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/intermediate.go

@@ -0,0 +1,115 @@
+package codec
+
+import (
+	"io"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/bin"
+)
+
+// IntermediateClientStart is starting bytes sent by client in Intermediate mode.
+//
+// Note that server does not respond with it.
+var IntermediateClientStart = [4]byte{0xee, 0xee, 0xee, 0xee}
+
+// Intermediate is intermediate MTProto transport.
+//
+// See https://core.telegram.org/mtproto/mtproto-transports#intermediate
+type Intermediate struct{}
+
+var (
+	_ TaggedCodec = Intermediate{}
+)
+
+// WriteHeader sends protocol tag.
+func (i Intermediate) WriteHeader(w io.Writer) (err error) {
+	if _, err := w.Write(IntermediateClientStart[:]); err != nil {
+		return errors.Wrap(err, "write intermediate header")
+	}
+
+	return nil
+}
+
+// ReadHeader reads protocol tag.
+func (i Intermediate) ReadHeader(r io.Reader) (err error) {
+	var b [4]byte
+	if _, err := io.ReadFull(r, b[:]); err != nil {
+		return errors.Wrap(err, "read intermediate header")
+	}
+
+	if b != IntermediateClientStart {
+		return ErrProtocolHeaderMismatch
+	}
+
+	return nil
+}
+
+// ObfuscatedTag returns protocol tag for obfuscation.
+func (i Intermediate) ObfuscatedTag() [4]byte {
+	return IntermediateClientStart
+}
+
+// Write encode to writer message from given buffer.
+func (i Intermediate) 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 := writeIntermediate(w, b); err != nil {
+		return errors.Wrap(err, "write intermediate")
+	}
+
+	return nil
+}
+
+// Read fills buffer with received message.
+func (i Intermediate) Read(r io.Reader, b *bin.Buffer) error {
+	if err := readIntermediate(r, b, false); err != nil {
+		return errors.Wrap(err, "read intermediate")
+	}
+
+	return checkProtocolError(b)
+}
+
+// writeIntermediate encodes b as payload to w.
+func writeIntermediate(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]
+
+	inner := bin.Buffer{Buf: b.Buf[length:length]}
+	inner.PutInt(b.Len())
+	if _, err := w.Write(inner.Buf); err != nil {
+		return err
+	}
+	if _, err := w.Write(b.Buf); err != nil {
+		return err
+	}
+	return nil
+}
+
+// readIntermediate reads payload from r to b.
+func readIntermediate(r io.Reader, b *bin.Buffer, padding bool) error {
+	n, err := readLen(r, b)
+	if err != nil {
+		return err
+	}
+
+	b.ResetN(n)
+	if _, err := io.ReadFull(r, b.Buf); err != nil {
+		return errors.Wrap(err, "read payload")
+	}
+
+	if padding {
+		paddingLength := n % 4
+		b.Buf = b.Buf[:n-paddingLength]
+	}
+
+	return nil
+}