365 lines
8.9 KiB
Go
365 lines
8.9 KiB
Go
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package socks5
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import (
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"fmt"
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"io"
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"net"
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"strconv"
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"strings"
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"golang.org/x/net/context"
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)
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const (
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ConnectCommand = uint8(1)
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BindCommand = uint8(2)
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AssociateCommand = uint8(3)
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ipv4Address = uint8(1)
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fqdnAddress = uint8(3)
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ipv6Address = uint8(4)
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)
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const (
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successReply uint8 = iota
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serverFailure
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ruleFailure
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networkUnreachable
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hostUnreachable
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connectionRefused
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ttlExpired
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commandNotSupported
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addrTypeNotSupported
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)
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var (
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unrecognizedAddrType = fmt.Errorf("Unrecognized address type")
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)
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// AddressRewriter is used to rewrite a destination transparently
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type AddressRewriter interface {
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Rewrite(ctx context.Context, request *Request) (context.Context, *AddrSpec)
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}
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// AddrSpec is used to return the target AddrSpec
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// which may be specified as IPv4, IPv6, or a FQDN
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type AddrSpec struct {
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FQDN string
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IP net.IP
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Port int
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}
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func (a *AddrSpec) String() string {
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if a.FQDN != "" {
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return fmt.Sprintf("%s (%s):%d", a.FQDN, a.IP, a.Port)
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}
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return fmt.Sprintf("%s:%d", a.IP, a.Port)
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}
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// Address returns a string suitable to dial; prefer returning IP-based
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// address, fallback to FQDN
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func (a AddrSpec) Address() string {
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if 0 != len(a.IP) {
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return net.JoinHostPort(a.IP.String(), strconv.Itoa(a.Port))
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}
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return net.JoinHostPort(a.FQDN, strconv.Itoa(a.Port))
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}
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// A Request represents request received by a server
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type Request struct {
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// Protocol version
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Version uint8
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// Requested command
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Command uint8
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// AuthContext provided during negotiation
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AuthContext *AuthContext
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// AddrSpec of the the network that sent the request
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RemoteAddr *AddrSpec
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// AddrSpec of the desired destination
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DestAddr *AddrSpec
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// AddrSpec of the actual destination (might be affected by rewrite)
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realDestAddr *AddrSpec
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bufConn io.Reader
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}
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type conn interface {
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Write([]byte) (int, error)
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RemoteAddr() net.Addr
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}
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// NewRequest creates a new Request from the tcp connection
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func NewRequest(bufConn io.Reader) (*Request, error) {
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// Read the version byte
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header := []byte{0, 0, 0}
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if _, err := io.ReadAtLeast(bufConn, header, 3); err != nil {
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return nil, fmt.Errorf("Failed to get command version: %v", err)
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}
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// Ensure we are compatible
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if header[0] != socks5Version {
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return nil, fmt.Errorf("Unsupported command version: %v", header[0])
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}
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// Read in the destination address
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dest, err := readAddrSpec(bufConn)
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if err != nil {
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return nil, err
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}
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request := &Request{
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Version: socks5Version,
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Command: header[1],
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DestAddr: dest,
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bufConn: bufConn,
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}
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return request, nil
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}
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// handleRequest is used for request processing after authentication
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func (s *Server) handleRequest(req *Request, conn conn) error {
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ctx := context.Background()
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// Resolve the address if we have a FQDN
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dest := req.DestAddr
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if dest.FQDN != "" {
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ctx_, addr, err := s.config.Resolver.Resolve(ctx, dest.FQDN)
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if err != nil {
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if err := sendReply(conn, hostUnreachable, nil); err != nil {
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return fmt.Errorf("Failed to send reply: %v", err)
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}
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return fmt.Errorf("Failed to resolve destination '%v': %v", dest.FQDN, err)
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}
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ctx = ctx_
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dest.IP = addr
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}
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// Apply any address rewrites
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req.realDestAddr = req.DestAddr
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if s.config.Rewriter != nil {
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ctx, req.realDestAddr = s.config.Rewriter.Rewrite(ctx, req)
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}
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// Switch on the command
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switch req.Command {
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case ConnectCommand:
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return s.handleConnect(ctx, conn, req)
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case BindCommand:
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return s.handleBind(ctx, conn, req)
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case AssociateCommand:
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return s.handleAssociate(ctx, conn, req)
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default:
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if err := sendReply(conn, commandNotSupported, nil); err != nil {
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return fmt.Errorf("Failed to send reply: %v", err)
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}
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return fmt.Errorf("Unsupported command: %v", req.Command)
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}
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}
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// handleConnect is used to handle a connect command
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func (s *Server) handleConnect(ctx context.Context, conn conn, req *Request) error {
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// Check if this is allowed
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if ctx_, ok := s.config.Rules.Allow(ctx, req); !ok {
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if err := sendReply(conn, ruleFailure, nil); err != nil {
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return fmt.Errorf("Failed to send reply: %v", err)
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}
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return fmt.Errorf("Connect to %v blocked by rules", req.DestAddr)
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} else {
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ctx = ctx_
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}
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// Attempt to connect
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dial := s.config.Dial
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if dial == nil {
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dial = func(ctx context.Context, net_, addr string) (net.Conn, error) {
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return net.Dial(net_, addr)
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}
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}
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target, err := dial(ctx, "tcp", req.realDestAddr.Address())
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if err != nil {
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msg := err.Error()
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resp := hostUnreachable
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if strings.Contains(msg, "refused") {
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resp = connectionRefused
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} else if strings.Contains(msg, "network is unreachable") {
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resp = networkUnreachable
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}
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if err := sendReply(conn, resp, nil); err != nil {
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return fmt.Errorf("Failed to send reply: %v", err)
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}
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return fmt.Errorf("Connect to %v failed: %v", req.DestAddr, err)
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}
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defer target.Close()
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// Send success
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local := target.LocalAddr().(*net.TCPAddr)
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bind := AddrSpec{IP: local.IP, Port: local.Port}
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if err := sendReply(conn, successReply, &bind); err != nil {
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return fmt.Errorf("Failed to send reply: %v", err)
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}
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// Start proxying
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errCh := make(chan error, 2)
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go proxy(target, req.bufConn, errCh)
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go proxy(conn, target, errCh)
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// Wait
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for i := 0; i < 2; i++ {
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e := <-errCh
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if e != nil {
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// return from this function closes target (and conn).
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return e
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}
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}
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return nil
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}
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// handleBind is used to handle a connect command
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func (s *Server) handleBind(ctx context.Context, conn conn, req *Request) error {
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// Check if this is allowed
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if ctx_, ok := s.config.Rules.Allow(ctx, req); !ok {
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if err := sendReply(conn, ruleFailure, nil); err != nil {
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return fmt.Errorf("Failed to send reply: %v", err)
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}
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return fmt.Errorf("Bind to %v blocked by rules", req.DestAddr)
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} else {
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ctx = ctx_
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}
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// TODO: Support bind
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if err := sendReply(conn, commandNotSupported, nil); err != nil {
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return fmt.Errorf("Failed to send reply: %v", err)
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}
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return nil
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}
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// handleAssociate is used to handle a connect command
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func (s *Server) handleAssociate(ctx context.Context, conn conn, req *Request) error {
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// Check if this is allowed
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if ctx_, ok := s.config.Rules.Allow(ctx, req); !ok {
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if err := sendReply(conn, ruleFailure, nil); err != nil {
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return fmt.Errorf("Failed to send reply: %v", err)
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}
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return fmt.Errorf("Associate to %v blocked by rules", req.DestAddr)
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} else {
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ctx = ctx_
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}
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// TODO: Support associate
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if err := sendReply(conn, commandNotSupported, nil); err != nil {
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return fmt.Errorf("Failed to send reply: %v", err)
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}
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return nil
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}
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// readAddrSpec is used to read AddrSpec.
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// Expects an address type byte, follwed by the address and port
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func readAddrSpec(r io.Reader) (*AddrSpec, error) {
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d := &AddrSpec{}
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// Get the address type
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addrType := []byte{0}
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if _, err := r.Read(addrType); err != nil {
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return nil, err
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}
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// Handle on a per type basis
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switch addrType[0] {
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case ipv4Address:
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addr := make([]byte, 4)
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if _, err := io.ReadAtLeast(r, addr, len(addr)); err != nil {
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return nil, err
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}
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d.IP = net.IP(addr)
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case ipv6Address:
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addr := make([]byte, 16)
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if _, err := io.ReadAtLeast(r, addr, len(addr)); err != nil {
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return nil, err
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}
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d.IP = net.IP(addr)
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case fqdnAddress:
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if _, err := r.Read(addrType); err != nil {
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return nil, err
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}
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addrLen := int(addrType[0])
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fqdn := make([]byte, addrLen)
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if _, err := io.ReadAtLeast(r, fqdn, addrLen); err != nil {
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return nil, err
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}
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d.FQDN = string(fqdn)
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default:
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return nil, unrecognizedAddrType
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}
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// Read the port
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port := []byte{0, 0}
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if _, err := io.ReadAtLeast(r, port, 2); err != nil {
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return nil, err
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}
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d.Port = (int(port[0]) << 8) | int(port[1])
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return d, nil
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}
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// sendReply is used to send a reply message
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func sendReply(w io.Writer, resp uint8, addr *AddrSpec) error {
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// Format the address
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var addrType uint8
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var addrBody []byte
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var addrPort uint16
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switch {
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case addr == nil:
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addrType = ipv4Address
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addrBody = []byte{0, 0, 0, 0}
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addrPort = 0
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case addr.FQDN != "":
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addrType = fqdnAddress
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addrBody = append([]byte{byte(len(addr.FQDN))}, addr.FQDN...)
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addrPort = uint16(addr.Port)
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case addr.IP.To4() != nil:
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addrType = ipv4Address
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addrBody = []byte(addr.IP.To4())
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addrPort = uint16(addr.Port)
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case addr.IP.To16() != nil:
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addrType = ipv6Address
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addrBody = []byte(addr.IP.To16())
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addrPort = uint16(addr.Port)
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default:
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return fmt.Errorf("Failed to format address: %v", addr)
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}
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// Format the message
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msg := make([]byte, 6+len(addrBody))
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msg[0] = socks5Version
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msg[1] = resp
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msg[2] = 0 // Reserved
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msg[3] = addrType
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copy(msg[4:], addrBody)
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msg[4+len(addrBody)] = byte(addrPort >> 8)
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msg[4+len(addrBody)+1] = byte(addrPort & 0xff)
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// Send the message
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_, err := w.Write(msg)
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return err
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}
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type closeWriter interface {
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CloseWrite() error
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}
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// proxy is used to suffle data from src to destination, and sends errors
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// down a dedicated channel
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func proxy(dst io.Writer, src io.Reader, errCh chan error) {
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_, err := io.Copy(dst, src)
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if tcpConn, ok := dst.(closeWriter); ok {
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tcpConn.CloseWrite()
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}
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errCh <- err
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}
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