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/internal/deeplink/domain.go

@@ -0,0 +1,40 @@
+package deeplink
+
+import (
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/ascii"
+)
+
+// ValidateDomain validate given domain (user) name
+func ValidateDomain(domain string) error {
+	return checkDomainSymbols(domain)
+}
+
+// checkDomainSymbols check that domain contains only a-z, A-Z, 0-9 and '_'
+// symbols.
+func checkDomainSymbols(domain string) error {
+	switch {
+	case domain == "":
+		return errors.New("is empty")
+	case len(domain) > 32:
+		return errors.New("is too big")
+	case !ascii.IsLatinLower(rune(domain[0])):
+		return errors.New("must start with lower letter")
+	case domain[len(domain)-1] == '_':
+		return errors.New("must not end with '_'")
+	}
+
+	for i, r := range domain {
+		switch {
+		case !ascii.IsLatinLetter(r) && !ascii.IsDigit(r) && r != '_':
+		case i > 0 && domain[i] == '_' && domain[i] == domain[i-1]:
+		default:
+			continue
+		}
+
+		return errors.Errorf("unexpected %c at %d", r, i)
+	}
+
+	return nil
+}