From a173f807b75348b6b472cdaed1b83febfc9786c7 Mon Sep 17 00:00:00 2001
From: Robert Sesek <rsesek@bluestatic.org>
Date: Sat, 17 Dec 2016 17:27:32 -0500
Subject: [PATCH] When receiving a message, the SMTP server must add its trace
 information.

This also computes a Message-ID for the Envelope.
---
 smtp/conn.go      | 55 ++++++++++++++++++++++++++++++++++++++-
 smtp/conn_test.go | 66 +++++++++++++++++++++++++++++++++++++++++++++++
 smtp/server.go    |  5 +++-
 3 files changed, 124 insertions(+), 2 deletions(-)

diff --git a/smtp/conn.go b/smtp/conn.go
index 3485894..bd91326 100644
--- a/smtp/conn.go
+++ b/smtp/conn.go
@@ -1,11 +1,13 @@
 package smtp
 
 import (
+	"crypto/rand"
 	"fmt"
 	"net"
 	"net/mail"
 	"net/textproto"
 	"strings"
+	"time"
 )
 
 type state int
@@ -24,6 +26,9 @@ type connection struct {
 	tp         *textproto.Conn
 	remoteAddr net.Addr
 
+	esmtp bool
+	tls   bool
+
 	state
 	line string
 
@@ -63,8 +68,10 @@ func AcceptConnection(netConn net.Conn, server Server) error {
 			conn.tp.Close()
 			break
 		case "HELO":
+			conn.esmtp = false
 			fallthrough
 		case "EHLO":
+			conn.esmtp = true
 			conn.doEHLO()
 		case "MAIL":
 			conn.doMAIL()
@@ -204,14 +211,20 @@ func (conn *connection) doDATA() {
 		return
 	}
 
+	received := time.Now()
 	env := Envelope{
 		RemoteAddr: conn.remoteAddr,
 		EHLO:       conn.ehlo,
 		MailFrom:   *conn.mailFrom,
 		RcptTo:     conn.rcptTo,
-		Data:       data,
+		Received:   received,
+		ID:         conn.envelopeID(received),
 	}
 
+	trace := conn.getReceivedInfo(env)
+
+	env.Data = append(trace, data...)
+
 	if reply := conn.server.OnMessageDelivered(env); reply != nil {
 		conn.reply(*reply)
 		return
@@ -221,6 +234,46 @@ func (conn *connection) doDATA() {
 	conn.reply(ReplyOK)
 }
 
+func (conn *connection) envelopeID(t time.Time) string {
+	var idBytes [4]byte
+	rand.Read(idBytes[:])
+	return fmt.Sprintf("m.%d.%x", t.UnixNano(), idBytes)
+}
+
+func (conn *connection) getReceivedInfo(envelope Envelope) []byte {
+	rhost, _, err := net.SplitHostPort(conn.remoteAddr.String())
+	if err != nil {
+		rhost = conn.remoteAddr.String()
+	}
+
+	rhosts, err := net.LookupAddr(rhost)
+	if err == nil {
+		rhost = fmt.Sprintf("%s [%s]", rhosts[0], rhost)
+	}
+
+	base := fmt.Sprintf("Received: from %s (%s)\r\n        ", conn.ehlo, rhost)
+
+	with := "SMTP"
+	if conn.esmtp {
+		with = "E" + with
+	}
+	if conn.tls {
+		with += "S"
+	}
+	base += fmt.Sprintf("by %s (mailpopbox) with %s id %s\r\n        ", conn.server.Name(), with, envelope.ID)
+
+	base += fmt.Sprintf("for <%s>\r\n        ", envelope.RcptTo[0].Address)
+
+	transport := "PLAINTEXT"
+	if conn.tls {
+		// TODO: TLS version, cipher, bits
+	}
+	date := envelope.Received.Format(time.RFC1123Z) // Same as RFC 5322 § 3.3
+	base += fmt.Sprintf("(using %s);\r\n        %s\r\n", transport, date)
+
+	return []byte(base)
+}
+
 func (conn *connection) doRSET() {
 	conn.state = stateInitial
 	conn.resetBuffers()
diff --git a/smtp/conn_test.go b/smtp/conn_test.go
index 32ca484..cd75299 100644
--- a/smtp/conn_test.go
+++ b/smtp/conn_test.go
@@ -9,6 +9,7 @@ import (
 	"runtime"
 	"strings"
 	"testing"
+	"time"
 )
 
 func _fl(depth int) string {
@@ -188,3 +189,68 @@ func TestCaseSensitivty(t *testing.T) {
 		{"QUiT", 221, nil},
 	})
 }
+
+func TestGetReceivedInfo(t *testing.T) {
+	conn := connection{
+		server:     &testServer{},
+		remoteAddr: &net.IPAddr{net.IPv4(127, 0, 0, 1), ""},
+	}
+
+	now := time.Now()
+
+	const crlf = "\r\n"
+	const line1 = "Received: from remote.test. (localhost [127.0.0.1])" + crlf
+	const line2 = "by Test-Server (mailpopbox) with "
+	const msgId = "abcdef.hijk"
+	lineLast := now.Format(time.RFC1123Z) + crlf
+
+	type params struct {
+		ehlo    string
+		esmtp   bool
+		tls     bool
+		address string
+	}
+
+	tests := []struct {
+		params params
+
+		expect []string
+	}{
+		{params{"remote.test.", true, false, "foo@bar.com"},
+			[]string{line1,
+				line2 + "ESMTP id " + msgId + crlf,
+				"for <foo@bar.com>" + crlf,
+				"(using PLAINTEXT);" + crlf,
+				lineLast, ""}},
+	}
+
+	for _, test := range tests {
+		t.Logf("%#v", test.params)
+
+		conn.ehlo = test.params.ehlo
+		conn.esmtp = test.params.esmtp
+		conn.tls = test.params.tls
+
+		envelope := Envelope{
+			RcptTo:   []mail.Address{{"", test.params.address}},
+			Received: now,
+			ID:       msgId,
+		}
+
+		actual := conn.getReceivedInfo(envelope)
+		actualLines := strings.SplitAfter(string(actual), crlf)
+
+		if len(actualLines) != len(test.expect) {
+			t.Errorf("wrong numbber of lines, expected %d, got %d", len(test.expect), len(actualLines))
+			continue
+		}
+
+		for i, line := range actualLines {
+			expect := test.expect[i]
+			if expect != strings.TrimLeft(line, " ") {
+				t.Errorf("Expected equal string %q, got %q", expect, line)
+			}
+		}
+	}
+
+}
diff --git a/smtp/server.go b/smtp/server.go
index e992cda..a574ef9 100644
--- a/smtp/server.go
+++ b/smtp/server.go
@@ -4,6 +4,7 @@ import (
 	"crypto/tls"
 	"net"
 	"net/mail"
+	"time"
 )
 
 type ReplyLine struct {
@@ -24,6 +25,8 @@ type Envelope struct {
 	MailFrom   mail.Address
 	RcptTo     []mail.Address
 	Data       []byte
+	Received   time.Time
+	ID         string
 }
 
 type Server interface {
@@ -34,7 +37,7 @@ type Server interface {
 	OnMessageDelivered(Envelope) *ReplyLine
 }
 
-type EmptyServerCallbacks struct {}
+type EmptyServerCallbacks struct{}
 
 func (*EmptyServerCallbacks) TLSConfig() *tls.Config {
 	return nil
-- 
2.22.5