move gotd fork into repo. (#111)

- update to latest telegram layer
- remove some references to fields in tg.Entities that don't exist in
the schema
- originally added here:
https://github.com/beeper/td/commit/820929062a2ba0104397bc01235ab58a9cff780e
  - referenced here
-
https://github.com/mautrix/telegramgo/commit/124f0967ed195b5a380c9bd02e170ada9710dde3
-
https://github.com/mautrix/telegramgo/commit/4205047aab2e0639217148b5d125bfaab668bd8e

pkg/gotd/session/tdesktop/mtp_authorization.go

@@ -0,0 +1,115 @@
+package tdesktop
+
+import (
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/crypto"
+)
+
+// MTPAuthorization is a Telegram Desktop storage structure which stores MTProto session info.
+//
+// See https://github.com/telegramdesktop/tdesktop/blob/dev/Telegram/SourceFiles/main/main_account.cpp#L359.
+type MTPAuthorization struct {
+	// UserID is a Telegram user ID.
+	UserID uint64
+	// MainDC is a main DC ID of this user.
+	MainDC int
+	// Key is a map of keys per DC ID.
+	Keys map[int]crypto.Key // DC ID -> Key
+}
+
+// See https://github.com/telegramdesktop/tdesktop/blob/v2.9.8/Telegram/SourceFiles/storage/storage_account.cpp#L898.
+func readMTPData(tgf *tdesktopFile, localKey crypto.Key) (MTPAuthorization, error) {
+	encrypted, err := tgf.readArray()
+	if err != nil {
+		return MTPAuthorization{}, errors.Wrap(err, "read encrypted data")
+	}
+
+	decrypted, err := decryptLocal(encrypted, localKey)
+	if err != nil {
+		return MTPAuthorization{}, errors.Wrap(err, "decrypt data")
+	}
+	// Skip decrypted data length (uint32).
+	decrypted = decrypted[4:]
+	r := qtReader{buf: bin.Buffer{Buf: decrypted}}
+
+	// TODO(tdakkota): support other IDs.
+	var m MTPAuthorization
+	if err := m.deserialize(&r); err != nil {
+		return MTPAuthorization{}, errors.Wrap(err, "deserialize MTPAuthorization")
+	}
+	return m, err
+}
+
+func readKey(r *qtReader, k *crypto.Key) (uint32, error) {
+	dcID, err := r.readUint32()
+	if err != nil {
+		return 0, errors.Wrap(err, "read DC ID")
+	}
+
+	if err := r.consumeN(k[:], 256); err != nil {
+		return 0, errors.Wrap(err, "read auth key")
+	}
+
+	return dcID, nil
+}
+
+func (m *MTPAuthorization) deserialize(r *qtReader) error {
+	id, err := r.readUint32()
+	if err != nil {
+		return errors.Wrap(err, "read dbi ID")
+	}
+	if id != dbiMtpAuthorization {
+		return errors.Errorf("unexpected id %d", id)
+	}
+
+	if err := r.skip(4); err != nil {
+		return errors.Wrap(err, "read mainLength")
+	}
+
+	legacyUserID, err := r.readUint32()
+	if err != nil {
+		return errors.Wrap(err, "read legacyUserID")
+	}
+	legacyMainDCID, err := r.readUint32()
+	if err != nil {
+		return errors.Wrap(err, "read legacyMainDCID")
+	}
+	if (uint64(legacyUserID)<<32)|uint64(legacyMainDCID) == kWideIdsTag {
+		userID, err := r.readUint64()
+		if err != nil {
+			return errors.Wrap(err, "read userID")
+		}
+		mainDC, err := r.readUint32()
+		if err != nil {
+			return errors.Wrap(err, "read mainDcID")
+		}
+
+		m.UserID = userID
+		m.MainDC = int(mainDC)
+	} else {
+		m.UserID = uint64(legacyUserID)
+		m.MainDC = int(legacyMainDCID)
+	}
+
+	keys, err := r.readUint32()
+	if err != nil {
+		return errors.Wrap(err, "read keys length")
+	}
+
+	if m.Keys == nil {
+		m.Keys = make(map[int]crypto.Key, keys)
+	}
+	for i := 0; i < int(keys); i++ {
+		var key crypto.Key
+		dcID, err := readKey(r, &key)
+		if err != nil {
+			return errors.Wrapf(err, "read key %d", i)
+		}
+		// FIXME(tdakkota): what if there is more than one session per DC?
+		m.Keys[int(dcID)] = key
+	}
+
+	return nil
+}