Add scheme to URL if needed

Question

To create a Uri from a string you can do this:

Uri u = new Uri(\"example.com\");

But the problem is if the string (like the one above) does

Answer 1

If you just want to add the scheme, without validating the URL, the fastest/easiest way is to use string lookups, eg:

string url = "mydomain.com";
if (!url.StartsWith("http://", StringComparison.OrdinalIgnoreCase)) url = "http://" + url;

A better approach would be to use Uri to also validate the URL using the TryCreate method:

string url = "mydomain.com";
Uri uri;
if ((Uri.TryCreate(url, UriKind.Absolute, out uri) || Uri.TryCreate("http://" + url, UriKind.Absolute, out uri)) &&
    (uri.Scheme == Uri.UriSchemeHttp || uri.Scheme == Uri.UriSchemeHttps))
{
    // Use validated URI here
}

As @JanDavidNarkiewicz pointed out in the comments, validating the Scheme is necessary to guard against invalid schemes when a port is specified without scheme, e.g. mydomain.com:80.