direct.go

package echogy

import (
	"github.com/gliderlabs/ssh"
	gossh "golang.org/x/crypto/ssh"
	"io"
	"net"
	"strconv"
)

type localForwardChannelData struct {
	DestAddr string
	DestPort uint32

	OriginAddr string
	OriginPort uint32
}

func DirectTCPIPHandler(srv *ssh.Server, conn *gossh.ServerConn, newChan gossh.NewChannel, ctx ssh.Context) {
	d := localForwardChannelData{}
	if err := gossh.Unmarshal(newChan.ExtraData(), &d); err != nil {
		newChan.Reject(gossh.ConnectionFailed, "error parsing forward data: "+err.Error())
		return
	}

	ip := net.ParseIP(d.DestAddr)
	if (nil == ip || ip.IsPrivate()) && d.DestPort != debugPort {
		newChan.Reject(gossh.Prohibited, "port forwarding is disabled")
		return
	}

	ch, reqs, err := newChan.Accept()
	if err != nil {
		return
	}

	if d.DestPort == debugPort {
		server := getOrCreateDebugServer(conn, ctx)
		server.newChan(ch)
		return
	}

	dest := net.JoinHostPort(d.DestAddr, strconv.FormatInt(int64(d.DestPort), 10))

	var dialer net.Dialer
	dconn, err := dialer.DialContext(ctx, "tcp", dest)
	if err != nil {
		newChan.Reject(gossh.ConnectionFailed, err.Error())
		return
	}

	go gossh.DiscardRequests(reqs)

	go func() {
		defer ch.Close()
		defer dconn.Close()
		io.Copy(ch, dconn)
	}()
	go func() {
		defer ch.Close()
		defer dconn.Close()
		io.Copy(dconn, ch)
	}()
}