update image api *os.File to io.Reader (#994)

* update image api *os.File to io.Reader

* update code style

* add reader test

* supplementary reader test

* update the reader in the form builder test

* add commnet

* update comment

* update code style

internal/form_builder_test.go

@@ -43,3 +43,32 @@ func TestFormBuilderWithClosedFile(t *testing.T) {
 	checks.HasError(t, err, "formbuilder should return error if file is closed")
 	checks.ErrorIs(t, err, os.ErrClosed, "formbuilder should return error if file is closed")
 }
+
+type failingReader struct {
+}
+
+var errMockFailingReaderError = errors.New("mock reader failed")
+
+func (*failingReader) Read([]byte) (int, error) {
+	return 0, errMockFailingReaderError
+}
+
+func TestFormBuilderWithReader(t *testing.T) {
+	file, err := os.CreateTemp(t.TempDir(), "")
+	if err != nil {
+		t.Fatalf("Error creating tmp file: %v", err)
+	}
+	defer file.Close()
+	builder := NewFormBuilder(&failingWriter{})
+	err = builder.CreateFormFileReader("file", file, file.Name())
+	checks.ErrorIs(t, err, errMockFailingWriterError, "formbuilder should return error if writer fails")
+
+	builder = NewFormBuilder(&bytes.Buffer{})
+	reader := &failingReader{}
+	err = builder.CreateFormFileReader("file", reader, "")
+	checks.ErrorIs(t, err, errMockFailingReaderError, "formbuilder should return error if copy reader fails")
+
+	successReader := &bytes.Buffer{}
+	err = builder.CreateFormFileReader("file", successReader, "")
+	checks.NoError(t, err, "formbuilder should not return error")
+}