Let's use different codes

server.go

@@ -27,8 +27,8 @@ func init() {
 	toSave = make(chan string, 100)
 }
 
-func returnError(w http.ResponseWriter, err string) {
-	w.WriteHeader(http.StatusBadRequest)
+func returnError(w http.ResponseWriter, err string, statusCode int) {
+	w.WriteHeader(statusCode)
 	errorTemplate.Execute(w, err)
 }
 
@@ -40,7 +40,7 @@ func shorten(w http.ResponseWriter, r *http.Request) {
 
 	addStatus, linkID := addLink(link, toSave)
 	if !addStatus {
-		returnError(w, linkID)
+		returnError(w, linkID, http.StatusBadRequest)
 		return
 	}
 
@@ -68,7 +68,7 @@ func decode(w http.ResponseWriter, r *http.Request) {
 		}
 	}
 
-	returnError(w, "Not found!")
+	returnError(w, "Not found!", http.StatusNotFound)
 }
 
 func redirectOrServe(w http.ResponseWriter, r *http.Request) {

server_test.go

@@ -81,7 +81,7 @@ func TestDecodeMissing(t *testing.T) {
 			resetServer(t)
 			w := httptest.NewRecorder()
 			decode(w, httptest.NewRequest(http.MethodGet, target, nil))
-			if w.Code != http.StatusBadRequest || !strings.Contains(w.Body.String(), "Not found!") {
+			if w.Code != http.StatusNotFound || !strings.Contains(w.Body.String(), "Not found!") {
 				t.Fatalf("status = %d, body = %s", w.Code, w.Body.String())
 			}
 		})
@@ -114,7 +114,7 @@ func TestRedirectOrServe(t *testing.T) {
 func TestReturnErrorEscapesHTML(t *testing.T) {
 	message := `<script>alert("oops")</script>`
 	w := httptest.NewRecorder()
-	returnError(w, message)
+	returnError(w, message, http.StatusBadRequest)
 	if w.Code != http.StatusBadRequest || !strings.Contains(w.Body.String(), html.EscapeString(message)) {
 		t.Fatalf("status = %d, body = %s", w.Code, w.Body.String())
 	}