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/tgtest/loop.go

@@ -0,0 +1,92 @@
+package tgtest
+
+import (
+	"context"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/exchange"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/proto/codec"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/transport"
+)
+
+func (s *Server) read(ctx context.Context, conn transport.Conn, b *bin.Buffer) error {
+	b.Reset()
+
+	ctx, cancel := context.WithTimeout(ctx, s.readTimeout)
+	defer cancel()
+	if err := conn.Recv(ctx, b); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (s *Server) sendProtoError(ctx context.Context, conn transport.Conn, e int32) error {
+	var buf bin.Buffer
+	buf.PutInt32(-e)
+
+	ctx, cancel := context.WithTimeout(ctx, s.writeTimeout)
+	defer cancel()
+
+	if err := conn.Send(ctx, &buf); err != nil {
+		return errors.Wrap(err, "send")
+	}
+	return nil
+}
+
+func (s *Server) serveConn(ctx context.Context, conn transport.Conn) error {
+	s.log.Debug("User connected")
+	defer func() {
+		_ = conn.Close()
+		s.log.Debug("User disconnected")
+	}()
+
+	b := new(bin.Buffer)
+	for {
+		if err := s.read(ctx, conn, b); err != nil {
+			return errors.Wrap(err, "read")
+		}
+
+		var authKeyID [8]byte
+		if err := b.PeekN(authKeyID[:], len(authKeyID)); err != nil {
+			return errors.Wrap(err, "peek id")
+		}
+
+		// TODO(tdakkota): dispatch by type ID instead?
+		if _, ok := s.users.getSession(authKeyID); ok {
+			if err := s.rpcHandle(ctx, conn, b); err != nil {
+				return errors.Wrap(err, "handle")
+			}
+			continue
+		}
+
+		// If authKeyID not found and is not zero, so send protocol error.
+		if authKeyID != [8]byte{} {
+			if err := s.sendProtoError(ctx, conn, codec.CodeAuthKeyNotFound); err != nil {
+				return errors.Wrap(err, "send AuthKeyNotFound")
+			}
+			continue
+		}
+
+		s.log.Debug("Starting key exchange")
+		c := newBufferedConn(conn)
+		c.Push(b)
+
+		key, err := s.exchange(ctx, exchangeConn{Conn: c})
+		if err != nil {
+			var exchangeErr *exchange.ServerExchangeError
+			if errors.As(err, &exchangeErr) {
+				code := exchangeErr.Code
+				if err := s.sendProtoError(ctx, c, code); err != nil {
+					return errors.Wrapf(err, "send proto error %v", code)
+				}
+				return nil
+			}
+			return errors.Wrap(err, "key exchange failed")
+		}
+
+		s.users.addSession(key)
+	}
+}