log: ensure the correct status is always logged

in the case of error (>=400) then no response may have been sent

middleware/log/log.go

@@ -2,6 +2,7 @@
 package log
 
 import (
+	"fmt"
 	"log"
 	"net/http"
 
@@ -19,6 +20,11 @@ func (l Logger) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
 		if middleware.Path(r.URL.Path).Matches(rule.PathScope) {
 			responseRecorder := middleware.NewResponseRecorder(w)
 			status, err := l.Next.ServeHTTP(responseRecorder, r)
+			if status >= 400 {
+				responseRecorder.WriteHeader(status)
+				fmt.Fprintf(responseRecorder, "%d %s", status, http.StatusText(status))
+				status = 0
+			}
 			rep := middleware.NewReplacer(r, responseRecorder)
 			rule.Log.Println(rep.Replace(rule.Format))
 			return status, err

middleware/log/log_test.go

+package log
+
+import (
+	"bytes"
+	"log"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+)
+
+type erroringMiddleware struct{}
+
+func (erroringMiddleware) ServeHTTP(w http.ResponseWriter, r *http.Request) (int, error) {
+	return http.StatusNotFound, nil
+}
+
+func TestLoggedStatus(t *testing.T) {
+	var f bytes.Buffer
+	var next erroringMiddleware
+	rule := Rule{
+		PathScope: "/",
+		Format:    DefaultLogFormat,
+		Log:       log.New(&f, "", 0),
+	}
+
+	logger := Logger{
+		Rules: []Rule{rule},
+		Next:  next,
+	}
+
+	r, err := http.NewRequest("GET", "/", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	rec := httptest.NewRecorder()
+
+	status, err := logger.ServeHTTP(rec, r)
+	if status != 0 {
+		t.Error("Expected status to be 0 - was", status)
+	}
+
+	logged := f.String()
+	if !strings.Contains(logged, "404 13") {
+		t.Error("Expected 404 to be logged. Logged string -", logged)
+	}
+}