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/downloader/master.go

@@ -0,0 +1,64 @@
+package downloader
+
+import (
+	"context"
+	"strconv"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+// RedirectError error is returned when Downloader get CDN redirect.
+// See https://core.telegram.org/constructor/upload.fileCdnRedirect.
+type RedirectError struct {
+	Redirect *tg.UploadFileCDNRedirect
+}
+
+// Error implements error interface.
+func (r *RedirectError) Error() string {
+	return "redirect to CDN DC " + strconv.Itoa(r.Redirect.DCID)
+}
+
+// master is a master DC download schema.
+// See https://core.telegram.org/api/files#downloading-files.
+type master struct {
+	client Client
+
+	precise  bool
+	allowCDN bool
+	location tg.InputFileLocationClass
+}
+
+var _ schema = master{}
+
+func (c master) Chunk(ctx context.Context, offset int64, limit int) (chunk, error) {
+	req := &tg.UploadGetFileRequest{
+		Offset:   offset,
+		Limit:    limit,
+		Location: c.location,
+	}
+	req.SetCDNSupported(c.allowCDN)
+	req.SetPrecise(c.precise)
+
+	r, err := c.client.UploadGetFile(ctx, req)
+	if err != nil {
+		return chunk{}, err
+	}
+
+	switch result := r.(type) {
+	case *tg.UploadFile:
+		return chunk{data: result.Bytes, tag: result.Type}, nil
+	case *tg.UploadFileCDNRedirect:
+		return chunk{}, &RedirectError{Redirect: result}
+	default:
+		return chunk{}, errors.Errorf("unexpected type %T", r)
+	}
+}
+
+func (c master) Hashes(ctx context.Context, offset int64) ([]tg.FileHash, error) {
+	return c.client.UploadGetFileHashes(ctx, &tg.UploadGetFileHashesRequest{
+		Location: c.location,
+		Offset:   offset,
+	})
+}