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/exchange/flow.go

@@ -0,0 +1,105 @@
+// Package exchange contains Telegram key exchange algorithm flows.
+// See https://core.telegram.org/mtproto/auth_key.
+package exchange
+
+import (
+	"io"
+	"time"
+
+	"go.uber.org/zap"
+
+	"go.mau.fi/mautrix-telegram/pkg/gotd/clock"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/crypto"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/proto"
+	"go.mau.fi/mautrix-telegram/pkg/gotd/transport"
+)
+
+// DefaultTimeout is default WithTimeout parameter value.
+const DefaultTimeout = 1 * time.Minute
+
+// Exchanger is builder for key exchangers.
+type Exchanger struct {
+	conn transport.Conn
+
+	clock   clock.Clock
+	rand    io.Reader
+	log     *zap.Logger
+	timeout time.Duration
+	dc      int
+}
+
+// WithClock sets exchange flow clock.
+func (e Exchanger) WithClock(c clock.Clock) Exchanger {
+	e.clock = c
+	return e
+}
+
+// WithRand sets exchange flow random source.
+func (e Exchanger) WithRand(reader io.Reader) Exchanger {
+	e.rand = reader
+	return e
+}
+
+// WithLogger sets exchange flow logger.
+func (e Exchanger) WithLogger(log *zap.Logger) Exchanger {
+	e.log = log
+	return e
+}
+
+// WithTimeout sets write/read deadline of every exchange request.
+func (e Exchanger) WithTimeout(timeout time.Duration) Exchanger {
+	e.timeout = timeout
+	return e
+}
+
+// NewExchanger creates new Exchanger.
+func NewExchanger(conn transport.Conn, dc int) Exchanger {
+	return Exchanger{
+		conn: conn,
+
+		clock:   clock.System,
+		rand:    crypto.DefaultRand(),
+		log:     zap.NewNop(),
+		timeout: DefaultTimeout,
+		dc:      dc,
+	}
+}
+
+func (e Exchanger) unencryptedWriter(input, output proto.MessageType) unencryptedWriter {
+	return unencryptedWriter{
+		clock:   e.clock,
+		conn:    e.conn,
+		timeout: e.timeout,
+		input:   input,
+		output:  output,
+	}
+}
+
+// Client creates new ClientExchange using parameters from Exchanger.
+func (e Exchanger) Client(keys []PublicKey) ClientExchange {
+	return ClientExchange{
+		unencryptedWriter: e.unencryptedWriter(
+			proto.MessageServerResponse,
+			proto.MessageFromClient,
+		),
+		rand: e.rand,
+		log:  e.log,
+		keys: keys,
+		dc:   e.dc,
+	}
+}
+
+// Server creates new ServerExchange using parameters from Exchanger.
+func (e Exchanger) Server(key PrivateKey) ServerExchange {
+	return ServerExchange{
+		unencryptedWriter: e.unencryptedWriter(
+			proto.MessageFromClient,
+			proto.MessageServerResponse,
+		),
+		rand: e.rand,
+		log:  e.log,
+		rng:  TestServerRNG{rand: e.rand},
+		key:  key,
+		dc:   e.dc,
+	}
+}