From 40afef8ffd6424e295aa7d4ef968d633a906fa5d Mon Sep 17 00:00:00 2001
From: Jens-Hilmar Bradt <17177271+jenshb@users.noreply.github.com>
Date: Fri, 13 Jun 2025 13:13:51 +0200
Subject: [PATCH] Fix: Add optional message_num argument in POP3 LIST command
 (#518)

https://datatracker.ietf.org/doc/html/rfc1939#page-6

> If an argument was given and the POP3 server issues a positive response with a line containing information for that message.  This line is called a "scan listing" for that message.
---
 internal/pop3/server.go | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/internal/pop3/server.go b/internal/pop3/server.go
index 0ad614a..19dc82a 100644
--- a/internal/pop3/server.go
+++ b/internal/pop3/server.go
@@ -221,12 +221,23 @@ func handleTransactionCommand(conn net.Conn, cmd string, args []string, messages
 		for _, m := range messages {
 			totalSize += m.Size
 		}
-		sendResponse(conn, fmt.Sprintf("+OK %d messages (%d octets)", len(messages), int64(totalSize)))
 
-		for row, m := range messages {
-			sendResponse(conn, fmt.Sprintf("%d %d", row+1, int64(m.Size))) // Convert Size to int64 when printing
+		if len(args) > 0 {
+			arg, _ := getSafeArg(args, 0)
+			nr, err := strconv.Atoi(arg)
+			if err != nil || nr < 1 || nr > len(messages) {
+				sendResponse(conn, "-ERR no such message")
+				return
+			}
+			sendResponse(conn, fmt.Sprintf("+OK %d %d", nr, int64(messages[nr-1].Size)))
+		} else {
+			sendResponse(conn, fmt.Sprintf("+OK %d messages (%d octets)", len(messages), int64(totalSize)))
+
+			for row, m := range messages {
+				sendResponse(conn, fmt.Sprintf("%d %d", row+1, int64(m.Size))) // Convert Size to int64 when printing
+			}
+			sendResponse(conn, ".")
 		}
-		sendResponse(conn, ".")
 	case "UIDL":
 		sendResponse(conn, "+OK unique-id listing follows")
 		for row, m := range messages {