Powershell: .NET UTF-7 encoding obsoletion

[xtqqczze]

According to https://github.com/dotnet/designs/blob/master/accepted/2020/better-obsoletion/obsoletions-in-net5.md, .NET 5 will obsolete the UTF-7 encoding:

The UTF-7 encoding is insecure and should not be used. Consider using UTF-8 instead.

[jborean93]

I'm curious, is UTF-7 being used anywhere in PowerShell? I've certainly never come across it in the wild.

[xtqqczze]

I'm curious, is UTF-7 being used anywhere in PowerShell? I've certainly never come across it in the wild.

It is exposed in public APIs such as Get-Content -Encoding UTF7

[iSazonov]

Yes, it is public and removing it will be a breaking change. But if .Net 5.0 will deprecate this we will have to do the same.

/cc @SteveL-MSFT @daxian-dbw It is for PowerShell Committee review.

Update: as an option we could keep UTF7 name but replace with UTF8 implementation.

[xtqqczze]

@iSazonov System.Text.Encoding.UTF7 and System.Text.UTF7Encoding APIs are not being removed from .NET 5, they are being marked with ObsoleteAttribute. So we have a choice whether to remove the APIs or to suppress the warnings.

https://github.com/dotnet/designs/blob/master/accepted/2020/better-obsoletion/better-obsoletion.md

[iSazonov]

Search on GiHub https://github.com/search?l=PowerShell&q=UTF7&type=Code returns ~1K results. It is very small and it seems they simply replicate PowerShell support. I'd speculate that nobody uses UTF7 and we can remove it at all. The same for C#.

[SteveL-MSFT]

@PowerShell/powershell-committee discussed this, we have code that handles Encoding passed to cmdlets that accept that type for parameters. We agreed to add a warning message if the user specifies "UTF-7" as part of type conversion to warn the user that this encoding is obsolete, but we should not remove it while .NET itself still implements it even though obsolete.

[xtqqczze]

See also: #13484

[xtqqczze]

Related: #13430

[msftbot[bot]]

:tada:This issue was addressed in #13484, which has now been successfully released as v7.1.0-preview.7.:tada:

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