Add a per-request counter to the Prometheus metrics

server/server.go

@@ -13,10 +13,23 @@ import (
 
 	"git.autistici.org/ai3/go-common/clientutil"
 	"git.autistici.org/ai3/go-common/serverutil"
+	"github.com/prometheus/client_golang/prometheus"
 
 	as "git.autistici.org/ai3/accountserver"
 )
 
+var (
+	requestCounter = prometheus.NewCounterVec(prometheus.CounterOpts{
+		Name: "accountserver_requests_total",
+		Help: "Total number of requests, by type",
+	},
+		[]string{"method", "status"})
+)
+
+func init() {
+	prometheus.MustRegister(requestCounter)
+}
+
 type actionRegistry struct {
 	service  *as.AccountService
 	handlers map[string]reflect.Type
@@ -33,18 +46,22 @@ func (r *actionRegistry) Register(path string, rtype as.Request) {
 	r.handlers[path] = reflect.ValueOf(rtype).Elem().Type()
 }
 
-func (r *actionRegistry) newRequest(path string) (as.Request, bool) {
+// Create a new instance of a Request type, along with the type name
+// (used for monitoring).
+func (r *actionRegistry) newRequest(path string) (as.Request, string, bool) {
 	h, ok := r.handlers[path]
 	if !ok {
-		return nil, false
+		return nil, "", false
 	}
-	return reflect.New(h).Interface().(as.Request), true
+	return reflect.New(h).Interface().(as.Request),
+		strings.TrimSuffix(h.Name(), "Request"),
+		true
 }
 
 func (r *actionRegistry) ServeHTTP(w http.ResponseWriter, httpReq *http.Request) {
 	// Create a new empty request object based on the request
 	// path, then decode the HTTP request JSON body onto it.
-	req, ok := r.newRequest(httpReq.URL.Path)
+	req, reqTypeName, ok := r.newRequest(httpReq.URL.Path)
 	if !ok {
 		http.NotFound(w, httpReq)
 		return
@@ -76,12 +93,17 @@ func (r *actionRegistry) ServeHTTP(w http.ResponseWriter, httpReq *http.Request)
 	// Now that all is done, we can log the request/response
 	// (sanitization might modify the objects in place).
 	reqData := marshalJSONSanitized(req)
+	reqStatus := "error"
 	if err != nil {
 		log.Printf("request: %s %s -> ERROR: %v", httpReq.URL.Path, reqData, err)
 	} else {
 		respData := marshalJSONSanitized(resp)
 		log.Printf("request: %s %s -> %s", httpReq.URL.Path, reqData, respData)
+		reqStatus = "ok"
 	}
+
+	// Increment the request metric.
+	requestCounter.WithLabelValues(reqTypeName, reqStatus).Inc()
 }
 
 // APIServer is the HTTP API interface to AccountService. It