path: root/contrib/libs/curl/lib/socks.c

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2020, Daniel Stenberg, <daniel@haxx.se>, et al. 
 *
 * This software is licensed as described in the file COPYING, which
 * you should have received as part of this distribution. The terms
 * are also available at https://curl.se/docs/copyright.html. 
 *
 * You may opt to use, copy, modify, merge, publish, distribute and/or sell
 * copies of the Software, and permit persons to whom the Software is
 * furnished to do so, under the terms of the COPYING file.
 *
 * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
 * KIND, either express or implied.
 *
 ***************************************************************************/

#include "curl_setup.h"

#if !defined(CURL_DISABLE_PROXY)

#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#ifdef HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif

#include "urldata.h"
#include "sendf.h"
#include "select.h"
#include "connect.h"
#include "timeval.h"
#include "socks.h"
#include "multiif.h" /* for getsock macros */ 

/* The last 3 #include files should be in this order */ 
#include "curl_printf.h" 
#include "curl_memory.h" 
#include "memdebug.h"

#if defined(HAVE_GSSAPI) || defined(USE_WINDOWS_SSPI) 
/*
 * Helper read-from-socket functions. Does the same as Curl_read() but it
 * blocks until all bytes amount of buffersize will be read. No more, no less.
 *
 * This is STUPID BLOCKING behavior. Only used by the SOCKS GSSAPI functions. 
 */
int Curl_blockread_all(struct connectdata *conn, /* connection data */
                       curl_socket_t sockfd,     /* read from this socket */
                       char *buf,                /* store read data here */
                       ssize_t buffersize,       /* max amount to read */
                       ssize_t *n)               /* amount bytes read */
{
  ssize_t nread = 0;
  ssize_t allread = 0;
  int result;
  *n = 0;
  for(;;) {
    timediff_t timeout_ms = Curl_timeleft(conn->data, NULL, TRUE); 
    if(timeout_ms < 0) { 
      /* we already got the timeout */
      result = CURLE_OPERATION_TIMEDOUT;
      break;
    }
    if(!timeout_ms) 
      timeout_ms = TIMEDIFF_T_MAX; 
    if(SOCKET_READABLE(sockfd, timeout_ms) <= 0) { 
      result = ~CURLE_OK;
      break;
    }
    result = Curl_read_plain(sockfd, buf, buffersize, &nread);
    if(CURLE_AGAIN == result)
      continue;
    if(result)
      break;

    if(buffersize == nread) {
      allread += nread;
      *n = allread;
      result = CURLE_OK;
      break;
    }
    if(!nread) {
      result = ~CURLE_OK;
      break;
    }

    buffersize -= nread;
    buf += nread;
    allread += nread;
  }
  return result;
}
#endif 

#ifndef DEBUGBUILD 
#define sxstate(x,y) socksstate(x,y) 
#else 
#define sxstate(x,y) socksstate(x,y, __LINE__) 
#endif 
 
 
/* always use this function to change state, to make debugging easier */ 
static void socksstate(struct connectdata *conn, 
                       enum connect_t state 
#ifdef DEBUGBUILD 
                       , int lineno 
#endif 
) 
{ 
  enum connect_t oldstate = conn->cnnct.state; 
#if defined(DEBUGBUILD) && !defined(CURL_DISABLE_VERBOSE_STRINGS) 
  /* synced with the state list in urldata.h */ 
  static const char * const statename[] = { 
    "INIT", 
    "SOCKS_INIT", 
    "SOCKS_SEND", 
    "SOCKS_READ_INIT", 
    "SOCKS_READ", 
    "GSSAPI_INIT", 
    "AUTH_INIT", 
    "AUTH_SEND", 
    "AUTH_READ", 
    "REQ_INIT", 
    "RESOLVING", 
    "RESOLVED", 
    "RESOLVE_REMOTE", 
    "REQ_SEND", 
    "REQ_SENDING", 
    "REQ_READ", 
    "REQ_READ_MORE", 
    "DONE" 
  }; 
#endif 
 
  if(oldstate == state) 
    /* don't bother when the new state is the same as the old state */ 
    return; 
 
  conn->cnnct.state = state; 
 
#if defined(DEBUGBUILD) && !defined(CURL_DISABLE_VERBOSE_STRINGS) 
  infof(conn->data, 
        "SXSTATE: %s => %s conn %p; line %d\n", 
        statename[oldstate], statename[conn->cnnct.state], conn, 
        lineno); 
#endif 
} 
 
int Curl_SOCKS_getsock(struct connectdata *conn, curl_socket_t *sock, 
                       int sockindex) 
{ 
  int rc = 0; 
  sock[0] = conn->sock[sockindex]; 
  switch(conn->cnnct.state) { 
  case CONNECT_RESOLVING: 
  case CONNECT_SOCKS_READ: 
  case CONNECT_AUTH_READ: 
  case CONNECT_REQ_READ: 
  case CONNECT_REQ_READ_MORE: 
    rc = GETSOCK_READSOCK(0); 
    break; 
  default: 
    rc = GETSOCK_WRITESOCK(0); 
    break; 
  } 
  return rc; 
} 
 
/*
* This function logs in to a SOCKS4 proxy and sends the specifics to the final
* destination server.
*
* Reference :
*   https://www.openssh.com/txt/socks4.protocol
*
* Note :
*   Set protocol4a=true for  "SOCKS 4A (Simple Extension to SOCKS 4 Protocol)"
*   Nonsupport "Identification Protocol (RFC1413)"
*/
CURLproxycode Curl_SOCKS4(const char *proxy_user, 
                          const char *hostname, 
                          int remote_port, 
                          int sockindex, 
                          struct connectdata *conn, 
                          bool *done) 
{
  const bool protocol4a =
    (conn->socks_proxy.proxytype == CURLPROXY_SOCKS4A) ? TRUE : FALSE;
  unsigned char *socksreq = &conn->cnnct.socksreq[0]; 
  CURLcode result; 
  curl_socket_t sockfd = conn->sock[sockindex]; 
  struct Curl_easy *data = conn->data;
  struct connstate *sx = &conn->cnnct; 
  struct Curl_dns_entry *dns = NULL; 
  ssize_t actualread; 
  ssize_t written; 

  if(!SOCKS_STATE(sx->state) && !*done) 
    sxstate(conn, CONNECT_SOCKS_INIT); 

  switch(sx->state) { 
  case CONNECT_SOCKS_INIT: 
    /* SOCKS4 can only do IPv4, insist! */ 
    conn->ip_version = CURL_IPRESOLVE_V4; 
    if(conn->bits.httpproxy) 
      infof(conn->data, "SOCKS4%s: connecting to HTTP proxy %s port %d\n", 
            protocol4a ? "a" : "", hostname, remote_port); 

    infof(data, "SOCKS4 communication to %s:%d\n", hostname, remote_port); 

    /* 
     * Compose socks4 request 
     * 
     * Request format 
     * 
     *     +----+----+----+----+----+----+----+----+----+----+....+----+ 
     *     | VN | CD | DSTPORT |      DSTIP        | USERID       |NULL| 
     *     +----+----+----+----+----+----+----+----+----+----+....+----+ 
     * # of bytes:  1    1      2              4           variable       1 
     */ 

    socksreq[0] = 4; /* version (SOCKS4) */ 
    socksreq[1] = 1; /* connect */ 
    socksreq[2] = (unsigned char)((remote_port >> 8) & 0xff); /* PORT MSB */ 
    socksreq[3] = (unsigned char)(remote_port & 0xff);        /* PORT LSB */ 

    /* DNS resolve only for SOCKS4, not SOCKS4a */ 
    if(!protocol4a) { 
      enum resolve_t rc = 
        Curl_resolv(conn, hostname, remote_port, FALSE, &dns); 

      if(rc == CURLRESOLV_ERROR) 
        return CURLPX_RESOLVE_HOST; 
      else if(rc == CURLRESOLV_PENDING) { 
        sxstate(conn, CONNECT_RESOLVING); 
        infof(data, "SOCKS4 non-blocking resolve of %s\n", hostname); 
        return CURLPX_OK; 
      } 
      sxstate(conn, CONNECT_RESOLVED); 
      goto CONNECT_RESOLVED; 
    } 

    /* socks4a doesn't resolve anything locally */ 
    sxstate(conn, CONNECT_REQ_INIT); 
    goto CONNECT_REQ_INIT; 

  case CONNECT_RESOLVING: 
    /* check if we have the name resolved by now */ 
    dns = Curl_fetch_addr(conn, hostname, (int)conn->port); 

    if(dns) { 
#ifdef CURLRES_ASYNCH 
      conn->async.dns = dns; 
      conn->async.done = TRUE; 
#endif 
      infof(data, "Hostname '%s' was found\n", hostname); 
      sxstate(conn, CONNECT_RESOLVED); 
    } 
    else { 
      result = Curl_resolv_check(data->conn, &dns); 
      if(!dns) { 
        if(result) 
          return CURLPX_RESOLVE_HOST; 
        return CURLPX_OK; 
      } 
    } 
    /* FALLTHROUGH */ 
  CONNECT_RESOLVED: 
  case CONNECT_RESOLVED: { 
    struct Curl_addrinfo *hp = NULL; 
    char buf[64]; 
    /*
     * We cannot use 'hostent' as a struct that Curl_resolv() returns.  It
     * returns a Curl_addrinfo pointer that may not always look the same.
     */
    if(dns)
      hp = dns->addr;
    if(hp) {
      Curl_printable_address(hp, buf, sizeof(buf));

      if(hp->ai_family == AF_INET) {
        struct sockaddr_in *saddr_in;

        saddr_in = (struct sockaddr_in *)(void *)hp->ai_addr;
        socksreq[4] = ((unsigned char *)&saddr_in->sin_addr.s_addr)[0];
        socksreq[5] = ((unsigned char *)&saddr_in->sin_addr.s_addr)[1];
        socksreq[6] = ((unsigned char *)&saddr_in->sin_addr.s_addr)[2];
        socksreq[7] = ((unsigned char *)&saddr_in->sin_addr.s_addr)[3];

        infof(data, "SOCKS4 connect to IPv4 %s (locally resolved)\n", buf);
      }
      else {
        hp = NULL; /* fail! */
        failf(data, "SOCKS4 connection to %s not supported\n", buf);
      }

      Curl_resolv_unlock(data, dns); /* not used anymore from now on */
    }
    if(!hp) {
      failf(data, "Failed to resolve \"%s\" for SOCKS4 connect.",
            hostname);
      return CURLPX_RESOLVE_HOST; 
    }
  }
    /* FALLTHROUGH */ 
  CONNECT_REQ_INIT: 
  case CONNECT_REQ_INIT: 
    /* 
     * This is currently not supporting "Identification Protocol (RFC1413)". 
     */ 
    socksreq[8] = 0; /* ensure empty userid is NUL-terminated */ 
    if(proxy_user) { 
      size_t plen = strlen(proxy_user); 
      if(plen >= sizeof(sx->socksreq) - 8) { 
        failf(data, "Too long SOCKS proxy user name, can't use!\n"); 
        return CURLPX_LONG_USER; 
      } 
      /* copy the proxy name WITH trailing zero */ 
      memcpy(socksreq + 8, proxy_user, plen + 1); 
    }

    /* 
     * Make connection 
     */ 
    { 
      size_t packetsize = 9 + 
        strlen((char *)socksreq + 8); /* size including NUL */ 

      /* If SOCKS4a, set special invalid IP address 0.0.0.x */ 
      if(protocol4a) { 
        size_t hostnamelen = 0; 
        socksreq[4] = 0; 
        socksreq[5] = 0; 
        socksreq[6] = 0; 
        socksreq[7] = 1; 
        /* append hostname */ 
        hostnamelen = strlen(hostname) + 1; /* length including NUL */ 
        if(hostnamelen <= 255) 
          strcpy((char *)socksreq + packetsize, hostname); 
        else { 
          failf(data, "SOCKS4: too long host name"); 
          return CURLPX_LONG_HOSTNAME; 
        } 
        packetsize += hostnamelen; 
      } 
      sx->outp = socksreq; 
      sx->outstanding = packetsize; 
      sxstate(conn, CONNECT_REQ_SENDING); 
    }
    /* FALLTHROUGH */ 
  case CONNECT_REQ_SENDING: 
    /* Send request */
    result = Curl_write_plain(conn, sockfd, (char *)sx->outp, 
                              sx->outstanding, &written); 
    if(result && (CURLE_AGAIN != result)) { 
      failf(data, "Failed to send SOCKS4 connect request.");
      return CURLPX_SEND_CONNECT; 
    }
    if(written != sx->outstanding) { 
      /* not done, remain in state */ 
      sx->outstanding -= written; 
      sx->outp += written; 
      return CURLPX_OK; 
    }

    /* done sending! */ 
    sx->outstanding = 8; /* receive data size */ 
    sx->outp = socksreq; 
    sxstate(conn, CONNECT_SOCKS_READ); 

    /* FALLTHROUGH */ 
  case CONNECT_SOCKS_READ: 
    /* Receive response */
    result = Curl_read_plain(sockfd, (char *)sx->outp, 
                             sx->outstanding, &actualread); 
    if(result && (CURLE_AGAIN != result)) { 
      failf(data, "SOCKS4: Failed receiving connect request ack: %s", 
            curl_easy_strerror(result)); 
      return CURLPX_RECV_CONNECT; 
    }
    else if(!result && !actualread) { 
      /* connection closed */ 
      failf(data, "connection to proxy closed"); 
      return CURLPX_CLOSED; 
    } 
    else if(actualread != sx->outstanding) { 
      /* remain in reading state */ 
      sx->outstanding -= actualread; 
      sx->outp += actualread; 
      return CURLPX_OK; 
    } 
    sxstate(conn, CONNECT_DONE); 
    break; 
  default: /* lots of unused states in SOCKS4 */ 
    break; 
  } 

  /* 
   * Response format 
   * 
   *     +----+----+----+----+----+----+----+----+ 
   *     | VN | CD | DSTPORT |      DSTIP        | 
   *     +----+----+----+----+----+----+----+----+ 
   * # of bytes:  1    1      2              4 
   * 
   * VN is the version of the reply code and should be 0. CD is the result 
   * code with one of the following values: 
   * 
   * 90: request granted 
   * 91: request rejected or failed 
   * 92: request rejected because SOCKS server cannot connect to 
   *     identd on the client 
   * 93: request rejected because the client program and identd 
   *     report different user-ids 
   */ 

  /* wrong version ? */ 
  if(socksreq[0] != 0) { 
    failf(data, 
          "SOCKS4 reply has wrong version, version should be 0."); 
    return CURLPX_BAD_VERSION; 
  } 

  /* Result */ 
  switch(socksreq[1]) { 
  case 90: 
    infof(data, "SOCKS4%s request granted.\n", protocol4a?"a":""); 
    break; 
  case 91: 
    failf(data, 
          "Can't complete SOCKS4 connection to %d.%d.%d.%d:%d. (%d)" 
          ", request rejected or failed.", 
          (unsigned char)socksreq[4], (unsigned char)socksreq[5], 
          (unsigned char)socksreq[6], (unsigned char)socksreq[7], 
          (((unsigned char)socksreq[2] << 8) | (unsigned char)socksreq[3]), 
          (unsigned char)socksreq[1]); 
    return CURLPX_REQUEST_FAILED; 
  case 92: 
    failf(data, 
          "Can't complete SOCKS4 connection to %d.%d.%d.%d:%d. (%d)" 
          ", request rejected because SOCKS server cannot connect to " 
          "identd on the client.", 
          (unsigned char)socksreq[4], (unsigned char)socksreq[5], 
          (unsigned char)socksreq[6], (unsigned char)socksreq[7], 
          (((unsigned char)socksreq[2] << 8) | (unsigned char)socksreq[3]), 
          (unsigned char)socksreq[1]); 
    return CURLPX_IDENTD; 
  case 93: 
    failf(data, 
          "Can't complete SOCKS4 connection to %d.%d.%d.%d:%d. (%d)" 
          ", request rejected because the client program and identd " 
          "report different user-ids.", 
          (unsigned char)socksreq[4], (unsigned char)socksreq[5], 
          (unsigned char)socksreq[6], (unsigned char)socksreq[7], 
          (((unsigned char)socksreq[2] << 8) | (unsigned char)socksreq[3]), 
          (unsigned char)socksreq[1]); 
    return CURLPX_IDENTD_DIFFER; 
  default: 
    failf(data, 
          "Can't complete SOCKS4 connection to %d.%d.%d.%d:%d. (%d)" 
          ", Unknown.", 
          (unsigned char)socksreq[4], (unsigned char)socksreq[5], 
          (unsigned char)socksreq[6], (unsigned char)socksreq[7], 
          (((unsigned char)socksreq[2] << 8) | (unsigned char)socksreq[3]), 
          (unsigned char)socksreq[1]); 
    return CURLPX_UNKNOWN_FAIL; 
  }

  *done = TRUE; 
  return CURLPX_OK; /* Proxy was successful! */ 
}

/*
 * This function logs in to a SOCKS5 proxy and sends the specifics to the final
 * destination server.
 */
CURLproxycode Curl_SOCKS5(const char *proxy_user, 
                          const char *proxy_password, 
                          const char *hostname, 
                          int remote_port, 
                          int sockindex, 
                          struct connectdata *conn, 
                          bool *done) 
{
  /*
    According to the RFC1928, section "6.  Replies". This is what a SOCK5
    replies:

        +----+-----+-------+------+----------+----------+
        |VER | REP |  RSV  | ATYP | BND.ADDR | BND.PORT |
        +----+-----+-------+------+----------+----------+
        | 1  |  1  | X'00' |  1   | Variable |    2     |
        +----+-----+-------+------+----------+----------+

    Where:

    o  VER    protocol version: X'05'
    o  REP    Reply field:
    o  X'00' succeeded
  */
  unsigned char *socksreq = &conn->cnnct.socksreq[0]; 
  char dest[256] = "unknown";  /* printable hostname:port */ 
  int idx;
  ssize_t actualread;
  ssize_t written;
  CURLcode result; 
  curl_socket_t sockfd = conn->sock[sockindex]; 
  struct Curl_easy *data = conn->data;
  bool socks5_resolve_local =
    (conn->socks_proxy.proxytype == CURLPROXY_SOCKS5) ? TRUE : FALSE;
  const size_t hostname_len = strlen(hostname);
  ssize_t len = 0;
  const unsigned long auth = data->set.socks5auth;
  bool allow_gssapi = FALSE;
  struct connstate *sx = &conn->cnnct; 
  struct Curl_dns_entry *dns = NULL; 

  if(!SOCKS_STATE(sx->state) && !*done) 
    sxstate(conn, CONNECT_SOCKS_INIT); 

  switch(sx->state) { 
  case CONNECT_SOCKS_INIT: 
    if(conn->bits.httpproxy) 
      infof(conn->data, "SOCKS5: connecting to HTTP proxy %s port %d\n", 
            hostname, remote_port); 

    /* RFC1928 chapter 5 specifies max 255 chars for domain name in packet */ 
    if(!socks5_resolve_local && hostname_len > 255) { 
      infof(conn->data, "SOCKS5: server resolving disabled for hostnames of " 
            "length > 255 [actual len=%zu]\n", hostname_len); 
      socks5_resolve_local = TRUE; 
    } 

    if(auth & ~(CURLAUTH_BASIC | CURLAUTH_GSSAPI)) 
      infof(conn->data, 
            "warning: unsupported value passed to CURLOPT_SOCKS5_AUTH: %lu\n", 
            auth); 
    if(!(auth & CURLAUTH_BASIC)) 
      /* disable username/password auth */ 
      proxy_user = NULL; 
#if defined(HAVE_GSSAPI) || defined(USE_WINDOWS_SSPI)
    if(auth & CURLAUTH_GSSAPI) 
      allow_gssapi = TRUE; 
#endif

    idx = 0; 
    socksreq[idx++] = 5;   /* version */ 
    idx++;                 /* number of authentication methods */ 
    socksreq[idx++] = 0;   /* no authentication */ 
    if(allow_gssapi) 
      socksreq[idx++] = 1; /* GSS-API */ 
    if(proxy_user) 
      socksreq[idx++] = 2; /* username/password */ 
    /* write the number of authentication methods */ 
    socksreq[1] = (unsigned char) (idx - 2); 

    result = Curl_write_plain(conn, sockfd, (char *)socksreq, idx, &written); 
    if(result && (CURLE_AGAIN != result)) { 
      failf(data, "Unable to send initial SOCKS5 request."); 
      return CURLPX_SEND_CONNECT; 
    } 
    if(written != idx) { 
      sxstate(conn, CONNECT_SOCKS_SEND); 
      sx->outstanding = idx - written; 
      sx->outp = &socksreq[written]; 
      return CURLPX_OK; 
    } 
    sxstate(conn, CONNECT_SOCKS_READ); 
    goto CONNECT_SOCKS_READ_INIT; 
  case CONNECT_SOCKS_SEND: 
    result = Curl_write_plain(conn, sockfd, (char *)sx->outp, 
                              sx->outstanding, &written); 
    if(result && (CURLE_AGAIN != result)) { 
      failf(data, "Unable to send initial SOCKS5 request."); 
      return CURLPX_SEND_CONNECT; 
    } 
    if(written != sx->outstanding) { 
      /* not done, remain in state */ 
      sx->outstanding -= written; 
      sx->outp += written; 
      return CURLPX_OK; 
    } 
    /* FALLTHROUGH */ 
  CONNECT_SOCKS_READ_INIT: 
  case CONNECT_SOCKS_READ_INIT: 
    sx->outstanding = 2; /* expect two bytes */ 
    sx->outp = socksreq; /* store it here */ 
    /* FALLTHROUGH */ 
  case CONNECT_SOCKS_READ: 
    result = Curl_read_plain(sockfd, (char *)sx->outp, 
                             sx->outstanding, &actualread); 
    if(result && (CURLE_AGAIN != result)) { 
      failf(data, "Unable to receive initial SOCKS5 response."); 
      return CURLPX_RECV_CONNECT; 
    } 
    else if(!result && !actualread) { 
      /* connection closed */ 
      failf(data, "Connection to proxy closed"); 
      return CURLPX_CLOSED; 
    } 
    else if(actualread != sx->outstanding) { 
      /* remain in reading state */ 
      sx->outstanding -= actualread; 
      sx->outp += actualread; 
      return CURLPX_OK; 
    } 
    else if(socksreq[0] != 5) { 
      failf(data, "Received invalid version in initial SOCKS5 response."); 
      return CURLPX_BAD_VERSION; 
    } 
    else if(socksreq[1] == 0) { 
      /* DONE! No authentication needed. Send request. */ 
      sxstate(conn, CONNECT_REQ_INIT); 
      goto CONNECT_REQ_INIT; 
    } 
    else if(socksreq[1] == 2) { 
      /* regular name + password authentication */ 
      sxstate(conn, CONNECT_AUTH_INIT); 
      goto CONNECT_AUTH_INIT; 
    } 
#if defined(HAVE_GSSAPI) || defined(USE_WINDOWS_SSPI)
    else if(allow_gssapi && (socksreq[1] == 1)) { 
      sxstate(conn, CONNECT_GSSAPI_INIT); 
      result = Curl_SOCKS5_gssapi_negotiate(sockindex, conn); 
      if(result) { 
        failf(data, "Unable to negotiate SOCKS5 GSS-API context."); 
        return CURLPX_GSSAPI; 
      } 
    }
#endif
    else { 
      /* error */ 
      if(!allow_gssapi && (socksreq[1] == 1)) { 
        failf(data, 
              "SOCKS5 GSSAPI per-message authentication is not supported."); 
        return CURLPX_GSSAPI_PERMSG; 
      } 
      else if(socksreq[1] == 255) { 
        failf(data, "No authentication method was acceptable."); 
        return CURLPX_NO_AUTH; 
      } 
    } 
    failf(data, 
          "Undocumented SOCKS5 mode attempted to be used by server."); 
    return CURLPX_UNKNOWN_MODE; 
#if defined(HAVE_GSSAPI) || defined(USE_WINDOWS_SSPI) 
  case CONNECT_GSSAPI_INIT: 
    /* GSSAPI stuff done non-blocking */ 
    break; 
#endif 
 
  default: /* do nothing! */ 
    break; 
 
  CONNECT_AUTH_INIT: 
  case CONNECT_AUTH_INIT: { 
    /* Needs user name and password */
    size_t proxy_user_len, proxy_password_len;
    if(proxy_user && proxy_password) {
      proxy_user_len = strlen(proxy_user);
      proxy_password_len = strlen(proxy_password);
    }
    else {
      proxy_user_len = 0;
      proxy_password_len = 0;
    }

    /*   username/password request looks like
     * +----+------+----------+------+----------+
     * |VER | ULEN |  UNAME   | PLEN |  PASSWD  |
     * +----+------+----------+------+----------+
     * | 1  |  1   | 1 to 255 |  1   | 1 to 255 |
     * +----+------+----------+------+----------+
     */
    len = 0;
    socksreq[len++] = 1;    /* username/pw subnegotiation version */
    socksreq[len++] = (unsigned char) proxy_user_len;
    if(proxy_user && proxy_user_len) {
      /* the length must fit in a single byte */
      if(proxy_user_len >= 255) {
        failf(data, "Excessive user name length for proxy auth");
        return CURLPX_LONG_USER; 
      }
      memcpy(socksreq + len, proxy_user, proxy_user_len);
    }
    len += proxy_user_len;
    socksreq[len++] = (unsigned char) proxy_password_len;
    if(proxy_password && proxy_password_len) {
      /* the length must fit in a single byte */
      if(proxy_password_len > 255) {
        failf(data, "Excessive password length for proxy auth");
        return CURLPX_LONG_PASSWD; 
      }
      memcpy(socksreq + len, proxy_password, proxy_password_len);
    }
    len += proxy_password_len;
    sxstate(conn, CONNECT_AUTH_SEND); 
    sx->outstanding = len; 
    sx->outp = socksreq; 
  } 
    /* FALLTHROUGH */ 
  case CONNECT_AUTH_SEND: 
    result = Curl_write_plain(conn, sockfd, (char *)sx->outp, 
                              sx->outstanding, &written); 
    if(result && (CURLE_AGAIN != result)) { 
      failf(data, "Failed to send SOCKS5 sub-negotiation request.");
      return CURLPX_SEND_AUTH; 
    }
    if(sx->outstanding != written) { 
      /* remain in state */ 
      sx->outstanding -= written; 
      sx->outp += written; 
      return CURLPX_OK; 
    } 
    sx->outp = socksreq; 
    sx->outstanding = 2; 
    sxstate(conn, CONNECT_AUTH_READ); 
    /* FALLTHROUGH */ 
  case CONNECT_AUTH_READ: 
    result = Curl_read_plain(sockfd, (char *)sx->outp, 
                             sx->outstanding, &actualread); 
    if(result && (CURLE_AGAIN != result)) { 
      failf(data, "Unable to receive SOCKS5 sub-negotiation response.");
      return CURLPX_RECV_AUTH; 
    }
    else if(!result && !actualread) { 
      /* connection closed */ 
      failf(data, "connection to proxy closed"); 
      return CURLPX_CLOSED; 
    } 
    else if(actualread != sx->outstanding) { 
      /* remain in state */ 
      sx->outstanding -= actualread; 
      sx->outp += actualread; 
      return CURLPX_OK; 
    } 
    /* ignore the first (VER) byte */
    else if(socksreq[1] != 0) { /* status */ 
      failf(data, "User was rejected by the SOCKS5 server (%d %d).",
            socksreq[0], socksreq[1]);
      return CURLPX_USER_REJECTED; 
    }

    /* Everything is good so far, user was authenticated! */
    sxstate(conn, CONNECT_REQ_INIT); 
    /* FALLTHROUGH */ 
  CONNECT_REQ_INIT: 
  case CONNECT_REQ_INIT: 
    if(socks5_resolve_local) { 
      enum resolve_t rc = Curl_resolv(conn, hostname, remote_port, 
                                      FALSE, &dns); 
 
      if(rc == CURLRESOLV_ERROR) 
        return CURLPX_RESOLVE_HOST; 
 
      if(rc == CURLRESOLV_PENDING) { 
        sxstate(conn, CONNECT_RESOLVING); 
        return CURLPX_OK; 
      }
      sxstate(conn, CONNECT_RESOLVED); 
      goto CONNECT_RESOLVED; 
    }
    goto CONNECT_RESOLVE_REMOTE; 

  case CONNECT_RESOLVING: 
    /* check if we have the name resolved by now */ 
    dns = Curl_fetch_addr(conn, hostname, remote_port); 

    if(dns) { 
#ifdef CURLRES_ASYNCH 
      conn->async.dns = dns; 
      conn->async.done = TRUE; 
#endif 
      infof(data, "SOCKS5: hostname '%s' found\n", hostname); 
    } 

    if(!dns) { 
      result = Curl_resolv_check(data->conn, &dns); 
      if(!dns) { 
        if(result) 
          return CURLPX_RESOLVE_HOST; 
        return CURLPX_OK; 
      } 
    }
    /* FALLTHROUGH */ 
  CONNECT_RESOLVED: 
  case CONNECT_RESOLVED: { 
    struct Curl_addrinfo *hp = NULL; 
    size_t destlen; 
    if(dns)
      hp = dns->addr;
    if(!hp) { 
      failf(data, "Failed to resolve \"%s\" for SOCKS5 connect.", 
            hostname); 
      return CURLPX_RESOLVE_HOST; 
    } 

    Curl_printable_address(hp, dest, sizeof(dest)); 
    destlen = strlen(dest); 
    msnprintf(dest + destlen, sizeof(dest) - destlen, ":%d", remote_port); 

    len = 0; 
    socksreq[len++] = 5; /* version (SOCKS5) */ 
    socksreq[len++] = 1; /* connect */ 
    socksreq[len++] = 0; /* must be zero */ 
    if(hp->ai_family == AF_INET) { 
      int i; 
      struct sockaddr_in *saddr_in; 
      socksreq[len++] = 1; /* ATYP: IPv4 = 1 */ 

      saddr_in = (struct sockaddr_in *)(void *)hp->ai_addr; 
      for(i = 0; i < 4; i++) { 
        socksreq[len++] = ((unsigned char *)&saddr_in->sin_addr.s_addr)[i]; 
      }
 
      infof(data, "SOCKS5 connect to IPv4 %s (locally resolved)\n", dest); 
    } 
#ifdef ENABLE_IPV6
    else if(hp->ai_family == AF_INET6) { 
      int i; 
      struct sockaddr_in6 *saddr_in6; 
      socksreq[len++] = 4; /* ATYP: IPv6 = 4 */ 

      saddr_in6 = (struct sockaddr_in6 *)(void *)hp->ai_addr; 
      for(i = 0; i < 16; i++) { 
        socksreq[len++] = 
          ((unsigned char *)&saddr_in6->sin6_addr.s6_addr)[i]; 
      }

      infof(data, "SOCKS5 connect to IPv6 %s (locally resolved)\n", dest); 
    }
#endif 
    else { 
      hp = NULL; /* fail! */ 
      failf(data, "SOCKS5 connection to %s not supported\n", dest); 
    }

    Curl_resolv_unlock(data, dns); /* not used anymore from now on */ 
    goto CONNECT_REQ_SEND; 
  }
  CONNECT_RESOLVE_REMOTE: 
  case CONNECT_RESOLVE_REMOTE: 
    /* Authentication is complete, now specify destination to the proxy */ 
    len = 0; 
    socksreq[len++] = 5; /* version (SOCKS5) */ 
    socksreq[len++] = 1; /* connect */ 
    socksreq[len++] = 0; /* must be zero */ 

    if(!socks5_resolve_local) { 
      socksreq[len++] = 3; /* ATYP: domain name = 3 */ 
      socksreq[len++] = (char) hostname_len; /* one byte address length */ 
      memcpy(&socksreq[len], hostname, hostname_len); /* address w/o NULL */ 
      len += hostname_len; 
      infof(data, "SOCKS5 connect to %s:%d (remotely resolved)\n", 
            hostname, remote_port); 
    } 
    /* FALLTHROUGH */ 

  CONNECT_REQ_SEND: 
  case CONNECT_REQ_SEND: 
    /* PORT MSB */ 
    socksreq[len++] = (unsigned char)((remote_port >> 8) & 0xff); 
    /* PORT LSB */ 
    socksreq[len++] = (unsigned char)(remote_port & 0xff); 

#if defined(HAVE_GSSAPI) || defined(USE_WINDOWS_SSPI)
    if(conn->socks5_gssapi_enctype) { 
      failf(data, "SOCKS5 GSS-API protection not yet implemented."); 
      return CURLPX_GSSAPI_PROTECTION; 
    } 
#endif
    sx->outp = socksreq; 
    sx->outstanding = len; 
    sxstate(conn, CONNECT_REQ_SENDING); 
    /* FALLTHROUGH */ 
  case CONNECT_REQ_SENDING: 
    result = Curl_write_plain(conn, sockfd, (char *)sx->outp, 
                              sx->outstanding, &written); 
    if(result && (CURLE_AGAIN != result)) { 
      failf(data, "Failed to send SOCKS5 connect request."); 
      return CURLPX_SEND_REQUEST; 
    } 
    if(sx->outstanding != written) { 
      /* remain in state */ 
      sx->outstanding -= written; 
      sx->outp += written; 
      return CURLPX_OK; 
    } 
#if defined(HAVE_GSSAPI) || defined(USE_WINDOWS_SSPI) 
    if(conn->socks5_gssapi_enctype) { 
      failf(data, "SOCKS5 GSS-API protection not yet implemented."); 
      return CURLPX_GSSAPI_PROTECTION; 
    } 
#endif 
    sx->outstanding = 10; /* minimum packet size is 10 */ 
    sx->outp = socksreq; 
    sxstate(conn, CONNECT_REQ_READ); 
    /* FALLTHROUGH */ 
  case CONNECT_REQ_READ: 
    result = Curl_read_plain(sockfd, (char *)sx->outp, 
                             sx->outstanding, &actualread); 
    if(result && (CURLE_AGAIN != result)) { 
      failf(data, "Failed to receive SOCKS5 connect request ack."); 
      return CURLPX_RECV_REQACK; 
    } 
    else if(!result && !actualread) { 
      /* connection closed */ 
      failf(data, "connection to proxy closed"); 
      return CURLPX_CLOSED; 
    } 
    else if(actualread != sx->outstanding) { 
      /* remain in state */ 
      sx->outstanding -= actualread; 
      sx->outp += actualread; 
      return CURLPX_OK; 
    } 

    if(socksreq[0] != 5) { /* version */ 
      failf(data, 
            "SOCKS5 reply has wrong version, version should be 5."); 
      return CURLPX_BAD_VERSION; 
    } 
    else if(socksreq[1] != 0) { /* Anything besides 0 is an error */ 
      CURLproxycode rc = CURLPX_REPLY_UNASSIGNED; 
      int code = socksreq[1]; 
      failf(data, "Can't complete SOCKS5 connection to %s. (%d)", 
            hostname, (unsigned char)socksreq[1]); 
      if(code < 9) { 
        /* RFC 1928 section 6 lists: */ 
        static const CURLproxycode lookup[] = { 
          CURLPX_OK, 
          CURLPX_REPLY_GENERAL_SERVER_FAILURE, 
          CURLPX_REPLY_NOT_ALLOWED, 
          CURLPX_REPLY_NETWORK_UNREACHABLE, 
          CURLPX_REPLY_HOST_UNREACHABLE, 
          CURLPX_REPLY_CONNECTION_REFUSED, 
          CURLPX_REPLY_TTL_EXPIRED, 
          CURLPX_REPLY_COMMAND_NOT_SUPPORTED, 
          CURLPX_REPLY_ADDRESS_TYPE_NOT_SUPPORTED, 
        }; 
        rc = lookup[code]; 
      } 
      return rc; 
    } 

    /* Fix: in general, returned BND.ADDR is variable length parameter by RFC 
       1928, so the reply packet should be read until the end to avoid errors 
       at subsequent protocol level. 

       +----+-----+-------+------+----------+----------+ 
       |VER | REP |  RSV  | ATYP | BND.ADDR | BND.PORT | 
       +----+-----+-------+------+----------+----------+ 
       | 1  |  1  | X'00' |  1   | Variable |    2     | 
       +----+-----+-------+------+----------+----------+ 

       ATYP: 
       o  IP v4 address: X'01', BND.ADDR = 4 byte 
       o  domain name:  X'03', BND.ADDR = [ 1 byte length, string ] 
       o  IP v6 address: X'04', BND.ADDR = 16 byte 
    */ 

    /* Calculate real packet size */ 
    if(socksreq[3] == 3) { 
      /* domain name */ 
      int addrlen = (int) socksreq[4]; 
      len = 5 + addrlen + 2; 
    } 
    else if(socksreq[3] == 4) { 
      /* IPv6 */ 
      len = 4 + 16 + 2; 
    } 
    else if(socksreq[3] == 1) { 
      len = 4 + 4 + 2; 
    } 
    else { 
      failf(data, "SOCKS5 reply has wrong address type."); 
      return CURLPX_BAD_ADDRESS_TYPE; 
    } 

    /* At this point we already read first 10 bytes */ 
#if defined(HAVE_GSSAPI) || defined(USE_WINDOWS_SSPI)
    if(!conn->socks5_gssapi_enctype) { 
      /* decrypt_gssapi_blockread already read the whole packet */ 
#endif
      if(len > 10) { 
        sx->outstanding = len - 10; /* get the rest */ 
        sx->outp = &socksreq[10]; 
        sxstate(conn, CONNECT_REQ_READ_MORE); 
      }
      else { 
        sxstate(conn, CONNECT_DONE); 
        break; 
      } 
#if defined(HAVE_GSSAPI) || defined(USE_WINDOWS_SSPI) 
    }
#endif
    /* FALLTHROUGH */ 
  case CONNECT_REQ_READ_MORE: 
    result = Curl_read_plain(sockfd, (char *)sx->outp, 
                             sx->outstanding, &actualread); 
    if(result && (CURLE_AGAIN != result)) { 
      failf(data, "Failed to receive SOCKS5 connect request ack."); 
      return CURLPX_RECV_ADDRESS; 
    }
    else if(!result && !actualread) { 
      /* connection closed */ 
      failf(data, "connection to proxy closed"); 
      return CURLPX_CLOSED; 
    }
    else if(actualread != sx->outstanding) { 
      /* remain in state */ 
      sx->outstanding -= actualread; 
      sx->outp += actualread; 
      return CURLPX_OK; 
    }
    sxstate(conn, CONNECT_DONE); 
  }
  infof(data, "SOCKS5 request granted.\n");

  *done = TRUE; 
  return CURLPX_OK; /* Proxy was successful! */ 
}

#endif /* CURL_DISABLE_PROXY */