Get HTTP status code descriptions in ASP.Net Core

This is close enough for my needs:

var statusCode = httpContext.Response.StatusCode
var description = ((HttpStatusCode)statusCode).ToString(); // 404 -> "NotFound"

You can use Microsoft.AspNetCore.WebUtilities.ReasonPhrases.GetReasonPhrase(int statusCode) (which can be got from the Microsoft.AspNetCore.WebUtilities package in NuGet if not already referenced in your project transiently by a package like Microsoft.AspNetCore.App):

using Microsoft.AspNetCore.WebUtilities;

int statusCode = 404;
string reasonPhrase = ReasonPhrases.GetReasonPhrase(statusCode);

Improving on the previous answer, you could split HttpStatusCode enum name with spaces, e.g.:

public string GetStatusReason(int statusCode)
{
    var key = ((HttpStatusCode) statusCode).ToString();

    return string.Concat(
        key.Select((c, i) =>
            char.IsUpper(c) && i > 0
                ? " " + c.ToString()
                : c.ToString()
        )
    );
}

Or if you prefer regular expressions:

public string GetStatusReason(int statusCode)
{
    var key = ((HttpStatusCode) statusCode).ToString();
    return Regex.Replace(key, "(\\B[A-Z])", " $1");
}

Also you can simplify it to just this:

public string GetStatusReason(HttpStatusCode statusCode)
{
    var key = statusCode.ToString();
    return Regex.Replace(key, "(\\B[A-Z])", " $1");
}

Looking at the enum key names they seem to be pretty reasonably named so most, if not all, status codes should yield acceptable reason messages.

Instead of using a NuGet or splicing a string, here's a simple implementation. These descriptions should match the source of HttpWorkerRequest.

        /// <summary>
        /// Descriptions for Http Status Code
        /// </summary>
        /// <param name="code"></param>
        /// <returns></returns>
        public static string GetHttpStatusDescription(int code)
        {
            switch (code)
            {
                case 100: return "Continue";
                case 101: return "Switching Protocols";
                case 102: return "Processing";
                case 200: return "OK";
                case 201: return "Created";
                case 202: return "Accepted";
                case 203: return "Non-Authoritative Information";
                case 204: return "No Content";
                case 205: return "Reset Content";
                case 206: return "Partial Content";
                case 207: return "Multi-Status";
                case 300: return "Multiple Choices";
                case 301: return "Moved Permanently";
                case 302: return "Found";
                case 303: return "See Other";
                case 304: return "Not Modified";
                case 305: return "Use Proxy";
                case 307: return "Temporary Redirect";
                case 400: return "Bad Request";
                case 401: return "Unauthorized";
                case 402: return "Payment Required";
                case 403: return "Forbidden";
                case 404: return "Not Found";
                case 405: return "Method Not Allowed";
                case 406: return "Not Acceptable";
                case 407: return "Proxy Authentication Required";
                case 408: return "Request Timeout";
                case 409: return "Conflict";
                case 410: return "Gone";
                case 411: return "Length Required";
                case 412: return "Precondition Failed";
                case 413: return "Request Entity Too Large";
                case 414: return "Request-Uri Too Long";
                case 415: return "Unsupported Media Type";
                case 416: return "Requested Range Not Satisfiable";
                case 417: return "Expectation Failed";
                case 422: return "Unprocessable Entity";
                case 423: return "Locked";
                case 424: return "Failed Dependency";
                case 500: return "Internal Server Error";
                case 501: return "Not Implemented";
                case 502: return "Bad Gateway";
                case 503: return "Service Unavailable";
                case 504: return "Gateway Timeout";
                case 505: return "Http Version Not Supported";
                case 507: return "Insufficient Storage";
            }
            return "";
        }