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/pool/session.go

@@ -0,0 +1,64 @@
+package pool
+
+import (
+	"sync"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/crypto"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/mtproto"
+)
+
+// Session represents DC session.
+type Session struct {
+	DC      int
+	AuthKey crypto.AuthKey
+	Salt    int64
+}
+
+// SyncSession is synchronization helper for Session.
+type SyncSession struct {
+	data Session
+	mux  sync.RWMutex
+}
+
+// NewSyncSession creates new SyncSession.
+func NewSyncSession(data Session) *SyncSession {
+	return &SyncSession{
+		data: data,
+	}
+}
+
+// Store saves given Session.
+func (s *SyncSession) Store(data Session) {
+	s.mux.Lock()
+	s.data = data
+	s.mux.Unlock()
+}
+
+// Migrate changes current DC and its addr, zeroes AuthKey and Salt.
+func (s *SyncSession) Migrate(dc int) {
+	s.mux.Lock()
+	s.data.DC = dc
+	s.data.AuthKey = crypto.AuthKey{}
+	s.data.Salt = 0
+	s.mux.Unlock()
+}
+
+// Options fills Key and Salt field of given Options using stored session and returns it.
+func (s *SyncSession) Options(opts mtproto.Options) (mtproto.Options, Session) {
+	s.mux.RLock()
+	data := s.data
+	s.mux.RUnlock()
+
+	opts.Key = data.AuthKey
+	opts.Salt = data.Salt
+	return opts, data
+}
+
+// Load gets session and returns it.
+func (s *SyncSession) Load() (data Session) {
+	s.mux.RLock()
+	data = s.data
+	s.mux.RUnlock()
+
+	return
+}