Uri.AbsoluteUri should be used instead of Uri.ToString()

There are multiple customer-reported issues where the root cause is incorrect usage of Uri.ToString():

• #11564
• #12069

The problem is Uri.ToString() un-escapes the URL, so http://foo.com/image%201.jpg is converted to http://foo.com/image 01.jpg which is no longer a valid URL. The API Uri.AbsoluteUri should be used instead.

All instances of Uri.ToString() in our codebase should be reviewed, and most or all should be convered to Uri.AbsoluteUri. Uri.ToString() should only be used to intentionally un-escape a URL, which should be rare. Even if a URL were included in an error message, I think the escaped URL would be preferred.

I recommend adding an analyzer rule to prevent calls to Uri.ToString(), using Microsoft.CodeAnalysis.BannedApiAnalyzers.

One complication is relative URIs, where Uri.AbsoluteUri throws. If we need to get an escaped representation of a relative URI, we can use Uri.EscapeUriString(relativeUri.ToString()).

[kasobol-msft]

Given how tempting ToString() is and how easy it is to get it wrong I suggest to prioritize this work.

[pakrym]

I’ll look into merging that PR today.