fix: Correctly handle error codes

nsd/download/download.go

@@ -6,7 +6,6 @@ import (
 	"io/ioutil"
 	"math"
 	"net/http"
-	"os"
 	"path"
 	"strconv"
 	"strings"
@@ -62,12 +61,12 @@ func File(url string) (filePath string, err error) {
 	if err != nil {
 		return
 	}
+
+	defer resp.Body.Close()
+
 	if resp.StatusCode != http.StatusOK {
-		fmt.Println(resp.Status)
-		os.Exit(1)
-		// exit if not ok
+		return "", fmt.Errorf("URL '%s' returned error code %s", url, resp.Status)
 	}
-	defer resp.Body.Close()
 
 	// the Header "Content-Length" will let us know
 	// the total file size to download

nsd/download/download_test.go

@@ -54,3 +54,16 @@ func TestDownloadZip(t *testing.T) {
 		t.Errorf("File() returned path to file, but file does not exist")
 	}
 }
+
+func TestDownloadInvalidFile(t *testing.T) {
+	router := mux.NewRouter()
+	router.PathPrefix("/").Handler(http.FileServer(http.Dir("./testdata/")))
+
+	server := httptest.NewServer(router)
+	defer server.Close()
+
+	_, err := File(server.URL + "/notexist.zip")
+	if err == nil {
+		t.Errorf("File() did not error")
+	}
+}