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/abridged.go

@@ -0,0 +1,145 @@
+package codec
+
+import (
+	"encoding/binary"
+	"io"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+)
+
+// AbridgedClientStart is starting bytes sent by client in Abridged mode.
+//
+// Note that server does not respond with it.
+var AbridgedClientStart = [1]byte{0xef}
+
+// Abridged is intermediate MTProto transport.
+//
+// See https://core.telegram.org/mtproto/mtproto-transports#abridged
+type Abridged struct{}
+
+var (
+	_ TaggedCodec = Abridged{}
+)
+
+// WriteHeader sends protocol tag.
+func (i Abridged) WriteHeader(w io.Writer) error {
+	if _, err := w.Write(AbridgedClientStart[:]); err != nil {
+		return errors.Wrap(err, "write abridged header")
+	}
+
+	return nil
+}
+
+// ReadHeader reads protocol tag.
+func (i Abridged) ReadHeader(r io.Reader) error {
+	var b [1]byte
+	if _, err := io.ReadFull(r, b[:]); err != nil {
+		return errors.Wrap(err, "read abridged header")
+	}
+
+	if b != AbridgedClientStart {
+		return ErrProtocolHeaderMismatch
+	}
+
+	return nil
+}
+
+// ObfuscatedTag returns protocol tag for obfuscation.
+func (i Abridged) ObfuscatedTag() (r [4]byte) {
+	d := AbridgedClientStart[0]
+	return [4]byte{d, d, d, d}
+}
+
+// Write encode to writer message from given buffer.
+func (i Abridged) Write(w io.Writer, b *bin.Buffer) error {
+	if err := checkOutgoingMessage(b); err != nil {
+		return err
+	}
+
+	if err := checkAlign(b, 4); err != nil {
+		return err
+	}
+
+	if err := writeAbridged(w, b); err != nil {
+		return errors.Wrap(err, "write abridged")
+	}
+
+	return nil
+}
+
+// Read fills buffer with received message.
+func (i Abridged) Read(r io.Reader, b *bin.Buffer) error {
+	if err := readAbridged(r, b); err != nil {
+		return errors.Wrap(err, "read abridged")
+	}
+
+	return checkProtocolError(b)
+}
+
+func writeAbridged(w io.Writer, b *bin.Buffer) error {
+	length := b.Len()
+	// Re-using b.Buf if possible to reduce allocations.
+	b.Expand(4)
+	b.Buf = b.Buf[:length]
+
+	// Re-using b.Buf if possible to reduce allocations.
+	inner := bin.Buffer{Buf: b.Buf[length:length]}
+
+	encodeLength := b.Len() >> 2
+	// `0x7f == 127`, literally use one bit to distinguish length byte size.
+	if encodeLength < 127 {
+		// Payloads are wrapped in the following envelope:
+		//
+		// Length: payload length, divided by four, and encoded as a single byte,
+		// only if the resulting packet length is a value between 0x01..0x7e.
+		inner.Put([]byte{byte(encodeLength)})
+	} else {
+		// If the packet length divided by four is bigger than or equal to 127 (>= 0x7f),
+		// the following envelope must be used, instead:
+		//
+		var buf [5]byte
+		// Header: A single byte of value 0x7f
+		buf[0] = 0x7f
+		// Length: payload length, divided by four, and encoded as 3 length bytes (little endian)
+		binary.LittleEndian.PutUint32(buf[1:], uint32(encodeLength))
+		inner.Put(buf[:4])
+	}
+
+	if _, err := w.Write(inner.Buf); err != nil {
+		return err
+	}
+	if _, err := w.Write(b.Raw()); err != nil {
+		return err
+	}
+	return nil
+}
+
+func readAbridged(r io.Reader, b *bin.Buffer) error {
+	b.ResetN(bin.Word)
+
+	_, err := io.ReadFull(r, b.Buf[:1])
+	if err != nil {
+		return err
+	}
+
+	if b.Buf[0] >= 127 {
+		_, err := io.ReadFull(r, b.Buf[0:3])
+		if err != nil {
+			return err
+		}
+	}
+
+	n, err := b.Int()
+	if err != nil {
+		return err
+	}
+
+	b.ResetN(n << 2)
+	if _, err := io.ReadFull(r, b.Buf); err != nil {
+		return errors.Wrap(err, "read payload")
+	}
+
+	return nil
+}