ApiVersionLinkGenerator.cs

namespace Microsoft.AspNetCore.Mvc.Routing
{
    using Microsoft.AspNetCore.Http;
    using Microsoft.AspNetCore.Mvc.Versioning;
    using Microsoft.AspNetCore.Routing;
    using System;

    /// <summary>
    /// Represents an API version aware <see cref="AspNetCore.Routing.LinkGenerator">link generator</see>.
    /// </summary>
    [CLSCompliant( false )]
    public class ApiVersionLinkGenerator : LinkGenerator
    {
        /// <summary>
        /// Initializes a new instance of the <see cref="ApiVersionLinkGenerator"/> class.
        /// </summary>
        /// <param name="linkGenerator">The inner <see cref="AspNetCore.Routing.LinkGenerator">link generator</see>.</param>
        public ApiVersionLinkGenerator( LinkGenerator linkGenerator ) => LinkGenerator = linkGenerator;

        /// <summary>
        /// Gets the inner link generator.
        /// </summary>
        /// <value>The inner <see cref="AspNetCore.Routing.LinkGenerator">link generator</see>.</value>
        protected LinkGenerator LinkGenerator { get; }

        /// <inheritdoc />
        public override string? GetPathByAddress<TAddress>(
            HttpContext httpContext,
            TAddress address,
            RouteValueDictionary values,
            RouteValueDictionary? ambientValues = null,
            PathString? pathBase = null,
            FragmentString fragment = default,
            LinkOptions? options = null )
        {
            AddApiVersionRouteValueIfNecessary( httpContext, values );
            return LinkGenerator.GetPathByAddress( httpContext, address, values, ambientValues, pathBase, fragment, options );
        }

        /// <inheritdoc />
        public override string? GetPathByAddress<TAddress>(
            TAddress address,
            RouteValueDictionary values,
            PathString pathBase = default,
            FragmentString fragment = default,
            LinkOptions? options = null ) => LinkGenerator.GetPathByAddress( address, values, pathBase, fragment, options );

        /// <inheritdoc />
        public override string? GetUriByAddress<TAddress>(
            HttpContext httpContext,
            TAddress address,
            RouteValueDictionary values,
            RouteValueDictionary? ambientValues = null,
            string? scheme = null,
            HostString? host = null,
            PathString? pathBase = null,
            FragmentString fragment = default,
            LinkOptions? options = null )
        {
            AddApiVersionRouteValueIfNecessary( httpContext, values );
            return LinkGenerator.GetUriByAddress( httpContext, address, values, ambientValues, scheme, host, pathBase, fragment, options );
        }

        /// <inheritdoc />
        public override string? GetUriByAddress<TAddress>(
            TAddress address,
            RouteValueDictionary values,
            string scheme,
            HostString host,
            PathString pathBase = default,
            FragmentString fragment = default,
            LinkOptions? options = null ) => LinkGenerator.GetUriByAddress( address, values, scheme, host, pathBase, fragment, options );

        static void AddApiVersionRouteValueIfNecessary( HttpContext httpContext, RouteValueDictionary values )
        {
            if ( httpContext == null )
            {
                throw new ArgumentNullException( nameof( httpContext ) );
            }

            if ( values == null )
            {
                throw new ArgumentNullException( nameof( values ) );
            }

            var feature = httpContext.Features.Get<IApiVersioningFeature>();
            var key = feature.RouteParameter;

            if ( string.IsNullOrEmpty( key ) )
            {
                return;
            }

            var value = feature.RawRequestedApiVersion;

            if ( !string.IsNullOrEmpty( value ) && !values.ContainsKey( key ) )
            {
                values.Add( key, value );
            }
        }
    }
}