How can I programmatically tell if a binary file on a website (e.g. image) has changed without downloading it?

Question

How can I programmatically tell if a binary file on a website (eg image) has changed without downloading it? Is there a way using HTTP methods (in C# in this case) to check prior to fully downloading it?

Answer 1

Really, you want to look for the Last-Modified header after issuing a HEAD request (rather than a GET ). I wrote some code to get the HEAD via WebClient here .

Answer 2

You can check that whether the file is changed or not by requesting with HEAD .

Then, returned response header may include Last-Modified , or ETag if the web server support.

Answer 3

您可以执行HEAD请求并检查上次修改的日期时间值以及内容长度。