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proxy.c

/*
 * Network proxy abstraction in PuTTY
 *
 * A proxy layer, if necessary, wedges itself between the network
 * code and the higher level backend.
 */

#include <assert.h>
#include <ctype.h>
#include <string.h>

#define DEFINE_PLUG_METHOD_MACROS
#include "putty.h"
#include "network.h"
#include "proxy.h"

#define do_proxy_dns(cfg) \
    (cfg->proxy_dns == FORCE_ON || \
       (cfg->proxy_dns == AUTO && \
              cfg->proxy_type != PROXY_SOCKS4 && \
              cfg->proxy_type != PROXY_SOCKS5))

/*
 * Call this when proxy negotiation is complete, so that this
 * socket can begin working normally.
 */
void proxy_activate (Proxy_Socket p)
{
    void *data;
    int len;
    long output_before, output_after;
    
    p->state = PROXY_STATE_ACTIVE;

    /* we want to ignore new receive events until we have sent
     * all of our buffered receive data.
     */
    sk_set_frozen(p->sub_socket, 1);

    /* how many bytes of output have we buffered? */
    output_before = bufchain_size(&p->pending_oob_output_data) +
      bufchain_size(&p->pending_output_data);
    /* and keep track of how many bytes do not get sent. */
    output_after = 0;
    
    /* send buffered OOB writes */
    while (bufchain_size(&p->pending_oob_output_data) > 0) {
      bufchain_prefix(&p->pending_oob_output_data, &data, &len);
      output_after += sk_write_oob(p->sub_socket, data, len);
      bufchain_consume(&p->pending_oob_output_data, len);
    }

    /* send buffered normal writes */
    while (bufchain_size(&p->pending_output_data) > 0) {
      bufchain_prefix(&p->pending_output_data, &data, &len);
      output_after += sk_write(p->sub_socket, data, len);
      bufchain_consume(&p->pending_output_data, len);
    }

    /* if we managed to send any data, let the higher levels know. */
    if (output_after < output_before)
      plug_sent(p->plug, output_after);

    /* if we were asked to flush the output during
     * the proxy negotiation process, do so now.
     */
    if (p->pending_flush) sk_flush(p->sub_socket);

    /* if the backend wanted the socket unfrozen, try to unfreeze.
     * our set_frozen handler will flush buffered receive data before
     * unfreezing the actual underlying socket.
     */
    if (!p->freeze)
      sk_set_frozen((Socket)p, 0);
}

/* basic proxy socket functions */

static Plug sk_proxy_plug (Socket s, Plug p)
{
    Proxy_Socket ps = (Proxy_Socket) s;
    Plug ret = ps->plug;
    if (p)
      ps->plug = p;
    return ret;
}

static void sk_proxy_close (Socket s)
{
    Proxy_Socket ps = (Proxy_Socket) s;

    sk_close(ps->sub_socket);
    sk_addr_free(ps->remote_addr);
    sfree(ps);
}

static int sk_proxy_write (Socket s, const char *data, int len)
{
    Proxy_Socket ps = (Proxy_Socket) s;

    if (ps->state != PROXY_STATE_ACTIVE) {
      bufchain_add(&ps->pending_output_data, data, len);
      return bufchain_size(&ps->pending_output_data);
    }
    return sk_write(ps->sub_socket, data, len);
}

static int sk_proxy_write_oob (Socket s, const char *data, int len)
{
    Proxy_Socket ps = (Proxy_Socket) s;

    if (ps->state != PROXY_STATE_ACTIVE) {
      bufchain_clear(&ps->pending_output_data);
      bufchain_clear(&ps->pending_oob_output_data);
      bufchain_add(&ps->pending_oob_output_data, data, len);
      return len;
    }
    return sk_write_oob(ps->sub_socket, data, len);
}

static void sk_proxy_flush (Socket s)
{
    Proxy_Socket ps = (Proxy_Socket) s;

    if (ps->state != PROXY_STATE_ACTIVE) {
      ps->pending_flush = 1;
      return;
    }
    sk_flush(ps->sub_socket);
}

static void sk_proxy_set_private_ptr (Socket s, void *ptr)
{
    Proxy_Socket ps = (Proxy_Socket) s;
    sk_set_private_ptr(ps->sub_socket, ptr);
}

static void * sk_proxy_get_private_ptr (Socket s)
{
    Proxy_Socket ps = (Proxy_Socket) s;
    return sk_get_private_ptr(ps->sub_socket);
}

static void sk_proxy_set_frozen (Socket s, int is_frozen)
{
    Proxy_Socket ps = (Proxy_Socket) s;

    if (ps->state != PROXY_STATE_ACTIVE) {
      ps->freeze = is_frozen;
      return;
    }
    
    /* handle any remaining buffered recv data first */
    if (bufchain_size(&ps->pending_input_data) > 0) {
      ps->freeze = is_frozen;

      /* loop while we still have buffered data, and while we are
       * unfrozen. the plug_receive call in the loop could result 
       * in a call back into this function refreezing the socket, 
       * so we have to check each time.
       */
        while (!ps->freeze && bufchain_size(&ps->pending_input_data) > 0) {
          void *data;
          char databuf[512];
          int len;
          bufchain_prefix(&ps->pending_input_data, &data, &len);
          if (len > lenof(databuf))
            len = lenof(databuf);
          memcpy(databuf, data, len);
          bufchain_consume(&ps->pending_input_data, len);
          plug_receive(ps->plug, 0, databuf, len);
      }

      /* if we're still frozen, we'll have to wait for another
       * call from the backend to finish unbuffering the data.
       */
      if (ps->freeze) return;
    }
    
    sk_set_frozen(ps->sub_socket, is_frozen);
}

static const char * sk_proxy_socket_error (Socket s)
{
    Proxy_Socket ps = (Proxy_Socket) s;
    if (ps->error != NULL || ps->sub_socket == NULL) {
      return ps->error;
    }
    return sk_socket_error(ps->sub_socket);
}

/* basic proxy plug functions */

static int plug_proxy_closing (Plug p, const char *error_msg,
                         int error_code, int calling_back)
{
    Proxy_Plug pp = (Proxy_Plug) p;
    Proxy_Socket ps = pp->proxy_socket;

    if (ps->state != PROXY_STATE_ACTIVE) {
      ps->closing_error_msg = error_msg;
      ps->closing_error_code = error_code;
      ps->closing_calling_back = calling_back;
      return ps->negotiate(ps, PROXY_CHANGE_CLOSING);
    }
    return plug_closing(ps->plug, error_msg,
                  error_code, calling_back);
}

static int plug_proxy_receive (Plug p, int urgent, char *data, int len)
{
    Proxy_Plug pp = (Proxy_Plug) p;
    Proxy_Socket ps = pp->proxy_socket;

    if (ps->state != PROXY_STATE_ACTIVE) {
      /* we will lose the urgentness of this data, but since most,
       * if not all, of this data will be consumed by the negotiation
       * process, hopefully it won't affect the protocol above us
       */
      bufchain_add(&ps->pending_input_data, data, len);
      ps->receive_urgent = urgent;
      ps->receive_data = data;
      ps->receive_len = len;
      return ps->negotiate(ps, PROXY_CHANGE_RECEIVE);
    }
    return plug_receive(ps->plug, urgent, data, len);
}

static void plug_proxy_sent (Plug p, int bufsize)
{
    Proxy_Plug pp = (Proxy_Plug) p;
    Proxy_Socket ps = pp->proxy_socket;

    if (ps->state != PROXY_STATE_ACTIVE) {
      ps->sent_bufsize = bufsize;
      ps->negotiate(ps, PROXY_CHANGE_SENT);
      return;
    }
    plug_sent(ps->plug, bufsize);
}

static int plug_proxy_accepting (Plug p, OSSocket sock)
{
    Proxy_Plug pp = (Proxy_Plug) p;
    Proxy_Socket ps = pp->proxy_socket;

    if (ps->state != PROXY_STATE_ACTIVE) {
      ps->accepting_sock = sock;
      return ps->negotiate(ps, PROXY_CHANGE_ACCEPTING);
    }
    return plug_accepting(ps->plug, sock);
}

/*
 * This function can accept a NULL pointer as `addr', in which case
 * it will only check the host name.
 */
static int proxy_for_destination (SockAddr addr, char *hostname, int port,
                          const Config *cfg)
{
    int s = 0, e = 0;
    char hostip[64];
    int hostip_len, hostname_len;
    const char *exclude_list;

    /*
     * Check the host name and IP against the hard-coded
     * representations of `localhost'.
     */
    if (!cfg->even_proxy_localhost &&
      (sk_hostname_is_local(hostname) ||
       (addr && sk_address_is_local(addr))))
      return 0;                /* do not proxy */

    /* we want a string representation of the IP address for comparisons */
    if (addr) {
      sk_getaddr(addr, hostip, 64);
      hostip_len = strlen(hostip);
    } else
      hostip_len = 0;                /* placate gcc; shouldn't be required */

    hostname_len = strlen(hostname);

    exclude_list = cfg->proxy_exclude_list;

    /* now parse the exclude list, and see if either our IP
     * or hostname matches anything in it.
     */

    while (exclude_list[s]) {
      while (exclude_list[s] &&
             (isspace((unsigned char)exclude_list[s]) ||
            exclude_list[s] == ',')) s++;

      if (!exclude_list[s]) break;

      e = s;

      while (exclude_list[e] &&
             (isalnum((unsigned char)exclude_list[e]) ||
            exclude_list[e] == '-' ||
            exclude_list[e] == '.' ||
            exclude_list[e] == '*')) e++;

      if (exclude_list[s] == '*') {
          /* wildcard at beginning of entry */

          if ((addr && strnicmp(hostip + hostip_len - (e - s - 1),
                          exclude_list + s + 1, e - s - 1) == 0) ||
            strnicmp(hostname + hostname_len - (e - s - 1),
                   exclude_list + s + 1, e - s - 1) == 0)
            return 0; /* IP/hostname range excluded. do not use proxy. */

      } else if (exclude_list[e-1] == '*') {
          /* wildcard at end of entry */

          if ((addr && strnicmp(hostip, exclude_list + s, e - s - 1) == 0) ||
            strnicmp(hostname, exclude_list + s, e - s - 1) == 0)
            return 0; /* IP/hostname range excluded. do not use proxy. */

      } else {
          /* no wildcard at either end, so let's try an absolute
           * match (ie. a specific IP)
           */

          if (addr && strnicmp(hostip, exclude_list + s, e - s) == 0)
            return 0; /* IP/hostname excluded. do not use proxy. */
          if (strnicmp(hostname, exclude_list + s, e - s) == 0)
            return 0; /* IP/hostname excluded. do not use proxy. */
      }

      s = e;

      /* Make sure we really have reached the next comma or end-of-string */
      while (exclude_list[s] &&
             !isspace((unsigned char)exclude_list[s]) &&
             exclude_list[s] != ',') s++;
    }

    /* no matches in the exclude list, so use the proxy */
    return 1;
}

SockAddr name_lookup(char *host, int port, char **canonicalname,
                 const Config *cfg)
{
    if (cfg->proxy_type != PROXY_NONE &&
      do_proxy_dns(cfg) &&
      proxy_for_destination(NULL, host, port, cfg)) {
      *canonicalname = dupstr(host);
      return sk_nonamelookup(host);
    }

    return sk_namelookup(host, canonicalname);
}

Socket new_connection(SockAddr addr, char *hostname,
                  int port, int privport,
                  int oobinline, int nodelay, int keepalive,
                  Plug plug, const Config *cfg)
{
    static const struct socket_function_table socket_fn_table = {
      sk_proxy_plug,
      sk_proxy_close,
      sk_proxy_write,
      sk_proxy_write_oob,
      sk_proxy_flush,
      sk_proxy_set_private_ptr,
      sk_proxy_get_private_ptr,
      sk_proxy_set_frozen,
      sk_proxy_socket_error
    };

    static const struct plug_function_table plug_fn_table = {
      plug_proxy_closing,
      plug_proxy_receive,
      plug_proxy_sent,
      plug_proxy_accepting
    };

    if (cfg->proxy_type != PROXY_NONE &&
      proxy_for_destination(addr, hostname, port, cfg))
    {
      Proxy_Socket ret;
      Proxy_Plug pplug;
      SockAddr proxy_addr;
      char *proxy_canonical_name;
      Socket sret;

      if ((sret = platform_new_connection(addr, hostname, port, privport,
                                  oobinline, nodelay, keepalive,
                                  plug, cfg)) !=
          NULL)
          return sret;

      ret = snew(struct Socket_proxy_tag);
      ret->fn = &socket_fn_table;
      ret->cfg = *cfg;         /* STRUCTURE COPY */
      ret->plug = plug;
      ret->remote_addr = addr;       /* will need to be freed on close */
      ret->remote_port = port;

      ret->error = NULL;
      ret->pending_flush = 0;
      ret->freeze = 0;

      bufchain_init(&ret->pending_input_data);
      bufchain_init(&ret->pending_output_data);
      bufchain_init(&ret->pending_oob_output_data);

      ret->sub_socket = NULL;
      ret->state = PROXY_STATE_NEW;
      ret->negotiate = NULL;
      
      if (cfg->proxy_type == PROXY_HTTP) {
          ret->negotiate = proxy_http_negotiate;
      } else if (cfg->proxy_type == PROXY_SOCKS4) {
            ret->negotiate = proxy_socks4_negotiate;
      } else if (cfg->proxy_type == PROXY_SOCKS5) {
            ret->negotiate = proxy_socks5_negotiate;
      } else if (cfg->proxy_type == PROXY_TELNET) {
          ret->negotiate = proxy_telnet_negotiate;
      } else {
          ret->error = "Proxy error: Unknown proxy method";
          return (Socket) ret;
      }

      /* create the proxy plug to map calls from the actual
       * socket into our proxy socket layer */
      pplug = snew(struct Plug_proxy_tag);
      pplug->fn = &plug_fn_table;
      pplug->proxy_socket = ret;

      /* look-up proxy */
      proxy_addr = sk_namelookup(cfg->proxy_host,
                           &proxy_canonical_name);
      if (sk_addr_error(proxy_addr) != NULL) {
          ret->error = "Proxy error: Unable to resolve proxy host name";
          return (Socket)ret;
      }
      sfree(proxy_canonical_name);

      /* create the actual socket we will be using,
       * connected to our proxy server and port.
       */
      ret->sub_socket = sk_new(proxy_addr, cfg->proxy_port,
                         privport, oobinline,
                         nodelay, keepalive, (Plug) pplug);
      if (sk_socket_error(ret->sub_socket) != NULL)
          return (Socket) ret;

      /* start the proxy negotiation process... */
      sk_set_frozen(ret->sub_socket, 0);
      ret->negotiate(ret, PROXY_CHANGE_NEW);

      return (Socket) ret;
    }

    /* no proxy, so just return the direct socket */
    return sk_new(addr, port, privport, oobinline, nodelay, keepalive, plug);
}

Socket new_listener(char *srcaddr, int port, Plug plug, int local_host_only,
                const Config *cfg)
{
    /* TODO: SOCKS (and potentially others) support inbound
     * TODO: connections via the proxy. support them.
     */

    return sk_newlistener(srcaddr, port, plug, local_host_only);
}

/* ----------------------------------------------------------------------
 * HTTP CONNECT proxy type.
 */

static int get_line_end (char * data, int len)
{
    int off = 0;

    while (off < len)
    {
      if (data[off] == '\n') {
          /* we have a newline */
          off++;

          /* is that the only thing on this line? */
          if (off <= 2) return off;

          /* if not, then there is the possibility that this header
           * continues onto the next line, if it starts with a space
           * or a tab.
           */

          if (off + 1 < len &&
            data[off+1] != ' ' &&
            data[off+1] != '\t') return off;

          /* the line does continue, so we have to keep going
           * until we see an the header's "real" end of line.
           */
          off++;
      }

      off++;
    }

    return -1;
}

int proxy_http_negotiate (Proxy_Socket p, int change)
{
    if (p->state == PROXY_STATE_NEW) {
      /* we are just beginning the proxy negotiate process,
       * so we'll send off the initial bits of the request.
       * for this proxy method, it's just a simple HTTP
       * request
       */
      char *buf, dest[512];

      sk_getaddr(p->remote_addr, dest, lenof(dest));

      buf = dupprintf("CONNECT %s:%i HTTP/1.1\r\nHost: %s:%i\r\n",
                  dest, p->remote_port, dest, p->remote_port);
      sk_write(p->sub_socket, buf, strlen(buf));
      sfree(buf);

      if (p->cfg.proxy_username[0] || p->cfg.proxy_password[0]) {
          char buf[sizeof(p->cfg.proxy_username)+sizeof(p->cfg.proxy_password)];
          char buf2[sizeof(buf)*4/3 + 100];
          int i, j, len;
          sprintf(buf, "%s:%s", p->cfg.proxy_username, p->cfg.proxy_password);
          len = strlen(buf);
          sprintf(buf2, "Proxy-Authorization: Basic ");
          for (i = 0, j = strlen(buf2); i < len; i += 3, j += 4)
            base64_encode_atom((unsigned char *)(buf+i),
                           (len-i > 3 ? 3 : len-i), buf2+j);
          strcpy(buf2+j, "\r\n");
          sk_write(p->sub_socket, buf2, strlen(buf2));
      }

      sk_write(p->sub_socket, "\r\n", 2);

      p->state = 1;
      return 0;
    }

    if (change == PROXY_CHANGE_CLOSING) {
      /* if our proxy negotiation process involves closing and opening
       * new sockets, then we would want to intercept this closing
       * callback when we were expecting it. if we aren't anticipating
       * a socket close, then some error must have occurred. we'll
       * just pass those errors up to the backend.
       */
      return plug_closing(p->plug, p->closing_error_msg,
                      p->closing_error_code,
                      p->closing_calling_back);
    }

    if (change == PROXY_CHANGE_SENT) {
      /* some (or all) of what we wrote to the proxy was sent.
       * we don't do anything new, however, until we receive the
       * proxy's response. we might want to set a timer so we can
       * timeout the proxy negotiation after a while...
       */
      return 0;
    }

    if (change == PROXY_CHANGE_ACCEPTING) {
      /* we should _never_ see this, as we are using our socket to
       * connect to a proxy, not accepting inbound connections.
       * what should we do? close the socket with an appropriate
       * error message?
       */
      return plug_accepting(p->plug, p->accepting_sock);
    }

    if (change == PROXY_CHANGE_RECEIVE) {
      /* we have received data from the underlying socket, which
       * we'll need to parse, process, and respond to appropriately.
       */

      char *data, *datap;
      int len;
      int eol;

      if (p->state == 1) {

          int min_ver, maj_ver, status;

          /* get the status line */
          len = bufchain_size(&p->pending_input_data);
          assert(len > 0);           /* or we wouldn't be here */
          data = snewn(len+1, char);
          bufchain_fetch(&p->pending_input_data, data, len);
          /*
           * We must NUL-terminate this data, because Windows
           * sscanf appears to require a NUL at the end of the
           * string because it strlens it _first_. Sigh.
           */
          data[len] = '\0';

          eol = get_line_end(data, len);
          if (eol < 0) {
            sfree(data);
            return 1;
          }

          status = -1;
          /* We can't rely on whether the %n incremented the sscanf return */
          if (sscanf((char *)data, "HTTP/%i.%i %n",
                   &maj_ver, &min_ver, &status) < 2 || status == -1) {
            plug_closing(p->plug, "Proxy error: HTTP response was absent",
                       PROXY_ERROR_GENERAL, 0);
            sfree(data);
            return 1;
          }

          /* remove the status line from the input buffer. */
          bufchain_consume(&p->pending_input_data, eol);
          if (data[status] != '2') {
            /* error */
            char *buf;
            data[eol] = '\0';
            while (eol > status &&
                   (data[eol-1] == '\r' || data[eol-1] == '\n'))
                data[--eol] = '\0';
            buf = dupprintf("Proxy error: %s", data+status);
            plug_closing(p->plug, buf, PROXY_ERROR_GENERAL, 0);
            sfree(buf);
            sfree(data);
            return 1;
          }

          sfree(data);

          p->state = 2;
      }

      if (p->state == 2) {

          /* get headers. we're done when we get a
           * header of length 2, (ie. just "\r\n")
           */

          len = bufchain_size(&p->pending_input_data);
          assert(len > 0);           /* or we wouldn't be here */
          data = snewn(len, char);
          datap = data;
          bufchain_fetch(&p->pending_input_data, data, len);

          eol = get_line_end(datap, len);
          if (eol < 0) {
            sfree(data);
            return 1;
          }
          while (eol > 2)
          {
            bufchain_consume(&p->pending_input_data, eol);
            datap += eol;
            len   -= eol;
            eol = get_line_end(datap, len);
          }

          if (eol == 2) {
            /* we're done */
            bufchain_consume(&p->pending_input_data, 2);
            proxy_activate(p);
            /* proxy activate will have dealt with
             * whatever is left of the buffer */
            sfree(data);
            return 1;
          }

          sfree(data);
          return 1;
      }
    }

    plug_closing(p->plug, "Proxy error: unexpected proxy error",
             PROXY_ERROR_UNEXPECTED, 0);
    return 1;
}

/* ----------------------------------------------------------------------
 * SOCKS proxy type.
 */

/* SOCKS version 4 */
int proxy_socks4_negotiate (Proxy_Socket p, int change)
{
    if (p->state == PROXY_CHANGE_NEW) {

      /* request format:
       *  version number (1 byte) = 4
       *  command code (1 byte)
       *    1 = CONNECT
       *    2 = BIND
       *  dest. port (2 bytes) [network order]
       *  dest. address (4 bytes)
       *  user ID (variable length, null terminated string)
       */

      int length, type, namelen;
      char *command, addr[4], hostname[512];

      type = sk_addrtype(p->remote_addr);
      if (type == ADDRTYPE_IPV6) {
          plug_closing(p->plug, "Proxy error: SOCKS version 4 does"
                   " not support IPv6", PROXY_ERROR_GENERAL, 0);
          return 1;
      } else if (type == ADDRTYPE_IPV4) {
          namelen = 0;
          sk_addrcopy(p->remote_addr, addr);
      } else {                 /* type == ADDRTYPE_NAME */
          assert(type == ADDRTYPE_NAME);
          sk_getaddr(p->remote_addr, hostname, lenof(hostname));
          namelen = strlen(hostname) + 1;   /* include the NUL */
          addr[0] = addr[1] = addr[2] = 0;
          addr[3] = 1;
      }

      length = strlen(p->cfg.proxy_username) + namelen + 9;
      command = snewn(length, char);
      strcpy(command + 8, p->cfg.proxy_username);

      command[0] = 4; /* version 4 */
      command[1] = 1; /* CONNECT command */

      /* port */
      command[2] = (char) (p->remote_port >> 8) & 0xff;
      command[3] = (char) p->remote_port & 0xff;

      /* address */
      memcpy(command + 4, addr, 4);

      /* hostname */
      memcpy(command + 8 + strlen(p->cfg.proxy_username) + 1,
             hostname, namelen);

      sk_write(p->sub_socket, command, length);
      sfree(command);

      p->state = 1;
      return 0;
    }

    if (change == PROXY_CHANGE_CLOSING) {
      /* if our proxy negotiation process involves closing and opening
       * new sockets, then we would want to intercept this closing
       * callback when we were expecting it. if we aren't anticipating
       * a socket close, then some error must have occurred. we'll
       * just pass those errors up to the backend.
       */
      return plug_closing(p->plug, p->closing_error_msg,
                      p->closing_error_code,
                      p->closing_calling_back);
    }

    if (change == PROXY_CHANGE_SENT) {
      /* some (or all) of what we wrote to the proxy was sent.
       * we don't do anything new, however, until we receive the
       * proxy's response. we might want to set a timer so we can
       * timeout the proxy negotiation after a while...
       */
      return 0;
    }

    if (change == PROXY_CHANGE_ACCEPTING) {
      /* we should _never_ see this, as we are using our socket to
       * connect to a proxy, not accepting inbound connections.
       * what should we do? close the socket with an appropriate
       * error message?
       */
      return plug_accepting(p->plug, p->accepting_sock);
    }

    if (change == PROXY_CHANGE_RECEIVE) {
      /* we have received data from the underlying socket, which
       * we'll need to parse, process, and respond to appropriately.
       */

      if (p->state == 1) {
          /* response format:
           *  version number (1 byte) = 4
           *  reply code (1 byte)
           *    90 = request granted
           *    91 = request rejected or failed
           *    92 = request rejected due to lack of IDENTD on client
           *    93 = request rejected due to difference in user ID 
           *         (what we sent vs. what IDENTD said)
           *  dest. port (2 bytes)
           *  dest. address (4 bytes)
           */

          char data[8];

          if (bufchain_size(&p->pending_input_data) < 8)
            return 1;          /* not got anything yet */
          
          /* get the response */
          bufchain_fetch(&p->pending_input_data, data, 8);

          if (data[0] != 0) {
            plug_closing(p->plug, "Proxy error: SOCKS proxy responded with "
                              "unexpected reply code version",
                       PROXY_ERROR_GENERAL, 0);
            return 1;
          }

          if (data[1] != 90) {

            switch (data[1]) {
              case 92:
                plug_closing(p->plug, "Proxy error: SOCKS server wanted IDENTD on client",
                         PROXY_ERROR_GENERAL, 0);
                break;
              case 93:
                plug_closing(p->plug, "Proxy error: Username and IDENTD on client don't agree",
                         PROXY_ERROR_GENERAL, 0);
                break;
              case 91:
              default:
                plug_closing(p->plug, "Proxy error: Error while communicating with proxy",
                         PROXY_ERROR_GENERAL, 0);
                break;
            }

            return 1;
          }
          bufchain_consume(&p->pending_input_data, 8);

          /* we're done */
          proxy_activate(p);
          /* proxy activate will have dealt with
           * whatever is left of the buffer */
          return 1;
      }
    }

    plug_closing(p->plug, "Proxy error: unexpected proxy error",
             PROXY_ERROR_UNEXPECTED, 0);
    return 1;
}

/* SOCKS version 5 */
int proxy_socks5_negotiate (Proxy_Socket p, int change)
{
    if (p->state == PROXY_CHANGE_NEW) {

      /* initial command:
       *  version number (1 byte) = 5
       *  number of available authentication methods (1 byte)
       *  available authentication methods (1 byte * previous value)
       *    authentication methods:
       *     0x00 = no authentication
       *     0x01 = GSSAPI
       *     0x02 = username/password
       *     0x03 = CHAP
       */

      char command[4];
      int len;

      command[0] = 5; /* version 5 */
      if (p->cfg.proxy_username[0] || p->cfg.proxy_password[0]) {
          command[1] = 2;            /* two methods supported: */
          command[2] = 0x00;         /* no authentication */
          command[3] = 0x02;         /* username/password */
          len = 4;
      } else {
          command[1] = 1;            /* one methods supported: */
          command[2] = 0x00;         /* no authentication */
          len = 3;
      }

      sk_write(p->sub_socket, command, len);

      p->state = 1;
      return 0;
    }

    if (change == PROXY_CHANGE_CLOSING) {
      /* if our proxy negotiation process involves closing and opening
       * new sockets, then we would want to intercept this closing
       * callback when we were expecting it. if we aren't anticipating
       * a socket close, then some error must have occurred. we'll
       * just pass those errors up to the backend.
       */
      return plug_closing(p->plug, p->closing_error_msg,
                      p->closing_error_code,
                      p->closing_calling_back);
    }

    if (change == PROXY_CHANGE_SENT) {
      /* some (or all) of what we wrote to the proxy was sent.
       * we don't do anything new, however, until we receive the
       * proxy's response. we might want to set a timer so we can
       * timeout the proxy negotiation after a while...
       */
      return 0;
    }

    if (change == PROXY_CHANGE_ACCEPTING) {
      /* we should _never_ see this, as we are using our socket to
       * connect to a proxy, not accepting inbound connections.
       * what should we do? close the socket with an appropriate
       * error message?
       */
      return plug_accepting(p->plug, p->accepting_sock);
    }

    if (change == PROXY_CHANGE_RECEIVE) {
      /* we have received data from the underlying socket, which
       * we'll need to parse, process, and respond to appropriately.
       */

      if (p->state == 1) {

          /* initial response:
           *  version number (1 byte) = 5
           *  authentication method (1 byte)
           *    authentication methods:
           *     0x00 = no authentication
           *     0x01 = GSSAPI
           *     0x02 = username/password 
           *     0x03 = CHAP
           *     0xff = no acceptable methods
           */
          char data[2];

          if (bufchain_size(&p->pending_input_data) < 2)
            return 1;          /* not got anything yet */

          /* get the response */
          bufchain_fetch(&p->pending_input_data, data, 2);

          if (data[0] != 5) {
            plug_closing(p->plug, "Proxy error: SOCKS proxy returned unexpected version",
                       PROXY_ERROR_GENERAL, 0);
            return 1;
          }

          if (data[1] == 0x00) p->state = 2; /* no authentication needed */
          else if (data[1] == 0x01) p->state = 4; /* GSSAPI authentication */
          else if (data[1] == 0x02) p->state = 5; /* username/password authentication */
          else if (data[1] == 0x03) p->state = 6; /* CHAP authentication */
          else {
            plug_closing(p->plug, "Proxy error: SOCKS proxy did not accept our authentication",
                       PROXY_ERROR_GENERAL, 0);
            return 1;
          }
          bufchain_consume(&p->pending_input_data, 2);
      }

      if (p->state == 7) {

          /* password authentication reply format:
           *  version number (1 bytes) = 1
           *  reply code (1 byte)
           *    0 = succeeded
           *    >0 = failed
           */
          char data[2];

          if (bufchain_size(&p->pending_input_data) < 2)
            return 1;          /* not got anything yet */

          /* get the response */
          bufchain_fetch(&p->pending_input_data, data, 2);

          if (data[0] != 1) {
            plug_closing(p->plug, "Proxy error: SOCKS password "
                       "subnegotiation contained wrong version number",
                       PROXY_ERROR_GENERAL, 0);
            return 1;
          }

          if (data[1] != 0) {

            plug_closing(p->plug, "Proxy error: SOCKS proxy refused"
                       " password authentication",
                       PROXY_ERROR_GENERAL, 0);
            return 1;
          }

          bufchain_consume(&p->pending_input_data, 2);
          p->state = 2;        /* now proceed as authenticated */
      }

      if (p->state == 2) {

          /* request format:
           *  version number (1 byte) = 5
           *  command code (1 byte)
           *    1 = CONNECT
           *    2 = BIND
           *    3 = UDP ASSOCIATE
           *  reserved (1 byte) = 0x00
           *  address type (1 byte)
           *    1 = IPv4
           *    3 = domainname (first byte has length, no terminating null)
           *    4 = IPv6
           *  dest. address (variable)
           *  dest. port (2 bytes) [network order]
           */

          char command[512];
          int len;
          int type;

          type = sk_addrtype(p->remote_addr);
          if (type == ADDRTYPE_IPV4) {
            len = 10;          /* 4 hdr + 4 addr + 2 trailer */
            command[3] = 1; /* IPv4 */
            sk_addrcopy(p->remote_addr, command+4);
          } else if (type == ADDRTYPE_IPV6) {
            len = 22;          /* 4 hdr + 16 addr + 2 trailer */
            command[3] = 4; /* IPv6 */
            sk_addrcopy(p->remote_addr, command+4);
          } else {
            assert(type == ADDRTYPE_NAME);
            command[3] = 3;
            sk_getaddr(p->remote_addr, command+5, 256);
            command[4] = strlen(command+5);
            len = 7 + command[4];  /* 4 hdr, 1 len, N addr, 2 trailer */
          }

          command[0] = 5; /* version 5 */
          command[1] = 1; /* CONNECT command */
          command[2] = 0x00;

          /* port */
          command[len-2] = (char) (p->remote_port >> 8) & 0xff;
          command[len-1] = (char) p->remote_port & 0xff;

          sk_write(p->sub_socket, command, len);

          p->state = 3;
          return 1;
      }

      if (p->state == 3) {

          /* reply format:
           *  version number (1 bytes) = 5
           *  reply code (1 byte)
           *    0 = succeeded
           *    1 = general SOCKS server failure
           *    2 = connection not allowed by ruleset
           *    3 = network unreachable
           *    4 = host unreachable
           *    5 = connection refused
           *    6 = TTL expired
           *    7 = command not supported
           *    8 = address type not supported
           * reserved (1 byte) = x00
           * address type (1 byte)
           *    1 = IPv4
           *    3 = domainname (first byte has length, no terminating null)
           *    4 = IPv6
           * server bound address (variable)
           * server bound port (2 bytes) [network order]
           */
          char data[5];
          int len;

          /* First 5 bytes of packet are enough to tell its length. */ 
          if (bufchain_size(&p->pending_input_data) < 5)
            return 1;          /* not got anything yet */

          /* get the response */
          bufchain_fetch(&p->pending_input_data, data, 5);

          if (data[0] != 5) {
            plug_closing(p->plug, "Proxy error: SOCKS proxy returned wrong version number",
                       PROXY_ERROR_GENERAL, 0);
            return 1;
          }

          if (data[1] != 0) {
            char buf[256];

            strcpy(buf, "Proxy error: ");

            switch (data[1]) {
              case 1: strcat(buf, "General SOCKS server failure"); break;
              case 2: strcat(buf, "Connection not allowed by ruleset"); break;
              case 3: strcat(buf, "Network unreachable"); break;
              case 4: strcat(buf, "Host unreachable"); break;
              case 5: strcat(buf, "Connection refused"); break;
              case 6: strcat(buf, "TTL expired"); break;
              case 7: strcat(buf, "Command not supported"); break;
              case 8: strcat(buf, "Address type not supported"); break;
              default: sprintf(buf+strlen(buf),
                           "Unrecognised SOCKS error code %d",
                           data[1]);
                break;
            }
            plug_closing(p->plug, buf, PROXY_ERROR_GENERAL, 0);

            return 1;
          }

          /*
           * Eat the rest of the reply packet.
           */
          len = 6;                   /* first 4 bytes, last 2 */
          switch (data[3]) {
            case 1: len += 4; break; /* IPv4 address */
            case 4: len += 16; break;/* IPv6 address */
            case 3: len += (unsigned char)data[4]; break; /* domain name */
            default:
            plug_closing(p->plug, "Proxy error: SOCKS proxy returned "
                       "unrecognised address format",
                       PROXY_ERROR_GENERAL, 0);
            return 1;
          }
          if (bufchain_size(&p->pending_input_data) < len)
            return 1;          /* not got whole reply yet */
          bufchain_consume(&p->pending_input_data, len);

          /* we're done */
          proxy_activate(p);
          return 1;
      }

      if (p->state == 4) {
          /* TODO: Handle GSSAPI authentication */
          plug_closing(p->plug, "Proxy error: We don't support GSSAPI authentication",
                   PROXY_ERROR_GENERAL, 0);
          return 1;
      }

      if (p->state == 5) {
          if (p->cfg.proxy_username[0] || p->cfg.proxy_password[0]) {
            char userpwbuf[514];
            int ulen, plen;
            ulen = strlen(p->cfg.proxy_username);
            if (ulen > 255) ulen = 255; if (ulen < 1) ulen = 1;
            plen = strlen(p->cfg.proxy_password);
            if (plen > 255) plen = 255; if (plen < 1) plen = 1;
            userpwbuf[0] = 1;      /* version number of subnegotiation */
            userpwbuf[1] = ulen;
            memcpy(userpwbuf+2, p->cfg.proxy_username, ulen);
            userpwbuf[ulen+2] = plen;
            memcpy(userpwbuf+ulen+3, p->cfg.proxy_password, plen);
            sk_write(p->sub_socket, userpwbuf, ulen + plen + 3);
            p->state = 7;
          } else 
            plug_closing(p->plug, "Proxy error: Server chose "
                       "username/password authentication but we "
                       "didn't offer it!",
                   PROXY_ERROR_GENERAL, 0);
          return 1;
      }

      if (p->state == 6) {
          /* TODO: Handle CHAP authentication */
          plug_closing(p->plug, "Proxy error: We don't support CHAP authentication",
                   PROXY_ERROR_GENERAL, 0);
          return 1;
      }

    }

    plug_closing(p->plug, "Proxy error: Unexpected proxy error",
             PROXY_ERROR_UNEXPECTED, 0);
    return 1;
}

/* ----------------------------------------------------------------------
 * `Telnet' proxy type.
 *
 * (This is for ad-hoc proxies where you connect to the proxy's
 * telnet port and send a command such as `connect host port'. The
 * command is configurable, since this proxy type is typically not
 * standardised or at all well-defined.)
 */

char *format_telnet_command(SockAddr addr, int port, const Config *cfg)
{
    char *ret = NULL;
    int retlen = 0, retsize = 0;
    int so = 0, eo = 0;
#define ENSURE(n) do { \
    if (retsize < retlen + n) { \
      retsize = retlen + n + 512; \
      ret = sresize(ret, retsize, char); \
    } \
} while (0)

    /* we need to escape \\, \%, \r, \n, \t, \x??, \0???, 
     * %%, %host, %port, %user, and %pass
     */

    while (cfg->proxy_telnet_command[eo] != 0) {

      /* scan forward until we hit end-of-line,
       * or an escape character (\ or %) */
      while (cfg->proxy_telnet_command[eo] != 0 &&
             cfg->proxy_telnet_command[eo] != '%' &&
             cfg->proxy_telnet_command[eo] != '\\') eo++;

      /* if we hit eol, break out of our escaping loop */
      if (cfg->proxy_telnet_command[eo] == 0) break;

      /* if there was any unescaped text before the escape
       * character, send that now */
      if (eo != so) {
          ENSURE(eo - so);
          memcpy(ret + retlen, cfg->proxy_telnet_command + so, eo - so);
          retlen += eo - so;
      }

      so = eo++;

      /* if the escape character was the last character of
       * the line, we'll just stop and send it. */
      if (cfg->proxy_telnet_command[eo] == 0) break;

      if (cfg->proxy_telnet_command[so] == '\\') {

          /* we recognize \\, \%, \r, \n, \t, \x??.
           * anything else, we just send unescaped (including the \).
           */

          switch (cfg->proxy_telnet_command[eo]) {

            case '\\':
            ENSURE(1);
            ret[retlen++] = '\\';
            eo++;
            break;

            case '%':
            ENSURE(1);
            ret[retlen++] = '%';
            eo++;
            break;

            case 'r':
            ENSURE(1);
            ret[retlen++] = '\r';
            eo++;
            break;

            case 'n':
            ENSURE(1);
            ret[retlen++] = '\n';
            eo++;
            break;

            case 't':
            ENSURE(1);
            ret[retlen++] = '\t';
            eo++;
            break;

            case 'x':
            case 'X':
            {
                /* escaped hexadecimal value (ie. \xff) */
                unsigned char v = 0;
                int i = 0;

                for (;;) {
                  eo++;
                  if (cfg->proxy_telnet_command[eo] >= '0' &&
                      cfg->proxy_telnet_command[eo] <= '9')
                      v += cfg->proxy_telnet_command[eo] - '0';
                  else if (cfg->proxy_telnet_command[eo] >= 'a' &&
                         cfg->proxy_telnet_command[eo] <= 'f')
                      v += cfg->proxy_telnet_command[eo] - 'a' + 10;
                  else if (cfg->proxy_telnet_command[eo] >= 'A' &&
                         cfg->proxy_telnet_command[eo] <= 'F')
                      v += cfg->proxy_telnet_command[eo] - 'A' + 10;
                  else {
                      /* non hex character, so we abort and just
                       * send the whole thing unescaped (including \x)
                       */
                      ENSURE(1);
                      ret[retlen++] = '\\';
                      eo = so + 1;
                      break;
                  }

                  /* we only extract two hex characters */
                  if (i == 1) {
                      ENSURE(1);
                      ret[retlen++] = v;
                      eo++;
                      break;
                  }

                  i++;
                  v <<= 4;
                }
            }
            break;

            default:
            ENSURE(2);
            memcpy(ret+retlen, cfg->proxy_telnet_command + so, 2);
            retlen += 2;
            eo++;
            break;
          }
      } else {

          /* % escape. we recognize %%, %host, %port, %user, %pass.
           * anything else, we just send unescaped (including the %).
           */

          if (cfg->proxy_telnet_command[eo] == '%') {
            ENSURE(1);
            ret[retlen++] = '%';
            eo++;
          }
          else if (strnicmp(cfg->proxy_telnet_command + eo,
                        "host", 4) == 0) {
            char dest[512];
            int destlen;
            sk_getaddr(addr, dest, lenof(dest));
            destlen = strlen(dest);
            ENSURE(destlen);
            memcpy(ret+retlen, dest, destlen);
            retlen += destlen;
            eo += 4;
          }
          else if (strnicmp(cfg->proxy_telnet_command + eo,
                        "port", 4) == 0) {
            char portstr[8], portlen;
            portlen = sprintf(portstr, "%i", port);
            ENSURE(portlen);
            memcpy(ret + retlen, portstr, portlen);
            retlen += portlen;
            eo += 4;
          }
          else if (strnicmp(cfg->proxy_telnet_command + eo,
                        "user", 4) == 0) {
            int userlen = strlen(cfg->proxy_username);
            ENSURE(userlen);
            memcpy(ret+retlen, cfg->proxy_username, userlen);
            retlen += userlen;
            eo += 4;
          }
          else if (strnicmp(cfg->proxy_telnet_command + eo,
                        "pass", 4) == 0) {
            int passlen = strlen(cfg->proxy_password);
            ENSURE(passlen);
            memcpy(ret+retlen, cfg->proxy_password, passlen);
            retlen += passlen;
            eo += 4;
          }
          else {
            /* we don't escape this, so send the % now, and
             * don't advance eo, so that we'll consider the
             * text immediately following the % as unescaped.
             */
            ENSURE(1);
            ret[retlen++] = '%';
          }
      }

      /* resume scanning for additional escapes after this one. */
      so = eo;
    }

    /* if there is any unescaped text at the end of the line, send it */
    if (eo != so) {
      ENSURE(eo - so);
      memcpy(ret + retlen, cfg->proxy_telnet_command + so, eo - so);
      retlen += eo - so;
    }

    ENSURE(1);
    ret[retlen] = '\0';
    return ret;

#undef ENSURE
}

int proxy_telnet_negotiate (Proxy_Socket p, int change)
{
    if (p->state == PROXY_CHANGE_NEW) {
      char *formatted_cmd;

      formatted_cmd = format_telnet_command(p->remote_addr, p->remote_port,
                                    &p->cfg);

      sk_write(p->sub_socket, formatted_cmd, strlen(formatted_cmd));
      sfree(formatted_cmd);

      p->state = 1;
      return 0;
    }

    if (change == PROXY_CHANGE_CLOSING) {
      /* if our proxy negotiation process involves closing and opening
       * new sockets, then we would want to intercept this closing
       * callback when we were expecting it. if we aren't anticipating
       * a socket close, then some error must have occurred. we'll
       * just pass those errors up to the backend.
       */
      return plug_closing(p->plug, p->closing_error_msg,
                      p->closing_error_code,
                      p->closing_calling_back);
    }

    if (change == PROXY_CHANGE_SENT) {
      /* some (or all) of what we wrote to the proxy was sent.
       * we don't do anything new, however, until we receive the
       * proxy's response. we might want to set a timer so we can
       * timeout the proxy negotiation after a while...
       */
      return 0;
    }

    if (change == PROXY_CHANGE_ACCEPTING) {
      /* we should _never_ see this, as we are using our socket to
       * connect to a proxy, not accepting inbound connections.
       * what should we do? close the socket with an appropriate
       * error message?
       */
      return plug_accepting(p->plug, p->accepting_sock);
    }

    if (change == PROXY_CHANGE_RECEIVE) {
      /* we have received data from the underlying socket, which
       * we'll need to parse, process, and respond to appropriately.
       */

      /* we're done */
      proxy_activate(p);
      /* proxy activate will have dealt with
       * whatever is left of the buffer */
      return 1;
    }

    plug_closing(p->plug, "Proxy error: Unexpected proxy error",
             PROXY_ERROR_UNEXPECTED, 0);
    return 1;
}

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