From 4c8c0d855e206ea3135960f8fc403e093763205d Mon Sep 17 00:00:00 2001
From: Winni Neessen <wn@neessen.net>
Date: Thu, 3 Oct 2024 12:38:39 +0200
Subject: [PATCH] Handle read errors in SMTP authentication flow

Add checks to handle errors when reading client messages. This ensures that an appropriate error message is sent back to the client if reading fails, improving the robustness of the SMTP authentication process.
---
 smtp/smtp_test.go | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/smtp/smtp_test.go b/smtp/smtp_test.go
index dc8dbdb..0d47760 100644
--- a/smtp/smtp_test.go
+++ b/smtp/smtp_test.go
@@ -1731,8 +1731,12 @@ func (s *testSCRAMSMTPServer) handleSCRAMAuth(conn net.Conn) {
 	}
 
 	data, err := reader.ReadString('\n')
-	clientMessage := strings.TrimSpace(data)
-	decodedMessage, err := base64.StdEncoding.DecodeString(clientMessage)
+	if err != nil {
+		_ = writeLine("535 Authentication failed")
+		return
+	}
+	data = strings.TrimSpace(data)
+	decodedMessage, err := base64.StdEncoding.DecodeString(data)
 	if err != nil {
 		_ = writeLine("535 Authentication failed")
 		return
@@ -1765,8 +1769,12 @@ func (s *testSCRAMSMTPServer) handleSCRAMAuth(conn net.Conn) {
 	_ = writeLine(fmt.Sprintf("334 %s", base64.StdEncoding.EncodeToString([]byte(serverFirstMessage))))
 
 	data, err = reader.ReadString('\n')
-	clientFinalMessage := strings.TrimSpace(data)
-	decodedFinalMessage, err := base64.StdEncoding.DecodeString(clientFinalMessage)
+	if err != nil {
+		_ = writeLine("535 Authentication failed")
+		return
+	}
+	data = strings.TrimSpace(data)
+	decodedFinalMessage, err := base64.StdEncoding.DecodeString(data)
 	if err != nil {
 		_ = writeLine("535 Authentication failed")
 		return
@@ -1794,7 +1802,6 @@ func (s *testSCRAMSMTPServer) handleSCRAMAuth(conn net.Conn) {
 		return
 	}
 	_ = writeLine("235 Authentication successful")
-	return
 }
 
 func (s *testSCRAMSMTPServer) extractNonce(message string) string {