feat: rate limit emails to two per address per hour

Foxnouns.Backend/Services/DataCleanupService.cs

@@ -33,13 +33,24 @@ public class DataCleanupService(
 
     public async Task InvokeAsync(CancellationToken ct = default)
     {
-        _logger.Information("Cleaning up expired users");
+        _logger.Debug("Cleaning up sent email cache");
+        await CleanEmailsAsync(ct);
+
+        _logger.Debug("Cleaning up expired users");
         await CleanUsersAsync(ct);
 
-        _logger.Information("Cleaning up expired data exports");
+        _logger.Debug("Cleaning up expired data exports");
         await CleanExportsAsync(ct);
     }
 
+    private async Task CleanEmailsAsync(CancellationToken ct = default)
+    {
+        Instant expiry = clock.GetCurrentInstant() - Duration.FromHours(2);
+        int count = await db.SentEmails.Where(e => e.SentAt < expiry).ExecuteDeleteAsync(ct);
+        if (count != 0)
+            _logger.Information("Deleted {Count} entries from the sent email cache", expiry);
+    }
+
     private async Task CleanUsersAsync(CancellationToken ct = default)
     {
         Instant selfDeleteExpires = clock.GetCurrentInstant() - User.DeleteAfter;

Foxnouns.Backend/Services/MailService.cs

@@ -12,13 +12,25 @@
 //
 // You should have received a copy of the GNU Affero General Public License
 // along with this program.  If not, see <https://www.gnu.org/licenses/>.
+using Coravel.Mailer.Mail;
 using Coravel.Mailer.Mail.Interfaces;
 using Coravel.Queuing.Interfaces;
+using Foxnouns.Backend.Database;
+using Foxnouns.Backend.Database.Models;
 using Foxnouns.Backend.Mailables;
+using Microsoft.EntityFrameworkCore;
+using NodaTime;
 
 namespace Foxnouns.Backend.Services;
 
-public class MailService(ILogger logger, IMailer mailer, IQueue queue, Config config)
+public class MailService(
+    ILogger logger,
+    IMailer mailer,
+    IQueue queue,
+    IClock clock,
+    Config config,
+    IServiceProvider serviceProvider
+)
 {
     private readonly ILogger _logger = logger.ForContext<MailService>();
 
@@ -26,25 +38,18 @@ public class MailService(ILogger logger, IMailer mailer, IQueue queue, Config co
     {
         queue.QueueAsyncTask(async () =>
         {
-            _logger.Debug("Sending account creation email to {ToEmail}", to);
-            try
-            {
-                await mailer.SendAsync(
-                    new AccountCreationMailable(
-                        config,
-                        new AccountCreationMailableView
-                        {
-                            BaseUrl = config.BaseUrl,
-                            To = to,
-                            Code = code,
-                        }
-                    )
-                );
-            }
-            catch (Exception exc)
-            {
-                _logger.Error(exc, "Sending account creation email");
-            }
+            await SendEmailAsync(
+                to,
+                new AccountCreationMailable(
+                    config,
+                    new AccountCreationMailableView
+                    {
+                        BaseUrl = config.BaseUrl,
+                        To = to,
+                        Code = code,
+                    }
+                )
+            );
         });
     }
 
@@ -53,25 +58,53 @@ public class MailService(ILogger logger, IMailer mailer, IQueue queue, Config co
         _logger.Debug("Sending add email address email to {ToEmail}", to);
         queue.QueueAsyncTask(async () =>
         {
-            try
-            {
-                await mailer.SendAsync(
-                    new AddEmailMailable(
-                        config,
-                        new AddEmailMailableView
-                        {
-                            BaseUrl = config.BaseUrl,
-                            To = to,
-                            Code = code,
-                            Username = username,
-                        }
-                    )
-                );
-            }
-            catch (Exception exc)
-            {
-                _logger.Error(exc, "Sending add email address email");
-            }
+            await SendEmailAsync(
+                to,
+                new AddEmailMailable(
+                    config,
+                    new AddEmailMailableView
+                    {
+                        BaseUrl = config.BaseUrl,
+                        To = to,
+                        Code = code,
+                        Username = username,
+                    }
+                )
+            );
         });
     }
+
+    private async Task SendEmailAsync<T>(string to, Mailable<T> mailable)
+    {
+        try
+        {
+            // ReSharper disable SuggestVarOrType_SimpleTypes
+            await using var scope = serviceProvider.CreateAsyncScope();
+            await using var db = scope.ServiceProvider.GetRequiredService<DatabaseContext>();
+            // ReSharper restore SuggestVarOrType_SimpleTypes
+
+            Instant now = clock.GetCurrentInstant();
+
+            int count = await db.SentEmails.CountAsync(e =>
+                e.Email == to && e.SentAt > (now - Duration.FromHours(1))
+            );
+            if (count >= 2)
+            {
+                _logger.Information(
+                    "Have already sent 2 or more emails to {ToAddress} in the past hour, not sending new email",
+                    to
+                );
+                return;
+            }
+
+            await mailer.SendAsync(mailable);
+
+            db.SentEmails.Add(new SentEmail { Email = to, SentAt = now });
+            await db.SaveChangesAsync();
+        }
+        catch (Exception exc)
+        {
+            _logger.Error(exc, "Sending email");
+        }
+    }
 }