From 3bec7010fbb9c0fe559d526d2417b1dfb82ba236 Mon Sep 17 00:00:00 2001
From: Robert Sesek <rsesek@bluestatic.org>
Date: Sun, 9 Nov 2025 16:11:27 -0500
Subject: [PATCH] Implement POP3 `LIST <msg>` to get the scan listing for a
 single message by ID.

---
 pkg/pop3/conn.go      | 29 ++++++++++++++++++++-----
 pkg/pop3/conn_test.go | 50 +++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 74 insertions(+), 5 deletions(-)

diff --git a/pkg/pop3/conn.go b/pkg/pop3/conn.go
index 2b0d15a..e3737bf 100644
--- a/pkg/pop3/conn.go
+++ b/pkg/pop3/conn.go
@@ -212,11 +212,30 @@ func (conn *connection) doLIST() {
 		return
 	}
 
-	msgs, err := conn.mb.ListMessages()
-	if err != nil {
-		conn.log.Error("failed to list messages", zap.Error(err))
-		conn.err(err.Error())
-		return
+	var msgs []Message
+
+	var cmd string
+	var id int
+	n, _ := fmt.Sscanf(conn.line, "%s %d", &cmd, &id)
+	if n == 2 {
+		msg := conn.mb.GetMessage(id)
+		if msg == nil {
+			conn.err("No message with that ID")
+			return
+		}
+		if msg.Deleted() {
+			conn.err(errDeletedMsg)
+			return
+		}
+		msgs = []Message{msg}
+	} else {
+		var err error
+		msgs, err = conn.mb.ListMessages()
+		if err != nil {
+			conn.log.Error("failed to list messages", zap.Error(err))
+			conn.err(err.Error())
+			return
+		}
 	}
 
 	conn.ok("scan listing")
diff --git a/pkg/pop3/conn_test.go b/pkg/pop3/conn_test.go
index c5ad731..c90ee0d 100644
--- a/pkg/pop3/conn_test.go
+++ b/pkg/pop3/conn_test.go
@@ -309,6 +309,56 @@ func TestCaseSensitivty(t *testing.T) {
 	})
 }
 
+func TestList(t *testing.T) {
+	s := newTestServer()
+	s.mb.msgs[1] = &testMessage{1, 5, false, "hello"}
+	s.mb.msgs[2] = &testMessage{2, 5, false, "world"}
+
+	clientServerTest(t, s, []requestResponse{
+		{"USER u", responseOK},
+		{"PASS p", responseOK},
+		{"LIST", func(t testing.TB, tp *textproto.Conn) string {
+			responseOK(t, tp)
+			lines, err := tp.ReadDotLines()
+			if err != nil {
+				t.Error(err)
+				return ""
+			}
+			if want, got := 2, len(lines); want != got {
+				t.Errorf("Expected %d lines, got %d", want, got)
+				return ""
+			}
+			if want, got := "1 5", lines[0]; want != got {
+				t.Errorf("Expected first line to be %q, got %q", want, got)
+				return ""
+			}
+			if want, got := "2 5", lines[1]; want != got {
+				t.Errorf("Expected second line to be %q, got %q", want, got)
+				return ""
+			}
+			return ""
+		}},
+		{"LIST 2", func(t testing.TB, tp *textproto.Conn) string {
+			responseOK(t, tp)
+			lines, err := tp.ReadDotLines()
+			if err != nil {
+				t.Error(err)
+				return ""
+			}
+			if want, got := 1, len(lines); want != got {
+				t.Errorf("Expected %d lines, got %d", want, got)
+				return ""
+			}
+			if want, got := "2 5", lines[0]; want != got {
+				t.Errorf("Expected line to be %q, got %q", want, got)
+				return ""
+			}
+			return ""
+		}},
+		{"LIST 5", responseERR},
+	})
+}
+
 func TestRetr(t *testing.T) {
 	s := newTestServer()
 	s.mb.msgs[1] = &testMessage{1, 5, false, "hello"}
-- 
2.43.5