Completely untested and totally experimental rate limit feature

KfChatDotNetBot/Services/RateLimitService.cs

@@ -0,0 +1,149 @@
+using System.Runtime.Caching;
+using System.Security.Cryptography;
+using System.Text;
+using System.Text.Json;
+using KfChatDotNetBot.Commands;
+using KfChatDotNetBot.Models;
+using KfChatDotNetBot.Models.DbModels;
+using NLog;
+
+namespace KfChatDotNetBot.Services;
+
+public static class RateLimitService
+{
+    private static Logger _logger = LogManager.GetCurrentClassLogger();
+
+    /// <summary>
+    /// Check whether a user is rate limited for a given command
+    /// </summary>
+    /// <param name="user">User you wish to check</param>
+    /// <param name="command">Command the user is invoking</param>
+    /// <param name="message">Message the user sent</param>
+    /// <returns></returns>
+    public static IsRateLimitedModel IsRateLimited(UserDbModel user, ICommand command, string message)
+    {
+        var result = new IsRateLimitedModel
+        {
+            IsRateLimited = false
+        };
+        if (command.RateLimitOptions == null) return result;
+        if (command.RateLimitOptions.Flags.HasFlag(RateLimitFlags.ExemptPrivilegedUsers) &&
+            user.UserRight > UserRight.Guest) return result;
+        var entries = GetBucketEntries(command.GetType().Name);
+        if (!command.RateLimitOptions.Flags.HasFlag(RateLimitFlags.Global))
+        {
+            entries = entries.Where(x => x.UserId == user.Id).ToList();
+        }
+
+        if (command.RateLimitOptions.Flags.HasFlag(RateLimitFlags.UseEntireMessage))
+        {
+            var hash = Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(message)));
+            entries = entries.Where(x => x.MessageHash == hash).ToList();
+        }
+
+        var now = DateTimeOffset.UtcNow;
+        entries = entries.Where(x => x.EntryExpires > now).ToList();
+        if (entries.Count >= command.RateLimitOptions.MaxInvocations)
+        {
+            result.IsRateLimited = true;
+            result.OldestEntryExpires = entries.OrderBy(x => x.EntryCreated).Last().EntryExpires;
+        }
+        return result;
+    }
+
+    /// <summary>
+    /// Get all the bucket entries for a given command
+    /// </summary>
+    /// <param name="commandName">String representation of the command.
+    /// Get it by running command.GetType().Name</param>
+    /// <returns>A list of entries</returns>
+    /// <exception cref="InvalidOperationException">Thrown if the cached entries were somehow null when converted to a string</exception>
+    public static List<RateLimitBucketEntryModel> GetBucketEntries(string commandName)
+    {
+        var cache = MemoryCache.Default;
+        var entries = cache.Get($"RateLimitBucket:{commandName}");
+        if (entries == null) return [];
+        List<RateLimitBucketEntryModel> bucketEntries;
+        try
+        {
+            bucketEntries = JsonSerializer.Deserialize<List<RateLimitBucketEntryModel>>((string)entries) ??
+                            throw new InvalidOperationException();
+        }
+        catch (Exception e)
+        {
+            _logger.Error($"Caught an exception when trying to deserialize RateLimitBucket entries for {commandName}. JSON follows");
+            _logger.Error(entries);
+            _logger.Error("Exception follows");
+            _logger.Error(e);
+            return [];
+        }
+
+        return bucketEntries;
+    }
+
+    /// <summary>
+    /// Save the current state of bucket entries for a given command
+    /// </summary>
+    /// <param name="commandName">String representation of the command.
+    /// Get it by running command.GetType().Name</param>
+    /// <param name="entries">Entries you wish to save</param>
+    public static void SaveBucketEntries(string commandName, List<RateLimitBucketEntryModel> entries)
+    {
+        var cache = MemoryCache.Default;
+        cache.Set($"RateLimitBucket:{commandName}", JsonSerializer.Serialize(entries),
+            new CacheItemPolicy { AbsoluteExpiration = DateTimeOffset.UtcNow.AddDays(1) });
+    }
+
+    /// <summary>
+    /// Remove the most recent entry for a given user and command
+    /// Use this if you want to invalidate an entry as forgiveness for invalid user input
+    /// </summary>
+    /// <param name="user">User to remove the entry for</param>
+    /// <param name="command">Command the user ran</param>
+    public static void RemoveMostRecentEntry(UserDbModel user, ICommand command)
+    {
+        var entries = GetBucketEntries(command.GetType().Name);
+        var lastEntry = entries.Where(x => x.UserId == user.Id).OrderBy(x => x.EntryCreated).LastOrDefault();
+        if (lastEntry == null) return;
+        entries.Remove(lastEntry);
+        SaveBucketEntries(command.GetType().Name, entries);
+    }
+
+    /// <summary>
+    /// Add an entry to the rate limit bucket for the given command
+    /// </summary>
+    /// <param name="user">User the entry belongs to</param>
+    /// <param name="command">Command the user ran</param>
+    /// <param name="message">The user's message</param>
+    public static void AddEntry(UserDbModel user, ICommand command, string message)
+    {
+        if (command.RateLimitOptions == null) return;
+        var commandName = command.GetType().Name;
+        var entries = GetBucketEntries(commandName);
+        entries.Add(new RateLimitBucketEntryModel
+        {
+            UserId = user.Id,
+            EntryCreated = DateTimeOffset.UtcNow,
+            EntryExpires = DateTimeOffset.UtcNow + command.RateLimitOptions.Window,
+            CommandInvoked = commandName,
+            MessageHash = Convert.ToHexString(SHA256.HashData(Encoding.UTF8.GetBytes(message)))
+        });
+        SaveBucketEntries(commandName, entries);
+    }
+
+    /// <summary>
+    /// Removes entries which have expired for all commands in the rate limit bucket
+    /// </summary>
+    public static void CleanupExpiredEntries()
+    {
+        var cache = MemoryCache.Default;
+        var now = DateTimeOffset.UtcNow;
+        foreach (var entry in cache.Select(kvp => kvp.Key).Where(kvp => kvp.StartsWith("RateLimitBucket:")).ToList().OfType<string>())
+        {
+            _logger.Info($"Cleaning up expired entries for {entry}");
+            var commandName = entry.Replace("RateLimitBucket:", string.Empty);
+            var entries = GetBucketEntries(commandName);
+            SaveBucketEntries(commandName, entries.Where(x => x.EntryExpires > now).ToList());
+        }
+    }
+}