ipn/ipnlocal: add a few metrics for PeerAPI and LocalAPI

Mainly motivated by wanting to know how much Taildrop is used, but
also useful when tracking down how many invalid requests are
generated.

Signed-off-by: Mihai Parparita <mihai@tailscale.com>

ipn/ipnlocal/peerapi.go

@@ -678,6 +678,7 @@ func peerAPIRequestShouldGetSecurityHeaders(r *http.Request) bool {
 
 func (h *peerAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if err := h.validatePeerAPIRequest(r); err != nil {
+		metricInvalidRequests.Add(1)
 		h.logf("invalid request from %v: %v", h.remoteAddr, err)
 		http.Error(w, "invalid peerapi request", http.StatusForbidden)
 		return
@@ -688,10 +689,12 @@ func (h *peerAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("X-Content-Type-Options", "nosniff")
 	}
 	if strings.HasPrefix(r.URL.Path, "/v0/put/") {
+		metricPutCalls.Add(1)
 		h.handlePeerPut(w, r)
 		return
 	}
 	if strings.HasPrefix(r.URL.Path, "/dns-query") {
+		metricDNSCalls.Add(1)
 		h.handleDNSQuery(w, r)
 		return
 	}
@@ -712,12 +715,14 @@ func (h *peerAPIHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		h.handleServeDNSFwd(w, r)
 		return
 	case "/v0/wol":
+		metricWakeOnLANCalls.Add(1)
 		h.handleWakeOnLAN(w, r)
 		return
 	case "/v0/interfaces":
 		h.handleServeInterfaces(w, r)
 		return
 	case "/v0/ingress":
+		metricIngressCalls.Add(1)
 		h.handleServeIngress(w, r)
 		return
 	}
@@ -1441,3 +1446,13 @@ func (fl *fakePeerAPIListener) Accept() (net.Conn, error) {
 }
 
 func (fl *fakePeerAPIListener) Addr() net.Addr { return fl.addr }
+
+var (
+	metricInvalidRequests = clientmetric.NewCounter("peerapi_invalid_requests")
+
+	// Non-debug PeerAPI endpoints.
+	metricPutCalls       = clientmetric.NewCounter("peerapi_put")
+	metricDNSCalls       = clientmetric.NewCounter("peerapi_dns")
+	metricWakeOnLANCalls = clientmetric.NewCounter("peerapi_wol")
+	metricIngressCalls   = clientmetric.NewCounter("peerapi_ingress")
+)

ipn/localapi/localapi.go

@@ -146,6 +146,7 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 	if r.Referer() != "" || r.Header.Get("Origin") != "" || !validHost(r.Host) {
+		metricInvalidRequests.Add(1)
 		http.Error(w, "invalid localapi request", http.StatusForbidden)
 		return
 	}
@@ -156,10 +157,12 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if h.RequiredPassword != "" {
 		_, pass, ok := r.BasicAuth()
 		if !ok {
+			metricInvalidRequests.Add(1)
 			http.Error(w, "auth required", http.StatusUnauthorized)
 			return
 		}
 		if pass != h.RequiredPassword {
+			metricInvalidRequests.Add(1)
 			http.Error(w, "bad password", http.StatusForbidden)
 			return
 		}
@@ -895,6 +898,8 @@ func (h *Handler) serveFileTargets(w http.ResponseWriter, r *http.Request) {
 //
 //   - PUT /localapi/v0/file-put/:stableID/:escaped-filename
 func (h *Handler) serveFilePut(w http.ResponseWriter, r *http.Request) {
+	metricFilePutCalls.Add(1)
+
 	if !h.PermitWrite {
 		http.Error(w, "file access denied", http.StatusForbidden)
 		return
@@ -1425,3 +1430,10 @@ func defBool(a string, def bool) bool {
 	}
 	return v
 }
+
+var (
+	metricInvalidRequests = clientmetric.NewCounter("localapi_invalid_requests")
+
+	// User-visible LocalAPI endpoints.
+	metricFilePutCalls = clientmetric.NewCounter("localapi_file_put")
+)