Sitecore Site Specific Link Provider for up to SC 8.1

SwitchingLinkProvider

using System;
using System.Collections.Specialized;
using System.Web;

using Sitecore.Data.Items;
using Sitecore.Diagnostics;
using Sitecore.Links;
using Sitecore.Web;

namespace Sitecore.Custom.Links
{

    public class SwitchingLinkProvider : Sitecore.Links.LinkProvider
    {
        private const String FALLBACK_ATTRIBUTE_KEY = "fallback";
        private const String LINKPROVIDER_ATTRIBUTE_KEY = "linkProvider";
        private string Fallback { get; set; }

        public override void Initialize(string name, NameValueCollection config)
        {
            base.Initialize(name, config);
            this.Fallback = config[FALLBACK_ATTRIBUTE_KEY];
            Assert.IsNotNullOrEmpty(this.Fallback, "fallback");
        }
        
        private Sitecore.Links.LinkProvider SiteLinkProvider
        {
            get
            {
                var siteLinkProvider = (Sitecore.Context.Site != null)
                                        ? Sitecore.Context.Site.Properties[LINKPROVIDER_ATTRIBUTE_KEY] : String.Empty;

                if (String.IsNullOrEmpty(siteLinkProvider))
                    siteLinkProvider = this.Fallback;

                return LinkManager.Providers[siteLinkProvider] 
                    ?? LinkManager.Providers[this.Fallback];
            }
        }


        #region LinkProvider Options

        public override bool AddAspxExtension
        {
            get
            {
                return SiteLinkProvider.AddAspxExtension;
            }
        }

        public override bool AlwaysIncludeServerUrl
        {
            get
            {
                return SiteLinkProvider.AlwaysIncludeServerUrl;
            }
        }

        public override bool EncodeNames
        {
            get
            {
                return SiteLinkProvider.EncodeNames;
            }
        }

        public override LanguageEmbedding LanguageEmbedding
        {
            get
            {
                return SiteLinkProvider.LanguageEmbedding;
            }
        }

        public override LanguageLocation LanguageLocation
        {
            get
            {
                return SiteLinkProvider.LanguageLocation;
            }
        }

        public override bool LowercaseUrls
        {
            get
            {
                return SiteLinkProvider.LowercaseUrls;
            }
        }

        public override bool ShortenUrls
        {
            get
            {
                return SiteLinkProvider.ShortenUrls;
            }
        }

        public override bool UseDisplayName
        {
            get
            {
                return SiteLinkProvider.UseDisplayName;
            }
        }

        #endregion

        #region LinkProvider Methods

        public override string ExpandDynamicLinks(string text, bool resolveSites)
        {
            return SiteLinkProvider.ExpandDynamicLinks(text, resolveSites);
        }

        public override UrlOptions GetDefaultUrlOptions()
        {
            return SiteLinkProvider.GetDefaultUrlOptions();
        }

        public override string GetItemUrl(Item item, UrlOptions options)
        {
            return SiteLinkProvider.GetItemUrl(item, options);
        }

        public override string GetDynamicUrl(Item item, LinkUrlOptions options)
        {
            return SiteLinkProvider.GetDynamicUrl(item, options);
        }

        public override bool IsDynamicLink(string linkText)
        {
            return SiteLinkProvider.IsDynamicLink(linkText);
        }

        public override DynamicLink ParseDynamicLink(string linkText)
        {
            return SiteLinkProvider.ParseDynamicLink(linkText);
        }

        public override RequestUrl ParseRequestUrl(HttpRequest request)
        {
            return SiteLinkProvider.ParseRequestUrl(request);
        }

        #endregion

    }
}

SwitchingLinkProvider.Example.config

<linkManager>
  <providers>
    <add name="provider-site1" type="Sitecore.Links.LinkProvider, Sitecore.Kernel" addAspxExtension="false" languageEmbedding="never" useDisplayName="true" ... />
    <add name="provider-site2" type="Sitecore.Custom.LinkProvider, Sitecore.Custom" alwaysIncludeServerUrl="true" languageEmbedding="always" lowercaseUrls="true" />    
  </providers>
</linkManager>

<sites>
  <site name="site1" linkProvider="provider-site1" ... />
  <site name="site2" linkProvider="provider-site2" ... />
  <site name="site3" ... />
</sites>

SwitchingLinkProvider.Patch.Example.config

<linkManager>
  <patch:attribute name="defaultProvider" value="switcher" />
  <providers>
    <add name="switcher" fallback="sitecore" type="Sitecore.Custom.Links.SwitchingLinkProvider, Sitecore.Custom" />
  </providers>
</linkManager>

@mrosiak

Thanks for the heads up and the gist. I'll be looking into it.