Bug fix and added void filter

Author: Eric Boumendil

README.md

@@ -14,6 +14,7 @@ Internally, [MailKit](https://github.com/jstedfast/MailKit) is used for SMTP for
 - Replace subject of some messages with LLM completion based on message body (OpenAI-compatible API like [llama.cpp](https://github.com/ggerganov/llama.cpp/tree/master)).
 - Filter by destination address (if enabled, SMTP will reject unknown recipients).
 - Filter by message size (SMTP will reject message reaching a threshold).
+- Void filter (trash messages based on regular expressions).
 - Catch up on next program startup (messages not send yet at shutdown are sent on startup).
 - Unsecure Basic authentication (user/password without TLS) and anonymous authentication.
 

examples/configuration/README.md

@@ -121,3 +121,23 @@ The previous example will replace subject of messages that contain "notification
 
 The prompt sent to LLM will contain default user instructions followed by message body. You can customize the user prompt with a parameter *UserPrompt* inside a rule (it must contain a placeholder `%1` for replacement with message body). You also can customize system prompt with a parameter *SystemPrompt* in section *LlmEnrichment* (no variable placeholder required for the system prompt), or directly in primary configuration of *LlmClient* (see related section in this page).
 Unless for complex configuration, custom system prompt should be in *LlmClient* (shared for any usage of the LLM client).
+
+## Trash messages (void filter)
+
+If an SMTP client repeatedly sends notifications you're not interested in, it may be useful to filter them out from SmtpLocalRelay this way:
+
+```js
+{
+    "SmtpForwarder": {
+        "Void": {
+            "Matchers": [
+                {
+                    "RegexOnField": "Subject, Body",
+                    "Regex": "Arpwatch Notification : flip flop.+?old ethernet address: ab:cd:ef",
+                }
+            ]
+        }
+    }
+}
+```
+

examples/docker/docker-compose.yml

@@ -1,7 +1,7 @@
 version: '3.1'
 services:
   localsmtprelay:
-    image: eric1901/localsmtprelay:1.2.0
+    image: eric1901/localsmtprelay:1.2.1
     ports:
      - "25:25/tcp"
     environment:

examples/kubernetes/localsmtprelay-deployment.yaml

@@ -27,7 +27,7 @@ spec:
       containers:
       - name: localsmtprelay
         imagePullPolicy: IfNotPresent
-        image: eric1901/localsmtprelay:1.2.0
+        image: eric1901/localsmtprelay:1.2.1
         ports:
         - containerPort: 25
         volumeMounts:

src/LocalSmtpRelay/Components/AlertManager/AlertManagerForwarder.cs

@@ -1,4 +1,5 @@
-using LocalSmtpRelay.Model;
+using LocalSmtpRelay.Helpers;
+using LocalSmtpRelay.Model;
 using Microsoft.Extensions.Logging;
 using Microsoft.Extensions.Options;
 using MimeKit;
@@ -17,8 +18,6 @@ public sealed class AlertManagerForwarder(IOptions<AlertManagerForwarderOptions>
                                               LlmAlertSummarizer llm,
                                               ILogger<AlertManagerForwarder> logger)
     {
-        private static readonly TimeSpan RegexTimeout = TimeSpan.FromSeconds(10);
-
         private readonly bool _disable = options.Value.Disable;
         private readonly MessageRule[] _rules = options.Value.MessageRules ?? [];
         private readonly Dictionary<string, int> defaultAlertNumberBySubject = new(StringComparer.OrdinalIgnoreCase);
@@ -98,7 +97,7 @@ public async Task<bool> TrySendAlert(MimeMessage message, CancellationToken canc
                         input += $"\r\n{textBody}";
 
                     if (rule.ResolutionRegex != null &&
-                        Regex.IsMatch(input, rule.ResolutionRegex, RegexOptions.None, RegexTimeout))
+                        RegexHelper.IsMatch(input, rule.ResolutionRegex))
                     {
                         if (alert is null)
                             alert = new Alert();
@@ -112,7 +111,7 @@ public async Task<bool> TrySendAlert(MimeMessage message, CancellationToken canc
                         if (!rule.EvaluateOtherRules)
                             break;
                     }
-                    else if (Regex.IsMatch(input, rule.AlertRegex, RegexOptions.None, RegexTimeout))
+                    else if (RegexHelper.IsMatch(input, rule.AlertRegex))
                     {
                         if (alert is null)
                             alert = new Alert();

src/LocalSmtpRelay/Components/SmtpForwarder.cs

@@ -22,6 +22,7 @@
 using LocalSmtpRelay.Components.Llm;
 using System.Text.RegularExpressions;
 using System.Text.Json;
+using LocalSmtpRelay.Helpers;
 
 namespace LocalSmtpRelay.Components
 {
@@ -140,6 +141,13 @@ private async Task ProcessSend(FileInfo file, CancellationToken cancellationToke
             {
                 using MimeMessage message = await MimeMessage.LoadAsync(file.FullName, cancellationToken).ConfigureAwait(continueOnCapturedContext: false);
                 TryFillTextBodyFromHtml(message);
+                if (ShouldSendToVoid(message))
+                {
+                    if (!Utility.TryDeleteFile(file))
+                        _logger.LogWarning("Failed to delete: {File}", file);
+                    return;
+                }
+
                 if (await _alertManagerForwarder.TrySendAlert(message, cancellationToken).ConfigureAwait(continueOnCapturedContext: false))
                 {
                     _logger.LogInformation("SmtpForwarder forwarded message to Alertmanager: {Subject}", message.Subject);
@@ -215,6 +223,20 @@ private async Task ProcessSend(FileInfo file, CancellationToken cancellationToke
             }
         }
 
+        private bool ShouldSendToVoid(MimeMessage message)
+        {
+            return Array.Exists(_options.CurrentValue.Void.Matchers, m =>
+            {
+                string regexInput = string.Empty;
+                if (m.RegexOnField.HasFlag(Model.MessageField.Subject))
+                    regexInput = message.Subject;
+                if (m.RegexOnField.HasFlag(Model.MessageField.Body))
+                    regexInput += $"\r\n{message.TextBody}";
+
+                return RegexHelper.IsMatch(regexInput, m.Regex);
+            });
+        }
+
         /// <summary>
         /// If a rule matches this message, LLM is applied to the text body
         /// to replace the subject.
@@ -235,9 +257,9 @@ private async Task TryReplaceSubjectWithLlm(MimeMessage message, CancellationTok
                 if (r.RegexOnField.HasFlag(Model.MessageField.Subject))
                     regexInput = message.Subject;
                 if (r.RegexOnField.HasFlag(Model.MessageField.Body))
-                    regexInput += $"\r\ntextBody";
+                    regexInput += $"\r\n{textBody}";
 
-                return Regex.IsMatch(regexInput, r.Regex, RegexOptions.IgnoreCase, TimeSpan.FromSeconds(10));
+                return RegexHelper.IsMatch(regexInput, r.Regex);
             });
 
             if (rule != null)

src/LocalSmtpRelay/Components/SmtpForwarderOptions.cs

@@ -24,6 +24,8 @@ public sealed class SmtpForwarderOptions
 
         public Llm LlmEnrichment { get; } = new();
 
+        public VoidFilter Void { get; } = new();
+
         public class AuthenticationParameters
         {
             public string Username { get; set; } = default!;
@@ -50,7 +52,22 @@ public sealed class Llm
             public string? UserPrompt { get; set; }
 
 
-            public LlmRule[] Rules { get; } = [];
+            public LlmRule[] Rules { get; set; } = [];
+        }
+
+        public sealed class VoidFilter 
+        {
+            public VoidMatcherRule[] Matchers { get; set; } = [];
+        }
+
+        public sealed class VoidMatcherRule
+        {
+            /// <summary>
+            /// If regex matches, message will be ignored.
+            /// </summary>
+            public string Regex { get; set; } = default!;
+
+            public MessageField RegexOnField { get; set; }
         }
 
         public sealed class LlmRule

src/LocalSmtpRelay/Helpers/RegexHelper.cs

@@ -0,0 +1,13 @@
+using System;
+using System.Text.RegularExpressions;
+
+namespace LocalSmtpRelay.Helpers
+{
+    internal static class RegexHelper
+    {
+        private static readonly TimeSpan RegexTimeout = TimeSpan.FromSeconds(10);
+
+        public static bool IsMatch(string input, string regex)
+            => Regex.IsMatch(input, regex, RegexOptions.IgnoreCase | RegexOptions.Singleline, RegexTimeout);
+    }
+}

src/LocalSmtpRelay/LocalSmtpRelay.csproj

@@ -12,7 +12,7 @@
 
   <PropertyGroup>
     <DockerfileRunArguments>-p 25:25</DockerfileRunArguments>
-    <Version>1.2.0</Version>
+    <Version>1.2.1</Version>
     <InvariantGlobalization>true</InvariantGlobalization>
     <DockerDefaultTargetOS>Linux</DockerDefaultTargetOS>
   </PropertyGroup>