gcsstore: Do not ignore errors when writing an object

Previously, any error returned from w.Close() would be ignored. This is
a problem since this function is responsible for returning any error
that occurred during the actual GCS transaction.

This fix also uncovered an issue in the corresponding test routine.

Furthermore, a "404 Not Found" error when writing an object is now
interpreted as if the bucket does not exist to ease debugging
(see https://github.com/tus/tusd/issues/241).

/cc @tab1293

gcsstore/gcsservice.go

@@ -10,6 +10,7 @@ import (
 
 	"cloud.google.com/go/storage"
 	"golang.org/x/net/context"
+	"google.golang.org/api/googleapi"
 	"google.golang.org/api/iterator"
 	"google.golang.org/api/option"
 
@@ -290,13 +291,19 @@ func (service *GCSService) WriteObject(ctx context.Context, params GCSObjectPara
 
 	w := obj.NewWriter(ctx)
 
-	defer w.Close()
-
 	n, err := io.Copy(w, r)
 	if err != nil {
 		return 0, err
 	}
 
+	err = w.Close()
+	if err != nil {
+		if gErr, ok := err.(*googleapi.Error); ok && gErr.Code == 404 {
+			return 0, fmt.Errorf("gcsstore: the bucket %s could not be found while trying to write an object", params.Bucket)
+		}
+		return 0, err
+	}
+
 	return n, err
 }
 

gcsstore/gcsservice_test.go

@@ -360,6 +360,13 @@ func TestWriteObject(t *testing.T) {
 		"expiry_date":   "1425333671141",
 	})
 
+	gock.New("https://googleapis.com").
+		Post("/upload/storage/v1/b/test-bucket/o").
+		MatchParam("alt", "json").
+		MatchParam("key", "foo").
+		Reply(200).
+		JSON(map[string]string{})
+
 	ctx := context.Background()
 	client, err := storage.NewClient(ctx, option.WithAPIKey("foo"))
 	if err != nil {
@@ -379,7 +386,7 @@ func TestWriteObject(t *testing.T) {
 	}, reader)
 
 	if err != nil {
-		t.Errorf("Error deleting object: %+v", err)
+		t.Errorf("Error writing object: %+v", err)
 	}
 
 	if size != 1 {