Split the concrete SMTP struct into separate MSA and MTA implementations

internal/smtp/mta.go

@@ -0,0 +1,71 @@
+package smtp
+
+import (
+	"context"
+	"fmt"
+	"log"
+	"sync/atomic"
+
+	"github.com/emersion/go-smtp"
+
+	"ur.gs/crockery/internal/store"
+)
+
+type mta struct {
+	cancel context.CancelFunc
+	store  store.Interface
+	server *smtp.Server
+
+	// Session IDs
+	sid uint64
+}
+
+func NewMTA(cancel context.CancelFunc, datastore store.Interface) Server {
+	out := &mta{
+		cancel: cancel,
+		store:  datastore,
+	}
+
+	out.server = smtp.NewServer(out)
+	out.server.Domain = datastore.Domain()
+	out.server.TLSConfig = datastore.TLSConfig()
+	out.server.Addr = ":25"
+	out.server.AuthDisabled = true // Don't allow login on the MTA port
+
+	return out
+}
+
+func (m *mta) Run() {
+	if err := m.server.ListenAndServe(); err != nil {
+		log.Printf("Error serving SMTP %s: %v", m.server.Addr, err)
+	} else {
+		log.Printf("Stopped listening on SMTP %s", m.server.Addr)
+	}
+
+	m.cancel()
+}
+
+func (m *mta) Close() error {
+	m.cancel() // FIXME: this doesn't touch the server
+
+	return nil
+}
+
+// Backend implementation for go-smtp after this point
+
+func (m *mta) Login(user, pass string) (smtp.User, error) {
+	return nil, fmt.Errorf("Submission to this MTA is not permitted.")
+}
+
+func (m *mta) AnonymousLogin() (smtp.User, error) {
+	session := &Session{
+		ID:      atomic.AddUint64(&m.sid, uint64(1)),
+		Account: nil,
+		Handler: &Receiver{},
+	}
+
+	log.Printf("Beginning SMTP session %d", session.ID)
+	// FIXME: TODO: Track ongoing sessions for termination or notifications
+
+	return session, nil
+}