feature/featuretags, all: add build features, use existing ones in more places

Saves 270 KB.

Updates #12614

Change-Id: I4c3fe06d32c49edb3a4bb0758a8617d83f291cf5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipnlocal/c2n.go

@@ -10,6 +10,7 @@ import (
 	"net/http"
 	"path"
 	"reflect"
+	"runtime"
 	"strconv"
 	"strings"
 	"time"
@@ -33,26 +34,34 @@ import (
 // exists for that, a map entry with an empty method is used as a fallback.
 var c2nHandlers = map[methodAndPath]c2nHandler{
 	// Debug.
-	req("/echo"):                    handleC2NEcho,
-	req("/debug/goroutines"):        handleC2NDebugGoroutines,
-	req("/debug/prefs"):             handleC2NDebugPrefs,
-	req("/debug/metrics"):           handleC2NDebugMetrics,
-	req("/debug/component-logging"): handleC2NDebugComponentLogging,
-	req("/debug/logheap"):           handleC2NDebugLogHeap,
-	req("/debug/netmap"):            handleC2NDebugNetMap,
+	req("/echo"): handleC2NEcho,
+}
 
-	// PPROF - We only expose a subset of typical pprof endpoints for security.
-	req("/debug/pprof/heap"):   handleC2NPprof,
-	req("/debug/pprof/allocs"): handleC2NPprof,
+func init() {
+	if buildfeatures.HasSSH {
+		RegisterC2N("/ssh/usernames", handleC2NSSHUsernames)
+	}
+	if buildfeatures.HasLogTail {
+		RegisterC2N("POST /logtail/flush", handleC2NLogtailFlush)
+	}
+	if buildfeatures.HasDebug {
+		RegisterC2N("POST /sockstats", handleC2NSockStats)
 
-	req("POST /logtail/flush"): handleC2NLogtailFlush,
-	req("POST /sockstats"):     handleC2NSockStats,
+		// pprof:
+		// we only expose a subset of typical pprof endpoints for security.
+		RegisterC2N("/debug/pprof/heap", handleC2NPprof)
+		RegisterC2N("/debug/pprof/allocs", handleC2NPprof)
 
-	// SSH
-	req("/ssh/usernames"): handleC2NSSHUsernames,
-
-	// Linux netfilter.
-	req("POST /netfilter-kind"): handleC2NSetNetfilterKind,
+		RegisterC2N("/debug/goroutines", handleC2NDebugGoroutines)
+		RegisterC2N("/debug/prefs", handleC2NDebugPrefs)
+		RegisterC2N("/debug/metrics", handleC2NDebugMetrics)
+		RegisterC2N("/debug/component-logging", handleC2NDebugComponentLogging)
+		RegisterC2N("/debug/logheap", handleC2NDebugLogHeap)
+		RegisterC2N("/debug/netmap", handleC2NDebugNetMap)
+	}
+	if runtime.GOOS == "linux" && buildfeatures.HasOSRouter {
+		RegisterC2N("POST /netfilter-kind", handleC2NSetNetfilterKind)
+	}
 }
 
 // RegisterC2N registers a new c2n handler for the given pattern.
@@ -265,6 +274,10 @@ func handleC2NPprof(b *LocalBackend, w http.ResponseWriter, r *http.Request) {
 }
 
 func handleC2NSSHUsernames(b *LocalBackend, w http.ResponseWriter, r *http.Request) {
+	if !buildfeatures.HasSSH {
+		http.Error(w, feature.ErrUnavailable.Error(), http.StatusNotImplemented)
+		return
+	}
 	var req tailcfg.C2NSSHUsernamesRequest
 	if r.Method == "POST" {
 		if err := json.NewDecoder(r.Body).Decode(&req); err != nil {

ipn/ipnlocal/local.go

@@ -1442,7 +1442,7 @@ func (b *LocalBackend) WhoIs(proto string, ipp netip.AddrPort) (n tailcfg.NodeVi
 
 	cn := b.currentNode()
 	nid, ok := cn.NodeByAddr(ipp.Addr())
-	if !ok {
+	if !ok && buildfeatures.HasNetstack {
 		var ip netip.Addr
 		if ipp.Port() != 0 {
 			var protos []string
@@ -5015,6 +5015,9 @@ func (b *LocalBackend) SetVarRoot(dir string) {
 //
 // It should only be called before the LocalBackend is used.
 func (b *LocalBackend) SetLogFlusher(flushFunc func()) {
+	if !buildfeatures.HasLogTail {
+		return
+	}
 	b.logFlushFunc = flushFunc
 }
 
@@ -5023,7 +5026,7 @@ func (b *LocalBackend) SetLogFlusher(flushFunc func()) {
 //
 // TryFlushLogs should not block.
 func (b *LocalBackend) TryFlushLogs() bool {
-	if b.logFlushFunc == nil {
+	if !buildfeatures.HasLogTail || b.logFlushFunc == nil {
 		return false
 	}
 	b.logFlushFunc()

ipn/ipnlocal/peerapi.go

@@ -354,33 +354,35 @@ func (h *peerAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 			return
 		}
 	}
-	if strings.HasPrefix(r.URL.Path, "/dns-query") {
+	if buildfeatures.HasDNS && strings.HasPrefix(r.URL.Path, "/dns-query") {
 		metricDNSCalls.Add(1)
 		h.handleDNSQuery(w, r)
 		return
 	}
-	switch r.URL.Path {
-	case "/v0/goroutines":
-		h.handleServeGoroutines(w, r)
-		return
-	case "/v0/env":
-		h.handleServeEnv(w, r)
-		return
-	case "/v0/metrics":
-		h.handleServeMetrics(w, r)
-		return
-	case "/v0/magicsock":
-		h.handleServeMagicsock(w, r)
-		return
-	case "/v0/dnsfwd":
-		h.handleServeDNSFwd(w, r)
-		return
-	case "/v0/interfaces":
-		h.handleServeInterfaces(w, r)
-		return
-	case "/v0/sockstats":
-		h.handleServeSockStats(w, r)
-		return
+	if buildfeatures.HasDebug {
+		switch r.URL.Path {
+		case "/v0/goroutines":
+			h.handleServeGoroutines(w, r)
+			return
+		case "/v0/env":
+			h.handleServeEnv(w, r)
+			return
+		case "/v0/metrics":
+			h.handleServeMetrics(w, r)
+			return
+		case "/v0/magicsock":
+			h.handleServeMagicsock(w, r)
+			return
+		case "/v0/dnsfwd":
+			h.handleServeDNSFwd(w, r)
+			return
+		case "/v0/interfaces":
+			h.handleServeInterfaces(w, r)
+			return
+		case "/v0/sockstats":
+			h.handleServeSockStats(w, r)
+			return
+		}
 	}
 	if ph, ok := peerAPIHandlers[r.URL.Path]; ok {
 		ph(h, w, r)