Add golang echo backend sample

src/envoy/prototype/README.md

@@ -33,8 +33,7 @@ This Proxy will use Envoy and talk to Mixer server.
 
 ```
   cd test/backend/echo
-  npm install
-  node echo.js
+  go run echo.go
 ```
 
 * Start Envoy proxy, run

test/backend/echo/README.md

@@ -1,3 +1,3 @@
-# Simple echo server for esp testing.
+# Simple echo server for proxy testing.
 
-Node.js implementation of echo server.
+golang implementation of echo server.

test/backend/echo/echo.go

@@ -0,0 +1,76 @@
+// Copyright 2016 Google Inc. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//    http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// An example implementation of Echo backend in go.
+
+package main
+
+import (
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"net/http"
+	"strconv"
+	"sync"
+	"time"
+)
+
+var (
+	port = flag.Int("port", 8080, "default http port")
+
+	mu       sync.Mutex
+	requests = 0
+	data     = 0
+)
+
+func handler(w http.ResponseWriter, r *http.Request) {
+	body, err := ioutil.ReadAll(r.Body)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+		return
+	}
+
+	// echo back the Content-Type and Content-Length in the response
+	for _, k := range []string{"Content-Type", "Content-Length"} {
+		if v := r.Header.Get(k); v != "" {
+			w.Header().Set(k, v)
+		}
+	}
+	w.WriteHeader(http.StatusOK)
+	w.Write(body)
+
+	mu.Lock()
+	requests++
+	data += len(body)
+	defer mu.Unlock()
+}
+
+func main() {
+	flag.Parse()
+
+	go func() {
+		for {
+			mu.Lock()
+			fmt.Printf("Requests Requests: %v  Data: %v\n", requests, data)
+			mu.Unlock()
+			time.Sleep(time.Second)
+		}
+	}()
+
+	fmt.Printf("Listening on port %v\n", *port)
+
+	http.HandleFunc("/", handler)
+	http.ListenAndServe(":"+strconv.Itoa(*port), nil)
+}