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: passphrase_stream.go
    path of file: ./repos/client/go/libkb
    
    the code of the file until where you have to start completion: // Copyright 2015 Keybase, Inc. All rights reserved. Use of
// this source code is governed by the included BSD license.

package libkb

import (
	"fmt"
	"runtime/debug"

	keybase1 "github.com/keybase/client/go/protocol/keybase1"
	triplesec "github.com/keybase/go-triplesec"
)

func NewSecureTriplesec(passphrase []byte, salt []byte) (Triplesec, error) {
	return triplesec.NewCipher(passphrase, salt, ClientTriplesecVersion)
}

func StretchPassphrase(g *GlobalContext, passphrase string, salt []byte) (tsec Triplesec, pps *PassphraseStream, err error) {
	if salt == nil {
		err = fmt.Errorf("no salt provided to StretchPassphrase")
		return nil, nil, err
	}
	var tmp []byte
	var fn func(pw []byte, salt []byte) (Triplesec, error)

	// free
    
func StretchPassphrase(g *GlobalContext, passphrase string, salt []byte) (tsec Triplesec, pps *PassphraseStream, err error) {
	if salt == nil {
		err = fmt.Errorf("no salt provided to StretchPassphrase")
		return nil, nil, err
	}
	var tmp []byte
	var fn func(pw []byte, salt []byte) (Triplesec, error)

	// free memory on mobile before we do this to reduce chance that we get killed because of the
	// large scrypt allocation coming
	if g != nil && g.IsMobileAppType() {
		debug.FreeOSMemory()
	}
	if g == nil {
		fn = NewSecureTriplesec
	} else {
		fn = g.NewTriplesec
	}

	tsec, err = fn([]byte(passphrase), salt)
	if err != nil {
		return nil, nil, err
	}
	_, tmp, err = tsec.DeriveKey(extraLen)
	if err != nil {
		return nil, nil, err
	}
	pps = NewPassphraseStream(tmp)
	return tsec, pps, nil
}