Instrument async handlers

- instruments async handler for report and for queueing async
requests
- make MustRegister only ever run once to prevent sync issues

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

gateway/handlers/queue_proxy.go

@@ -0,0 +1,69 @@
+// Copyright (c) Alex Ellis 2017. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+package handlers
+
+import (
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"net/url"
+
+	"github.com/gorilla/mux"
+	"github.com/openfaas/faas/gateway/metrics"
+	"github.com/openfaas/faas/gateway/queue"
+)
+
+// MakeQueuedProxy accepts work onto a queue
+func MakeQueuedProxy(metrics metrics.MetricOptions, wildcard bool, canQueueRequests queue.CanQueueRequests, pathTransformer URLPathTransformer) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		defer r.Body.Close()
+
+		body, err := ioutil.ReadAll(r.Body)
+
+		if err != nil {
+			w.WriteHeader(http.StatusBadRequest)
+			w.Write([]byte(err.Error()))
+			return
+		}
+
+		vars := mux.Vars(r)
+		name := vars["name"]
+
+		callbackURLHeader := r.Header.Get("X-Callback-Url")
+		var callbackURL *url.URL
+
+		if len(callbackURLHeader) > 0 {
+			urlVal, urlErr := url.Parse(callbackURLHeader)
+			if urlErr != nil {
+				w.WriteHeader(http.StatusBadRequest)
+				w.Write([]byte(urlErr.Error()))
+				return
+			}
+
+			callbackURL = urlVal
+		}
+
+		req := &queue.Request{
+			Function:    name,
+			Body:        body,
+			Method:      r.Method,
+			QueryString: r.URL.RawQuery,
+			Path:        pathTransformer.Transform(r),
+			Header:      r.Header,
+			Host:        r.Host,
+			CallbackURL: callbackURL,
+		}
+
+		err = canQueueRequests.Queue(req)
+
+		if err != nil {
+			w.WriteHeader(http.StatusInternalServerError)
+			w.Write([]byte(err.Error()))
+			fmt.Println(err)
+			return
+		}
+
+		w.WriteHeader(http.StatusAccepted)
+	}
+}