guile/libguile/fports.c

/* Copyright (C) 1995, 1996, 1997, 1998, 1999, 2000, 2001, 2002, 2003,
 *   2004, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Free Software Foundation, Inc.
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public License
 * as published by the Free Software Foundation; either version 3 of
 * the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
 * 02110-1301 USA
 */



#define _LARGEFILE64_SOURCE      /* ask for stat64 etc */
#define _GNU_SOURCE              /* ask for LONG_LONG_MAX/LONG_LONG_MIN */
#define _POSIX_C_SOURCE 200809L  /* F_DUPFD_CLOEXEC */

#ifdef HAVE_CONFIG_H
#  include <config.h>
#endif

#include <stdio.h>
#include <fcntl.h>
#include "libguile/_scm.h"
#include "libguile/strings.h"
#include "libguile/validate.h"
#include "libguile/gc.h"
#include "libguile/posix.h"
#include "libguile/dynwind.h"
#include "libguile/hashtab.h"

#include "libguile/fports.h"

#ifdef HAVE_STRING_H
#include <string.h>
#endif
#ifdef HAVE_UNISTD_H
#include <unistd.h>
#endif
#ifdef HAVE_IO_H
#include <io.h>
#endif
#ifdef HAVE_STRUCT_STAT_ST_BLKSIZE
#include <sys/stat.h>
#endif
#ifdef HAVE_POLL_H
#include <poll.h>
#endif
#include <errno.h>
#include <sys/types.h>

#include <full-write.h>

#include "libguile/iselect.h"

/* Some defines for Windows (native port, not Cygwin). */
#ifdef __MINGW32__
# include <sys/stat.h>
# include <winsock2.h>
#endif /* __MINGW32__ */

#include <full-write.h>

/* Mingw (version 3.4.5, circa 2006) has ftruncate as an alias for chsize
   already, but have this code here in case that wasn't so in past versions,
   or perhaps to help other minimal DOS environments.

   gnulib ftruncate.c has code using fcntl F_CHSIZE and F_FREESP, which
   might be possibilities if we've got other systems without ftruncate.  */

#if defined HAVE_CHSIZE && ! defined HAVE_FTRUNCATE
# define ftruncate(fd, size) chsize (fd, size)
# undef HAVE_FTRUNCATE
# define HAVE_FTRUNCATE 1
#endif

#if SIZEOF_OFF_T == SIZEOF_INT
#define OFF_T_MAX  INT_MAX
#define OFF_T_MIN  INT_MIN
#elif SIZEOF_OFF_T == SIZEOF_LONG
#define OFF_T_MAX  LONG_MAX
#define OFF_T_MIN  LONG_MIN
#elif SIZEOF_OFF_T == SIZEOF_LONG_LONG
#define OFF_T_MAX  LONG_LONG_MAX
#define OFF_T_MIN  LONG_LONG_MIN
#else
#error Oops, unknown OFF_T size
#endif

scm_t_bits scm_tc16_fport;


/* default buffer size, used if the O/S won't supply a value.  */
static const size_t default_buffer_size = 1024;

/* create FPORT buffer with specified sizes (or -1 to use default size or
   0 for no buffer.  */
static void
scm_fport_buffer_add (SCM port, long read_size, int write_size)
#define FUNC_NAME "scm_fport_buffer_add"
{
  scm_t_port *pt = SCM_PTAB_ENTRY (port);

  if (read_size == -1 || write_size == -1)
    {
      size_t default_size;
#ifdef HAVE_STRUCT_STAT_ST_BLKSIZE
      struct stat st;
      scm_t_fport *fp = SCM_FSTREAM (port);
      
      default_size = (fstat (fp->fdes, &st) == -1) ? default_buffer_size
	: st.st_blksize;
#else
      default_size = default_buffer_size;
#endif
      if (read_size == -1)
	read_size = default_size;
      if (write_size == -1)
	write_size = default_size;
    }

  if (SCM_INPUT_PORT_P (port) && read_size > 0)
    {
      pt->read_buf = scm_gc_malloc_pointerless (read_size, "port buffer");
      pt->read_pos = pt->read_end = pt->read_buf;
      pt->read_buf_size = read_size;
    }
  else
    {
      pt->read_pos = pt->read_buf = pt->read_end = &pt->shortbuf;
      pt->read_buf_size = 1;
    }

  if (SCM_OUTPUT_PORT_P (port) && write_size > 0)
    {
      pt->write_buf = scm_gc_malloc_pointerless (write_size, "port buffer");
      pt->write_pos = pt->write_buf;
      pt->write_buf_size = write_size;
    }
  else
    {
      pt->write_buf = pt->write_pos = &pt->shortbuf;
      pt->write_buf_size = 1;
    }

  pt->write_end = pt->write_buf + pt->write_buf_size;
  if (read_size > 0 || write_size > 0)
    SCM_SET_CELL_WORD_0 (port, SCM_CELL_WORD_0 (port) & ~SCM_BUF0);
  else
    SCM_SET_CELL_WORD_0 (port, SCM_CELL_WORD_0 (port) | SCM_BUF0);
}
#undef FUNC_NAME

SCM_DEFINE (scm_setvbuf, "setvbuf", 2, 1, 0, 
            (SCM port, SCM mode, SCM size),
	    "Set the buffering mode for @var{port}.  @var{mode} can be:\n"
	    "@table @code\n"
	    "@item _IONBF\n"
	    "non-buffered\n"
	    "@item _IOLBF\n"
	    "line buffered\n"
	    "@item _IOFBF\n"
	    "block buffered, using a newly allocated buffer of @var{size} bytes.\n"
	    "If @var{size} is omitted, a default size will be used.\n"
	    "@end table")
#define FUNC_NAME s_scm_setvbuf
{
  int cmode;
  long csize;
  SCM drained;
  scm_t_port *pt;

  port = SCM_COERCE_OUTPORT (port);

  SCM_VALIDATE_OPFPORT (1,port);
  cmode = scm_to_int (mode);
  if (cmode != _IONBF && cmode != _IOFBF && cmode != _IOLBF)
    scm_out_of_range (FUNC_NAME, mode);

  if (cmode == _IOLBF)
    {
      SCM_SET_CELL_WORD_0 (port, SCM_CELL_WORD_0 (port) | SCM_BUFLINE);
      cmode = _IOFBF;
    }
  else
    {
      SCM_SET_CELL_WORD_0 (port, SCM_CELL_WORD_0 (port) & ~(scm_t_bits)SCM_BUFLINE);
    }

  if (SCM_UNBNDP (size))
    {
      if (cmode == _IOFBF)
	csize = -1;
      else
	csize = 0;
    }
  else
    {
      csize = scm_to_int (size);
      if (csize < 0 || (cmode == _IONBF && csize > 0))
	scm_out_of_range (FUNC_NAME, size);
    }

  pt = SCM_PTAB_ENTRY (port);

  if (SCM_INPUT_PORT_P (port))
    drained = scm_drain_input (port);
  else
    drained = scm_nullstr;

  if (SCM_OUTPUT_PORT_P (port))
    scm_flush_unlocked (port);

  if (pt->read_buf == pt->putback_buf)
    {
      pt->read_buf = pt->saved_read_buf;
      pt->read_pos = pt->saved_read_pos;
      pt->read_end = pt->saved_read_end;
      pt->read_buf_size = pt->saved_read_buf_size;
    }
  if (pt->read_buf != &pt->shortbuf)
    scm_gc_free (pt->read_buf, pt->read_buf_size, "port buffer");
  if (pt->write_buf != &pt->shortbuf)
    scm_gc_free (pt->write_buf, pt->write_buf_size, "port buffer");

  scm_fport_buffer_add (port, csize, csize);

  if (scm_is_true (drained) && scm_c_string_length (drained))
    scm_unread_string (drained, port);

  return SCM_UNSPECIFIED;
}
#undef FUNC_NAME

/* Move ports with the specified file descriptor to new descriptors,
 * resetting the revealed count to 0.
 */
static void
scm_i_evict_port (void *closure, SCM port)
{
  int fd = * (int*) closure;

  if (SCM_FPORTP (port))
    {
      scm_t_port *p;
      scm_t_fport *fp;

      /* XXX: In some cases, we can encounter a port with no associated ptab
	 entry.  */
      p = SCM_PTAB_ENTRY (port);
      fp = (p != NULL) ? (scm_t_fport *) p->stream : NULL;

      if ((fp != NULL) && (fp->fdes == fd))
	{
          if (fp->cloexec_p)
            /* The result will be 3 or more.  Presumably we don't want
               to accidentally end on 0, 1, or 2.  */
            fp->fdes = fcntl (fd, F_DUPFD_CLOEXEC, 3);
          else
            fp->fdes = dup (fd);

	  if (fp->fdes == -1)
	    scm_syserror ("scm_evict_ports");
	  scm_set_port_revealed_x (port, scm_from_int (0));
	}
    }
}

void
scm_evict_ports (int fd)
{
  scm_c_port_for_each (scm_i_evict_port, (void *) &fd);
}


SCM_DEFINE (scm_file_port_p, "file-port?", 1, 0, 0,
	    (SCM obj),
	    "Determine whether @var{obj} is a port that is related to a file.")
#define FUNC_NAME s_scm_file_port_p
{
  return scm_from_bool (SCM_FPORTP (obj));
}
#undef FUNC_NAME


SCM_DEFINE (scm_file_port_close_on_exec_p, "file-port-close-on-exec?", 1, 0, 0,
	    (SCM fport),
	    "Determine whether @var{fobj} was created with the @code{FD_CLOEXEC} flag set.")
#define FUNC_NAME s_scm_file_port_close_on_exec_p
{
  SCM_VALIDATE_OPFPORT (1, fport);
  return scm_from_bool (SCM_FSTREAM (fport)->cloexec_p);
}
#undef FUNC_NAME


static SCM sys_file_port_name_canonicalization;
SCM_SYMBOL (sym_relative, "relative");
SCM_SYMBOL (sym_absolute, "absolute");

static SCM
fport_canonicalize_filename (SCM filename)
{
  SCM mode = scm_fluid_ref (sys_file_port_name_canonicalization);

  if (!scm_is_string (filename))
    {
      return filename;
    }
  else if (scm_is_eq (mode, sym_relative))
    {
      SCM path, rel;

      path = scm_variable_ref (scm_c_module_lookup (scm_the_root_module (),
                                                    "%load-path"));
      rel = scm_i_relativize_path (filename, path);

      return scm_is_true (rel) ? rel : filename;
    }
  else if (scm_is_eq (mode, sym_absolute))
    {
      char *str, *canon;
  
      str = scm_to_locale_string (filename);
      canon = canonicalize_file_name (str);
      free (str);
  
      return canon ? scm_take_locale_string (canon) : filename;
    }
  else
    {
      return filename;
    }
}


/* scm_open_file
 * Return a new port open on a given file.
 *
 * The mode string must match the pattern: [rwa+]** which
 * is interpreted in the usual unix way.
 *
 * Return the new port.
 */
SCM_DEFINE (scm_open_file, "open-file", 2, 0, 0,
	    (SCM filename, SCM mode),
	    "Open the file whose name is @var{filename}, and return a port\n"
	    "representing that file.  The attributes of the port are\n"
	    "determined by the @var{mode} string.  The way in which this is\n"
	    "interpreted is similar to C stdio.  The first character must be\n"
	    "one of the following:\n"
	    "@table @samp\n"
	    "@item r\n"
	    "Open an existing file for input.\n"
	    "@item w\n"
	    "Open a file for output, creating it if it doesn't already exist\n"
	    "or removing its contents if it does.\n"
	    "@item a\n"
	    "Open a file for output, creating it if it doesn't already\n"
	    "exist.  All writes to the port will go to the end of the file.\n"
	    "The \"append mode\" can be turned off while the port is in use\n"
	    "@pxref{Ports and File Descriptors, fcntl}\n"
	    "@end table\n"
	    "The following additional characters can be appended:\n"
	    "@table @samp\n"
	    "@item b\n"
	    "Open the underlying file in binary mode, if supported by the system.\n"
	    "Also, open the file using the binary-compatible character encoding\n"
	    "\"ISO-8859-1\", ignoring the port's encoding and the coding declaration\n"
	    "at the top of the input file, if any.\n"
	    "@item +\n"
	    "Open the port for both input and output.  E.g., @code{r+}: open\n"
	    "an existing file for both input and output.\n"
	    "@item 0\n"
	    "Create an \"unbuffered\" port.  In this case input and output\n"
	    "operations are passed directly to the underlying port\n"
	    "implementation without additional buffering.  This is likely to\n"
	    "slow down I/O operations.  The buffering mode can be changed\n"
	    "while a port is in use @pxref{Ports and File Descriptors,\n"
	    "setvbuf}\n"
	    "@item l\n"
	    "Add line-buffering to the port.  The port output buffer will be\n"
	    "automatically flushed whenever a newline character is written.\n"
	    "@end table\n"
	    "When the file is opened, this procedure will scan for a coding\n"
	    "declaration@pxref{Character Encoding of Source Files}. If present\n"
	    "will use that encoding for interpreting the file.  Otherwise, the\n"
	    "port's encoding will be used.\n"
	    "\n"
	    "In theory we could create read/write ports which were buffered\n"
	    "in one direction only.  However this isn't included in the\n"
	    "current interfaces.  If a file cannot be opened with the access\n"
	    "requested, @code{open-file} throws an exception.")
#define FUNC_NAME s_scm_open_file
{
  SCM port;
  int fdes, flags = 0, use_encoding = 1;
  unsigned int retries;
  char *file, *md, *ptr;

  scm_dynwind_begin (0);

  file = scm_to_locale_string (filename);
  scm_dynwind_free (file);

  md = scm_to_locale_string (mode);
  scm_dynwind_free (md);

  switch (*md)
    {
    case 'r':
      flags |= O_RDONLY;
      break;
    case 'w':
      flags |= O_WRONLY | O_CREAT | O_TRUNC;
      break;
    case 'a':
      flags |= O_WRONLY | O_CREAT | O_APPEND;
      break;
    default:
      scm_out_of_range (FUNC_NAME, mode);
    }
  ptr = md + 1;
  while (*ptr != '\0')
    {
      switch (*ptr)
	{
	case '+':
	  flags = (flags & ~(O_RDONLY | O_WRONLY)) | O_RDWR;
	  break;
	case 'b':
	  use_encoding = 0;
#if defined (O_BINARY)
	  flags |= O_BINARY;
#endif
	  break;
	case '0':  /* unbuffered: handled later.  */
	case 'l':  /* line buffered: handled during output.  */
	  break;
	default:
	  scm_out_of_range (FUNC_NAME, mode);
	}
      ptr++;
    }

  for (retries = 0, fdes = -1;
       fdes < 0 && retries < 2;
       retries++)
    {
      SCM_SYSCALL (fdes = open_or_open64 (file, flags, 0666));
      if (fdes == -1)
	{
	  int en = errno;

	  if (en == EMFILE && retries == 0)
	    /* Run the GC in case it collects open file ports that are no
	       longer referenced.  */
	    scm_i_gc (FUNC_NAME);
	  else
	    SCM_SYSERROR_MSG ("~A: ~S",
			      scm_cons (scm_strerror (scm_from_int (en)),
					scm_cons (filename, SCM_EOL)), en);
	}
    }

  /* Create a port from this file descriptor.  The port's encoding is initially
     %default-port-encoding.  */
  port = scm_i_fdes_to_port (fdes, scm_i_mode_bits (mode),
                             fport_canonicalize_filename (filename));

  if (use_encoding)
    {
      /* If this file has a coding declaration, use that as the port
	 encoding.  */
      if (SCM_INPUT_PORT_P (port))
	{
	  char *enc = scm_i_scan_for_encoding (port);
	  if (enc != NULL)
	    scm_i_set_port_encoding_x (port, enc);
	}
    }
  else
    /* If this is a binary file, use the binary-friendly ISO-8859-1
       encoding.  */
    scm_i_set_port_encoding_x (port, NULL);

  scm_dynwind_end ();

  return port;
}
#undef FUNC_NAME


#ifdef __MINGW32__
/*
 * Try getting the appropiate file flags for a given file descriptor
 * under Windows. This incorporates some fancy operations because Windows
 * differentiates between file, pipe and socket descriptors.
 */
#ifndef O_ACCMODE
# define O_ACCMODE 0x0003
#endif

static int getflags (int fdes)
{
  int flags = 0;
  struct stat buf;
  int error, optlen = sizeof (int);

  /* Is this a socket ? */
  if (getsockopt (fdes, SOL_SOCKET, SO_ERROR, (void *) &error, &optlen) >= 0)
    flags = O_RDWR;
  /* Maybe a regular file ? */
  else if (fstat (fdes, &buf) < 0)
    flags = -1;
  else
    {
      /* Or an anonymous pipe handle ? */
      if (buf.st_mode & _S_IFIFO)
	flags = PeekNamedPipe ((HANDLE) _get_osfhandle (fdes), NULL, 0, 
			       NULL, NULL, NULL) ? O_RDONLY : O_WRONLY;
      /* stdin ? */
      else if (fdes == fileno (stdin) && isatty (fdes))
	flags = O_RDONLY;
      /* stdout / stderr ? */
      else if ((fdes == fileno (stdout) || fdes == fileno (stderr)) && 
	       isatty (fdes))
	flags = O_WRONLY;
      else
	flags = buf.st_mode;
    }
  return flags;
}
#endif /* __MINGW32__ */

/* Building Guile ports from a file descriptor.  */

/* Build a Scheme port from an open file descriptor `fdes'.
   MODE indicates whether FILE is open for reading or writing; it uses
      the same notation as open-file's second argument.
   NAME is a string to be used as the port's filename.
*/
SCM
scm_i_fdes_to_port (int fdes, long mode_bits, SCM name)
#define FUNC_NAME "scm_fdes_to_port"
{
  SCM port;
  scm_t_fport *fp;
  int flags;
  int fd_flags;

  /* test that fdes is valid.  */
#ifdef __MINGW32__
  flags = getflags (fdes);
#else
  flags = fcntl (fdes, F_GETFL, 0);
#endif
  if (flags == -1)
    SCM_SYSERROR;
  flags &= O_ACCMODE;
  if (flags != O_RDWR
      && ((flags != O_WRONLY && (mode_bits & SCM_WRTNG))
	  || (flags != O_RDONLY && (mode_bits & SCM_RDNG))))
    {
      SCM_MISC_ERROR ("requested file mode not available on fdes", SCM_EOL);
    }

#ifdef F_GETFD
  fd_flags = fcntl (fdes, F_GETFD, 0);
#else
  fd_flags = 0;
#endif
  if (fd_flags == -1)
    SCM_SYSERROR;

  fp = (scm_t_fport *) scm_gc_malloc_pointerless (sizeof (scm_t_fport),
                                                  "file port");
  fp->fdes = fdes;
  fp->cloexec_p = fd_flags & FD_CLOEXEC ? 1 : 0;
  fp->reserved = 0;

  port = scm_c_make_port (scm_tc16_fport, mode_bits, (scm_t_bits)fp);
  
  SCM_PTAB_ENTRY (port)->rw_random = SCM_FDES_RANDOM_P (fdes);

  if (mode_bits & SCM_BUF0)
    scm_fport_buffer_add (port, 0, 0);
  else
    scm_fport_buffer_add (port, -1, -1);

  SCM_SET_FILENAME (port, name);

  return port;
}
#undef FUNC_NAME

SCM
scm_fdes_to_port (int fdes, char *mode, SCM name)
{
  return scm_i_fdes_to_port (fdes, scm_mode_bits (mode), name);
}

/* Return a lower bound on the number of bytes available for input.  */
static int
fport_input_waiting (SCM port)
{
  int fdes = SCM_FSTREAM (port)->fdes;

  /* `FD_SETSIZE', which is 1024 on GNU systems, effectively limits the
     highest numerical value of file descriptors that can be monitored.
     Thus, use poll(2) whenever that is possible.  */

#ifdef HAVE_POLL
  struct pollfd pollfd = { fdes, POLLIN, 0 };

  if (poll (&pollfd, 1, 0) < 0)
    scm_syserror ("fport_input_waiting");

  return pollfd.revents & POLLIN ? 1 : 0;

#elif defined(HAVE_SELECT)
  struct timeval timeout;
  SELECT_TYPE read_set;
  SELECT_TYPE write_set;
  SELECT_TYPE except_set;

  FD_ZERO (&read_set);
  FD_ZERO (&write_set);
  FD_ZERO (&except_set);

  FD_SET (fdes, &read_set);
  
  timeout.tv_sec = 0;
  timeout.tv_usec = 0;

  if (select (SELECT_SET_SIZE,
	      &read_set, &write_set, &except_set, &timeout)
      < 0)
    scm_syserror ("fport_input_waiting");
  return FD_ISSET (fdes, &read_set) ? 1 : 0;

#elif HAVE_IOCTL && defined (FIONREAD)
  /* Note: cannot test just defined(FIONREAD) here, since mingw has FIONREAD
     (for use with winsock ioctlsocket()) but not ioctl().  */
  int fdes = SCM_FSTREAM (port)->fdes;
  int remir;
  ioctl(fdes, FIONREAD, &remir);
  return remir;

#else    
  scm_misc_error ("fport_input_waiting",
		  "Not fully implemented on this platform",
		  SCM_EOL);
#endif
}


static int 
fport_print (SCM exp, SCM port, scm_print_state *pstate SCM_UNUSED)
{
  scm_puts_unlocked ("#<", port);
  scm_print_port_mode (exp, port);    
  if (SCM_OPFPORTP (exp))
    {
      int fdes;
      SCM name = SCM_FILENAME (exp);
      if (scm_is_string (name) || scm_is_symbol (name))
	scm_display (name, port);
      else
	scm_puts_unlocked (SCM_PTOBNAME (SCM_PTOBNUM (exp)), port);
      scm_putc_unlocked (' ', port);
      fdes = (SCM_FSTREAM (exp))->fdes;

#if (defined HAVE_TTYNAME) && (defined HAVE_POSIX)
      if (isatty (fdes))
	scm_display (scm_ttyname (exp), port);
      else
#endif /* HAVE_TTYNAME */
	scm_intprint (fdes, 10, port);
    }
  else
    {
      scm_puts_unlocked (SCM_PTOBNAME (SCM_PTOBNUM (exp)), port);
      scm_putc_unlocked (' ', port);
      scm_uintprint ((scm_t_bits) SCM_PTAB_ENTRY (exp), 16, port);
    }
  scm_putc_unlocked ('>', port);
  return 1;
}

static void fport_flush (SCM port);

/* fill a port's read-buffer with a single read.  returns the first
   char or EOF if end of file.  */
static scm_t_wchar
fport_fill_input (SCM port)
{
  long count;
  scm_t_port *pt = SCM_PTAB_ENTRY (port);
  scm_t_fport *fp = SCM_FSTREAM (port);

  SCM_SYSCALL (count = read (fp->fdes, pt->read_buf, pt->read_buf_size));
  if (count == -1)
    scm_syserror ("fport_fill_input");
  if (count == 0)
    return (scm_t_wchar) EOF;
  else
    {
      pt->read_pos = pt->read_buf;
      pt->read_end = pt->read_buf + count;
      return *pt->read_buf;
    }
}

static scm_t_off
fport_seek (SCM port, scm_t_off offset, int whence)
{
  scm_t_port *pt = SCM_PTAB_ENTRY (port);
  scm_t_fport *fp = SCM_FSTREAM (port);
  off_t_or_off64_t rv;
  off_t_or_off64_t result;

  if (pt->rw_active == SCM_PORT_WRITE)
    {
      if (offset != 0 || whence != SEEK_CUR)
	{
	  fport_flush (port);
	  result = rv = lseek_or_lseek64 (fp->fdes, offset, whence);
	}
      else
	{
	  /* read current position without disturbing the buffer.  */
	  rv = lseek_or_lseek64 (fp->fdes, offset, whence);
	  result = rv + (pt->write_pos - pt->write_buf);
	}
    }
  else if (pt->rw_active == SCM_PORT_READ)
    {
      if (offset != 0 || whence != SEEK_CUR)
	{
	  /* could expand to avoid a second seek.  */
	  scm_end_input_unlocked (port);
	  result = rv = lseek_or_lseek64 (fp->fdes, offset, whence);
	}
      else
	{
	  /* read current position without disturbing the buffer
	     (particularly the unread-char buffer).  */
	  rv = lseek_or_lseek64 (fp->fdes, offset, whence);
	  result = rv - (pt->read_end - pt->read_pos);

	  if (pt->read_buf == pt->putback_buf)
	    result -= pt->saved_read_end - pt->saved_read_pos;
	}
    }
  else /* SCM_PORT_NEITHER */
    {
      result = rv = lseek_or_lseek64 (fp->fdes, offset, whence);
    }

  if (rv == -1)
    scm_syserror ("fport_seek");

  return result;
}

static void
fport_truncate (SCM port, scm_t_off length)
{
  scm_t_fport *fp = SCM_FSTREAM (port);

  if (ftruncate (fp->fdes, length) == -1)
    scm_syserror ("ftruncate");
}

static void
fport_write (SCM port, const void *data, size_t size)
#define FUNC_NAME "fport_write"
{
  /* this procedure tries to minimize the number of writes/flushes.  */
  scm_t_port *pt = SCM_PTAB_ENTRY (port);

  if (pt->write_buf == &pt->shortbuf
      || (pt->write_pos == pt->write_buf && size >= pt->write_buf_size))
    {
      /* Unbuffered port, or port with empty buffer and data won't fit in
	 buffer.  */
      if (full_write (SCM_FPORT_FDES (port), data, size) < size)
	SCM_SYSERROR;

      return;
    }

  {
    scm_t_off space = pt->write_end - pt->write_pos;

    if (size <= space)
      {
	/* data fits in buffer.  */
	memcpy (pt->write_pos, data, size);
	pt->write_pos += size;
	if (pt->write_pos == pt->write_end)
	  {
	    fport_flush (port);
	    /* we can skip the line-buffering check if nothing's buffered. */
	    return;
	  }
      }
    else
      {
	memcpy (pt->write_pos, data, space);
	pt->write_pos = pt->write_end;
	fport_flush (port);
	{
	  const void *ptr = ((const char *) data) + space;
	  size_t remaining = size - space;

	  if (size >= pt->write_buf_size)
	    {
	      if (full_write (SCM_FPORT_FDES (port), ptr, remaining)
		  < remaining)
		SCM_SYSERROR;
	      return;
	    }
	  else
	    {
	      memcpy (pt->write_pos, ptr, remaining);
	      pt->write_pos += remaining;
	    }
	}
      }

    /* handle line buffering.  */     
    if ((SCM_CELL_WORD_0 (port) & SCM_BUFLINE) && memchr (data, '\n', size))
      fport_flush (port);
  }
}
#undef FUNC_NAME

static void
fport_flush (SCM port)
{
  size_t written;
  scm_t_port *pt = SCM_PTAB_ENTRY (port);
  scm_t_fport *fp = SCM_FSTREAM (port);
  size_t count = pt->write_pos - pt->write_buf;

  written = full_write (fp->fdes, pt->write_buf, count);
  if (written < count)
    scm_syserror ("scm_flush");

  pt->write_pos = pt->write_buf;
  pt->rw_active = SCM_PORT_NEITHER;
}

/* clear the read buffer and adjust the file position for unread bytes. */
static void
fport_end_input (SCM port, int offset)
{
  scm_t_fport *fp = SCM_FSTREAM (port);
  scm_t_port *pt = SCM_PTAB_ENTRY (port);
  
  offset += pt->read_end - pt->read_pos;

  if (offset > 0)
    {
      pt->read_pos = pt->read_end;
      /* will throw error if unread-char used at beginning of file
	 then attempting to write.  seems correct.  */
      if (lseek (fp->fdes, -offset, SEEK_CUR) == -1)
	scm_syserror ("fport_end_input");
    }
  pt->rw_active = SCM_PORT_NEITHER;
}

static void
close_the_fd (void *data)
{
  scm_t_fport *fp = data;

  close (fp->fdes);
  /* There's already one exception.  That's probably enough!  */
  errno = 0;
}

static int
fport_close (SCM port)
{
  scm_t_fport *fp = SCM_FSTREAM (port);
  int rv;

  scm_dynwind_begin (0);
  scm_dynwind_unwind_handler (close_the_fd, fp, 0);
  fport_flush (port);
  scm_dynwind_end ();

  scm_port_non_buffer (SCM_PTAB_ENTRY (port));

  rv = close (fp->fdes);
  if (rv)
    /* It's not useful to retry after EINTR, as the file descriptor is
       in an undefined state.  See http://lwn.net/Articles/365294/.
       Instead just throw an error if close fails, trusting that the fd
       was cleaned up.  */
    scm_syserror ("fport_close");

  return 0;
}

static size_t
fport_free (SCM port)
{
  fport_close (port);
  return 0;
}

static scm_t_bits
scm_make_fptob ()
{
  scm_t_bits tc = scm_make_port_type ("file", fport_fill_input, fport_write);

  scm_set_port_free            (tc, fport_free);
  scm_set_port_print           (tc, fport_print);
  scm_set_port_flush           (tc, fport_flush);
  scm_set_port_end_input       (tc, fport_end_input);
  scm_set_port_close           (tc, fport_close);
  scm_set_port_seek            (tc, fport_seek);
  scm_set_port_truncate        (tc, fport_truncate);
  scm_set_port_input_waiting   (tc, fport_input_waiting);

  return tc;
}

void
scm_init_fports ()
{
  scm_tc16_fport = scm_make_fptob ();

  scm_c_define ("_IOFBF", scm_from_int (_IOFBF));
  scm_c_define ("_IOLBF", scm_from_int (_IOLBF));
  scm_c_define ("_IONBF", scm_from_int (_IONBF));

  sys_file_port_name_canonicalization = scm_make_fluid ();
  scm_c_define ("%file-port-name-canonicalization",
                sys_file_port_name_canonicalization);
                                    
#include "libguile/fports.x"
}

/*
  Local Variables:
  c-file-style: "gnu"
  End:
*/