Support *.localhost TLD for local dev #62593
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DamianEdwards
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DamianEdwards
commented
Jul 8, 2025
| @@ -166,6 +166,11 @@ static string ExpandPorts(string ports, string scheme) | |||
| foreach (var address in addresses) | |||
| { | |||
| Log.ListeningOnAddress(LifetimeLogger, address); | |||
| if (address.Contains(".localhost") && Uri.TryCreate(address, UriKind.Absolute, out var uri) && uri.Host.EndsWith(".localhost", StringComparison.OrdinalIgnoreCase)) | |||
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Do the check for contains first to avoid extra Uri allocations.
DamianEdwards
commented
Jul 8, 2025
| } | ||
| ], | ||
| "shortName": "blazor", | ||
| "sourceName": "BlazorWeb-CSharp", | ||
| "sourceName": "BlazorWebCSharp.1", |
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This change was required in order to support all the default value forms for the sourceName in accordance with the docs for sourceName. Specifically, we want to use the lower case class name form for the value of "applicationUrl" in the launchSettings.json file.
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Support *.localhost TLD for local dev
Description
This PR adds support to ASP.NET Core for local dev with a
*.localhostaddress, i.e. an address using the.localhostTLD.The
.localhostTLD is always resolved to the localhost loopback address in modern browsers without any DNS configuration required (as per RFC 6761). It's effectively an alias forlocalhost, allowing for infinite variations on the host name while maintaining the benefits of the localhost address. An ASP.NET Core application started with anASPNETCORE_URLSconfig value (or"applicationUrl"in launchSettings.json) will be resolvable on any address that binds to the loopback address, so a value ofhttp://myapp.localhost:12345will also be resolvable viahttp://localhost:12345. Note that non-browser scenarios should continue to use the plain localhost address as they rely on regular DNS configuration to resolve a.localhostTLD address to the loopback address.The empty and blazor web templates have been updated with a new option,
--localhost-tld, that can be specified to opt the new project into using the.localhostTLD for the application URL. The other templates focusing on non-browser scenarios or using parts of ASP.NET Core not considered our primary, modern, recommended approach, have not been updated but users are free to manually change their launch profiles to use the.localhostTLD.Kestrel itself was updated to treat
.localhostaddresses the same as thelocalhostaddress. In the case a.localhostaddress is being used, Kestrel will print out that it's listening on both the.localhostaddress, and regularlocalhostwithout the sub-domain prefix too so it's obvious that both are resolvable, e.g.:The developer certificate logic had the certificate version incremented, and was updated to include new SANs for the following addresses:
*.localhost*.internalFixes #62592