library/src/main/java/com/liulishuo/filedownloader/model/FileDownloadHeader.java
public void add(String line) {
        String[] parsed = line.split(":");
        final String name = parsed[0].trim();
        final String value = parsed[1].trim();

        add(name, value);
    }
public void add(String line) {
        String[] parsed = line.split(":");
        final String name = parsed[0].trim();
        final String value = parsed[1].trim();

        add(name, value);
    }
We have already handled etag, and will add 'If-Match' & 'Range' value if it works.

@see com.liulishuo.filedownloader.download.ConnectTask#addUserRequiredHeader