Add proof of concepts in hack/

hack/failonceserver/main.go

@@ -0,0 +1,32 @@
+package main
+
+import (
+	"net/http"
+	"sync"
+)
+
+func main() {
+	// HTTP server that fails once and then succeeds for a given request path
+	var mtx sync.RWMutex
+	paths := map[string]bool{}
+
+	http.ListenAndServe(":8080", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		mtx.RLock()
+		shouldSucceed := paths[r.URL.Path]
+		mtx.RUnlock()
+
+		defer func() {
+			mtx.Lock()
+			paths[r.URL.Path] = true
+			mtx.Unlock()
+		}()
+
+		if !shouldSucceed {
+			w.WriteHeader(http.StatusServiceUnavailable)
+			w.Write([]byte("failure\n"))
+			return
+		}
+
+		w.Write([]byte("success\n"))
+	}))
+}

hack/failserver/main.go

@@ -0,0 +1,10 @@
+package main
+
+import "net/http"
+
+func main() {
+	http.ListenAndServe(":8081", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.WriteHeader(http.StatusServiceUnavailable)
+		w.Write([]byte("unavailable\n"))
+	}))
+}

hack/retryproxy/main.go

@@ -0,0 +1,48 @@
+package main
+
+import (
+	"errors"
+	"log"
+	"net/http"
+	"net/http/httputil"
+	"net/url"
+)
+
+func main() {
+	// go run ./hack/failserver
+	u1, err := url.Parse("http://localhost:8081")
+	if err != nil {
+		panic(err)
+	}
+	p1 := httputil.NewSingleHostReverseProxy(u1)
+
+	// go run ./hack/successserver
+	u2, err := url.Parse("http://localhost:8082")
+	if err != nil {
+		panic(err)
+	}
+	p2 := httputil.NewSingleHostReverseProxy(u2)
+
+	p1.ModifyResponse = func(r *http.Response) error {
+		if r.StatusCode == http.StatusServiceUnavailable {
+			// Returning an error will trigger the ErrorHandler.
+			return errRetry
+		}
+		return nil
+	}
+
+	p1.ErrorHandler = func(w http.ResponseWriter, r *http.Request, err error) {
+		if err == errRetry {
+			log.Println("retrying")
+			// Simulate calling the next backend.
+			p2.ServeHTTP(w, r)
+			return
+		}
+	}
+
+	http.ListenAndServe(":8080", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		p1.ServeHTTP(w, r)
+	}))
+}
+
+var errRetry = errors.New("retry")

hack/successserver/main.go

@@ -0,0 +1,9 @@
+package main
+
+import "net/http"
+
+func main() {
+	http.ListenAndServe(":8082", http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		w.Write([]byte("success\n"))
+	}))
+}