refactor(client): add AuthTransferHandler type

telegram/client.go

@@ -129,8 +129,8 @@ type Client struct {
 	// Tracing.
 	tracer trace.Tracer
 
-	// onTransfer is called on authorization transfer.
-	onTransfer func(ctx context.Context, client *Client, tx func(ctx context.Context) error) error
+	// onTransfer is called in transfer.
+	onTransfer AuthTransferHandler
 }
 
 // NewClient creates new unstarted client.

telegram/options.go

@@ -95,13 +95,9 @@ type Options struct {
 	// OpenTelemetry.
 	TracerProvider trace.TracerProvider
 
-	// OnTransfer is called on authorization transfer to acquire external lock.
-	//
-	// The function should call tx function to perform transfer, serializing it
-	// with external lock.
-	//
-	// The function must return error if tx function returned error.
-	OnTransfer func(ctx context.Context, c *Client, tx func(context.Context) error) error
+	// OnTransfer is called during authorization transfer.
+	// See [AuthTransferHandler] for details.
+	OnTransfer AuthTransferHandler
 }
 
 func (opt *Options) setDefaults() {

telegram/transfer.go

@@ -17,6 +17,14 @@ func (c *Client) exportAuth(ctx context.Context, dcID int) (*tg.AuthExportedAuth
 	return export, nil
 }
 
+// AuthTransferHandler is a function that is called during authorization transfer.
+//
+// The fn callback should be serialized by user id via external locking.
+// You can call [Client.Self] to acquire current user id.
+//
+// The fn callback must return fn error if any.
+type AuthTransferHandler func(ctx context.Context, client *Client, fn func(context.Context) error) error
+
 func noopOnTransfer(ctx context.Context, _ *Client, fn func(context.Context) error) error {
 	return fn(ctx)
 }