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/key_data.go

@@ -0,0 +1,71 @@
+package tdesktop
+
+import (
+	"encoding/binary"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/crypto"
+)
+
+type keyData struct {
+	localKey    crypto.Key
+	accountsIDx []uint32
+}
+
+// See https://github.com/telegramdesktop/tdesktop/blob/v2.9.8/Telegram/SourceFiles/storage/storage_domain.cpp#L119-L159.
+func readKeyData(tgf *tdesktopFile, passcode []byte) (_ keyData, rErr error) {
+	salt, err := tgf.readArray()
+	if err != nil {
+		return keyData{}, errors.Wrap(err, "read salt")
+	}
+	if l := len(salt); l != localEncryptSaltSize {
+		return keyData{}, errors.Errorf("invalid salt length %d", l)
+	}
+
+	passcodeKey := createLocalKey(passcode, salt)
+	keyEncrypted, err := tgf.readArray()
+	if err != nil {
+		return keyData{}, errors.Wrap(err, "read keyEncrypted")
+	}
+	keyInnerData, err := decryptLocal(keyEncrypted, passcodeKey)
+	if err != nil {
+		return keyData{}, errors.Wrap(err, "decrypt keyEncrypted")
+	}
+	key, _, err := readArray(keyInnerData, binary.LittleEndian)
+	if err != nil {
+		return keyData{}, errors.Wrap(err, "read key")
+	}
+
+	if l := len(key); l < len(crypto.Key{}) {
+		return keyData{}, errors.Errorf("key too small (%d)", l)
+	}
+	var localKey crypto.Key
+	copy(localKey[:], key)
+
+	infoEncrypted, err := tgf.readArray()
+	if err != nil {
+		return keyData{}, errors.Wrap(err, "read infoEncrypted")
+	}
+	infoDecrypted, err := decryptLocal(infoEncrypted, localKey)
+	if err != nil {
+		return keyData{}, ErrKeyInfoDecrypt
+	}
+	// Skip decrypted data length.
+	infoDecrypted = infoDecrypted[4:]
+	// Read count of accounts.
+	count := int(binary.BigEndian.Uint32(infoDecrypted))
+	infoDecrypted = infoDecrypted[4:]
+
+	// Preallocate accountsIDx.
+	accountsIDx := make([]uint32, 0, count)
+	for i := 0; i < count; i++ {
+		idx := binary.BigEndian.Uint32(infoDecrypted[i*4:])
+		accountsIDx = append(accountsIDx, idx)
+	}
+
+	return keyData{
+		localKey:    localKey,
+		accountsIDx: accountsIDx,
+	}, nil
+}