You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: extended_packets.go
    path of file: ./repos/podman/vendor/github.com/pkg/sftp/internal/encoding/ssh/filexfer
    
    the code of the file until where you have to start completion: package sshfx

import (
	"encoding"
	"sync"
)

// ExtendedData aliases the untyped interface composition of encoding.BinaryMarshaler and encoding.BinaryUnmarshaler.
type ExtendedData = interface {
	encoding.BinaryMarshaler
	encod
    
func RegisterExtendedPacketType(extension string, constructor ExtendedDataConstructor) {
	extendedPacketTypes.mu.Lock()
	defer extendedPacketTypes.mu.Unlock()

	if _, exist := extendedPacketTypes.constructors[extension]; exist {
		panic("encoding/ssh/filexfer: multiple registration of extended packet type " + extension)
	}

	extendedPacketTypes.constructors[extension] = constructor
}