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/proto/codec/errors.go

@@ -0,0 +1,106 @@
+package codec
+
+import (
+	"fmt"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+)
+
+const (
+	// CodeAuthKeyNotFound means that specified auth key ID cannot be found by the DC.
+	// Also, may be returned during key exchange.
+	CodeAuthKeyNotFound = 404
+
+	// CodeWrongDC means that current DC is wrong.
+	// Usually returned by server when key exchange sends wrong DC ID.
+	CodeWrongDC = 444
+
+	// CodeTransportFlood means that too many transport connections are
+	// established to the same IP in a too short lapse of time, or if any
+	// of the container/service message limits are reached.
+	CodeTransportFlood = 429
+)
+
+// ProtocolErr represents protocol level error.
+type ProtocolErr struct {
+	Code int32
+}
+
+func (p ProtocolErr) Error() string {
+	switch p.Code {
+	case CodeAuthKeyNotFound:
+		return "auth key not found"
+	case CodeTransportFlood:
+		return "transport flood"
+	case CodeWrongDC:
+		return "wrong DC"
+	default:
+		return fmt.Sprintf("protocol error %d", p.Code)
+	}
+}
+
+// Can be bigger that 1mb.
+//
+// See https://github.com/gotd/td/issues/412
+//
+// See https://github.com/tdlib/td/blob/550ccc8d9bbbe9cff1dc618aef5764d2cbd2cd91/td/mtproto/TcpTransport.cpp#L53
+const maxMessageSize = 1 << 24 // 16 MB
+
+func checkOutgoingMessage(b *bin.Buffer) error {
+	length := b.Len()
+	if length > maxMessageSize || length == 0 {
+		return invalidMsgLenErr{n: length}
+	}
+	return nil
+}
+
+func checkAlign(b *bin.Buffer, n int) error {
+	length := b.Len()
+	if length%n != 0 {
+		return alignedPayloadExpectedErr{expected: n}
+	}
+	return nil
+}
+
+func checkProtocolError(b *bin.Buffer) error {
+	if b.Len() != bin.Word {
+		return nil
+	}
+	code, err := b.Int32()
+	if err != nil {
+		return err
+	}
+	return &ProtocolErr{Code: -code}
+}
+
+type alignedPayloadExpectedErr struct {
+	expected int
+}
+
+func (e alignedPayloadExpectedErr) Error() string {
+	return fmt.Sprintf("payload is not aligned, expected align by %d", e.expected)
+}
+
+func (e alignedPayloadExpectedErr) Is(err error) bool {
+	_, ok := err.(alignedPayloadExpectedErr)
+	return ok
+}
+
+type invalidMsgLenErr struct {
+	n int
+}
+
+func (e invalidMsgLenErr) Error() string {
+	return fmt.Sprintf("invalid message length %d", e.n)
+}
+
+func (e invalidMsgLenErr) Is(err error) bool {
+	_, ok := err.(invalidMsgLenErr)
+	return ok
+}
+
+// ErrProtocolHeaderMismatch means that received protocol header
+// is mismatched with expected.
+var ErrProtocolHeaderMismatch = errors.New("protocol header mismatch")