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/keyparser/parser.go

@@ -0,0 +1,96 @@
+// Package keyparser extracts public keys from code.
+package keyparser
+
+import (
+	"bufio"
+	"io"
+	"strings"
+)
+
+const (
+	rsaBegin = "BEGIN"
+	rsaEnd   = "END"
+	rsaSep   = "-----"
+)
+
+func isBegin(s string) bool {
+	if !strings.Contains(s, rsaSep) {
+		return false
+	}
+	return strings.Contains(s, rsaBegin)
+}
+
+func isEnd(s string) bool {
+	if !strings.Contains(s, rsaSep) {
+		return false
+	}
+	return strings.Contains(s, rsaEnd)
+}
+
+// cleanHeader cleans out any suffix from header.
+//
+// If s is not header, s is returned unchanged.
+func cleanHeader(s string) string {
+	if !strings.HasPrefix(s, rsaSep) {
+		return s
+	}
+	idx := strings.LastIndex(s, rsaSep)
+	if idx <= 0 {
+		return s
+	}
+
+	return s[:idx+len(rsaSep)]
+}
+
+// Extract public keys from C++ code in r to w.
+func Extract(r io.Reader, w io.Writer) error {
+	s := bufio.NewScanner(r)
+
+	var (
+		parts []string
+		body  bool
+		b     strings.Builder
+	)
+
+	for s.Scan() {
+		text := strings.TrimSuffix(
+			strings.TrimSpace(s.Text()), `\n\`,
+		)
+		text = strings.Trim(text, `"`)
+		text = strings.TrimSuffix(text, `\n`)
+
+		text = cleanHeader(text)
+
+		if isBegin(text) {
+			// Public key started.
+			body = true
+		}
+
+		if body {
+			parts = append(parts, text)
+		}
+
+		if isEnd(text) {
+			// Public key completed.
+			// Writing single public key to w.
+			for _, part := range parts {
+				b.WriteString(part)
+				b.WriteRune('\n')
+			}
+			if _, err := io.WriteString(w, b.String()); err != nil {
+				return err
+			}
+
+			// Reset state.
+			b.Reset()
+			body = false
+			parts = parts[:0]
+		}
+	}
+
+	if s.Err() != nil {
+		return s.Err()
+	}
+
+	return nil
+}