From bb427850af72b481a467df7de0bfa095735397b6 Mon Sep 17 00:00:00 2001
From: Robert Sesek <rsesek@bluestatic.org>
Date: Mon, 2 Jan 2017 03:14:15 -0500
Subject: [PATCH] Implement the POP3 CAPA command from RFC 2449.

---
 README.md         |  1 +
 pop3/conn.go      | 15 +++++++++++++
 pop3/conn_test.go | 54 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 70 insertions(+)

diff --git a/README.md b/README.md
index e957228..827db6b 100644
--- a/README.md
+++ b/README.md
@@ -11,3 +11,4 @@ This server implements the following RFCs:
 - [Post Office Protocol - Version 3, RFC 1939](https://tools.ietf.org/html/rfc1939)
 - [Simple Mail Transfer Protocol, RFC 5321](https://tools.ietf.org/html/rfc5321)
 - [SMTP Service Extension for Secure SMTP over Transport Layer Security, RFC 3207](https://tools.ietf.org/html/rfc3207)
+- [POP3 Extension Mechanism, RFC 2449](https://tools.ietf.org/html/rfc2449)
diff --git a/pop3/conn.go b/pop3/conn.go
index a15c1f6..0af5724 100644
--- a/pop3/conn.go
+++ b/pop3/conn.go
@@ -92,6 +92,8 @@ func AcceptConnection(netConn net.Conn, po PostOffice, log zap.Logger) {
 			conn.doRSET()
 		case "UIDL":
 			conn.doUIDL()
+		case "CAPA":
+			conn.doCAPA()
 		default:
 			conn.err("unknown command")
 		}
@@ -306,6 +308,19 @@ func (conn *connection) doUIDL() {
 	conn.tp.PrintfLine(".")
 }
 
+func (conn *connection) doCAPA() {
+	conn.ok("capabilitiy list")
+
+	caps := []string{
+		"USER",
+		"UIDL",
+		".",
+	}
+	for _, c := range caps {
+		conn.tp.PrintfLine(c)
+	}
+}
+
 func (conn *connection) getRequestedMessage() Message {
 	var cmd string
 	var idx int
diff --git a/pop3/conn_test.go b/pop3/conn_test.go
index 31baad9..50115e7 100644
--- a/pop3/conn_test.go
+++ b/pop3/conn_test.go
@@ -425,3 +425,57 @@ func TestDele(t *testing.T) {
 		t.Errorf("DELE the wrong message")
 	}
 }
+
+func TestCapa(t *testing.T) {
+	s := newTestServer()
+
+	capaTest := func(t testing.TB, tp *textproto.Conn) string {
+		responseOK(t, tp)
+		if t.Failed() {
+			return ""
+		}
+
+		resp, err := tp.ReadDotLines()
+		if err != nil {
+			t.Error(err)
+			return ""
+		}
+
+		const (
+			capNeeded = iota
+			capSeen
+			capOK
+		)
+
+		caps := map[string]int{
+			"USER": capNeeded,
+			"UIDL": capNeeded,
+		}
+		for _, line := range resp {
+			if val, ok := caps[line]; ok {
+				if val == capNeeded {
+					caps[line] = capOK
+				} else {
+					t.Errorf("unxpected capa value %q", line)
+				}
+			} else {
+				caps[line] = capSeen
+			}
+		}
+		for c, val := range caps {
+			if val != capOK {
+				t.Errorf("unexpected capa value for %q: %d", c, val)
+			}
+		}
+		return ""
+	}
+
+	clientServerTest(t, s, []requestResponse{
+		{"CAPA", capaTest},
+		{"USER u", responseOK},
+		{"CAPA", capaTest},
+		{"PASS p", responseOK},
+		{"CAPA", capaTest},
+		{"QUIT", responseOK},
+	})
+}
-- 
2.22.5