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

• [BUG] Getting error for FormRecognizerClient StartRecognizeCustomFormsFromUri for Azure SAS Uri #11564
• [bug] [generator] Uri gets unencoded by calling .ToString() #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()).