Add instrumentation to the alert handler

Signed-off-by: Alex Ellis (VMware) <alexellis2@gmail.com>

gateway/handlers/notifier_handler.go

@@ -0,0 +1,44 @@
+// Copyright (c) OpenFaaS Author(s) 2018. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+package handlers
+
+import (
+	"net/http"
+	"time"
+)
+
+// MakeNotifierWrapper wraps a http.HandlerFunc in an interceptor to pass to HTTPNotifier
+func MakeNotifierWrapper(next http.HandlerFunc, notifiers []HTTPNotifier) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		then := time.Now()
+
+		writer := newCustomWriter(w)
+		next(w, r)
+
+		url := r.URL.String()
+		for _, notifier := range notifiers {
+			notifier.Notify(r.Method, url, url, writer.CapturedStatusCode, time.Since(then))
+		}
+	}
+}
+
+func newCustomWriter(w http.ResponseWriter) customWriter {
+	return customWriter{
+		w: w,
+	}
+}
+
+type customWriter struct {
+	CapturedStatusCode int
+	w                  http.ResponseWriter
+}
+
+func (c *customWriter) Write(data []byte) (int, error) {
+	return c.w.Write(data)
+}
+
+func (c *customWriter) WriteHeader(code int) {
+	c.CapturedStatusCode = code
+	c.w.WriteHeader(code)
+}

gateway/server.go

@@ -96,7 +96,7 @@ func main() {
 	faasHandlers.SecretHandler = handlers.MakeForwardingProxyHandler(reverseProxy, forwardingNotifiers, urlResolver, nilURLTransformer)
 
 	alertHandler := plugin.NewExternalServiceQuery(*config.FunctionsProviderURL, credentials)
-	faasHandlers.Alert = handlers.MakeAlertHandler(alertHandler)
+	faasHandlers.Alert = handlers.MakeNotifierWrapper(handlers.MakeAlertHandler(alertHandler), forwardingNotifiers)
 
 	if config.UseNATS() {
 		log.Println("Async enabled: Using NATS Streaming.")
@@ -174,7 +174,7 @@ func main() {
 		r.HandleFunc("/async-function/{name:[-a-zA-Z_0-9]+}", faasHandlers.QueuedProxy).Methods(http.MethodPost)
 		r.HandleFunc("/async-function/{name:[-a-zA-Z_0-9]+}/{params:.*}", faasHandlers.QueuedProxy).Methods(http.MethodPost)
 
-		r.HandleFunc("/system/async-report", faasHandlers.AsyncReport)
+		r.HandleFunc("/system/async-report", handlers.MakeNotifierWrapper(faasHandlers.AsyncReport, forwardingNotifiers))
 	}
 
 	fs := http.FileServer(http.Dir("./assets/"))