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/session/session.go

@@ -0,0 +1,158 @@
+// Package session implements session storage.
+package session
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/go-faster/errors"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/tg"
+)
+
+// Config is subset of tg.Config.
+type Config struct {
+	// Indicates that telegram is probably censored by governments/ISPs in the current region
+	BlockedMode bool
+	// Whether to forcefully try connecting using IPv6 dcOptions¹
+	//
+	// Links:
+	//  1) https://core.telegram.org/type/DcOption
+	ForceTryIpv6 bool
+	// Current date at the server
+	Date int
+	// Expiration date of this config: when it expires it'll have to be refetched using help
+	// getConfig¹
+	//
+	// Links:
+	//  1) https://core.telegram.org/method/help.getConfig
+	Expires int
+	// Whether we're connected to the test DCs
+	TestMode bool
+	// ID of the DC that returned the reply
+	ThisDC int
+	// DC IP list
+	DCOptions []tg.DCOption
+	// Domain name for fetching encrypted DC list from DNS TXT record
+	DCTxtDomainName string
+	// Temporary passport¹ sessions
+	//
+	// Links:
+	//  1) https://core.telegram.org/passport
+	//
+	// Use SetTmpSessions and GetTmpSessions helpers.
+	TmpSessions int
+	// DC ID to use to download webfiles¹
+	//
+	// Links:
+	//  1) https://core.telegram.org/api/files#downloading-webfiles
+	WebfileDCID int
+}
+
+// ConfigFromTG converts tg.Config to Config.
+//
+// Note that Config is the subset of tg.Config, so data loss is possible.
+func ConfigFromTG(c tg.Config) Config {
+	return Config{
+		BlockedMode:     c.BlockedMode,
+		ForceTryIpv6:    c.ForceTryIpv6,
+		Date:            c.Date,
+		Expires:         c.Expires,
+		TestMode:        c.TestMode,
+		ThisDC:          c.ThisDC,
+		DCOptions:       c.DCOptions,
+		DCTxtDomainName: c.DCTxtDomainName,
+		WebfileDCID:     c.WebfileDCID,
+		TmpSessions:     c.TmpSessions,
+	}
+}
+
+// TG returns tg.Config from Config.
+//
+// Note that config is the subset of tg.Config, so some fields will be unset.
+func (c Config) TG() tg.Config {
+	return tg.Config{
+		BlockedMode:     c.BlockedMode,
+		ForceTryIpv6:    c.ForceTryIpv6,
+		Date:            c.Date,
+		Expires:         c.Expires,
+		TestMode:        c.TestMode,
+		ThisDC:          c.ThisDC,
+		DCOptions:       c.DCOptions,
+		DCTxtDomainName: c.DCTxtDomainName,
+		WebfileDCID:     c.WebfileDCID,
+		TmpSessions:     c.TmpSessions,
+	}
+}
+
+// Data of session.
+type Data struct {
+	Config    Config
+	DC        int
+	Addr      string
+	AuthKey   []byte
+	AuthKeyID []byte
+	Salt      int64
+}
+
+// Storage is secure persistent storage for client session.
+//
+// NB: Implementation security is important, attacker can abuse it not only for
+// connecting as authenticated user or bot, but even decrypting previous
+// messages in some situations.
+type Storage interface {
+	LoadSession(ctx context.Context) ([]byte, error)
+	StoreSession(ctx context.Context, data []byte) error
+}
+
+// ErrNotFound means that session is not found in storage.
+var ErrNotFound = errors.New("session storage: not found")
+
+// Loader wraps Storage implementing Data (un-)marshaling.
+type Loader struct {
+	Storage Storage
+}
+
+type jsonData struct {
+	Version int
+	Data    Data
+}
+
+const latestVersion = 1
+
+// Load loads Data from Storage.
+func (l *Loader) Load(ctx context.Context) (*Data, error) {
+	buf, err := l.Storage.LoadSession(ctx)
+	if err != nil {
+		return nil, errors.Wrap(err, "load")
+	}
+	if len(buf) == 0 {
+		return nil, ErrNotFound
+	}
+
+	var v jsonData
+	if err := json.Unmarshal(buf, &v); err != nil {
+		return nil, errors.Wrap(err, "unmarshal")
+	}
+	if v.Version != latestVersion {
+		// HACK(ernado): backward compatibility super shenanigan.
+		return nil, errors.Wrapf(ErrNotFound, "version mismatch (%d != %d)", v.Version, latestVersion)
+	}
+	return &v.Data, err
+}
+
+// Save saves Data to Storage.
+func (l *Loader) Save(ctx context.Context, data *Data) error {
+	v := jsonData{
+		Version: latestVersion,
+		Data:    *data,
+	}
+	buf, err := json.Marshal(v)
+	if err != nil {
+		return errors.Wrap(err, "marshal")
+	}
+	if err := l.Storage.StoreSession(ctx, buf); err != nil {
+		return errors.Wrap(err, "store")
+	}
+	return nil
+}