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/mtproxy/obfuscated2/obfuscated2.go

@@ -0,0 +1,59 @@
+package obfuscated2
+
+import (
+	"io"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/mtproxy"
+)
+
+// Obfuscated2 implements obfuscated2 obfuscation protocol.
+type Obfuscated2 struct {
+	rand io.Reader
+	conn io.ReadWriter
+
+	keys
+}
+
+// NewObfuscated2 creates new Obfuscated2.
+func NewObfuscated2(r io.Reader, conn io.ReadWriter) *Obfuscated2 {
+	return &Obfuscated2{
+		rand: r,
+		conn: conn,
+	}
+}
+
+// Handshake sends obfuscated2 header.
+func (o *Obfuscated2) Handshake(protocol [4]byte, dc int, s mtproxy.Secret) error {
+	k, err := generateKeys(o.rand, protocol, s.Secret, dc)
+	if err != nil {
+		return errors.Wrap(err, "generate keys")
+	}
+	o.keys = k
+
+	if _, err := o.conn.Write(o.header); err != nil {
+		return errors.Wrap(err, "write obfuscated header")
+	}
+
+	return nil
+}
+
+// Write implements io.Writer.
+func (o *Obfuscated2) Write(b []byte) (n int, err error) {
+	cpyB := append([]byte(nil), b...)
+	o.encrypt.XORKeyStream(cpyB, b)
+	return o.conn.Write(cpyB)
+}
+
+// Read implements io.Reader.
+func (o *Obfuscated2) Read(b []byte) (int, error) {
+	n, err := o.conn.Read(b)
+	if err != nil {
+		return n, err
+	}
+	if n > 0 {
+		o.decrypt.XORKeyStream(b, b)
+	}
+	return n, err
+}