retry only on real network errors

Now retries only happen when actual network errors occur and not only
anymore based on the HTTP status code. This is because the backend could
also send this status codes as their normal interface and in that case
we don't want to retry.

middlewares/retry_test.go

@@ -1,6 +1,7 @@
 package middlewares
 
 import (
+	"context"
 	"fmt"
 	"io/ioutil"
 	"net/http"
@@ -41,7 +42,7 @@ func TestRetry(t *testing.T) {
 			t.Parallel()
 
 			var httpHandler http.Handler
-			httpHandler = &networkFailingHTTPHandler{failAtCalls: tc.failAtCalls}
+			httpHandler = &networkFailingHTTPHandler{failAtCalls: tc.failAtCalls, netErrorRecorder: &DefaultNetErrorRecorder{}}
 			httpHandler = NewRetry(tc.attempts, httpHandler, tc.listener)
 
 			recorder := httptest.NewRecorder()
@@ -62,10 +63,38 @@ func TestRetry(t *testing.T) {
 	}
 }
 
+func TestDefaultNetErrorRecorderSuccess(t *testing.T) {
+	boolNetErrorOccurred := false
+	recorder := DefaultNetErrorRecorder{}
+	recorder.Record(context.WithValue(context.Background(), defaultNetErrCtxKey, &boolNetErrorOccurred))
+	if !boolNetErrorOccurred {
+		t.Errorf("got %v after recording net error, wanted %v", boolNetErrorOccurred, true)
+	}
+}
+
+func TestDefaultNetErrorRecorderInvalidValueType(t *testing.T) {
+	stringNetErrorOccured := "nonsense"
+	recorder := DefaultNetErrorRecorder{}
+	recorder.Record(context.WithValue(context.Background(), defaultNetErrCtxKey, &stringNetErrorOccured))
+	if stringNetErrorOccured != "nonsense" {
+		t.Errorf("got %v after recording net error, wanted %v", stringNetErrorOccured, "nonsense")
+	}
+}
+
+func TestDefaultNetErrorRecorderNilValue(t *testing.T) {
+	nilNetErrorOccured := interface{}(nil)
+	recorder := DefaultNetErrorRecorder{}
+	recorder.Record(context.WithValue(context.Background(), defaultNetErrCtxKey, &nilNetErrorOccured))
+	if nilNetErrorOccured != interface{}(nil) {
+		t.Errorf("got %v after recording net error, wanted %v", nilNetErrorOccured, interface{}(nil))
+	}
+}
+
 // networkFailingHTTPHandler is an http.Handler implementation you can use to test retries.
 type networkFailingHTTPHandler struct {
-	failAtCalls []int
-	callNumber  int
+	netErrorRecorder NetErrorRecorder
+	failAtCalls      []int
+	callNumber       int
 }
 
 func (handler *networkFailingHTTPHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
@@ -73,6 +102,8 @@ func (handler *networkFailingHTTPHandler) ServeHTTP(w http.ResponseWriter, r *ht
 
 	for _, failAtCall := range handler.failAtCalls {
 		if handler.callNumber == failAtCall {
+			handler.netErrorRecorder.Record(r.Context())
+
 			w.WriteHeader(http.StatusBadGateway)
 			return
 		}