From 1193d76838268563455407fc66ca2a4a2939c051 Mon Sep 17 00:00:00 2001
From: Mia Winter <mia@miawinter.de>
Date: Mon, 8 Apr 2024 11:46:54 +0200
Subject: [PATCH] Added Smtp reconnect on connection loss

---
 Wave/Services/IEmailService.cs    |  4 ++--
 Wave/Services/SmtpEmailService.cs | 33 ++++++++++++++++++++++++++++---
 2 files changed, 32 insertions(+), 5 deletions(-)

diff --git a/Wave/Services/IEmailService.cs b/Wave/Services/IEmailService.cs
index 4f823d4..0b3cd06 100644
--- a/Wave/Services/IEmailService.cs
+++ b/Wave/Services/IEmailService.cs
@@ -4,7 +4,7 @@ public interface IEmailService : IAsyncDisposable {
 	ValueTask ConnectAsync(CancellationToken cancellation);
 	ValueTask DisconnectAsync(CancellationToken cancellation);
 
-	ValueTask SendEmailAsync(IEmail email);
+	ValueTask SendEmailAsync(IEmail email, CancellationToken cancellation = default);
 }
 
 public sealed class NoOpEmailService : IEmailService {
@@ -12,5 +12,5 @@ public sealed class NoOpEmailService : IEmailService {
 
 	public ValueTask ConnectAsync(CancellationToken cancellation) => ValueTask.CompletedTask;
 	public ValueTask DisconnectAsync(CancellationToken cancellation) => ValueTask.CompletedTask;
-	public ValueTask SendEmailAsync(IEmail email) => ValueTask.CompletedTask;
+	public ValueTask SendEmailAsync(IEmail email, CancellationToken cancellation = default) => ValueTask.CompletedTask;
 }
\ No newline at end of file
diff --git a/Wave/Services/SmtpEmailService.cs b/Wave/Services/SmtpEmailService.cs
index 0138cf8..6c3241e 100644
--- a/Wave/Services/SmtpEmailService.cs
+++ b/Wave/Services/SmtpEmailService.cs
@@ -1,4 +1,5 @@
-using MailKit.Net.Smtp;
+using MailKit;
+using MailKit.Net.Smtp;
 using MailKit.Security;
 using Microsoft.Extensions.Options;
 using MimeKit;
@@ -43,7 +44,7 @@ public class SmtpEmailService(ILogger<SmtpEmailService> logger, IOptions<EmailCo
 		Client = null;
 	}
 
-	public async ValueTask SendEmailAsync(IEmail email) {
+	public async ValueTask SendEmailAsync(IEmail email, CancellationToken cancellation = default) {
 		if (Client is null) throw new ApplicationException("Not connected.");
 		
 		var message = new MimeMessage {
@@ -66,10 +67,13 @@ public class SmtpEmailService(ILogger<SmtpEmailService> logger, IOptions<EmailCo
 		int retryCount = 0;
 		while (retryCount < 3) {
 			try {
-				await Client.SendAsync(message);
+				await Client.SendAsync(message, cancellation);
 				Logger.LogInformation("Successfully send mail to {email} (subject: {subject}).",
 					email.ReceiverEmail, email.Subject);
 				return;
+			} catch (ServiceNotConnectedException ex) {
+				Logger.LogWarning(ex, "Not connected, attempting reconnect.");
+				if (!await TryReconnect(cancellation)) throw;
 			} catch (Exception ex) {
 				retryCount++;
 				Logger.LogWarning(ex, "Error sending E-Mail to {email}. Try: {RetryCount}.", 
@@ -80,4 +84,27 @@ public class SmtpEmailService(ILogger<SmtpEmailService> logger, IOptions<EmailCo
 		// throw new EmailNotSendException();
 		Logger.LogError("Giving up");
 	}
+
+	private async ValueTask<bool> TryReconnect(CancellationToken cancellation) {
+		int reconnectCount = 0;
+		while (true) {
+			try {
+				await DisconnectAsync(cancellation);
+				await ConnectAsync(cancellation);
+				return true;
+			} catch (Exception ex1) {
+				reconnectCount++;
+				// 2^11 = 2048 seconds ~= 34 minutes
+				if (reconnectCount <= 11) {
+					// 2 4 6 8 16 32 64... seconds
+					int waitTime = (int)Math.Pow(2, reconnectCount);
+					Logger.LogError(ex1, "Reconnect failed, Try: {ReconnectTry}. Will wait {ReconnectWaitTime} Seconds for next attempt.", reconnectCount, waitTime);
+					await Task.Delay(TimeSpan.FromSeconds(waitTime), cancellation);
+				} else {
+					Logger.LogCritical(ex1, "Reconnect retry count exceeded, giving up.");
+					return false;
+				}
+			}
+		}
+	}
 }
\ No newline at end of file