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/mtproto/connect.go

@@ -0,0 +1,93 @@
+package mtproto
+
+import (
+	"context"
+
+	"github.com/go-faster/errors"
+	"go.uber.org/multierr"
+	"go.uber.org/zap"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/exchange"
+)
+
+// connect establishes connection using configured transport, creating
+// new auth key if needed.
+func (c *Conn) connect(ctx context.Context) (rErr error) {
+	ctx, cancel := context.WithTimeout(ctx, c.dialTimeout)
+	defer cancel()
+
+	conn, err := c.dialer(ctx)
+	if err != nil {
+		return errors.Wrap(err, "dial failed")
+	}
+	c.conn = conn
+	defer func() {
+		if rErr != nil {
+			multierr.AppendInto(&rErr, conn.Close())
+		}
+	}()
+
+	session := c.session()
+	if session.Key.Zero() {
+		c.log.Info("Generating new auth key")
+		start := c.clock.Now()
+		if err := c.createAuthKey(ctx); err != nil {
+			return errors.Wrap(err, "create auth key")
+		}
+
+		c.log.Info("Auth key generated",
+			zap.Duration("duration", c.clock.Now().Sub(start)),
+		)
+		return nil
+	}
+
+	c.log.Info("Key already exists")
+	if session.ID == 0 {
+		// NB: Telegram can return 404 error if session id is zero.
+		//
+		// See https://github.com/gotd/td/issues/107.
+		c.log.Debug("Generating new session id")
+		if err := c.newSessionID(); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
+
+// createAuthKey generates new authorization key.
+func (c *Conn) createAuthKey(ctx context.Context) error {
+	// Grab exclusive lock for writing.
+	// It prevents message sending during key regeneration if server forgot current auth key.
+	c.exchangeLock.Lock()
+	defer c.exchangeLock.Unlock()
+
+	if ce := c.log.Check(zap.DebugLevel, "Initializing new key exchange"); ce != nil {
+		// Useful for debugging i/o timeout errors on tcp reads or writes.
+		fields := []zap.Field{
+			zap.Duration("timeout", c.exchangeTimeout),
+		}
+		if deadline, ok := ctx.Deadline(); ok {
+			fields = append(fields, zap.Time("context_deadline", deadline))
+		}
+		ce.Write(fields...)
+	}
+
+	r, err := exchange.NewExchanger(c.conn, c.dcID).
+		WithClock(c.clock).
+		WithLogger(c.log.Named("exchange")).
+		WithTimeout(c.exchangeTimeout).
+		WithRand(c.rand).
+		Client(c.rsaPublicKeys).Run(ctx)
+	if err != nil {
+		return err
+	}
+
+	c.sessionMux.Lock()
+	c.authKey = r.AuthKey
+	c.sessionID = r.SessionID
+	c.salt = r.ServerSalt
+	c.sessionMux.Unlock()
+
+	return nil
+}