Tracking number of pages scraped by web crawlers

To count the number of web pages scraped, we can use a simple middleware with a predefined list of known bots, and increment a measurement with IMetricsService everytime a request comes from a bot.

using Microsoft.AspNetCore.Http;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Toggly.FeatureManagement;

namespace Web.Helpers
{
    public class BotTrackerMiddleware
    {
        private readonly RequestDelegate _next;
        private readonly IMetricsService _metricsService;

        List<string> _crawlers = new List<string>()
        {
            "bot","crawler","spider","80legs","baidu","yahoo! slurp","ia_archiver","mediapartners-google",
            "lwp-trivial","nederland.zoek","ahoy","anthill","appie","arale","araneo","ariadne",
            "atn_worldwide","atomz","bjaaland","ukonline","calif","combine","cosmos","cusco",
            "cyberspyder","digger","grabber","downloadexpress","ecollector","ebiness","esculapio",
            "esther","felix ide","hamahakki","kit-fireball","fouineur","freecrawl","desertrealm",
            "gcreep","golem","griffon","gromit","gulliver","gulper","whowhere","havindex","hotwired",
            "htdig","ingrid","informant","inspectorwww","iron33","teoma","ask jeeves","jeeves",
            "image.kapsi.net","kdd-explorer","label-grabber","larbin","linkidator","linkwalker",
            "lockon","marvin","mattie","mediafox","merzscope","nec-meshexplorer","udmsearch","moget",
            "motor","muncher","muninn","muscatferret","mwdsearch","sharp-info-agent","webmechanic",
            "netscoop","newscan-online","objectssearch","orbsearch","packrat","pageboy","parasite",
            "patric","pegasus","phpdig","piltdownman","pimptrain","plumtreewebaccessor","getterrobo-plus",
            "raven","roadrunner","robbie","robocrawl","robofox","webbandit","scooter","search-au",
            "searchprocess","senrigan","shagseeker","site valet","skymob","slurp","snooper","speedy",
            "curl_image_client","suke","www.sygol.com","tach_bw","templeton","titin","topiclink","udmsearch",
            "urlck","valkyrie libwww-perl","verticrawl","victoria","webscout","voyager","crawlpaper",
            "webcatcher","t-h-u-n-d-e-r-s-t-o-n-e","webmoose","pagesinventory","webquest","webreaper",
            "webwalker","winona","occam","robi","fdse","jobo","rhcs","gazz","dwcp","yeti","fido","wlm",
            "wolp","wwwc","xget","legs","curl","webs","wget","sift","cmc"
        };

        public BotTrackerMiddleware(RequestDelegate next, IMetricsService metricsService)
        {
            _next = next;
            _metricsService = metricsService;
        }

        /// <summary>
        /// Increase measurement for BotScrape metric each time the user agent matches a bot
        /// </summary>
        /// <param name="context"></param>
        /// <returns></returns>
        public async Task InvokeAsync(HttpContext context)
        {
            string ua = context.Request.Headers.UserAgent.FirstOrDefault().ToLower() ?? string.Empty;
            if (_crawlers.Exists(x => ua.Contains(x)))
                await _metricsService.MeasureAsync("BotScrape", 1);

            await _next(context);
        }
    }
}

Then in Startup.cs we can include our middleware conditionally, based on a feature flag, before we call app.UseEndpoints

app.UseMiddlewareForFeature<BotTrackerMiddleware>(FeatureFlags.BotTracker);

Next, in Toggly we’ll go to Features under our Application

And we’ll add a definition for our BotScrape flag

Finally, we’ll define the metric on our Metrics tab