* Make the external url of cache server configurable if necessary Signed-off-by: Zoupers <qy@zouper.cn> * optimize code and doc and fix test and add test Signed-off-by: Zoupers <qy@zouper.cn> * optimize code and adjust description Signed-off-by: Zoupers <qy@zouper.cn> --------- Signed-off-by: Zoupers <qy@zouper.cn> Co-authored-by: 林玮 (Jade Lin) <linw1995@icloud.com>