Make it easy to configure a host/scheme for absolute URLs with LinkGenerator

[RehanSaeed]

Is your feature request related to a problem? Please describe.

LinkGenerator

LinkGenerator requires the HttpContext to generate a full absolute URL which also contains the scheme, hostname and optional port. Outside of the controller, this means I have to also inject the IHttpContextAccessor into my constructor and pass it in like so:

this.linkGenerator.GetUriByRouteValues(
    this.httpContextAccessor.HttpContext,
    "GetPage",
    new() { First = 1, Last = 10 });

This requires a lot of ceremony and additional noise.

IUrlHelper

IUrlHelper does not require the HttpContext if you add this code to the Startup. We use the IActionContextAccessor and IUrlHelperFactory to register IUrlHelper into the IoC container.

services
    .AddSingleton<IActionContextAccessor, ActionContextAccessor>()
    .AddScoped(x => x
        .GetRequiredService<IUrlHelperFactory>()
        .GetUrlHelper(x.GetRequiredService<IActionContextAccessor>().ActionContext))

Then if you use the following extension method to create your URL's:

public static string AbsoluteRouteUrl(
    this IUrlHelper urlHelper,
    string routeName,
    object routeValues = null) =>
    urlHelper.RouteUrl(routeName, routeValues, urlHelper.ActionContext.HttpContext.Request.Scheme);

Here is the usage:

this.urlHelper.AbsoluteRouteUrl("GetPage", new() { First = 1, Last = 10 });

I think you'll agree this is much nicer.

Describe the solution you'd like

I would like a way to generate URL's without having to inject the IHttpContextAccessor and LinkGenerator just to generate a single URL. Or a way to use IUrlHelper without all the setup code to get it working nicely.

[FilipVanBouwel]

I agree. This should be less cumbersome. I don't care if it's IUrlHelper or IUrlGenerator, as long as it is fully setup by the DI system as part of ASP.NET.

[rynowak]

LinkGenerator requires the HttpContext to generate a URL.

This is not true. LinkGenerator is specifically designed to work without an HTTP context.

See: https://github.com/aspnet/AspNetCore/blob/master/src/Mvc/Mvc.Core/src/Routing/ControllerLinkGeneratorExtensions.cs#L84 and similar methods.

[RehanSaeed]

As far as I can work out this is not true for absolute URL's containing the scheme, host and port. Using this code:

this.linkGenerator.GetPathByRouteValues("GetPage", new { First = 1, Last = 10 });

Outputs:

/foo?first=1&last=10

[rynowak]

@RehanSaeed - can you provide some more information? I'm not sure how I'm supposed to draw a conclusion from that.

[RehanSaeed]

I want to generate absolute URL's with the full scheme, host and optionally a port i.e. https://example.com/foo?bar=1. Why? Well, one reason is that in API's a full URL is much easier to consume from JavaScript.

Today, if you want to do this, you have to have the HttpContext and pass it into the LinkGenerator or IUrlHelper as I've shown in my code samples above. This is used to pull the scheme and host from the current request and stick it into the URL.

That's all well and good in a controller where you have easy access to the HttpContext. However, if I'm outside of the controller and want to generate a URL, then if I use LinkGenerator, then I am forced to also inject IHttpContextAccessor or if I'm using IUrlHelper, it's possible to avoid injecting IHttpContextAccessor but you have to add some additional setup in Startup and use an extension method. All code is shown above.

Both of these solutions are noisy and require extra work, just to get an absolute URL. Ideally, I'd want a method that does all of that for me and allows me to generate URL's without all the extra noise and ceremony.

Does that clear things up?

[FilipVanBouwel]

I agree with RehanSaeed. I had the need to generate absolute urls in a module that sends out emails to clients (which is outside the web project). I only want the IUrlHelper or LinkGenerator as dependency and don't want to do all the IHttpContextAccessor setup as described above.

[rynowak]

I want to generate absolute URL's with the full scheme, host and optionally a port i.e. https://example.com/foo?bar=1. Why? Well, one reason is that in API's a full URL is much easier to consume from JavaScript.

This is something we can work with. Do you actually care about the current request? Or do you just want it to be easier to generate absolute URLs?

I can imagine a feature where you can centrally configure a default scheme and host that will be used in URLs - or it could fallback to the listening address if nothing is configured and there is only one listening address.

---

There reason I'm making this distinction is that passing in the "current request" does more than just set up scheme/host/pathbase - it also includes ambient route values. Trying to make a service that will magically use ambient values from the current request is a recipe for failure because it's going to do different things depending on which route reached the current thing.

[RehanSaeed]

I don't care about the current request at all, I'm just forced to care to generate a URL based on the current requests scheme, host and URL.

I can imagine a feature where you can centrally configure a default scheme and host that will be used in URLs - or it could fallback to the listening address if nothing is configured and there is only one listening address.

I could get behind such a feature. The fallback sounds like the correct default with the option to override it.

[FilipVanBouwel]

That sounds good to me as well!

[rynowak]

Great, I'm sticking this in the 5.0 milestone so it will get looked at.