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/telegram/dcs/mtproxy.go

@@ -0,0 +1,140 @@
+package dcs
+
+import (
+	"context"
+	"io"
+	"net"
+
+	"github.com/go-faster/errors"
+	"go.uber.org/multierr"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/crypto"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/mtproxy"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/mtproxy/obfuscator"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/proto/codec"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/transport"
+)
+
+var _ Resolver = mtProxy{}
+
+type mtProxy struct {
+	dial          DialFunc
+	protocol      protocol
+	addr, network string
+
+	secret mtproxy.Secret
+	tag    [4]byte
+	rand   io.Reader
+}
+
+func (m mtProxy) Primary(ctx context.Context, dc int, _ List) (transport.Conn, error) {
+	return m.resolve(ctx, dc)
+}
+
+func (m mtProxy) MediaOnly(ctx context.Context, dc int, _ List) (transport.Conn, error) {
+	if dc > 0 {
+		dc *= -1
+	}
+	return m.resolve(ctx, dc)
+}
+
+func (m mtProxy) CDN(ctx context.Context, dc int, _ List) (transport.Conn, error) {
+	return m.resolve(ctx, dc)
+}
+
+func (m mtProxy) resolve(ctx context.Context, dc int) (transport.Conn, error) {
+	c, err := m.dial(ctx, m.network, m.addr)
+	if err != nil {
+		return nil, errors.Wrapf(err, "connect to the MTProxy %q", m.addr)
+	}
+
+	conn, err := m.handshakeConn(c, dc)
+	if err != nil {
+		err = errors.Wrap(err, "handshake")
+		return nil, multierr.Combine(err, c.Close())
+	}
+
+	return conn, nil
+}
+
+// handshakeConn inits given net.Conn as MTProto connection.
+func (m mtProxy) handshakeConn(c net.Conn, dc int) (transport.Conn, error) {
+	var obsConn *obfuscator.Conn
+	switch m.secret.Type {
+	case mtproxy.Simple, mtproxy.Secured:
+		obsConn = obfuscator.Obfuscated2(m.rand, c)
+	case mtproxy.TLS:
+		obsConn = obfuscator.FakeTLS(m.rand, c)
+	default:
+		return nil, errors.Errorf("unknown MTProxy secret type: %d", m.secret.Type)
+	}
+
+	secret := m.secret
+	if err := obsConn.Handshake(m.tag, dc, secret); err != nil {
+		return nil, errors.Wrap(err, "MTProxy handshake")
+	}
+
+	transportConn, err := m.protocol.Handshake(obsConn)
+	if err != nil {
+		return nil, errors.Wrap(err, "transport handshake")
+	}
+
+	return transportConn, nil
+}
+
+// MTProxyOptions is MTProxy resolver creation options.
+type MTProxyOptions struct {
+	// Dial specifies the dial function for creating unencrypted TCP connections.
+	// If Dial is nil, then the resolver dials using package net.
+	Dial DialFunc
+	// Network to use. Defaults to "tcp"
+	Network string
+	// Random source for MTProxy obfuscator.
+	Rand io.Reader
+}
+
+func (m *MTProxyOptions) setDefaults() {
+	if m.Dial == nil {
+		var d net.Dialer
+		m.Dial = d.DialContext
+	}
+	if m.Network == "" {
+		m.Network = "tcp"
+	}
+	if m.Rand == nil {
+		m.Rand = crypto.DefaultRand()
+	}
+}
+
+// MTProxy creates MTProxy obfuscated DC resolver.
+//
+// See https://core.telegram.org/mtproto/mtproto-transports#transport-obfuscation.
+func MTProxy(addr string, secret []byte, opts MTProxyOptions) (Resolver, error) {
+	s, err := mtproxy.ParseSecret(secret)
+	if err != nil {
+		return nil, err
+	}
+
+	var cdc codec.Codec = codec.PaddedIntermediate{}
+	tag := codec.PaddedIntermediateClientStart
+
+	// FIXME(tdakkota): some proxies forces to use Padded (Secure) Intermediate
+	// 	even if secret denotes to use another transport type.
+	if s.Type != mtproxy.TLS {
+		if c, ok := s.ExpectedCodec(); ok {
+			cdc = c
+			tag = [4]byte{s.Tag, s.Tag, s.Tag, s.Tag}
+		}
+	}
+
+	opts.setDefaults()
+	return mtProxy{
+		dial:     opts.Dial,
+		addr:     addr,
+		network:  opts.Network,
+		protocol: transport.NewProtocol(func() transport.Codec { return codec.NoHeader{Codec: cdc} }),
+		secret:   s,
+		tag:      tag,
+		rand:     opts.Rand,
+	}, nil
+}