Example code for expiring outdated links in Statiq. Example code for a blog post: https://blog.jermdavis.dev/posts/2024/expiring-outdated-blog-links - More info there.

ExpiringLinkConfigurator.cs

using Statiq.App;
using Statiq.Common;
using StatiqGenerator.Customisations.ReadingTime;

namespace StatiqGenerator.Customisations.DisappearingLinks
{

    public class ExpiringLinkConfigurator : IConfigurator<Bootstrapper>
    {
        public void Configure(Bootstrapper configurable)
        {
            configurable.ModifyPipeline("Content", p => {
                p.ProcessModules.Insert(4, new ExpiringLinkProcessor());
            });
        }
    }

}

ExpiringLinkProcessor.cs

using System;
using Statiq.Common;
using System.Collections.Generic;
using System.Text.RegularExpressions;
using System.Threading.Tasks;
using System.Transactions;

namespace StatiqGenerator.Customisations.DisappearingLinks
{
    
    public class ExpiringLinkProcessor : ParallelModule
    {
        private static readonly Regex _links = new Regex("<a\\s?(?<attrs>.*?)>(?<inner>.*?)</a>\\s?", RegexOptions.Compiled | RegexOptions.IgnoreCase);
        private static readonly Regex _date = new Regex("until=\"(?<date>.*?)\"", RegexOptions.Compiled | RegexOptions.IgnoreCase);

        protected override async Task<IEnumerable<IDocument>> ExecuteInputAsync(IDocument input, IExecutionContext context)
        {
            if (input.Source.Extension == ".md")
            {
                var footnoteToAppend = string.Empty;
                var hasChanged = false;
                var content = await input.GetContentStringAsync();

                var links = _links.Matches(content);
                foreach(Match link in links)
                {
                    var attrs = link.Groups["attrs"].Value;

                    var date = _date.Match(attrs);
                    if(date.Success)
                    {
                        var txt = date.Groups["date"].Value;
                        if(DateTime.TryParse(txt, out DateTime parsedDate))
                        {
                            if(parsedDate.Date < DateTime.Now.Date)
                            {
                                // remove link and return
                                content = content.Replace(link.Value, link.Groups["inner"].Value + "<a class=\"expired\" href=\"#expired\">**</a> ");
                                hasChanged = true;

                                footnoteToAppend += $"<li>{link.Value}</li>";

                                continue;
                            }
                        }

                        // remove until="??" and return
                        content = content.Replace($" {date.Value}", "");
                        hasChanged = true;

                        continue;
                    }
                }

                if(hasChanged)
                {
                    if(footnoteToAppend.Length > 0)
                    {
                        content += "<blockquote><h4>Expired links</h4><div><a class=\"expired\" name=\"expired\">**</a> Some links in this page have expired. The originals are listed here, but they may no longer point to the correct content:</div><ol>" + footnoteToAppend + "</ol></blockquote>";
                    }

                    var mt = input.GetContentProvider().MediaType;
                    return input
                        .Clone(new MetadataItems { { "ChangedLinks", "true" } })
                        .Clone(context.GetContentProvider(content, mt))
                        .Yield();
                }
            }

            return input.Yield();
        }
    }

}