sockfilt.c

/***************************************************************************
 *                                  _   _ ____  _
 *  Project                     ___| | | |  _ \| |
 *                             / __| | | | |_) | |
 *                            | (__| |_| |  _ <| |___
 *                             \___|\___/|_| \_\_____|
 *
 * Copyright (C) 1998 - 2009, 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 http://curl.haxx.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.
 *
 * $Id$
 ***************************************************************************/

/* Purpose
 *
 * 1. Accept a TCP connection on a custom port (ipv4 or ipv6), or connect
 *    to a given (localhost) port.
 *
 * 2. Get commands on STDIN. Pass data on to the TCP stream.
 *    Get data from TCP stream and pass on to STDOUT.
 *
 * This program is made to perform all the socket/stream/connection stuff for
 * the test suite's (perl) FTP server. Previously the perl code did all of
 * this by its own, but I decided to let this program do the socket layer
 * because of several things:
 *
 * o We want the perl code to work with rather old perl installations, thus
 *   we cannot use recent perl modules or features.
 *
 * o We want IPv6 support for systems that provide it, and doing optional IPv6
 *   support in perl seems if not impossible so at least awkward.
 *
 * o We want FTP-SSL support, which means that a connection that starts with
 *   plain sockets needs to be able to "go SSL" in the midst. This would also
 *   require some nasty perl stuff I'd rather avoid.
 *
 * (Source originally based on sws.c)
 */

/*
 * Signal handling notes for sockfilt
 * ----------------------------------
 *
 * This program is a single-threaded process.
 *
 * This program is intended to be highly portable and as such it must be kept as
 * simple as possible, due to this the only signal handling mechanisms used will
 * be those of ANSI C, and used only in the most basic form which is good enough
 * for the purpose of this program.
 *
 * For the above reason and the specific needs of this program signals SIGHUP,
 * SIGPIPE and SIGALRM will be simply ignored on systems where this can be done.
 * If possible, signals SIGINT and SIGTERM will be handled by this program as an
 * indication to cleanup and finish execution as soon as possible.  This will be
 * achieved with a single signal handler 'exit_signal_handler' for both signals.
 *
 * The 'exit_signal_handler' upon the first SIGINT or SIGTERM received signal
 * will just set to one the global var 'got_exit_signal' storing in global var
 * 'exit_signal' the signal that triggered this change.
 *
 * Nothing fancy that could introduce problems is used, the program at certain
 * points in its normal flow checks if var 'got_exit_signal' is set and in case
 * this is true it just makes its way out of loops and functions in structured
 * and well behaved manner to achieve proper program cleanup and termination.
 *
 * Even with the above mechanism implemented it is worthwile to note that other
 * signals might still be received, or that there might be systems on which it
 * is not possible to trap and ignore some of the above signals.  This implies
 * that for increased portability and reliability the program must be coded as
 * if no signal was being ignored or handled at all.  Enjoy it!
 */

#include "setup.h" /* portability help from the lib directory */

#ifdef HAVE_SIGNAL_H
#include <signal.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_SYS_SOCKET_H
#include <sys/socket.h>
#endif
#ifdef HAVE_NETINET_IN_H
#include <netinet/in.h>
#endif
#ifdef HAVE_ARPA_INET_H
#include <arpa/inet.h>
#endif
#ifdef HAVE_NETDB_H
#include <netdb.h>
#endif

#define ENABLE_CURLX_PRINTF
/* make the curlx header define all printf() functions to use the curlx_*
   versions instead */
#include "curlx.h" /* from the private lib dir */
#include "getpart.h"
#include "inet_pton.h"
#include "util.h"

/* include memdebug.h last */
#include "memdebug.h"

#define DEFAULT_PORT 8999

#ifndef DEFAULT_LOGFILE
#define DEFAULT_LOGFILE "log/sockfilt.log"
#endif

const char *serverlogfile = DEFAULT_LOGFILE;

static bool verbose = FALSE;
#ifdef ENABLE_IPV6
static bool use_ipv6 = FALSE;
#endif
static const char *ipv_inuse = "IPv4";
static unsigned short port = DEFAULT_PORT;
static unsigned short connectport = 0; /* if non-zero, we activate this mode */

enum sockmode {
  PASSIVE_LISTEN,    /* as a server waiting for connections */
  PASSIVE_CONNECT,   /* as a server, connected to a client */
  ACTIVE,            /* as a client, connected to a server */
  ACTIVE_DISCONNECT  /* as a client, disconnected from server */
};

/* do-nothing macro replacement for systems which lack siginterrupt() */

#ifndef HAVE_SIGINTERRUPT
#define siginterrupt(x,y) do {} while(0)
#endif

/* vars used to keep around previous signal handlers */

typedef RETSIGTYPE (*SIGHANDLER_T)(int);

#ifdef SIGHUP
static SIGHANDLER_T old_sighup_handler  = SIG_ERR;
#endif

#ifdef SIGPIPE
static SIGHANDLER_T old_sigpipe_handler = SIG_ERR;
#endif

#ifdef SIGALRM
static SIGHANDLER_T old_sigalrm_handler = SIG_ERR;
#endif

#ifdef SIGINT
static SIGHANDLER_T old_sigint_handler  = SIG_ERR;
#endif

#ifdef SIGTERM
static SIGHANDLER_T old_sigterm_handler = SIG_ERR;
#endif

/* var which if set indicates that the program should finish execution */

SIG_ATOMIC_T got_exit_signal = 0;

/* if next is set indicates the first signal handled in exit_signal_handler */

static volatile int exit_signal = 0;

/* signal handler that will be triggered to indicate that the program
  should finish its execution in a controlled manner as soon as possible.
  The first time this is called it will set got_exit_signal to one and
  store in exit_signal the signal that triggered its execution. */

static RETSIGTYPE exit_signal_handler(int signum)
{
  int old_errno = ERRNO;
  if(got_exit_signal == 0) {
    got_exit_signal = 1;
    exit_signal = signum;
  }
  (void)signal(signum, exit_signal_handler);
  SET_ERRNO(old_errno);
}

static void install_signal_handlers(void)
{
#ifdef SIGHUP
  /* ignore SIGHUP signal */
  if((old_sighup_handler = signal(SIGHUP, SIG_IGN)) == SIG_ERR)
    logmsg("cannot install SIGHUP handler: %s", strerror(ERRNO));
#endif
#ifdef SIGPIPE
  /* ignore SIGPIPE signal */