Initial commit

internal/smtpserver/backend.go

@@ -0,0 +1,79 @@
+package smtpserver
+
+import (
+	"encoding/hex"
+	"fmt"
+	"log"
+
+	"github.com/emersion/go-smtp"
+	"github.com/neilalexander/yggmail/internal/config"
+	"github.com/neilalexander/yggmail/internal/smtpsender"
+	"github.com/neilalexander/yggmail/internal/storage"
+)
+
+type BackendMode int
+
+const (
+	BackendModeInternal BackendMode = iota
+	BackendModeExternal
+)
+
+type Backend struct {
+	Mode    BackendMode
+	Log     *log.Logger
+	Config  *config.Config
+	Queues  *smtpsender.Queues
+	Storage storage.Storage
+}
+
+func (b *Backend) Login(state *smtp.ConnectionState, username, password string) (smtp.Session, error) {
+	switch b.Mode {
+	case BackendModeInternal:
+		// The connection came from our local listener
+		if authed, err := b.Storage.TryAuthenticate(username, password); err != nil {
+			b.Log.Printf("Failed to authenticate SMTP user %q due to error: %s", username, err)
+			return nil, fmt.Errorf("failed to authenticate: %w", err)
+		} else if !authed {
+			b.Log.Printf("Failed to authenticate SMTP user %q\n", username)
+			return nil, smtp.ErrAuthRequired
+		}
+		defer b.Log.Printf("Authenticated SMTP user %q\n", username)
+		return &SessionLocal{
+			backend: b,
+			state:   state,
+		}, nil
+
+	case BackendModeExternal:
+		return nil, fmt.Errorf("Not expecting authenticated connection on external backend")
+	}
+
+	return nil, fmt.Errorf("Authenticated login failed")
+}
+
+func (b *Backend) AnonymousLogin(state *smtp.ConnectionState) (smtp.Session, error) {
+	switch b.Mode {
+	case BackendModeInternal:
+		return nil, fmt.Errorf("Not expecting anonymous connection on internal backend")
+
+	case BackendModeExternal:
+		// The connection came from our overlay listener, so we should check
+		// that they are who they claim to be
+		if state.Hostname != state.RemoteAddr.String() {
+			return nil, fmt.Errorf("You are not who you claim to be")
+		}
+
+		pks, err := hex.DecodeString(state.RemoteAddr.String())
+		if err != nil {
+			return nil, fmt.Errorf("hex.DecodeString: %w", err)
+		}
+
+		b.Log.Println("Incoming SMTP session from", state.RemoteAddr.String())
+		return &SessionRemote{
+			backend: b,
+			state:   state,
+			public:  pks[:],
+		}, nil
+	}
+
+	return nil, fmt.Errorf("Anonymous login failed")
+}