C# Http文件下载公共类(支持断点续传)
http://www.cnblogs.com/hayden/archive/2012/04/26/2472815.html
C# Http方式下载文件到本地类改进版
https://www.cnblogs.com/xiandedanteng/p/7079322.html
C#实现文件上传下载工具类
https://blog.csdn.net/jianyuerensheng/article/details/78184730
WebAPI文件上传与下载
https://www.cnblogs.com/GarsonZhang/p/5511427.html