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/file.go

@@ -0,0 +1,177 @@
+package tdesktop
+
+import (
+	"bytes"
+	"crypto/md5" // #nosec G501
+	"encoding/binary"
+	"io"
+	"io/fs"
+	"math"
+
+	"github.com/go-faster/errors"
+	"go.uber.org/multierr"
+)
+
+type tdesktopFile struct {
+	data    []byte
+	n       int
+	version uint32
+}
+
+func open(filesystem fs.FS, fileName string) (*tdesktopFile, error) {
+	suffixes := []string{"0", "1", "s"}
+
+	tryRead := func(p string) (_ *tdesktopFile, rErr error) {
+		f, err := filesystem.Open(p)
+		if err != nil {
+			return nil, errors.Wrap(err, "open")
+		}
+		defer multierr.AppendInvoke(&rErr, multierr.Close(f))
+
+		return fromFile(f)
+	}
+
+	for _, suffix := range suffixes {
+		p := fileName + suffix
+		if _, err := fs.Stat(filesystem, p); err != nil {
+			if errors.Is(err, fs.ErrNotExist) ||
+				errors.Is(err, fs.ErrPermission) {
+				continue
+			}
+			return nil, errors.Wrap(err, "stat")
+		}
+
+		f, err := tryRead(p)
+		if err != nil {
+			if errors.Is(err, io.ErrUnexpectedEOF) {
+				continue
+			}
+
+			var magicErr *WrongMagicError
+			if errors.As(err, &magicErr) {
+				continue
+			}
+			return nil, errors.Wrap(err, "read tdesktop file")
+		}
+
+		return f, nil
+	}
+
+	return nil, errors.Errorf("file %q not found", fileName)
+}
+
+var tdesktopFileMagic = [4]byte{'T', 'D', 'F', '$'}
+
+// fromFile creates new Telegram Desktop storage file.
+// Based on https://github.com/telegramdesktop/tdesktop/blob/v2.9.8/Telegram/SourceFiles/storage/details/storage_file_utilities.cpp#L473.
+func fromFile(r io.Reader) (*tdesktopFile, error) {
+	buf := make([]byte, 16)
+	if _, err := io.ReadFull(r, buf[:8]); err != nil {
+		return nil, errors.Wrap(err, "read magic and version")
+	}
+
+	var magic, version [4]byte
+	copy(magic[:], buf[:4])
+	// TODO(tdakkota): check version
+	copy(version[:], buf[4:8])
+	if magic != tdesktopFileMagic {
+		return nil, &WrongMagicError{
+			Magic: magic,
+		}
+	}
+
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return nil, errors.Wrap(err, "read data")
+	}
+	if l := len(data); l < 16 {
+		return nil, errors.Errorf("invalid data length %d", l)
+	}
+	hash := data[len(data)-16:]
+	data = data[:len(data)-16]
+
+	computedHash := telegramFileHash(data, version)
+	if !bytes.Equal(computedHash[:], hash) {
+		return nil, errors.New("hash mismatch")
+	}
+
+	v := binary.LittleEndian.Uint32(version[:])
+	return &tdesktopFile{
+		data:    data,
+		version: v,
+	}, nil
+}
+
+func writeFile(w io.Writer, data []byte, version [4]byte) error {
+	if _, err := w.Write(tdesktopFileMagic[:]); err != nil {
+		return errors.Wrap(err, "write magic")
+	}
+	if _, err := w.Write(version[:]); err != nil {
+		return errors.Wrap(err, "write version")
+	}
+	if _, err := w.Write(data); err != nil {
+		return errors.Wrap(err, "write data")
+	}
+	hash := telegramFileHash(data, version)
+	if _, err := w.Write(hash[:]); err != nil {
+		return errors.Wrap(err, "write hash")
+	}
+	return nil
+}
+
+func telegramFileHash(data []byte, version [4]byte) (r [md5.Size]byte) {
+	h := md5.New() // #nosec G401
+	_, _ = h.Write(data)
+	var packedLength [4]byte
+	binary.LittleEndian.PutUint32(packedLength[:], uint32(len(data)))
+	_, _ = h.Write(packedLength[:])
+	_, _ = h.Write(version[:])
+	_, _ = h.Write(tdesktopFileMagic[:])
+	h.Sum(r[:0])
+	return r
+}
+
+func (f *tdesktopFile) readArray() ([]byte, error) {
+	data, skip, err := readArray(f.data[f.n:], binary.BigEndian)
+	if err != nil {
+		return nil, err
+	}
+	f.n += skip
+	return data, nil
+}
+
+func readArray(data []byte, order binary.ByteOrder) (array []byte, n int, _ error) {
+	if len(data) < 4 {
+		return nil, 0, io.ErrUnexpectedEOF
+	}
+	// See https://github.com/qt/qtbase/blob/5.15.2/src/corelib/text/qbytearray.cpp#L3314.
+	length := order.Uint32(data)
+	if length == 0xffffffff {
+		return nil, 4, nil
+	}
+
+	if uint64(length) >= uint64(len(data)) {
+		return nil, 0, io.ErrUnexpectedEOF
+	}
+	r := data[4 : 4+length]
+	return r, len(r) + 4, nil
+}
+
+func writeArray(writer io.Writer, data []byte, order binary.ByteOrder) error {
+	length := len(data)
+	if uint64(length) > uint64(math.MaxUint32) {
+		return errors.Errorf("data length too big (%d)", length)
+	}
+
+	r := make([]byte, 4)
+	order.PutUint32(r, uint32(length))
+	if _, err := writer.Write(r); err != nil {
+		return errors.Wrap(err, "write length")
+	}
+
+	if _, err := writer.Write(data); err != nil {
+		return errors.Wrap(err, "write data")
+	}
+
+	return nil
+}