Blazor: Navigation.BaseUri Incorrect on Forwarded Ports

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Environment: GitHub Codespaces launchSettings URL: http://localhost:5000

NavigationManager.BaseUri does not properly resolve when running in an environment with port forwarding (to either the initial port or the forwarded port). It will initially be set to http://localhost/ before flashing to the forwarded port. This prevents the use of NavigationManager.BaseUri for composing API calls in OnInitializedAsync.

Initial Component Render

Moments After Render

Expected Behavior

NavigationManager.BaseUri should immediately reflect the forwarded port URL so that API calls can be reliably constructed.

Steps To Reproduce

Run the following repo in a GitHub Codespace:

https://github.com/JaimeStill/BlazorPortForwardedBaseUriIssue

See Index.razor.

Exceptions (if any)

No response

.NET Version

6.0.402

Anything else?

.NET SDK (reflecting any global.json): Version: 6.0.402 Commit: 6862418796

Runtime Environment: OS Name: ubuntu OS Version: 20.04 OS Platform: Linux RID: ubuntu.20.04-x64 Base Path: /usr/local/dotnet/6/sdk/6.0.402/

global.json file: Not found

Host: Version: 6.0.10 Architecture: x64 Commit: 5a400c212a

.NET SDKs installed: 6.0.402 [/usr/local/dotnet/6/sdk]

.NET runtimes installed: Microsoft.AspNetCore.App 6.0.10 [/usr/local/dotnet/6/shared/Microsoft.AspNetCore.App] Microsoft.NETCore.App 6.0.10 [/usr/local/dotnet/6/shared/Microsoft.NETCore.App]

[javiercn]

@JaimeStill thanks for contacting us.

That is because https://jaimestill-literate-space-waffle-v6qgjjj56rvcw596-5000.preview.app.github.dev is only accessible “from outside”. (meaning your browser).

Codespaces apparently has not setup jaimestill-literate-space-waffle-v6qgjjj56rvcw596-5000.preview.app.github.dev to redirect to localhost, which is what should happen.

This seems to be something specific to how codespaces sets up the environment and port forwarding. NavigationManager is initialized with HttpContext.Request values during prerendering and it is initialized with the value from the document.baseUri and location.href when it becomes interactive, so that will explain the flashing.

The fact that it does not happen when the app is not prerendered is also strong evidence of that, tied to the fact that you can only reach yourself from within the app via localhost.

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