commit 786f71c7f72d7311a083f13197582b28bb29d2a6
Author: Anton Zadvorny <thcheetah@gmail.com>
Date:   Fri Jul 9 19:50:43 2021 +0300

    Initial commit

diff --git a/addr.go b/addr.go
new file mode 100644
index 0000000..5231447
--- /dev/null
+++ b/addr.go
@@ -0,0 +1,116 @@
+package socks5
+
+import (
+	"encoding/binary"
+	"errors"
+	"net"
+	"strconv"
+)
+
+var (
+	// AddrZero is zero address
+	AddrZero = &Addr{IP: net.IPv4zero, Port: 0}
+)
+
+// Addr implements net.Addr interface
+type Addr struct {
+	IP   net.IP
+	Host string
+	Port int
+}
+
+// AddrFromString returns new address from string representation
+func AddrFromString(address string) (*Addr, error) {
+	if address == "" {
+		return AddrZero, nil
+	}
+
+	host, port, err := splitHostPort(address)
+	if err != nil {
+		return nil, err
+	}
+
+	addr := &Addr{Port: port}
+	addr.IP = net.ParseIP(host)
+	if addr.IP == nil {
+		addr.Host = host
+	}
+
+	return addr, nil
+}
+
+func AddrFromSocks(atyp ATYP, host []byte, port []byte) *Addr {
+	addr := &Addr{Port: int(binary.BigEndian.Uint16(port))}
+
+	switch atyp {
+	case ATYPFQDN:
+		addr.Host = string(host[1:])
+	default:
+		addr.IP = net.IP(host)
+	}
+
+	return addr
+}
+
+// Socks returns socks protocol formatted address type, address and port
+func (s *Addr) Socks() (ATYP, []byte, []byte) {
+	portBytes := make([]byte, 2)
+	binary.BigEndian.PutUint16(portBytes, uint16(s.Port))
+
+	if s.IP != nil {
+		if ip4 := s.IP.To4(); ip4 != nil {
+			return ATYPIPv4, []byte(ip4), portBytes
+		} else if ip6 := s.IP.To16(); ip6 != nil {
+			return ATYPIPv6, []byte(ip6), portBytes
+		}
+	}
+
+	addr := []byte{byte(len(s.Host))}
+	addr = append(addr, []byte(s.Host)...)
+	return ATYPFQDN, addr, portBytes
+}
+
+// UDP returns udp address
+func (s *Addr) UDP() (*net.UDPAddr, error) {
+	if s.IP != nil {
+		return &net.UDPAddr{IP: s.IP, Port: s.Port}, nil
+	}
+
+	return net.ResolveUDPAddr("udp", s.Host)
+}
+
+// Network returns address Network
+func (s *Addr) Network() string {
+	return "socks"
+}
+
+func (s *Addr) String() string {
+	if s == nil {
+		return "<nil>"
+	}
+
+	port := strconv.Itoa(s.Port)
+	if s.IP == nil {
+		return net.JoinHostPort(s.Host, port)
+	}
+
+	return net.JoinHostPort(s.IP.String(), port)
+}
+
+func splitHostPort(address string) (string, int, error) {
+	host, port, err := net.SplitHostPort(address)
+	if err != nil {
+		return "", 0, err
+	}
+
+	portInt, err := strconv.Atoi(port)
+	if err != nil {
+		return "", 0, err
+	}
+
+	if 1 > portInt || portInt > 0xffff {
+		return "", 0, errors.New("port number out of range " + port)
+	}
+
+	return host, portInt, nil
+}
diff --git a/datagram.go b/datagram.go
new file mode 100644
index 0000000..7277065
--- /dev/null
+++ b/datagram.go
@@ -0,0 +1,83 @@
+package socks5
+
+import (
+	"bytes"
+	"io"
+)
+
+// Datagram is the datagram packet
+type Datagram struct {
+	ATYP    ATYP
+	DstAddr []byte
+	DstPort []byte
+	Data    []byte
+}
+
+// NewDatagram creates new datagram packet
+func NewDatagram(atyp ATYP, host []byte, port []byte, data []byte) *Datagram {
+	return &Datagram{
+		ATYP:    atyp,
+		DstAddr: host,
+		DstPort: port,
+		Data:    data,
+	}
+}
+
+// NewDatagramFrom reads datagram packet from reader
+func NewDatagramFrom(r io.Reader) (*Datagram, error) {
+	buf := make([]byte, 4)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+
+	if !bytes.Equal([]byte{Reserved, Reserved}, buf[:1]) {
+		return nil, ErrBadDatagram
+	}
+
+	if buf[2] != DatagramStandalone {
+		return nil, ErrFragmentedDatagram
+	}
+
+	addr, err := ReadAddress(r, ATYP(buf[3]))
+	if err != nil {
+		return nil, err
+	}
+
+	port := make([]byte, 2)
+	if _, err := io.ReadFull(r, port); err != nil {
+		return nil, err
+	}
+
+	data, err := io.ReadAll(r)
+	if err != nil {
+		return nil, err
+	}
+
+	datagram := &Datagram{
+		ATYP:    ATYP(buf[3]),
+		DstAddr: addr,
+		DstPort: port,
+		Data:    data,
+	}
+
+	return datagram, nil
+}
+
+// WriteTo writes datagram packet
+func (s *Datagram) WriteTo(w io.Writer) (int64, error) {
+	n, err := w.Write(s.Bytes())
+	if err != nil {
+		return int64(n), err
+	}
+
+	return int64(n), nil
+}
+
+func (s *Datagram) Bytes() []byte {
+	buf := bytes.NewBuffer([]byte{Reserved, Reserved, DatagramStandalone, byte(s.ATYP)})
+	buf.Write(s.DstAddr)
+	buf.Write(s.DstPort)
+	buf.Write(s.Data)
+
+	return buf.Bytes()
+}
diff --git a/dialer.go b/dialer.go
new file mode 100644
index 0000000..e28cf85
--- /dev/null
+++ b/dialer.go
@@ -0,0 +1,237 @@
+package socks5
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"time"
+)
+
+var (
+	// ErrNetworkNotImplemented is the network not implemented error
+	ErrNetworkNotImplemented = errors.New("network not implemented")
+)
+
+var (
+	noDeadline      = time.Time{}
+	expiredDeadline = time.Unix(1, 0)
+)
+
+// Dialer is the socks5 dialer
+type Dialer struct {
+	Server    string
+	Username  string
+	Password  string
+	ProxyDial func(ctx context.Context, network string, addr string) (net.Conn, error)
+}
+
+func (s *Dialer) Dial(network string, address string) (net.Conn, error) {
+	return s.DialContext(context.Background(), network, address)
+}
+
+func (s *Dialer) DialContext(ctx context.Context, network string, address string) (net.Conn, error) {
+	proxy, err := AddrFromString(s.Server)
+	if err != nil {
+		return nil, &net.OpError{Op: "socks", Net: network, Source: proxy, Addr: AddrZero, Err: err}
+	}
+
+	addr, err := AddrFromString(address)
+	if err != nil {
+		return nil, &net.OpError{Op: "socks", Net: network, Source: proxy, Addr: AddrZero, Err: err}
+	}
+
+	switch network {
+	case "tcp", "tcp4", "tcp6":
+	case "udp", "udp4", "udp6":
+	default:
+		return nil, &net.OpError{Op: "socks", Net: network, Source: proxy, Addr: addr, Err: ErrNetworkNotImplemented}
+	}
+
+	var conn net.Conn
+	if s.ProxyDial != nil {
+		conn, err = s.ProxyDial(ctx, "tcp", s.Server)
+	} else {
+		var dd net.Dialer
+		conn, err = dd.DialContext(ctx, "tcp", s.Server)
+	}
+
+	if err != nil {
+		return nil, &net.OpError{Op: "socks", Net: "tcp", Source: proxy, Addr: addr, Err: err}
+	}
+
+	if deadline, ok := ctx.Deadline(); ok && !deadline.IsZero() {
+		conn.SetDeadline(deadline)
+		defer conn.SetDeadline(noDeadline)
+	}
+
+	var ctxErr error
+	if ctx != context.Background() {
+		errCh := make(chan error, 1)
+		doneCh := make(chan struct{})
+
+		defer func() {
+			close(doneCh)
+			if ctxErr == nil {
+				ctxErr = <-errCh
+			}
+		}()
+
+		go func() {
+			select {
+			case <-ctx.Done():
+				conn.SetDeadline(expiredDeadline)
+				errCh <- ctx.Err()
+			case <-doneCh:
+				errCh <- nil
+			}
+		}()
+	}
+
+	if err := s.negotiate(conn); err != nil {
+		conn.Close()
+		return nil, &net.OpError{Op: "socks", Net: "tcp", Source: proxy, Addr: addr, Err: err}
+	}
+
+	if network == "udp" || network == "udp4" || network == "udp6" {
+		uc, err := s.handleUDP(conn, addr)
+		if err != nil {
+			conn.Close()
+			return nil, &net.OpError{Op: "socks", Net: "udp", Source: proxy, Addr: addr, Err: err}
+		}
+
+		return uc, ctxErr
+	}
+
+	if err := s.handleTCP(conn, addr); err != nil {
+		conn.Close()
+		return nil, &net.OpError{Op: "socks", Net: "tcp", Source: proxy, Addr: addr, Err: err}
+	}
+
+	return conn, ctxErr
+}
+
+func (s *Dialer) DialUDP() (net.PacketConn, error) {
+	conn, err := s.DialContext(context.Background(), "udp", "")
+	return conn.(net.PacketConn), err
+}
+
+func (s *Dialer) handleTCP(conn net.Conn, addr *Addr) error {
+	atyp, host, port := addr.Socks()
+
+	req := NewRequest(CommandConnect, atyp, host, port)
+	if _, err := req.WriteTo(conn); err != nil {
+		return err
+	}
+
+	rep, err := NewReplyFrom(conn)
+	if err != nil {
+		return err
+	}
+
+	if rep.Status != ReplyStatusSuccess {
+		return fmt.Errorf("bad reply status: %s", rep.Status)
+	}
+
+	return nil
+}
+
+func (s *Dialer) handleUDP(conn net.Conn, addr *Addr) (*UDPConn, error) {
+	atyp, host, port := addr.Socks()
+
+	req := NewRequest(CommandUDPAssociate, atyp, host, port)
+	if _, err := req.WriteTo(conn); err != nil {
+		return nil, err
+	}
+
+	rep, err := NewReplyFrom(conn)
+	if err != nil {
+		return nil, err
+	}
+
+	if rep.Status != ReplyStatusSuccess {
+		return nil, fmt.Errorf("bad reply status: %s", rep.Status)
+	}
+
+	packetConn, err := net.ListenPacket("udp", "")
+	if err != nil {
+		return nil, err
+	}
+
+	go func() {
+		io.Copy(io.Discard, conn)
+		conn.Close()
+		packetConn.Close()
+	}()
+
+	remoteAddr, err := AddrFromSocks(rep.ATYP, rep.BindAddr, rep.BindPort).UDP()
+	if err != nil {
+		return nil, err
+	}
+
+	if remoteAddr.IP.IsUnspecified() {
+		serverAddr, err := net.ResolveUDPAddr("udp", s.Server)
+		if err != nil {
+			return nil, fmt.Errorf("resolve udp address %s: %w", s.Server, err)
+		}
+
+		remoteAddr.IP = serverAddr.IP
+	}
+
+	udpConn := &UDPConn{
+		PacketConn: packetConn,
+		TCPConn:    conn,
+		ServerAddr: remoteAddr,
+	}
+
+	if addr != AddrZero {
+		connectedAddr, err := addr.UDP()
+		if err != nil {
+			return nil, err
+		}
+
+		udpConn.ConnectedAddr = connectedAddr
+	}
+
+	return udpConn, nil
+}
+
+func (s *Dialer) negotiate(conn net.Conn) error {
+	method := AuthMethodNone
+	if s.Username != "" && s.Password != "" {
+		method = AuthMethodPassword
+	}
+
+	negReq := NewNegotiationRequest([]AuthMethod{method})
+	if _, err := negReq.WriteTo(conn); err != nil {
+		return err
+	}
+
+	negRep, err := NewNegotiationReplyFrom(conn)
+	if err != nil {
+		return err
+	}
+
+	if negRep.Method != method {
+		return ErrAuthMethodNotSupported
+	}
+
+	if negRep.Method == AuthMethodPassword {
+		passReq := NewPasswordNegotiationRequest(s.Username, s.Password)
+		if _, err := passReq.WriteTo(conn); err != nil {
+			return err
+		}
+
+		passRep, err := NewPasswordNegotiationReplyFrom(conn)
+		if err != nil {
+			return err
+		}
+
+		if passRep.Status != PasswordStatusSuccess {
+			return ErrPasswordAuth
+		}
+	}
+
+	return nil
+}
diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..885137a
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,3 @@
+module go.pkg.cx/socks5
+
+go 1.16
diff --git a/negotiation.go b/negotiation.go
new file mode 100644
index 0000000..3271227
--- /dev/null
+++ b/negotiation.go
@@ -0,0 +1,108 @@
+package socks5
+
+import (
+	"io"
+)
+
+// NegotiationRequest is the negotiation request packet
+type NegotiationRequest struct {
+	NMethods int
+	Methods  []AuthMethod
+}
+
+// NewNegotiationRequest returns new negotiation request packet
+func NewNegotiationRequest(methods []AuthMethod) *NegotiationRequest {
+	return &NegotiationRequest{
+		NMethods: len(methods),
+		Methods:  methods,
+	}
+}
+
+// NewNegotiationRequestFrom reads negotiation request packet from reader
+func NewNegotiationRequestFrom(r io.Reader) (*NegotiationRequest, error) {
+	buf := make([]byte, 2)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+
+	if buf[0] != Version {
+		return nil, ErrVersion
+	}
+
+	methodsLen := int(buf[1])
+	if methodsLen == 0 {
+		return nil, ErrBadRequest
+	}
+
+	methodsBytes := make([]byte, methodsLen)
+	if _, err := io.ReadFull(r, methodsBytes); err != nil {
+		return nil, err
+	}
+
+	methods := make([]AuthMethod, methodsLen)
+	for i := range methodsBytes {
+		methods[i] = AuthMethod(methodsBytes[i])
+	}
+
+	req := &NegotiationRequest{
+		NMethods: methodsLen,
+		Methods:  methods,
+	}
+
+	return req, nil
+}
+
+// WriteTo writes negotiation request packet
+func (s *NegotiationRequest) WriteTo(w io.Writer) (int64, error) {
+	buf := []byte{Version, byte(s.NMethods)}
+	for i := range s.Methods {
+		buf = append(buf, byte(s.Methods[i]))
+	}
+
+	n, err := w.Write(buf)
+	if err != nil {
+		return int64(n), err
+	}
+
+	return int64(n), nil
+}
+
+// NegotiationReply is the negotiation reply packet
+type NegotiationReply struct {
+	Method AuthMethod
+}
+
+// NewNegotiationReply returns new negotiation reply packet
+func NewNegotiationReply(method AuthMethod) *NegotiationReply {
+	return &NegotiationReply{
+		Method: method,
+	}
+}
+
+// NewNegotiationReplyFrom reads negotiation reply packet from reader
+func NewNegotiationReplyFrom(r io.Reader) (*NegotiationReply, error) {
+	buf := make([]byte, 2)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+
+	if buf[0] != Version {
+		return nil, ErrVersion
+	}
+
+	rep := &NegotiationReply{
+		Method: AuthMethod(buf[1]),
+	}
+
+	return rep, nil
+}
+
+// WriteTo writes negotiation reply packet
+func (s *NegotiationReply) WriteTo(w io.Writer) (int64, error) {
+	n, err := w.Write([]byte{Version, byte(s.Method)})
+	if err != nil {
+		return int64(n), err
+	}
+
+	return int64(n), nil
+}
diff --git a/password_negotiation.go b/password_negotiation.go
new file mode 100644
index 0000000..fcce119
--- /dev/null
+++ b/password_negotiation.go
@@ -0,0 +1,114 @@
+package socks5
+
+import (
+	"io"
+)
+
+// PasswordNegotiationRequest is the password negotiation reqeust packet
+type PasswordNegotiationRequest struct {
+	UsernameLen byte
+	Username    string
+	PasswordLen byte
+	Password    string
+}
+
+// NewPasswordNegotiationRequest returns new password negotiation request packet
+func NewPasswordNegotiationRequest(username string, password string) *PasswordNegotiationRequest {
+	return &PasswordNegotiationRequest{
+		UsernameLen: byte(len(username)),
+		Username:    username,
+		PasswordLen: byte(len(password)),
+		Password:    password,
+	}
+}
+
+// NewPasswordNegotiationRequestFrom reads password negotiation request packet from reader
+func NewPasswordNegotiationRequestFrom(r io.Reader) (*PasswordNegotiationRequest, error) {
+	buf := make([]byte, 2)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+
+	if buf[0] != PasswordVersion {
+		return nil, ErrPasswordAuthVersion
+	}
+
+	if buf[1] == 0 {
+		return nil, ErrBadRequest
+	}
+
+	usernameBuf := make([]byte, int(buf[1])+1)
+	if _, err := io.ReadFull(r, usernameBuf); err != nil {
+		return nil, err
+	}
+
+	var passwordBuf []byte
+	if usernameBuf[int(buf[1])] != 0 {
+		passwordBuf = make([]byte, int(usernameBuf[int(buf[1])]))
+		if _, err := io.ReadFull(r, passwordBuf); err != nil {
+			return nil, err
+		}
+	}
+
+	return &PasswordNegotiationRequest{
+		UsernameLen: buf[1],
+		Username:    string(usernameBuf[:int(buf[1])]),
+		PasswordLen: usernameBuf[int(buf[1])],
+		Password:    string(passwordBuf),
+	}, nil
+}
+
+// WriteTo writes password negotiation request packet
+func (s *PasswordNegotiationRequest) WriteTo(w io.Writer) (int64, error) {
+	buf := []byte{PasswordVersion, s.UsernameLen}
+	buf = append(buf, []byte(s.Username)...)
+	buf = append(buf, s.PasswordLen)
+	buf = append(buf, []byte(s.Password)...)
+
+	n, err := w.Write(buf)
+	if err != nil {
+		return int64(n), err
+	}
+
+	return int64(n), nil
+}
+
+// PasswordNegotiationReply is the password negotiation reply packet
+type PasswordNegotiationReply struct {
+	Status PasswordStatus
+}
+
+// NewPasswordNegotiationReply returns password negotiation reply packet
+func NewPasswordNegotiationReply(status PasswordStatus) *PasswordNegotiationReply {
+	return &PasswordNegotiationReply{
+		Status: status,
+	}
+}
+
+// NewPasswordNegotiationReplyFrom reads password negotiation reply packet from reader
+func NewPasswordNegotiationReplyFrom(r io.Reader) (*PasswordNegotiationReply, error) {
+	buf := make([]byte, 2)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+
+	if buf[0] != PasswordVersion {
+		return nil, ErrPasswordAuthVersion
+	}
+
+	rep := &PasswordNegotiationReply{
+		Status: PasswordStatus(buf[1]),
+	}
+
+	return rep, nil
+}
+
+// WriteTo writes password negotiation reply packet
+func (s *PasswordNegotiationReply) WriteTo(w io.Writer) (int64, error) {
+	n, err := w.Write([]byte{PasswordVersion, byte(s.Status)})
+	if err != nil {
+		return int64(n), err
+	}
+
+	return int64(n), nil
+}
diff --git a/reply.go b/reply.go
new file mode 100644
index 0000000..088f6c1
--- /dev/null
+++ b/reply.go
@@ -0,0 +1,68 @@
+package socks5
+
+import (
+	"io"
+)
+
+// Reply is the reply packet
+type Reply struct {
+	Status   ReplyStatus
+	ATYP     ATYP
+	BindAddr []byte
+	BindPort []byte
+}
+
+// NewReply returns new reply packet
+func NewReply(status ReplyStatus, atyp ATYP, host []byte, port []byte) *Reply {
+	return &Reply{
+		Status:   status,
+		ATYP:     atyp,
+		BindAddr: host,
+		BindPort: port,
+	}
+}
+
+// NewReplyFrom reads reply packet from reader
+func NewReplyFrom(r io.Reader) (*Reply, error) {
+	buf := make([]byte, 4)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+
+	if buf[0] != Version {
+		return nil, ErrVersion
+	}
+
+	addr, err := ReadAddress(r, ATYP(buf[3]))
+	if err != nil {
+		return nil, err
+	}
+
+	port := make([]byte, 2)
+	if _, err := io.ReadFull(r, port); err != nil {
+		return nil, err
+	}
+
+	rep := &Reply{
+		Status:   ReplyStatus(buf[1]),
+		ATYP:     ATYP(buf[3]),
+		BindAddr: addr,
+		BindPort: port,
+	}
+
+	return rep, nil
+}
+
+// WriteTo writes reply packet
+func (s *Reply) WriteTo(w io.Writer) (int64, error) {
+	buf := []byte{Version, byte(s.Status), Reserved, byte(s.ATYP)}
+	buf = append(buf, s.BindAddr...)
+	buf = append(buf, s.BindPort...)
+
+	n, err := w.Write(buf)
+	if err != nil {
+		return int64(n), err
+	}
+
+	return int64(n), nil
+}
diff --git a/request.go b/request.go
new file mode 100644
index 0000000..3bcdd2d
--- /dev/null
+++ b/request.go
@@ -0,0 +1,68 @@
+package socks5
+
+import (
+	"io"
+)
+
+// Request is the request packet
+type Request struct {
+	Command Command
+	ATYP    ATYP
+	DstAddr []byte
+	DstPort []byte
+}
+
+// NewRequest returns new request packet
+func NewRequest(command Command, atyp ATYP, host []byte, port []byte) *Request {
+	return &Request{
+		Command: command,
+		ATYP:    atyp,
+		DstAddr: host,
+		DstPort: port,
+	}
+}
+
+// NewRequestFrom reads request packet from client
+func NewRequestFrom(r io.Reader) (*Request, error) {
+	buf := make([]byte, 4)
+	if _, err := io.ReadFull(r, buf); err != nil {
+		return nil, err
+	}
+
+	if buf[0] != Version {
+		return nil, ErrVersion
+	}
+
+	addr, err := ReadAddress(r, ATYP(buf[3]))
+	if err != nil {
+		return nil, err
+	}
+
+	port := make([]byte, 2)
+	if _, err := io.ReadFull(r, port); err != nil {
+		return nil, err
+	}
+
+	req := &Request{
+		Command: Command(buf[1]),
+		ATYP:    ATYP(buf[3]),
+		DstAddr: addr,
+		DstPort: port,
+	}
+
+	return req, nil
+}
+
+// WriteTo writes request packet
+func (s *Request) WriteTo(w io.Writer) (int64, error) {
+	buf := []byte{Version, byte(s.Command), Reserved, byte(s.ATYP)}
+	buf = append(buf, s.DstAddr...)
+	buf = append(buf, s.DstPort...)
+
+	n, err := w.Write(buf)
+	if err != nil {
+		return int64(n), err
+	}
+
+	return int64(n), nil
+}
diff --git a/socks5.go b/socks5.go
new file mode 100644
index 0000000..7c03c1f
--- /dev/null
+++ b/socks5.go
@@ -0,0 +1,151 @@
+package socks5
+
+import (
+	"errors"
+)
+
+const (
+	// Version is the protocol version
+	Version byte = 0x05
+	// Reserved is the reserved field value
+	Reserved byte = 0x00
+	// PasswordVersion is the username/password auth protocol version
+	PasswordVersion byte = 0x01
+	// DatagramStandalone is the standalone datagram fragment field value
+	DatagramStandalone byte = 0x00
+)
+
+// AuthMethod is the auth method
+type AuthMethod byte
+
+// Auth methods
+const (
+	AuthMethodNone         AuthMethod = 0x00
+	AuthMethodGSSAPI       AuthMethod = 0x01
+	AuthMethodPassword     AuthMethod = 0x02
+	AuthMethodNotSupported AuthMethod = 0xFF
+)
+
+func (am AuthMethod) String() string {
+	return authMethodNames[am]
+}
+
+var authMethodNames = map[AuthMethod]string{
+	AuthMethodNone:         "none",
+	AuthMethodGSSAPI:       "gssapi",
+	AuthMethodPassword:     "password",
+	AuthMethodNotSupported: "not supported",
+}
+
+// PasswordStatus is the password auth status
+type PasswordStatus byte
+
+// Password statuses
+const (
+	PasswordStatusSuccess PasswordStatus = 0x00
+	PasswordStatusFailure PasswordStatus = 0x01
+)
+
+func (ps PasswordStatus) String() string {
+	return passwordStatusNames[ps]
+}
+
+var passwordStatusNames = map[PasswordStatus]string{
+	PasswordStatusSuccess: "success",
+	PasswordStatusFailure: "failure",
+}
+
+// Command is the command
+type Command byte
+
+// Commands
+const (
+	CommandConnect      Command = 0x01
+	CommandBind         Command = 0x02
+	CommandUDPAssociate Command = 0x03
+)
+
+func (c Command) String() string {
+	return commandNames[c]
+}
+
+var commandNames = map[Command]string{
+	CommandConnect:      "connect",
+	CommandBind:         "bind",
+	CommandUDPAssociate: "udp associate",
+}
+
+// ATYP is the address type
+type ATYP byte
+
+// Address types
+const (
+	ATYPIPv4 ATYP = 0x01
+	ATYPFQDN ATYP = 0x03
+	ATYPIPv6 ATYP = 0x04
+)
+
+func (a ATYP) String() string {
+	return atypNames[a]
+}
+
+var atypNames = map[ATYP]string{
+	ATYPIPv4: "ipv4",
+	ATYPFQDN: "fqdn",
+	ATYPIPv6: "ipv6",
+}
+
+// ReplyStatus is the reply status
+type ReplyStatus byte
+
+// Reply statuses
+const (
+	ReplyStatusSuccess             ReplyStatus = 0x00
+	ReplyStatusServerFailure       ReplyStatus = 0x01
+	ReplyStatusNotAllowed          ReplyStatus = 0x02
+	ReplyStatusNetworkUnreachable  ReplyStatus = 0x03
+	ReplyStatusHostUnreachable     ReplyStatus = 0x04
+	ReplyStatusConnectionRefused   ReplyStatus = 0x05
+	ReplyStatusTTLExpired          ReplyStatus = 0x06
+	ReplyStatusCommandNotSupported ReplyStatus = 0x07
+	ReplyStatusAddressNotSupported ReplyStatus = 0x08
+)
+
+func (rs ReplyStatus) String() string {
+	return replyStatusNames[rs]
+}
+
+var replyStatusNames = map[ReplyStatus]string{
+	ReplyStatusSuccess:             "success",
+	ReplyStatusServerFailure:       "server failure",
+	ReplyStatusNotAllowed:          "not allowed",
+	ReplyStatusNetworkUnreachable:  "network unreachable",
+	ReplyStatusHostUnreachable:     "host unreachable",
+	ReplyStatusConnectionRefused:   "connection refused",
+	ReplyStatusTTLExpired:          "TTL expired",
+	ReplyStatusCommandNotSupported: "command not supported",
+	ReplyStatusAddressNotSupported: "address not supported",
+}
+
+var (
+	// ErrVersion is the protocol version error
+	ErrVersion = errors.New("invalid protocol version")
+	// ErrBadReply is the bad reply error
+	ErrBadReply = errors.New("bad reply")
+	// ErrBadRequest is the bad request error
+	ErrBadRequest = errors.New("bad request")
+	// ErrBadDatagram is the bad datagram error
+	ErrBadDatagram = errors.New("bad datagram")
+	// ErrFragmentedDatagram us the fragmented datagram error
+	ErrFragmentedDatagram = errors.New("fragmented datagram")
+	// ErrIPAuth is the invalid ip error
+	ErrIPAuth = errors.New("invalid ip auth")
+	// ErrPasswordAuth is the invalid username or password error
+	ErrPasswordAuth = errors.New("invalid username or password")
+	// ErrAuthMethodNotSupported is the error when auth method not supported
+	ErrAuthMethodNotSupported = errors.New("auth method not supported")
+	// ErrCommandNotSupported is the error when command not supported
+	ErrCommandNotSupported = errors.New("command not supported")
+	// ErrPasswordAuthVersion is the password auth version error
+	ErrPasswordAuthVersion = errors.New("invalid password auth version")
+)
diff --git a/udp.go b/udp.go
new file mode 100644
index 0000000..f5fe64b
--- /dev/null
+++ b/udp.go
@@ -0,0 +1,68 @@
+package socks5
+
+import (
+	"bytes"
+	"errors"
+	"net"
+)
+
+var (
+	// ErrNoConnectedAddress is the no connected address error
+	ErrNoConnectedAddress = errors.New("no connected address")
+)
+
+type UDPConn struct {
+	net.PacketConn
+
+	TCPConn       net.Conn
+	ServerAddr    net.Addr
+	ConnectedAddr net.Addr
+}
+
+func (s *UDPConn) ReadFrom(b []byte) (int, net.Addr, error) {
+	_, _, err := s.PacketConn.ReadFrom(b)
+	if err != nil {
+		return 0, nil, err
+	}
+
+	datagram, err := NewDatagramFrom(bytes.NewReader(b))
+	if err != nil {
+		return 0, nil, err
+	}
+
+	n := copy(b, datagram.Data)
+	return n, AddrFromSocks(datagram.ATYP, datagram.DstAddr, datagram.DstPort), nil
+}
+
+func (s *UDPConn) Read(b []byte) (int, error) {
+	n, _, err := s.ReadFrom(b)
+	return n, err
+}
+
+func (s *UDPConn) WriteTo(b []byte, addr net.Addr) (int, error) {
+	socksAddr, err := AddrFromString(addr.String())
+	if err != nil {
+		return 0, err
+	}
+
+	atyp, host, port := socksAddr.Socks()
+	datagram := NewDatagram(atyp, host, port, b)
+	return s.PacketConn.WriteTo(datagram.Bytes(), s.ServerAddr)
+}
+
+func (s *UDPConn) Write(b []byte) (int, error) {
+	if s.ConnectedAddr == nil {
+		return 0, ErrNoConnectedAddress
+	}
+
+	return s.WriteTo(b, s.ConnectedAddr)
+}
+
+func (s *UDPConn) Close() error {
+	s.TCPConn.Close()
+	return s.PacketConn.Close()
+}
+
+func (s *UDPConn) RemoteAddr() net.Addr {
+	return s.ConnectedAddr
+}
diff --git a/util.go b/util.go
new file mode 100644
index 0000000..6b4565b
--- /dev/null
+++ b/util.go
@@ -0,0 +1,92 @@
+package socks5
+
+import (
+	"encoding/binary"
+	"io"
+	"net"
+	"strconv"
+)
+
+// NewEmptyAddrReply returns reply with empty address and port
+func NewEmptyAddrReply(status ReplyStatus, atyp ATYP) *Reply {
+	if atyp == ATYPIPv6 {
+		return NewReply(status, ATYPIPv6, []byte(net.IPv6zero), []byte{0x00, 0x00})
+	}
+
+	return NewReply(status, ATYPIPv4, []byte{0x00, 0x00, 0x00, 0x00}, []byte{0x00, 0x00})
+}
+
+// ReadAddress reads address from reader
+func ReadAddress(r io.Reader, atyp ATYP) ([]byte, error) {
+	var addr []byte
+
+	//nolint:exhaustive
+	switch atyp {
+	case ATYPIPv4:
+		addr = make([]byte, 4)
+		if _, err := io.ReadFull(r, addr); err != nil {
+			return nil, err
+		}
+	case ATYPIPv6:
+		addr = make([]byte, 16)
+		if _, err := io.ReadFull(r, addr); err != nil {
+			return nil, err
+		}
+	case ATYPFQDN:
+		domainLen := make([]byte, 1)
+		if _, err := io.ReadFull(r, domainLen); err != nil {
+			return nil, err
+		}
+
+		if domainLen[0] == 0 {
+			return nil, ErrBadRequest
+		}
+
+		addr = make([]byte, int(domainLen[0]))
+		if _, err := io.ReadFull(r, addr); err != nil {
+			return nil, err
+		}
+
+		addr = append(domainLen, addr...) //nolint:makezero
+	default:
+		return nil, ErrBadRequest
+	}
+
+	return addr, nil
+}
+
+// ParseAddress parses address from string
+func ParseAddress(address string) (ATYP, []byte, []byte, error) {
+	host, port, err := net.SplitHostPort(address)
+	if err != nil {
+		return 0x00, []byte{}, []byte{}, err
+	}
+
+	var (
+		atyp ATYP
+		addr []byte
+	)
+
+	ip := net.ParseIP(host)
+	if ip4 := ip.To4(); ip4 != nil {
+		atyp = ATYPIPv4
+		addr = []byte(ip4)
+	} else if ip6 := ip.To16(); ip6 != nil {
+		atyp = ATYPIPv6
+		addr = []byte(ip6)
+	} else {
+		atyp = ATYPFQDN
+		addr = []byte{byte(len(host))}
+		addr = append(addr, []byte(host)...)
+	}
+
+	portInt, err := strconv.Atoi(port)
+	if err != nil {
+		return 0x00, []byte{}, []byte{}, err
+	}
+
+	portBytes := make([]byte, 2)
+	binary.BigEndian.PutUint16(portBytes, uint16(portInt))
+
+	return atyp, addr, portBytes, nil
+}