// socks5 client:
// https://github.com/golang/net/tree/master/proxy
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// socks5 server:
// https://github.com/shadowsocks/go-shadowsocks2/tree/master/socks

package main

import (
	"errors"
	"io"
	"net"
	"strconv"
)

const socks5Version = 5

const (
	socks5AuthNone     = 0
	socks5AuthPassword = 2
)

// SOCKS request commands as defined in RFC 1928 section 4.
const (
	socks5Connect      = 1
	socks5Bind         = 2
	socks5UDPAssociate = 3
)

// SOCKS address types as defined in RFC 1928 section 5.
const (
	socks5IP4    = 1
	socks5Domain = 3
	socks5IP6    = 4
)

// MaxAddrLen is the maximum size of SOCKS address in bytes.
const MaxAddrLen = 1 + 1 + 255 + 2

// Addr represents a SOCKS address as defined in RFC 1928 section 5.
type Addr []byte

var socks5Errors = []string{
	"",
	"general failure",
	"connection forbidden",
	"network unreachable",
	"host unreachable",
	"connection refused",
	"TTL expired",
	"command not supported",
	"address type not supported",
}

// SOCKS5Proxy .
type SOCKS5Proxy struct {
	*proxy
	network  string
	user     string
	password string
}

// NewSOCKS5Proxy returns a Proxy that makes SOCKSv5 connections to the given address
// with an optional username and password. See RFC 1928.
func NewSOCKS5Proxy(network, addr, user, pass string, upProxy Proxy) (*SOCKS5Proxy, error) {
	s := &SOCKS5Proxy{
		proxy:    NewProxy(addr, upProxy),
		user:     user,
		password: pass,
	}

	return s, nil
}

// ListenAndServe connects to the address addr on the network net via the SOCKS5 proxy.
func (s *SOCKS5Proxy) ListenAndServe() {
	l, err := net.Listen("tcp", s.addr)
	if err != nil {
		logf("failed to listen on %s: %v", s.addr, err)
		return
	}

	logf("listening TCP on %s", s.addr)

	for {
		c, err := l.Accept()
		if err != nil {
			logf("failed to accept: %v", err)
			continue
		}

		go s.Serve(c)
	}
}

// Serve .
func (s *SOCKS5Proxy) Serve(c net.Conn) {
	defer c.Close()

	if c, ok := c.(*net.TCPConn); ok {
		c.SetKeepAlive(true)
	}

	tgt, err := s.handshake(c)
	if err != nil {
		logf("failed to get target address: %v", err)
		return
	}

	rc, err := s.GetProxy(tgt.String()).Dial("tcp", tgt.String())
	if err != nil {
		logf("failed to connect to target: %v", err)
		return
	}
	defer rc.Close()

	logf("proxy-socks5 %s <-> %s", c.RemoteAddr(), tgt)

	_, _, err = relay(c, rc)
	if err != nil {
		if err, ok := err.(net.Error); ok && err.Timeout() {
			return // ignore i/o timeout
		}
		logf("relay error: %v", err)
	}
}

// Dial connects to the address addr on the network net via the SOCKS5 proxy.
func (s *SOCKS5Proxy) Dial(network, addr string) (net.Conn, error) {
	switch network {
	case "tcp", "tcp6", "tcp4":
	default:
		return nil, errors.New("proxy: no support for SOCKS5 proxy connections of type " + network)
	}

	c, err := s.GetProxy(s.addr).Dial(s.network, s.addr)
	if err != nil {
		logf("dial to %s error: %s", s.addr, err)
		return nil, err
	}

	if c, ok := c.(*net.TCPConn); ok {
		c.SetKeepAlive(true)
	}

	if err := s.connect(c, addr); err != nil {
		c.Close()
		return nil, err
	}

	return c, nil
}

// connect takes an existing connection to a socks5 proxy server,
// and commands the server to extend that connection to target,
// which must be a canonical address with a host and port.
func (s *SOCKS5Proxy) connect(conn net.Conn, target string) error {
	host, portStr, err := net.SplitHostPort(target)
	if err != nil {
		return err
	}

	port, err := strconv.Atoi(portStr)
	if err != nil {
		return errors.New("proxy: failed to parse port number: " + portStr)
	}
	if port < 1 || port > 0xffff {
		return errors.New("proxy: port number out of range: " + portStr)
	}

	// the size here is just an estimate
	buf := make([]byte, 0, 6+len(host))

	buf = append(buf, socks5Version)
	if len(s.user) > 0 && len(s.user) < 256 && len(s.password) < 256 {
		buf = append(buf, 2 /* num auth methods */, socks5AuthNone, socks5AuthPassword)
	} else {
		buf = append(buf, 1 /* num auth methods */, socks5AuthNone)
	}

	if _, err := conn.Write(buf); err != nil {
		return errors.New("proxy: failed to write greeting to SOCKS5 proxy at " + s.addr + ": " + err.Error())
	}

	if _, err := io.ReadFull(conn, buf[:2]); err != nil {
		return errors.New("proxy: failed to read greeting from SOCKS5 proxy at " + s.addr + ": " + err.Error())
	}
	if buf[0] != 5 {
		return errors.New("proxy: SOCKS5 proxy at " + s.addr + " has unexpected version " + strconv.Itoa(int(buf[0])))
	}
	if buf[1] == 0xff {
		return errors.New("proxy: SOCKS5 proxy at " + s.addr + " requires authentication")
	}

	if buf[1] == socks5AuthPassword {
		buf = buf[:0]
		buf = append(buf, 1 /* password protocol version */)
		buf = append(buf, uint8(len(s.user)))
		buf = append(buf, s.user...)
		buf = append(buf, uint8(len(s.password)))
		buf = append(buf, s.password...)

		if _, err := conn.Write(buf); err != nil {
			return errors.New("proxy: failed to write authentication request to SOCKS5 proxy at " + s.addr + ": " + err.Error())
		}

		if _, err := io.ReadFull(conn, buf[:2]); err != nil {
			return errors.New("proxy: failed to read authentication reply from SOCKS5 proxy at " + s.addr + ": " + err.Error())
		}

		if buf[1] != 0 {
			return errors.New("proxy: SOCKS5 proxy at " + s.addr + " rejected username/password")
		}
	}

	buf = buf[:0]
	buf = append(buf, socks5Version, socks5Connect, 0 /* reserved */)

	if ip := net.ParseIP(host); ip != nil {
		if ip4 := ip.To4(); ip4 != nil {
			buf = append(buf, socks5IP4)
			ip = ip4
		} else {
			buf = append(buf, socks5IP6)
		}
		buf = append(buf, ip...)
	} else {
		if len(host) > 255 {
			return errors.New("proxy: destination hostname too long: " + host)
		}
		buf = append(buf, socks5Domain)
		buf = append(buf, byte(len(host)))
		buf = append(buf, host...)
	}
	buf = append(buf, byte(port>>8), byte(port))

	if _, err := conn.Write(buf); err != nil {
		return errors.New("proxy: failed to write connect request to SOCKS5 proxy at " + s.addr + ": " + err.Error())
	}

	if _, err := io.ReadFull(conn, buf[:4]); err != nil {
		return errors.New("proxy: failed to read connect reply from SOCKS5 proxy at " + s.addr + ": " + err.Error())
	}

	failure := "unknown error"
	if int(buf[1]) < len(socks5Errors) {
		failure = socks5Errors[buf[1]]
	}

	if len(failure) > 0 {
		return errors.New("proxy: SOCKS5 proxy at " + s.addr + " failed to connect: " + failure)
	}

	bytesToDiscard := 0
	switch buf[3] {
	case socks5IP4:
		bytesToDiscard = net.IPv4len
	case socks5IP6:
		bytesToDiscard = net.IPv6len
	case socks5Domain:
		_, err := io.ReadFull(conn, buf[:1])
		if err != nil {
			return errors.New("proxy: failed to read domain length from SOCKS5 proxy at " + s.addr + ": " + err.Error())
		}
		bytesToDiscard = int(buf[0])
	default:
		return errors.New("proxy: got unknown address type " + strconv.Itoa(int(buf[3])) + " from SOCKS5 proxy at " + s.addr)
	}

	if cap(buf) < bytesToDiscard {
		buf = make([]byte, bytesToDiscard)
	} else {
		buf = buf[:bytesToDiscard]
	}
	if _, err := io.ReadFull(conn, buf); err != nil {
		return errors.New("proxy: failed to read address from SOCKS5 proxy at " + s.addr + ": " + err.Error())
	}

	// Also need to discard the port number
	if _, err := io.ReadFull(conn, buf[:2]); err != nil {
		return errors.New("proxy: failed to read port from SOCKS5 proxy at " + s.addr + ": " + err.Error())
	}

	return nil
}

// Handshake fast-tracks SOCKS initialization to get target address to connect.
func (s *SOCKS5Proxy) handshake(rw io.ReadWriter) (Addr, error) {
	// Read RFC 1928 for request and reply structure and sizes.
	buf := make([]byte, MaxAddrLen)
	// read VER, NMETHODS, METHODS
	if _, err := io.ReadFull(rw, buf[:2]); err != nil {
		return nil, err
	}
	nmethods := buf[1]
	if _, err := io.ReadFull(rw, buf[:nmethods]); err != nil {
		return nil, err
	}
	// write VER METHOD
	if _, err := rw.Write([]byte{5, 0}); err != nil {
		return nil, err
	}
	// read VER CMD RSV ATYP DST.ADDR DST.PORT
	if _, err := io.ReadFull(rw, buf[:3]); err != nil {
		return nil, err
	}
	if buf[1] != socks5Connect {
		return nil, errors.New(socks5Errors[7])
	}
	addr, err := readAddr(rw, buf)
	if err != nil {
		return nil, err
	}
	// write VER REP RSV ATYP BND.ADDR BND.PORT
	_, err = rw.Write([]byte{5, 0, 0, 1, 0, 0, 0, 0, 0, 0})
	return addr, err
}

// String serializes SOCKS address a to string form.
func (a Addr) String() string {
	var host, port string

	switch a[0] { // address type
	case socks5Domain:
		host = string(a[2 : 2+int(a[1])])
		port = strconv.Itoa((int(a[2+int(a[1])]) << 8) | int(a[2+int(a[1])+1]))
	case socks5IP4:
		host = net.IP(a[1 : 1+net.IPv4len]).String()
		port = strconv.Itoa((int(a[1+net.IPv4len]) << 8) | int(a[1+net.IPv4len+1]))
	case socks5IP6:
		host = net.IP(a[1 : 1+net.IPv6len]).String()
		port = strconv.Itoa((int(a[1+net.IPv6len]) << 8) | int(a[1+net.IPv6len+1]))
	}

	return net.JoinHostPort(host, port)
}

func readAddr(r io.Reader, b []byte) (Addr, error) {
	if len(b) < MaxAddrLen {
		return nil, io.ErrShortBuffer
	}
	_, err := io.ReadFull(r, b[:1]) // read 1st byte for address type
	if err != nil {
		return nil, err
	}

	switch b[0] {
	case socks5Domain:
		_, err = io.ReadFull(r, b[1:2]) // read 2nd byte for domain length
		if err != nil {
			return nil, err
		}
		_, err = io.ReadFull(r, b[2:2+int(b[1])+2])
		return b[:1+1+int(b[1])+2], err
	case socks5IP4:
		_, err = io.ReadFull(r, b[1:1+net.IPv4len+2])
		return b[:1+net.IPv4len+2], err
	case socks5IP6:
		_, err = io.ReadFull(r, b[1:1+net.IPv6len+2])
		return b[:1+net.IPv6len+2], err
	}

	return nil, errors.New(socks5Errors[8])
}

// ReadAddr reads just enough bytes from r to get a valid Addr.
func ReadAddr(r io.Reader) (Addr, error) {
	return readAddr(r, make([]byte, MaxAddrLen))
}

// SplitAddr slices a SOCKS address from beginning of b. Returns nil if failed.
func SplitAddr(b []byte) Addr {
	addrLen := 1
	if len(b) < addrLen {
		return nil
	}

	switch b[0] {
	case socks5Domain:
		if len(b) < 2 {
			return nil
		}
		addrLen = 1 + 1 + int(b[1]) + 2
	case socks5IP4:
		addrLen = 1 + net.IPv4len + 2
	case socks5IP6:
		addrLen = 1 + net.IPv6len + 2
	default:
		return nil

	}

	if len(b) < addrLen {
		return nil
	}

	return b[:addrLen]
}

// ParseAddr parses the address in string s. Returns nil if failed.
func ParseAddr(s string) Addr {
	var addr Addr
	host, port, err := net.SplitHostPort(s)
	if err != nil {
		return nil
	}
	if ip := net.ParseIP(host); ip != nil {
		if ip4 := ip.To4(); ip4 != nil {
			addr = make([]byte, 1+net.IPv4len+2)
			addr[0] = socks5IP4
			copy(addr[1:], ip4)
		} else {
			addr = make([]byte, 1+net.IPv6len+2)
			addr[0] = socks5IP6
			copy(addr[1:], ip)
		}
	} else {
		if len(host) > 255 {
			return nil
		}
		addr = make([]byte, 1+1+len(host)+2)
		addr[0] = socks5Domain
		addr[1] = byte(len(host))
		copy(addr[2:], host)
	}

	portnum, err := strconv.ParseUint(port, 10, 16)
	if err != nil {
		return nil
	}

	addr[len(addr)-2], addr[len(addr)-1] = byte(portnum>>8), byte(portnum)

	return addr
}