How to download a file with plus symbol(+) filename in IIS?

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Today I get a ticket with our client that they could not download a file with plus symbol(+) filename, such as the filename is a+b.xls.

I have a try and get the 404 code as below.

Firstly, I consider if the file is deleted on the server by someone, so I remote to the server and have a check. But...all going well. The file is here.

Then I search if someone has had this problem on the Internet. A lot of answers say that + is a specific symbol in browser. It should be transcoded into %2B.

So I add the js code as below and try again.

fileName=fileName.replaceAll("\\+","%2B");window.location.href = conf.webAPIRoot + fileName;

But...it doesn't work for me.

In another answer found in . It should be set in IIS. After the setting, I try again and it works for me.

Request Filtering -> Edit Feature Settings -> Allow Double Escaping