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/fileid/decode.go

@@ -0,0 +1,45 @@
+package fileid
+
+import (
+	"encoding/base64"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+)
+
+const (
+	persistentIDVersionOld = 2
+	persistentIDVersionMap = 3
+	persistentIDVersion    = 4
+)
+
+// DecodeFileID parses FileID from a string.
+func DecodeFileID(s string) (fileID FileID, _ error) {
+	if s == "" {
+		return FileID{}, errors.New("input is empty")
+	}
+	data, err := base64Decode(s)
+	if err != nil {
+		return FileID{}, errors.Wrap(err, "base64")
+	}
+	data = rleDecode(data)
+	if len(data) < 2 {
+		return FileID{}, errors.New("RLE-decoded data is too small")
+	}
+
+	switch version := data[len(data)-1]; version {
+	case persistentIDVersionOld, persistentIDVersionMap:
+		return FileID{}, errors.Errorf("%v is unsupported now", version)
+	case persistentIDVersion:
+		data = data[:len(data)-1]
+		err := fileID.decodeLatestFileID(&bin.Buffer{Buf: data})
+		return fileID, err
+	default:
+		return FileID{}, errors.Errorf("unknown file_id version %x", version)
+	}
+}
+
+func base64Decode(s string) ([]byte, error) {
+	return base64.RawURLEncoding.DecodeString(s)
+}