feat: Add SMTPSession and BeforeRcptToAccepted event (#541)

Signed-off-by: James Hillyerd <james@hillyerd.com>

pkg/server/smtp/handler.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"net/mail"
 	"net/textproto"
 	"regexp"
 	"strconv"
@@ -495,7 +496,26 @@ func (s *Session) mailHandler(cmd string, arg string) {
 			s.logger.Warn().Str("to", addr).Err(err).Msg("Bad address as RCPT arg")
 			return
 		}
-		if !recip.ShouldAccept() {
+
+		// Append new address to extSession for inspection.
+		addrCopy := recip.Address
+		extSession := s.extSession()
+		extSession.To = append(extSession.To, &addrCopy)
+
+		// Process through extensions.
+		extAction := event.ActionDefer
+		extResult := s.extHost.Events.BeforeRcptToAccepted.Emit(extSession)
+		if extResult != nil {
+			extAction = extResult.Action
+		}
+		if extAction == event.ActionDeny {
+			s.send(fmt.Sprintf("%03d %s", extResult.ErrorCode, extResult.ErrorMsg))
+			s.logger.Warn().Msgf("Extension denied mail to <%v>", recip.Address)
+			return
+		}
+
+		// Ignore ShouldAccept if extensions explicitly allowed this Recipient.
+		if extAction == event.ActionDefer && !recip.ShouldAccept() {
 			s.logger.Warn().Str("to", addr).Msg("Rejecting recipient domain")
 			s.send("550 Relay not permitted")
 			return
@@ -687,3 +707,18 @@ func (s *Session) ooSeq(cmd string) {
 	s.send(fmt.Sprintf("503 Command %v is out of sequence", cmd))
 	s.logger.Warn().Msgf("Wasn't expecting %v here", cmd)
 }
+
+// extSession builds an SMTPSession for extensions.
+func (s *Session) extSession() *event.SMTPSession {
+	from := s.from.Address
+	to := make([]*mail.Address, 0, len(s.recipients))
+	for _, recip := range s.recipients {
+		addr := recip.Address
+		to = append(to, &addr)
+	}
+
+	return &event.SMTPSession{
+		From: &from,
+		To:   to,
+	}
+}

pkg/server/smtp/handler_test.go

@@ -18,6 +18,7 @@ import (
 	"github.com/inbucket/inbucket/v3/pkg/test"
 	"github.com/rs/zerolog"
 	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
 )
 
 type scriptStep struct {
@@ -457,7 +458,7 @@ func TestBeforeMailAcceptedEventResponse(t *testing.T) {
 			// Play and verify SMTP session.
 			script := []scriptStep{
 				{"HELO localhost", 250},
-				tc.script,
+				tc.script, // error code is the significant part.
 				{"QUIT", 221}}
 			playSession(t, server, script)
 
@@ -466,6 +467,175 @@ func TestBeforeMailAcceptedEventResponse(t *testing.T) {
 	}
 }
 
+// Tests "RCPT TO" emits BeforeRcptToAccepted event.
+func TestBeforeRcptToAcceptedSingleEventEmitted(t *testing.T) {
+	ds := test.NewStore()
+	extHost := extension.NewHost()
+	server := setupSMTPServer(ds, extHost)
+
+	var got *event.SMTPSession
+	extHost.Events.BeforeRcptToAccepted.AddListener(
+		"test",
+		func(session event.SMTPSession) *event.SMTPResponse {
+			got = &session
+			return &event.SMTPResponse{Action: event.ActionDefer}
+		})
+
+	// Play and verify SMTP session.
+	script := []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RCPT TO:<user@gmail.com>", 250},
+		{"QUIT", 221}}
+	playSession(t, server, script)
+
+	require.NotNil(t, got, "BeforeRcptToListener did not receive SMTPSession")
+	require.NotNil(t, got.From)
+	require.NotNil(t, got.To)
+	assert.Equal(t, "john@gmail.com", got.From.Address)
+	assert.Len(t, got.To, 1)
+	assert.Equal(t, "user@gmail.com", got.To[0].Address)
+}
+
+// Tests "RCPT TO" emits many BeforeRcptToAccepted events.
+func TestBeforeRcptToAcceptedManyEventsEmitted(t *testing.T) {
+	ds := test.NewStore()
+	extHost := extension.NewHost()
+	server := setupSMTPServer(ds, extHost)
+
+	var called int
+	var got *event.SMTPSession
+	extHost.Events.BeforeRcptToAccepted.AddListener(
+		"test",
+		func(session event.SMTPSession) *event.SMTPResponse {
+			called++
+			got = &session
+			return &event.SMTPResponse{Action: event.ActionDefer}
+		})
+
+	// Play and verify SMTP session.
+	script := []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RCPT TO:<user@gmail.com>", 250},
+		{"RCPT TO:<user2@gmail.com>", 250},
+		{"QUIT", 221}}
+	playSession(t, server, script)
+
+	require.Equal(t, 2, called, "2 events should have been emitted")
+	require.NotNil(t, got, "BeforeRcptToListener did not receive SMTPSession")
+	require.NotNil(t, got.From)
+	require.NotNil(t, got.To)
+	assert.Equal(t, "john@gmail.com", got.From.Address)
+	assert.Len(t, got.To, 2)
+	assert.Equal(t, "user@gmail.com", got.To[0].Address)
+	assert.Equal(t, "user2@gmail.com", got.To[1].Address)
+}
+
+// Tests we can continue after denying a "RCPT TO".
+func TestBeforeRcptToAcceptedEventDeny(t *testing.T) {
+	ds := test.NewStore()
+	extHost := extension.NewHost()
+	server := setupSMTPServer(ds, extHost)
+
+	var called int
+	var got *event.SMTPSession
+	extHost.Events.BeforeRcptToAccepted.AddListener(
+		"test",
+		func(session event.SMTPSession) *event.SMTPResponse {
+			called++
+
+			// Reject bad address.
+			action := event.ActionDefer
+			for _, to := range session.To {
+				if to.Address == "bad@apple.com" {
+					action = event.ActionDeny
+				}
+			}
+
+			got = &session
+			return &event.SMTPResponse{Action: action, ErrorCode: 550, ErrorMsg: "rotten"}
+		})
+
+	// Play and verify SMTP session.
+	script := []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"RCPT TO:<user@gmail.com>", 250},
+		{"RCPT TO:<bad@apple.com>", 550},
+		{"RCPT TO:<user2@gmail.com>", 250},
+		{"QUIT", 221}}
+	playSession(t, server, script)
+
+	require.Equal(t, 3, called, "3 events should have been emitted")
+	require.NotNil(t, got, "BeforeRcptToListener did not receive SMTPSession")
+	require.NotNil(t, got.From)
+	require.NotNil(t, got.To)
+	assert.Equal(t, "john@gmail.com", got.From.Address)
+
+	// Verify bad apple dropped from final event.
+	assert.Len(t, got.To, 2)
+	assert.Equal(t, "user@gmail.com", got.To[0].Address)
+	assert.Equal(t, "user2@gmail.com", got.To[1].Address)
+}
+
+// Test "RCPT TO" acts on BeforeRcptToAccepted event result.
+func TestBeforeRcptToAcceptedEventResponse(t *testing.T) {
+	ds := test.NewStore()
+	extHost := extension.NewHost()
+	server := setupSMTPServer(ds, extHost)
+
+	var shouldReturn *event.SMTPResponse
+	var gotEvent *event.SMTPSession
+	extHost.Events.BeforeRcptToAccepted.AddListener(
+		"test",
+		func(session event.SMTPSession) *event.SMTPResponse {
+			gotEvent = &session
+			return shouldReturn
+		})
+
+	tcs := map[string]struct {
+		script   scriptStep         // Command to send and SMTP code expected.
+		eventRes event.SMTPResponse // Response to send from event listener.
+	}{
+		"allow": {
+			script:   scriptStep{"RCPT TO:<john@gmail.com>", 250},
+			eventRes: event.SMTPResponse{Action: event.ActionAllow},
+		},
+		"deny": {
+			script: scriptStep{"RCPT TO:<john@gmail.com>", 550},
+			eventRes: event.SMTPResponse{
+				Action:    event.ActionDeny,
+				ErrorCode: 550,
+				ErrorMsg:  "meh",
+			},
+		},
+		"defer": {
+			script:   scriptStep{"RCPT TO:<john@gmail.com>", 250},
+			eventRes: event.SMTPResponse{Action: event.ActionDefer},
+		},
+	}
+
+	for name, tc := range tcs {
+		tc := tc
+		t.Run(name, func(t *testing.T) {
+			// Reset event listener.
+			shouldReturn = &tc.eventRes
+			gotEvent = nil
+
+			// Play and verify SMTP session.
+			script := []scriptStep{
+				{"HELO localhost", 250},
+				{"MAIL FROM:<user@gmail.com>", 250},
+				tc.script, // error code is the significant part.
+				{"QUIT", 221}}
+			playSession(t, server, script)
+
+			assert.NotNil(t, gotEvent, "BeforeRcptToListener did not receive SMTPSession")
+		})
+	}
+}
+
 // playSession creates a new session, reads the greeting and then plays the script
 func playSession(t *testing.T, server *Server, script []scriptStep) {
 	t.Helper()