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/cmd/dltl/main.go

@@ -0,0 +1,168 @@
+// Binary dltl fetches .tl schema from remote repo.
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"crypto/sha256"
+	"flag"
+	"fmt"
+	"io"
+	"net/http"
+	"net/url"
+	"os"
+	"path"
+	"strconv"
+	"strings"
+
+	"github.com/gotd/tl"
+)
+
+func mergeSchema(target, s *tl.Schema) {
+Definitions:
+	for _, d := range s.Definitions {
+		for _, targetD := range target.Definitions {
+			if targetD.Definition.ID == d.Definition.ID {
+				continue Definitions
+			}
+		}
+
+		target.Definitions = append(target.Definitions, d)
+	}
+Classes:
+	for _, c := range s.Classes {
+		for _, targetC := range target.Classes {
+			if targetC.Name == c.Name {
+				continue Classes
+			}
+		}
+
+		target.Classes = append(target.Classes, c)
+	}
+	if target.Layer == 0 {
+		target.Layer = s.Layer
+	}
+}
+
+func main() {
+	var (
+		name   = flag.String("f", "telegram_api.tl", "file name to download; api.tl or mtproto.tl")
+		base   = flag.String("base", "https://raw.githubusercontent.com/tdlib/td", "base url")
+		branch = flag.String("branch", "master", "branch to use")
+		dir    = flag.String("dir", "td/generate/scheme", "directory of schemas")
+		out    = flag.String("o", "", "output file name (blank to stdout)")
+		merge  = flag.String("merge", "", "path to schema(s) to merge with, comma-separated")
+	)
+	flag.Parse()
+
+	u, err := url.Parse(*base)
+	if err != nil {
+		panic(err)
+	}
+
+	u.Path = path.Join(u.Path, *branch, *dir, *name)
+
+	res, err := http.Get(u.String())
+	if err != nil {
+		panic(err)
+	}
+	defer func() { _ = res.Body.Close() }()
+	if res.StatusCode/100 != 2 {
+		panic(fmt.Sprintf("%s %d", u.String(), res.StatusCode))
+	}
+
+	// Parsing in-place.
+	h := sha256.New()
+	s, err := tl.Parse(io.TeeReader(res.Body, h))
+	if err != nil {
+		panic(err)
+	}
+
+	if *merge != "" {
+		for _, mergeName := range strings.Split(*merge, ",") {
+			data, err := os.ReadFile(mergeName)
+			if err != nil {
+				panic(err)
+			}
+
+			m, err := tl.Parse(bytes.NewReader(data))
+			if err != nil {
+				panic(err)
+			}
+
+			mergeSchema(s, m)
+		}
+	}
+
+	// Trying to detect layer of tdlib schema.
+	if s.Layer == 0 && *name == "telegram_api.tl" {
+		layerURL, err := url.Parse(*base)
+		if err != nil {
+			panic(err)
+		}
+		layerURL.Path = path.Join(layerURL.Path, *branch, "td/telegram/Version.h")
+		res, err := http.Get(layerURL.String())
+		if err != nil {
+			panic(err)
+		}
+		if res.StatusCode == http.StatusOK {
+			scanner := bufio.NewScanner(res.Body)
+			for scanner.Scan() {
+				t := strings.TrimSpace(scanner.Text())
+				// constexpr int32 MTPROTO_LAYER = 131;
+				const (
+					prefix = `constexpr int32 MTPROTO_LAYER = `
+					suffix = `;`
+				)
+				if !strings.HasPrefix(t, prefix) {
+					continue
+				}
+				t = strings.TrimPrefix(t, prefix)
+				t = strings.TrimSuffix(t, suffix)
+				t = strings.TrimSpace(t)
+				if layer, err := strconv.Atoi(t); err == nil {
+					s.Layer = layer
+				}
+			}
+		}
+	}
+	if s.Layer == 0 && *name == "telegram_api.tl" {
+		// Still failed.
+		panic("failed to detect layer")
+	}
+
+	var outWriter io.Writer = os.Stdout
+	if *out != "" {
+		w, err := os.Create(*out)
+		if err != nil {
+			panic(err)
+		}
+		defer func() {
+			if err := w.Close(); err != nil {
+				panic(err)
+			}
+		}()
+		outWriter = w
+	}
+
+	// Writing header to avoid manual edit.
+	var b strings.Builder
+	b.WriteString("// Code generated by ./cmd/dltl, DO NOT EDIT.\n")
+	b.WriteString("//\n")
+	b.WriteString(fmt.Sprintf("// Source: %s\n", u))
+	if *merge != "" {
+		b.WriteString(fmt.Sprintf("// Merge:  %s\n", *merge))
+	}
+	if s.Layer > 0 {
+		b.WriteString(fmt.Sprintf("// Layer:  %d\n", s.Layer))
+	}
+	b.WriteString(fmt.Sprintf("// SHA256: %x\n", h.Sum(nil)))
+	b.WriteRune('\n')
+	if _, err := io.WriteString(outWriter, b.String()); err != nil {
+		panic(err)
+	}
+
+	if _, err := s.WriteTo(outWriter); err != nil {
+		panic(err)
+	}
+}