extension: Add BeforeMailAccepted event (#320)

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

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

pkg/extension/event/events.go

@@ -5,6 +5,12 @@ import (
 	"time"
 )
 
+// AddressParts contains the local and domain parts of an email address.
+type AddressParts struct {
+	Local  string
+	Domain string
+}
+
 // MessageMetadata contains the basic header data for a message event.
 type MessageMetadata struct {
 	Mailbox string

pkg/extension/host.go

@@ -21,6 +21,7 @@ type Host struct {
 // listener will not be called until the one before it complets.
 type Events struct {
 	AfterMessageStored EventBroker[event.MessageMetadata, Void]
+	BeforeMailAccepted EventBroker[event.AddressParts, bool]
 }
 
 // Void indicates the event emitter will ignore any value returned by listeners.

pkg/server/lifecycle.go

@@ -56,7 +56,7 @@ func FullAssembly(conf *config.Root) (*Services, error) {
 	webServer := web.NewServer(conf, mmanager, msgHub)
 
 	pop3Server := pop3.NewServer(conf.POP3, store)
-	smtpServer := smtp.NewServer(conf.SMTP, mmanager, addrPolicy)
+	smtpServer := smtp.NewServer(conf.SMTP, mmanager, addrPolicy, extHost)
 
 	return &Services{
 		MsgHub:           msgHub,

pkg/server/smtp/handler.go

@@ -13,6 +13,7 @@ import (
 	"strings"
 	"time"
 
+	"github.com/inbucket/inbucket/pkg/extension/event"
 	"github.com/inbucket/inbucket/pkg/policy"
 	"github.com/rs/zerolog"
 )
@@ -383,7 +384,8 @@ func (s *Session) readyHandler(cmd string, arg string) {
 			return
 		}
 		from := m[1]
-		if _, _, err := policy.ParseEmailAddress(from); from != "" && err != nil {
+		localpart, domain, err := policy.ParseEmailAddress(from)
+		if from != "" && err != nil {
 			s.send("501 Bad sender address syntax")
 			s.logger.Warn().Msgf("Bad address as MAIL arg: %q, %s", from, err)
 			return
@@ -415,10 +417,22 @@ func (s *Session) readyHandler(cmd string, arg string) {
 				}
 			}
 		}
-		s.from = from
-		s.logger.Info().Msgf("Mail from: %v", from)
-		s.send(fmt.Sprintf("250 Roger, accepting mail from <%v>", from))
-		s.enterState(MAIL)
+
+		// Process through extensions.
+		extResult := s.extHost.Events.BeforeMailAccepted.Emit(
+			&event.AddressParts{Local: localpart, Domain: domain})
+
+		if extResult == nil || *extResult {
+			// Permitted by extension, or none had an opinion.
+			s.from = from
+			s.logger.Info().Msgf("Mail from: %v", from)
+			s.send(fmt.Sprintf("250 Roger, accepting mail from <%v>", from))
+			s.enterState(MAIL)
+		} else {
+			s.send("550 Mail denied by policy")
+			s.logger.Warn().Msgf("Extension denied mail from <%v>", from)
+			return
+		}
 	} else if cmd == "EHLO" {
 		// Reset session
 		s.logger.Debug().Msgf("Resetting session state on EHLO request")
@@ -614,7 +628,9 @@ func (s *Session) parseCmd(line string) (cmd string, arg string, ok bool) {
 // parseArgs takes the arguments proceeding a command and files them
 // into a map[string]string after uppercasing each key.  Sample arg
 // string:
-//		" BODY=8BITMIME SIZE=1024"
+//
+//	" BODY=8BITMIME SIZE=1024"
+//
 // The leading space is mandatory.
 func (s *Session) parseArgs(arg string) (args map[string]string, ok bool) {
 	args = make(map[string]string)

pkg/server/smtp/handler_test.go

@@ -10,11 +10,14 @@ import (
 	"time"
 
 	"github.com/inbucket/inbucket/pkg/config"
+	"github.com/inbucket/inbucket/pkg/extension"
+	"github.com/inbucket/inbucket/pkg/extension/event"
 	"github.com/inbucket/inbucket/pkg/message"
 	"github.com/inbucket/inbucket/pkg/policy"
 	"github.com/inbucket/inbucket/pkg/storage"
 	"github.com/inbucket/inbucket/pkg/test"
 	"github.com/rs/zerolog"
+	"github.com/stretchr/testify/assert"
 )
 
 type scriptStep struct {
@@ -25,7 +28,7 @@ type scriptStep struct {
 // Test valid commands in GREET state.
 func TestGreetStateValidCommands(t *testing.T) {
 	ds := test.NewStore()
-	server := setupSMTPServer(ds)
+	server := setupSMTPServer(ds, extension.NewHost())
 
 	tests := []scriptStep{
 		{"HELO mydomain", 250},
@@ -56,7 +59,7 @@ func TestGreetStateValidCommands(t *testing.T) {
 // Test invalid commands in GREET state.
 func TestGreetState(t *testing.T) {
 	ds := test.NewStore()
-	server := setupSMTPServer(ds)
+	server := setupSMTPServer(ds, extension.NewHost())
 	defer server.Drain() // Required to prevent test logging data race.
 
 	tests := []scriptStep{
@@ -83,7 +86,7 @@ func TestGreetState(t *testing.T) {
 
 func TestEmptyEnvelope(t *testing.T) {
 	ds := test.NewStore()
-	server := setupSMTPServer(ds)
+	server := setupSMTPServer(ds, extension.NewHost())
 	defer server.Drain()
 
 	// Test out some empty envelope without blanks
@@ -108,7 +111,7 @@ func TestEmptyEnvelope(t *testing.T) {
 // Test AUTH commands.
 func TestAuth(t *testing.T) {
 	ds := test.NewStore()
-	server := setupSMTPServer(ds)
+	server := setupSMTPServer(ds, extension.NewHost())
 	defer server.Drain()
 
 	// PLAIN AUTH
@@ -145,7 +148,7 @@ func TestAuth(t *testing.T) {
 // Test TLS commands.
 func TestTLS(t *testing.T) {
 	ds := test.NewStore()
-	server := setupSMTPServer(ds)
+	server := setupSMTPServer(ds, extension.NewHost())
 	defer server.Drain()
 
 	// Test Start TLS parsing.
@@ -162,7 +165,7 @@ func TestTLS(t *testing.T) {
 // Test valid commands in READY state.
 func TestReadyStateValidCommands(t *testing.T) {
 	ds := test.NewStore()
-	server := setupSMTPServer(ds)
+	server := setupSMTPServer(ds, extension.NewHost())
 
 	// Test out some valid MAIL commands
 	tests := []scriptStep{
@@ -198,7 +201,7 @@ func TestReadyStateValidCommands(t *testing.T) {
 // Test invalid commands in READY state.
 func TestReadyStateInvalidCommands(t *testing.T) {
 	ds := test.NewStore()
-	server := setupSMTPServer(ds)
+	server := setupSMTPServer(ds, extension.NewHost())
 
 	tests := []scriptStep{
 		{"FOOB", 500},
@@ -231,7 +234,7 @@ func TestReadyStateInvalidCommands(t *testing.T) {
 // Test commands in MAIL state
 func TestMailState(t *testing.T) {
 	mds := test.NewStore()
-	server := setupSMTPServer(mds)
+	server := setupSMTPServer(mds, extension.NewHost())
 	defer server.Drain()
 
 	// Test out some mangled READY commands
@@ -338,7 +341,7 @@ func TestMailState(t *testing.T) {
 // Test commands in DATA state
 func TestDataState(t *testing.T) {
 	mds := test.NewStore()
-	server := setupSMTPServer(mds)
+	server := setupSMTPServer(mds, extension.NewHost())
 	defer server.Drain()
 
 	var script []scriptStep
@@ -448,6 +451,93 @@ func playScriptAgainst(t *testing.T, c *textproto.Conn, script []scriptStep) err
 	return nil
 }
 
+// Tests "MAIL FROM" emits BeforeMailAccepted event.
+func TestBeforeMailAcceptedEventEmitted(t *testing.T) {
+	ds := test.NewStore()
+	extHost := extension.NewHost()
+	server := setupSMTPServer(ds, extHost)
+	defer server.Drain()
+
+	var got *event.AddressParts
+	extHost.Events.BeforeMailAccepted.AddListener(
+		"test",
+		func(addr event.AddressParts) *bool {
+			got = &addr
+			return nil
+		})
+
+	// Play and verify SMTP session.
+	script := []scriptStep{
+		{"HELO localhost", 250},
+		{"MAIL FROM:<john@gmail.com>", 250},
+		{"QUIT", 221}}
+	if err := playSession(t, server, script); err != nil {
+		t.Error(err)
+	}
+
+	assert.NotNil(t, got, "BeforeMailListener did not receive Address")
+	assert.Equal(t, "john", got.Local, "Address local part had wrong value")
+	assert.Equal(t, "gmail.com", got.Domain, "Address domain part had wrong value")
+}
+
+// Test "MAIL FROM" acts on BeforeMailAccepted event result.
+func TestBeforeMailAcceptedEventResponse(t *testing.T) {
+	ds := test.NewStore()
+	extHost := extension.NewHost()
+	server := setupSMTPServer(ds, extHost)
+	defer server.Drain()
+
+	var shouldReturn *bool
+	var gotEvent *event.AddressParts
+	extHost.Events.BeforeMailAccepted.AddListener(
+		"test",
+		func(addr event.AddressParts) *bool {
+			gotEvent = &addr
+			return shouldReturn
+		})
+
+	allowRes := true
+	denyRes := false
+	tcs := map[string]struct {
+		script   scriptStep // Command to send and SMTP code expected.
+		eventRes *bool      // Response to send from event listener.
+	}{
+		"allow": {
+			script:   scriptStep{"MAIL FROM:<john@gmail.com>", 250},
+			eventRes: &allowRes,
+		},
+		"deny": {
+			script:   scriptStep{"MAIL FROM:<john@gmail.com>", 550},
+			eventRes: &denyRes,
+		},
+		"defer": {
+			script:   scriptStep{"MAIL FROM:<john@gmail.com>", 250},
+			eventRes: nil,
+		},
+	}
+
+	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},
+				tc.script,
+				{"QUIT", 221}}
+			if err := playSession(t, server, script); err != nil {
+				t.Error(err)
+			}
+
+			assert.NotNil(t, gotEvent, "BeforeMailListener did not receive Address")
+		})
+	}
+
+}
+
 // net.Pipe does not implement deadlines
 type mockConn struct {
 	net.Conn
@@ -457,7 +547,7 @@ func (m *mockConn) SetDeadline(t time.Time) error      { return nil }
 func (m *mockConn) SetReadDeadline(t time.Time) error  { return nil }
 func (m *mockConn) SetWriteDeadline(t time.Time) error { return nil }
 
-func setupSMTPServer(ds storage.Store) *Server {
+func setupSMTPServer(ds storage.Store, extHost *extension.Host) *Server {
 	cfg := &config.Root{
 		MailboxNaming: config.FullNaming,
 		SMTP: config.SMTP{
@@ -475,7 +565,7 @@ func setupSMTPServer(ds storage.Store) *Server {
 	addrPolicy := &policy.Addressing{Config: cfg}
 	manager := &message.StoreManager{Store: ds}
 
-	return NewServer(cfg.SMTP, manager, addrPolicy)
+	return NewServer(cfg.SMTP, manager, addrPolicy, extHost)
 }
 
 var sessionNum int

pkg/server/smtp/listener.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/inbucket/inbucket/pkg/config"
+	"github.com/inbucket/inbucket/pkg/extension"
 	"github.com/inbucket/inbucket/pkg/message"
 	"github.com/inbucket/inbucket/pkg/metric"
 	"github.com/inbucket/inbucket/pkg/policy"
@@ -59,11 +60,12 @@ func init() {
 // Server holds the configuration and state of our SMTP server.
 type Server struct {
 	config     config.SMTP        // SMTP configuration.
+	tlsConfig  *tls.Config        // TLS encryption configuration.
 	addrPolicy *policy.Addressing // Address policy.
 	manager    message.Manager    // Used to deliver messages.
+	extHost    *extension.Host    // Extension event processor.
 	listener   net.Listener       // Incoming network connections.
 	wg         *sync.WaitGroup    // Waitgroup tracks individual sessions.
-	tlsConfig  *tls.Config        // TLS encryption configuration.
 	notify     chan error         // Notify on fatal error.
 }
 
@@ -72,6 +74,7 @@ func NewServer(
 	smtpConfig config.SMTP,
 	manager message.Manager,
 	apolicy *policy.Addressing,
+	extHost *extension.Host,
 ) *Server {
 	slog := log.With().Str("module", "smtp").Str("phase", "tls").Logger()
 	tlsConfig := &tls.Config{}
@@ -90,10 +93,11 @@ func NewServer(
 
 	return &Server{
 		config:     smtpConfig,
+		tlsConfig:  tlsConfig,
 		manager:    manager,
 		addrPolicy: apolicy,
+		extHost:    extHost,
 		wg:         new(sync.WaitGroup),
-		tlsConfig:  tlsConfig,
 		notify:     make(chan error, 1),
 	}
 }

pkg/test/integration_test.go

@@ -243,7 +243,7 @@ func startServer() (func(), error) {
 	go webServer.Start(svcCtx, func() {})
 
 	// Start SMTP server.
-	smtpServer := smtp.NewServer(conf.SMTP, mmanager, addrPolicy)
+	smtpServer := smtp.NewServer(conf.SMTP, mmanager, addrPolicy, extHost)
 	go smtpServer.Start(svcCtx, func() {})
 
 	// TODO Use a readyFunc to determine server readiness.