I would like to know if there is a way to know if a server supports resume download functionallity and if supported, how do I send a request to resume?
I was looking for a solution where my ASP.NET page can do a download from a server to mine, something like "rapidleech" does today, but I would like to check if the server where i'm requesting the download supports resume functionallity.
Resuming files is done by specifying the byte range of the file you would like to download using the Range HTTP header. This can be done in .NET with the HttpWebRequest.AddRange function.
For example:
request.AddRange(1000);
Will tell the server to begin sending at the 1000th byte of the file.
If the server supports the Range header, it will send the content with an HTTP status of 206 (Partial Content) instead of the normal 200 (OK). See the HTTP Spec.
To check if the server supports resuming before attempting the download, change the HttpWebRequest's Method "HEAD". The server will return 206 (Partial Content) if it supports resuming, and 200 (OK) if it does not.
You can find more information on Range specific requests by Scott Mitchell here
来源：https://stackoverflow.com/questions/1336203/httpwebrequest-or-webrequest-resume-download-asp-net