How can a web shared local html file be opened via Safari?

From system preferences/Internet & Wireless/Sharing I selected Web Sharing then clicked on Open Personal Website Folder, and there is an existing index.html file there with address

http://my ip address/~myusername/sites/index.html if online or if offline then
 http://MacBook-Pro/~myusername/sites/index.html
 

But if I try to open these URLs from Safari it doesn't work, perhaps as expected if using the http scheme, so I tried with file:// instead but it says

"No file exists at "/~myusername/sites/index.html". But the file does exist there, I can see it.

Are there some tricks involved in getting Safari to see this file?

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