ipn/ipnlocal: add c2n handler to flush logtail for support debugging

Updates tailscale/corp#8564

Change-Id: I0c619d4007069f90cffd319fba66bd034d63e84d
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/tailscaled.go

@@ -526,6 +526,9 @@ func getLocalBackend(ctx context.Context, logf logger.Logf, logid string) (_ *ip
 		return nil, fmt.Errorf("ipnlocal.NewLocalBackend: %w", err)
 	}
 	lb.SetVarRoot(opts.VarRoot)
+	if logPol != nil {
+		lb.SetLogFlusher(logPol.Logtail.StartFlush)
+	}
 	if root := lb.TailscaleVarRoot(); root != "" {
 		dnsfallback.SetCachePath(filepath.Join(root, "derpmap.cached.json"))
 	}

ipn/ipnlocal/c2n.go

@@ -26,6 +26,16 @@ func (b *LocalBackend) handleC2N(w http.ResponseWriter, r *http.Request) {
 		// Test handler.
 		body, _ := io.ReadAll(r.Body)
 		w.Write(body)
+	case "/logtail/flush":
+		if r.Method != "POST" {
+			http.Error(w, "bad method", http.StatusMethodNotAllowed)
+			return
+		}
+		if b.TryFlushLogs() {
+			w.WriteHeader(http.StatusNoContent)
+		} else {
+			http.Error(w, "no log flusher wired up", http.StatusInternalServerError)
+		}
 	case "/debug/goroutines":
 		w.Header().Set("Content-Type", "text/plain")
 		w.Write(goroutines.ScrubbedGoroutineDump())

ipn/ipnlocal/local.go

@@ -140,6 +140,7 @@ type LocalBackend struct {
 	gotPortPollRes        chan struct{}    // closed upon first readPoller result
 	newDecompressor       func() (controlclient.Decompressor, error)
 	varRoot               string // or empty if SetVarRoot never called
+	logFlushFunc          func() // or nil if SetLogFlusher wasn't called
 	sshAtomicBool         atomic.Bool
 	shutdownCalled        bool // if Shutdown has been called
 
@@ -3015,6 +3016,25 @@ func (b *LocalBackend) SetVarRoot(dir string) {
 	b.varRoot = dir
 }
 
+// SetLogFlusher sets a func to be called to flush log uploads.
+//
+// It should only be called before the LocalBackend is used.
+func (b *LocalBackend) SetLogFlusher(flushFunc func()) {
+	b.logFlushFunc = flushFunc
+}
+
+// TryFlushLogs calls the log flush function. It returns false if a log flush
+// function was never initialized with SetLogFlusher.
+//
+// TryFlushLogs should not block.
+func (b *LocalBackend) TryFlushLogs() bool {
+	if b.logFlushFunc == nil {
+		return false
+	}
+	b.logFlushFunc()
+	return true
+}
+
 // TailscaleVarRoot returns the root directory of Tailscale's writable
 // storage area. (e.g. "/var/lib/tailscale")
 //

ipn/localapi/localapi.go

@@ -292,6 +292,7 @@ func (h *Handler) serveBugReport(w http.ResponseWriter, r *http.Request) {
 		http.Error(w, "only POST allowed", http.StatusMethodNotAllowed)
 		return
 	}
+	defer h.b.TryFlushLogs() // kick off upload after bugreport's done logging
 
 	logMarker := func() string {
 		return fmt.Sprintf("BUG-%v-%v-%v", h.backendLogID, time.Now().UTC().Format("20060102150405Z"), randHex(8))

logtail/logtail.go

@@ -461,12 +461,24 @@ func (l *Logger) upload(ctx context.Context, body []byte, origlen int) (uploaded
 	return true, nil
 }
 
-// Flush uploads all logs to the server.
+// Flush uploads all logs to the server. It blocks until complete or there is an
-// It blocks until complete or there is an unrecoverable error.
+// unrecoverable error.
+//
+// TODO(bradfitz): this apparently just returns nil, as of tailscale/corp@9c2ec35.
+// Finish cleaning this up.
 func (l *Logger) Flush() error {
 	return nil
 }
 
+// StartFlush starts a log upload, if anything is pending.
+//
+// If l is nil, StartFlush is a no-op.
+func (l *Logger) StartFlush() {
+	if l != nil {
+		l.tryDrainWake()
+	}
+}
+
 // logtailDisabled is whether logtail uploads to logcatcher are disabled.
 var logtailDisabled atomic.Bool
 

tailcfg/tailcfg.go

@@ -88,7 +88,8 @@ type CapabilityVersion int
 //   - 49: 2022-11-03: Client understands EarlyNoise
 //   - 50: 2022-11-14: Client understands CapabilityIngress
 //   - 51: 2022-11-30: Client understands CapabilityTailnetLockAlpha
-const CurrentCapabilityVersion CapabilityVersion = 51
+//   - 52: 2023-01-05: client can handle c2n POST /logtail/flush
+const CurrentCapabilityVersion CapabilityVersion = 52
 
 type StableID string