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package obfsvpn
import (
"context"
"encoding/base64"
"fmt"
"net"
"strconv"
"git.torproject.org/pluggable-transports/goptlib.git"
"github.com/xtaci/kcp-go/v5"
"gitlab.com/yawning/obfs4.git/common/ntor"
"gitlab.com/yawning/obfs4.git/transports/base"
"gitlab.com/yawning/obfs4.git/transports/obfs4"
)
const netKCP = "kcp"
const (
ptArgNode = "node-id"
ptArgKey = "public-key"
ptArgMode = "iat-mode"
ptArgCert = "cert"
)
const (
certLength = ntor.NodeIDLength + ntor.PublicKeyLength
)
// IATMode determines the amount of time sent between packets.
type IATMode int
// Valid IAT modes.
const (
IATNone IATMode = iota
IATEnabled
IATParanoid
)
// Dialer contains options for connecting to an address and obfuscating traffic
// with the obfs4 protocol.
// It performs the ntor handshake on all dialed connections.
type Dialer struct {
Dialer net.Dialer
NodeID *ntor.NodeID
PublicKey *ntor.PublicKey
IATMode IATMode
ptArgs pt.Args
cf base.ClientFactory
}
func packCert(node *ntor.NodeID, public *ntor.PublicKey) string {
cert := make([]byte, 0, certLength)
cert = append(cert, node[:]...)
cert = append(cert, public[:]...)
return base64.RawStdEncoding.EncodeToString(cert)
}
func unpackCert(cert string) (*ntor.NodeID, *ntor.PublicKey, error) {
if l := base64.RawStdEncoding.DecodedLen(len(cert)); l != certLength {
return nil, nil, fmt.Errorf("cert length %d is invalid", l)
}
decoded, err := base64.RawStdEncoding.DecodeString(cert)
if err != nil {
return nil, nil, err
}
nodeID, err := ntor.NewNodeID(decoded[:ntor.NodeIDLength])
if err != nil {
return nil, nil, err
}
pubKey, err := ntor.NewPublicKey(decoded[ntor.NodeIDLength:])
if err != nil {
return nil, nil, err
}
return nodeID, pubKey, nil
}
// NewDialerCert creates a dialer from a node certificate.
func NewDialerCert(cert string) (*Dialer, error) {
nodeID, publicKey, err := unpackCert(cert)
if err != nil {
return nil, err
}
return &Dialer{
NodeID: nodeID,
PublicKey: publicKey,
}, nil
}
// NewDialerArgs creates a dialer from existing pluggable transport arguments.
func NewDialerArgs(args pt.Args) (*Dialer, error) {
cf, err := (&obfs4.Transport{}).ClientFactory("")
if err != nil {
return nil, err
}
nodeHex, _ := args.Get(ptArgNode)
node, err := ntor.NodeIDFromHex(nodeHex)
if err != nil {
return nil, err
}
keyHex, _ := args.Get(ptArgKey)
pub, err := ntor.PublicKeyFromHex(keyHex)
if err != nil {
return nil, err
}
iatModeStr, _ := args.Get(ptArgMode)
iatMode, err := strconv.Atoi(iatModeStr)
if err != nil {
return nil, fmt.Errorf("error parsing IAT mode to integer: %w", err)
}
return &Dialer{
NodeID: node,
PublicKey: pub,
IATMode: IATMode(iatMode),
ptArgs: args,
cf: cf,
}, nil
}
// Dial creates an outbound net.Conn and performs the ntor handshake.
//
// See func net.Dial for a description of the network and address parameters.
// In addition to the networks supported by net.Dial, Dial supports the network
// string "kcp" which creates a reliable UDP connection.
// If the kcp network is used, the underlying net.Dialer is ignored and options
// set on it do not apply.
func (d *Dialer) Dial(ctx context.Context, network, address string) (net.Conn, error) {
if d.cf == nil {
cf, err := (&obfs4.Transport{}).ClientFactory("")
if err != nil {
return nil, err
}
d.cf = cf
}
ptArgs := d.Args()
args, err := d.cf.ParseArgs(&ptArgs)
if err != nil {
return nil, err
}
return d.cf.Dial(network, address, func(network, address string) (net.Conn, error) {
switch network {
case netKCP:
return kcp.Dial(address)
}
return d.Dialer.DialContext(ctx, network, address)
}, args)
}
// Args returns the dialers options as pluggable transport arguments.
// The args include valid args for the "new" (version >= 0.0.3) bridge lines
// that use a unified "cert" argument as well as the legacy lines that use a
// separate Node ID and Public Key.
func (d *Dialer) Args() pt.Args {
if d.ptArgs == nil {
d.ptArgs = make(pt.Args)
d.ptArgs.Add(ptArgNode, d.NodeID.Hex())
d.ptArgs.Add(ptArgKey, d.PublicKey.Hex())
d.ptArgs.Add(ptArgMode, strconv.Itoa(int(d.IATMode)))
d.ptArgs.Add(ptArgCert, packCert(d.NodeID, d.PublicKey))
}
return d.ptArgs
}
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