How to Build a Link to SPA Site in ASP.NET Core

Problem

When your web application sends emails to its users they might need to contain links to the site. Like “click here to get more details” etc. If you use MVC it’s not a problem, since you can use a method of HttpContext.Request to get the address of request and then change it as needed.

It might work also with SPA, however in some cases it doesn’t. For example, during development your client site can be running on another port than your server. Because you probably use ng serve for Angular or any other tool relevant to your FE stack. And server can be either running locally via dotnet run, or you could connect to remote server. However you’d like to get links in your emails leading to your client site, not remote one.

Sub-optimal Solution

To workaround this issue we used something like:

IHttpContextAccessor accessor;
...
var requestUri = new Uri(accessor.HttpContext.Request.GetEncodedUrl();
var apiRoot = GetApiRoot(requestUri);
return apiRoot + $"/here-is-you-path?with=params";
...

private string GetApiRoot(Uri requestUri) => env.IsDevelopment() ? "http://localhost:4200" : $"{requestUri.Scheme}://{requestUri.Authority}";

It was neither elegant nor robust. And it did not work for remote servers, since it is not running in development mode.

Better Solution

At some point we realized that we could use another request property. It is Referer header.

Funny fact is that Referer is a misspelled Referrer, and not knowing that fact might cost few hours or debugging, when one can, for example, try to find a header by orthographically correct string Referrer. .NET Framework adds more confusion having HttpRequest.UrlReferrer

As result of our refactoring we’ve got nice method:

public string GetClientLink(string path, string query)
{
    var headers = accessor.HttpContext.Request.Headers;
    var refererAddress = headers[nameof(HttpRequestHeader.Referer)].ToString();
    return new UriBuilder(refererAddress)
    {
        Path = path,
        Query = query
    }.ToString();
}

Note the using of combination of constructor arguments and object initializers in a single statement. In this case it allows us to get the full referrer url and replace path and query with our values. It is very handy.

That’s all for now. Please let me know if this was useful, or there are better ways to build a link :)

Cheers!