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: tsig.go
    path of file: ./repos/moby/vendor/github.com/miekg/dns
    
    the code of the file until where you have to start completion: package dns

import (
	"crypto/hmac"
	"crypto/sha1"
	"crypto/sha256"
	"crypto/sha512"
	"encoding/binary"
	"encoding/hex"
	"hash"
	"strconv"
	"strings"
	"time"
)

// HMAC hashing codes. These are transmitted as domain names.
const (
	HmacSHA1   = "hmac-sha1."
	HmacSHA224 = "hmac-sha224."
	HmacSHA256 = "hmac-sha256."
	HmacSHA384 = "hmac-sha384."
	HmacSHA512 = "hmac-sha512."

	HmacMD5 = 
    
func tsigBuffer(msgbuf []byte, rr *TSIG, requestMAC string, timersOnly bool) ([]byte, error) {
	var buf []byte
	if rr.TimeSigned == 0 {
		rr.TimeSigned = uint64(time.Now().Unix())
	}
	if rr.Fudge == 0 {
		rr.Fudge = 300 // Standard (RFC) default.
	}

	// Replace message ID in header with original ID from TSIG
	binary.BigEndian.PutUint16(msgbuf[0:2], rr.OrigId)

	if requestMAC != "" {
		m := new(macWireFmt)
		m.MACSize = uint16(len(requestMAC) / 2)
		m.MAC = requestMAC
		buf = make([]byte, len(requestMAC)) // long enough
		n, err := packMacWire(m, buf)
		if err != nil {
			return nil, err
		}
		buf = buf[:n]
	}

	tsigvar := make([]byte, DefaultMsgSize)
	if timersOnly {
		tsig := new(timerWireFmt)
		tsig.TimeSigned = rr.TimeSigned
		tsig.Fudge = rr.Fudge
		n, err := packTimerWire(tsig, tsigvar)
		if err != nil {
			return nil, err
		}
		tsigvar = tsigvar[:n]
	} else {
		tsig := new(tsigWireFmt)
		tsig.Name = CanonicalName(rr.Hdr.Name)
		tsig.Class = ClassANY
		tsig.Ttl = rr.Hdr.Ttl
		tsig.Algorithm = CanonicalName(rr.Algorithm)
		tsig.TimeSigned = rr.TimeSigned
		tsig.Fudge = rr.Fudge
		tsig.Error = rr.Error
		tsig.OtherLen = rr.OtherLen
		tsig.OtherData = rr.OtherData
		n, err := packTsigWire(tsig, tsigvar)
		if err != nil {
			return nil, err
		}
		tsigvar = tsigvar[:n]
	}

	if requestMAC != "" {
		x := append(buf, msgbuf...)
		buf = append(x, tsigvar...)
	} else {
		buf = append(msgbuf, tsigvar...)
	}
	return buf, nil
}