Add exponential backoff example

Author: tomarrell

examples/exponential_backoff/main.go

@@ -0,0 +1,97 @@
+package main
+
+import (
+	"encoding/base64"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io"
+	"log"
+	"math"
+	"net/http"
+	"os"
+	"strings"
+)
+
+var (
+	url   = "https://localhost:8080"
+	topic = "test_topic"
+)
+
+func main() {
+	flag.Parse()
+
+	publish()
+	consume(0)
+}
+
+func publish() {
+	log := log.New(os.Stdout, "producer: ", 0)
+
+	msg := "hello_world"
+	res, err := http.Post(fmt.Sprintf("%s/publish/%s", url, topic), "application/json", strings.NewReader(msg))
+	if err != nil {
+		log.Fatalf("failed to publish: %v\n", err)
+	}
+	if res.StatusCode != http.StatusCreated {
+		log.Fatalf("failed to publish, received status code: %d\n", res.StatusCode)
+	}
+
+	log.Printf("published message %s\n", msg)
+}
+
+type subRes struct {
+	Msg       string `json:"msg"`
+	Error     string `json:"error"`
+	DackCount int    `json:"dackCount"`
+}
+
+func consume(id int) {
+	for {
+		log := log.New(os.Stdout, fmt.Sprintf("consumer-%d: ", id), 0)
+
+		reader, writer := io.Pipe()
+		enc := json.NewEncoder(writer)
+		go func() {
+			_ = enc.Encode("INIT")
+		}()
+
+		res, err := http.Post(fmt.Sprintf("%s/subscribe/%s", url, topic), "application/json", reader)
+		if err != nil {
+			log.Fatalf("failed to consume: %v", err)
+		}
+		if res.StatusCode != http.StatusOK {
+			log.Fatalf("failed to consume, received status code: %d", res.StatusCode)
+		}
+
+		dec := json.NewDecoder(res.Body)
+
+		for {
+			var out subRes
+			if _ = dec.Decode(&out); err != nil {
+				log.Fatalf("failed decode response body: %v\n", err)
+			}
+
+			if out.Error != "" {
+				log.Fatalf("received error: %s\n", out.Error)
+			}
+
+			delay := int(math.Pow(2, float64(out.DackCount)))
+
+			strMsg := mustBase64Decode(out.Msg)
+			log.Printf("consumed message: %s\n", strMsg)
+			log.Printf("delaying message: %s by %ds\n", strMsg, delay)
+
+			_ = enc.Encode(fmt.Sprintf("DACK %d", delay))
+		}
+	}
+}
+
+func mustBase64Decode(b string) string {
+	s, err := base64.StdEncoding.DecodeString(string(b))
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	return string(s)
+}