X-NuGet-Warning doesn't work when using proxy due to missing ServerWarningLogHandler

[zarenner]

The code that sets up ProxyAuthenticationHandler is missing ServerWarningLogHandler: https://github.com/NuGet/NuGet.Client/blob/7645448a1fbeff4bc17b9c74be115aa92c5b9b4a/src/NuGet.Core/NuGet.Protocol/HttpSource/HttpHandlerResourceV3Provider.cs#L55

As such, X-NuGet-Warning doesn't work when using a proxy (even fiddler).

[rohit21agrawal]

Thanks for the bug report @zarenner . We will investigate this as soon as we can.

[jotaylo]

Well over a year later, this is still an issue.

[0xced]

And almost 6 years later, this is still an issue. I've been hit by this because a private feed I'm using emits the X-NuGet-Warning header to inform me about an expired subscription. But I've never seen this warning because I'm using a proxy and I lost half a day debugging the NuGet restore task trying to figure out why the NuGet package would not restore properly. 🙄 (The NuGet feed redirects to the latest package version available for my subscription.)

[0xced]

The proxy issue could be easily solved by setting the inner handler, just like it's done for the StsAuthenticationHandler and HttpSourceAuthenticationHandler, i.e.:

var innerHandler = messageHandler;
messageHandler = new ProxyAuthenticationHandler(clientHandler, HttpHandlerResourceV3.CredentialService?.Value, ProxyCache.Instance)
{
    InnerHandler = innerHandler
};

instead of the current

messageHandler = new ProxyAuthenticationHandler(clientHandler, HttpHandlerResourceV3.CredentialService?.Value, ProxyCache.Instance);

For my particular private feed there was another issue that is not as easily solved: the X-NuGet-Warning header is issued during redirection (HTTP status 302) which is invisible since the HttpClientHandler is configured to automatically follow redirects.

curl --user my-user:my-password -i https://nuget.example.com/api/v3/packages/download/the.package/3.0.0/the.package.3.0.0.nupkg

HTTP/1.1 302 Found
Server: nginx/1.18.0 (Ubuntu)
Date: Thu, 20 Jan 2023 08:48:36 GMT
Content-Length: 0
Connection: keep-alive
Location: /api/v3/packages/download/the.package/2.5.0/the.package.2.5.0.nupkg
X-NuGet-Warning: Package 'The.Package 3.0.0' cannot be downloaded because required subscription has expired. Redirecting to the latest available version: 2.5.0

[zivkan]

Thank you @0xced for fixing the bug!

The fix will be available in NuGet 6.7, VS 17.7, .NET SDK 7.0.400