sub.Name()] = topic
-		}
-	}
-
-	// The top level map is not really needed for the client, convert to a list.
-	topics := eventbus.DebugTopics{}
-	for _, v := range graph {
-		topics.Topics = append(topics.Topics, v)
-	}
-
-	w.Header().Set("Content-Type", "application/json")
-	json.NewEncoder(w).Encode(topics)
-}
-
-func (h *Handler) serveComponentDebugLogging(w http.ResponseWriter, r *http.Request) {
-	if !h.PermitWrite {
-		http.Error(w, "debug access denied", http.StatusForbidden)
-		return
-	}
-	component := r.FormValue("component")
-	secs, _ := strconv.Atoi(r.FormValue("secs"))
-	err := h.b.SetComponentDebugLogging(component, h.clock.Now().Add(time.Duration(secs)*time.Second))
-	var res struct {
-		Error string
-	}
-	if err != nil {
-		res.Error = err.Error()
-	}
-	w.Header().Set("Content-Type", "application/json")
-	json.NewEncoder(w).Encode(res)
-}
-
-func (h *Handler) serveDebugDialTypes(w http.ResponseWriter, r *http.Request) {
-	if !h.PermitWrite {
-		http.Error(w, "debug-dial-types access denied", http.StatusForbidden)
-		return
-	}
-	if r.Method != httpm.POST {
-		http.Error(w, "only POST allowed", http.StatusMethodNotAllowed)
-		return
-	}
-
-	ip := r.FormValue("ip")
-	port := r.FormValue("port")
-	network := r.FormValue("network")
-
-	addr := ip + ":" + port
-	if _, err := netip.ParseAddrPort(addr); err != nil {
-		w.WriteHeader(http.StatusBadRequest)
-		fmt.Fprintf(w, "invalid address %q: %v", addr, err)
-		return
-	}
-
-	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
-	defer cancel()
-
-	var bareDialer net.Dialer
-
-	dialer := h.b.Dialer()
-
-	var peerDialer net.Dialer
-	peerDialer.Control = dialer.PeerDialControlFunc()
-
-	// Kick off a dial with each available dialer in parallel.
-	dialers := []struct {
-		name string
-		dial func(context.Context, string, string) (net.Conn, error)
-	}{
-		{"SystemDial", dialer.SystemDial},
-		{"UserDial", dialer.UserDial},
-		{"PeerDial", peerDialer.DialContext},
-		{"BareDial", bareDialer.DialContext},
-	}
-	type result struct {
-		name string
-		conn net.Conn
-		err  error
-	}
-	results := make(chan result, len(dialers))
-
-	var wg sync.WaitGroup
-	for _, dialer := range dialers {
-		dialer := dialer // loop capture
-
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			conn, err := dialer.dial(ctx, network, addr)
-			results <- result{dialer.name, conn, err}
-		}()
-	}
-
-	wg.Wait()
-	for range len(dialers) {
-		res := <-results
-		fmt.Fprintf(w, "[%s] connected=%v err=%v\n", res.name, res.conn != nil, res.err)
-		if res.conn != nil {
-			res.conn.Close()
-		}
-	}
-}
-
 // servePprofFunc is the implementation of Handler.servePprof, after auth,
 // for platforms where we want to link it in.
 var servePprofFunc func(http.ResponseWriter, *http.Request)
@@ -1116,6 +757,10 @@ func (h *Handler) serveCheckUDPGROForwarding(w http.ResponseWriter, r *http.Requ
 }
 
 func (h *Handler) serveSetUDPGROForwarding(w http.ResponseWriter, r *http.Request) {
+	if !buildfeatures.HasGRO {
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
+		return
+	}
 	if !h.PermitWrite {
 		http.Error(w, "UDP GRO forwarding set access denied", http.StatusForbidden)
 		return
@@ -1149,34 +794,6 @@ func (h *Handler) serveStatus(w http.ResponseWriter, r *http.Request) {
 	e.Encode(st)
 }
 
-func (h *Handler) serveDebugPeerEndpointChanges(w http.ResponseWriter, r *http.Request) {
-	if !h.PermitRead {
-		http.Error(w, "status access denied", http.StatusForbidden)
-		return
-	}
-
-	ipStr := r.FormValue("ip")
-	if ipStr == "" {
-		http.Error(w, "missing 'ip' parameter", http.StatusBadRequest)
-		return
-	}
-	ip, err := netip.ParseAddr(ipStr)
-	if err != nil {
-		http.Error(w, "invalid IP", http.StatusBadRequest)
-		return
-	}
-	w.Header().Set("Content-Type", "application/json")
-	chs, err := h.b.GetPeerEndpointChanges(r.Context(), ip)
-	if err != nil {
-		http.Error(w, err.Error(), http.StatusInternalServerError)
-		return
-	}
-
-	e := json.NewEncoder(w)
-	e.SetIndent("", "\t")
-	e.Encode(chs)
-}
-
 // InUseOtherUserIPNStream reports whether r is a request for the watch-ipn-bus
 // handler. If so, it writes an ipn.Notify InUseOtherUser message to the user
 // and returns true. Otherwise it returns false, in which case it doesn't write
@@ -1842,47 +1459,6 @@ func defBool(a string, def bool) bool {
 	return v
 }
 
-func (h *Handler) serveDebugLog(w http.ResponseWriter, r *http.Request) {
-	if !h.PermitRead {
-		http.Error(w, "debug-log access denied", http.StatusForbidden)
-		return
-	}
-	if r.Method != httpm.POST {
-		http.Error(w, "only POST allowed", http.StatusMethodNotAllowed)
-		return
-	}
-	defer h.b.TryFlushLogs() // kick off upload after we're done logging
-
-	type logRequestJSON struct {
-		Lines  []string
-		Prefix string
-	}
-
-	var logRequest logRequestJSON
-	if err := json.NewDecoder(r.Body).Decode(&logRequest); err != nil {
-		http.Error(w, "invalid JSON body", http.StatusBadRequest)
-		return
-	}
-
-	prefix := logRequest.Prefix
-	if prefix == "" {
-		prefix = "debug-log"
-	}
-	logf := logger.WithPrefix(h.logf, prefix+": ")
-
-	// We can write logs too fast for logtail to handle, even when
-	// opting-out of rate limits. Limit ourselves to at most one message
-	// per 20ms and a burst of 60 log lines, which should be fast enough to
-	// not block for too long but slow enough that we can upload all lines.
-	logf = logger.SlowLoggerWithClock(r.Context(), logf, 20*time.Millisecond, 60, h.clock.Now)
-
-	for _, line := range logRequest.Lines {
-		logf("%s", line)
-	}
-
-	w.WriteHeader(http.StatusNoContent)
-}
-
 // serveUpdateCheck returns the ClientVersion from Status, which contains
 // information on whether an update is available, and if so, what version,
 // *if* we support auto-updates on this platform. If we don't, this endpoint
@@ -1917,7 +1493,7 @@ func (h *Handler) serveUpdateCheck(w http.ResponseWriter, r *http.Request) {
 // supported by the OS.
 func (h *Handler) serveDNSOSConfig(w http.ResponseWriter, r *http.Request) {
 	if !buildfeatures.HasDNS {
-		http.NotFound(w, r)
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
 		return
 	}
 	if r.Method != httpm.GET {
@@ -1964,7 +1540,7 @@ func (h *Handler) serveDNSOSConfig(w http.ResponseWriter, r *http.Request) {
 // The response if successful is a DNSQueryResponse JSON object.
 func (h *Handler) serveDNSQuery(w http.ResponseWriter, r *http.Request) {
 	if !buildfeatures.HasDNS {
-		http.NotFound(w, r)
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
 		return
 	}
 	if r.Method != httpm.GET {

ipn/localapi/syspolicy_api.go

@@ -17,7 +17,7 @@ import (
 )
 
 func init() {
-	handler["policy/"] = (*Handler).servePolicy
+	Register("policy/", (*Handler).servePolicy)
 }
 
 func (h *Handler) servePolicy(w http.ResponseWriter, r *http.Request) {

ipn/localapi/tailnetlock.go

@@ -18,19 +18,19 @@ import (
 )
 
 func init() {
-	handler["tka/affected-sigs"] = (*Handler).serveTKAAffectedSigs
+	Register("tka/affected-sigs", (*Handler).serveTKAAffectedSigs)
-	handler["tka/cosign-recovery-aum"] = (*Handler).serveTKACosignRecoveryAUM
+	Register("tka/cosign-recovery-aum", (*Handler).serveTKACosignRecoveryAUM)
-	handler["tka/disable"] = (*Handler).serveTKADisable
+	Register("tka/disable", (*Handler).serveTKADisable)
-	handler["tka/force-local-disable"] = (*Handler).serveTKALocalDisable
+	Register("tka/force-local-disable", (*Handler).serveTKALocalDisable)
-	handler["tka/generate-recovery-aum"] = (*Handler).serveTKAGenerateRecoveryAUM
+	Register("tka/generate-recovery-aum", (*Handler).serveTKAGenerateRecoveryAUM)
-	handler["tka/init"] = (*Handler).serveTKAInit
+	Register("tka/init", (*Handler).serveTKAInit)
-	handler["tka/log"] = (*Handler).serveTKALog
+	Register("tka/log", (*Handler).serveTKALog)
-	handler["tka/modify"] = (*Handler).serveTKAModify
+	Register("tka/modify", (*Handler).serveTKAModify)
-	handler["tka/sign"] = (*Handler).serveTKASign
+	Register("tka/sign", (*Handler).serveTKASign)
-	handler["tka/status"] = (*Handler).serveTKAStatus
+	Register("tka/status", (*Handler).serveTKAStatus)
-	handler["tka/submit-recovery-aum"] = (*Handler).serveTKASubmitRecoveryAUM
+	Register("tka/submit-recovery-aum", (*Handler).serveTKASubmitRecoveryAUM)
-	handler["tka/verify-deeplink"] = (*Handler).serveTKAVerifySigningDeeplink
+	Register("tka/verify-deeplink", (*Handler).serveTKAVerifySigningDeeplink)
-	handler["tka/wrap-preauth-key"] = (*Handler).serveTKAWrapPreauthKey
+	Register("tka/wrap-preauth-key", (*Handler).serveTKAWrapPreauthKey)
 }
 
 func (h *Handler) serveTKAStatus(w http.ResponseWriter, r *http.Request) {

wgengine/magicsock/debughttp.go

@@ -13,6 +13,8 @@ import (
 	"strings"
 	"time"
 
+	"tailscale.com/feature"
+	"tailscale.com/feature/buildfeatures"
 	"tailscale.com/tailcfg"
 	"tailscale.com/tstime/mono"
 	"tailscale.com/types/key"
@@ -24,6 +26,11 @@ import (
 // /debug/magicsock) or via peerapi to a peer that's owned by the same
 // user (so they can e.g. inspect their phones).
 func (c *Conn) ServeHTTPDebug(w http.ResponseWriter, r *http.Request) {
+	if !buildfeatures.HasDebug {
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
+		return
+	}
+
 	c.mu.Lock()
 	defer c.mu.Unlock()