Allow custom blazor endpoint url

[Bouke]

Describe the bug

Blazor Server has some configuration possibilities to be hosted at a url other than _blazor. However there's a hard-coded path used that requires the hub to also be available under _blazor.

To Reproduce

app.UseEndpoints(
    endpoints =>
    {
        endpoints.MapBlazorHub("/_custom");
    });

<script src="/_framework/blazor.server.js" autostart="false"></script>
<script>
    Blazor.start({
        configureSignalR: builder => {
            builder.withUrl("_custom");
        }});
</script>

Workaround

Register the default url as well:

app.UseEndpoints(
    endpoints =>
    {
        endpoints.MapBlazorHub("/_custom");
        endpoints.MapBlazorHub();
    });

Exceptions (if any)

> GET /_blazor/initializers HTTP/1.1
< HTTP/1.1 404 Not Found

Further technical details

• ASP.NET Core version: 6.0.100

[Bouke]

After investigating some more I've concluded this to be user-error. After (correctly) setting <base href="/_custom" /> and dropping the custom JS startup, I can host blazor on a sub-path.