// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
 
using Microsoft.AspNetCore.Http.Features;
 
namespace Microsoft.AspNetCore.Http;
 
/// <summary>
/// Extensions for reading HTTP server variables.
/// </summary>
public static class HttpContextServerVariableExtensions
{
    /// <summary>
    /// Gets the value of a server variable for the current request.
    /// </summary>
    /// <param name="context">The http context for the request.</param>
    /// <param name="variableName">The name of the variable.</param>
    /// <returns>
    /// <c>null</c> if the server does not support the <see cref="IServerVariablesFeature"/> feature.
    /// May return null or empty if the variable does not exist or is not set.
    /// </returns>
    public static string? GetServerVariable(this HttpContext context, string variableName)
    {
        ArgumentNullException.ThrowIfNull(context);
        ArgumentNullException.ThrowIfNull(variableName);
        
        var feature = context.Features.Get<IServerVariablesFeature>();
 
        if (feature == null)
        {
            return null;
        }
 
        return feature[variableName];
    }
}