File: memfile.c

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/*  Part of SWI-Prolog

    Author:        Jan Wielemaker
    E-mail:        J.Wielemaker@vu.nl
    WWW:           http://www.swi-prolog.org
    Copyright (c)  2001-2015, University of Amsterdam
                              VU University Amsterdam
    All rights reserved.

    Redistribution and use in source and binary forms, with or without
    modification, are permitted provided that the following conditions
    are met:

    1. Redistributions of source code must retain the above copyright
       notice, this list of conditions and the following disclaimer.

    2. Redistributions in binary form must reproduce the above copyright
       notice, this list of conditions and the following disclaimer in
       the documentation and/or other materials provided with the
       distribution.

    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
    POSSIBILITY OF SUCH DAMAGE.
*/

#include <config.h>
#include <SWI-Stream.h>
#include <SWI-Prolog.h>
#include <string.h>
#include <stdlib.h>
#include <assert.h>
#include <errno.h>
#ifdef O_PLMT
#include <pthread.h>
#endif
#include "error.h"

#ifdef O_PLMT
#define LOCK(mf)   pthread_mutex_lock(&(mf)->mutex)
#define UNLOCK(mf) pthread_mutex_unlock(&(mf)->mutex)
#else
#define LOCK(mf)
#define UNLOCK(mf)
#endif

static atom_t ATOM_encoding;
static atom_t ATOM_unknown;
static atom_t ATOM_octet;
static atom_t ATOM_ascii;
static atom_t ATOM_iso_latin_1;
static atom_t ATOM_text;
static atom_t ATOM_utf8;
static atom_t ATOM_unicode_be;
static atom_t ATOM_unicode_le;
static atom_t ATOM_wchar_t;
static atom_t ATOM_read;
static atom_t ATOM_write;
static atom_t ATOM_append;
static atom_t ATOM_update;
static atom_t ATOM_insert;
static atom_t ATOM_free_on_close;

#define MEMFILE_MAGIC	0x5624a6b3L
#define MEMFILE_CMAGIC	0x5624a6b7L
#define NOSIZE ((size_t)-1)

#define	V_CHARCOUNT	0x01
#define	V_LINENO	0x02
#define	V_LINEPOS	0x04
#define V_ALL		0x07

typedef struct
{ size_t	byte_count;		/* Byte position in MF */
  size_t	char_count;		/* Corresponding logical char */
  size_t	line_no;		/* Line */
  size_t	line_pos;		/* Line position */
  unsigned int	valid;			/* Valid mask */
} pos_cache;


typedef struct
{ char	       *data;			/* data of the file */
  size_t	end;			/* End of buffer */
  size_t	gap_start;		/* Insertion point */
  size_t	gap_size;		/* Insertion hole */
  size_t	char_count;		/* size in characters */
  pos_cache	pcache;			/* Cached position */
  size_t	here;			/* read pointer */
  IOSTREAM     *stream;			/* Stream hanging onto it */
  atom_t	symbol;			/* <memory_file>(%p) */
  atom_t	atom;			/* Created from atom */
  atom_t	mode;			/* current open mode */
#ifdef O_PLMT
  pthread_mutex_t mutex;		/* Our lock */
#endif
  int		magic;			/* MEMFILE_MAGIC */
  int		free_on_close;		/* free if it is closed */
  IOENC		encoding;		/* encoding of the data */
} memfile;

static int	destroy_memory_file(memfile *m);


		 /*******************************
		 *	      SYMBOL		*
		 *******************************/

static void
acquire_memfile_symbol(atom_t symbol)
{ memfile *mf = PL_blob_data(symbol, NULL, NULL);
  mf->symbol = symbol;
}

static int
release_memfile_symbol(atom_t symbol)
{ memfile *mf = PL_blob_data(symbol, NULL, NULL);

  destroy_memory_file(mf);
  return TRUE;
}

static int
compare_memfile_symbols(atom_t a, atom_t b)
{ memfile *mfa = PL_blob_data(a, NULL, NULL);
  memfile *mfb = PL_blob_data(b, NULL, NULL);

  return ( mfa > mfb ?  1 :
	   mfa < mfb ? -1 : 0
	 );
}


static int
write_memfile_symbol(IOSTREAM *s, atom_t symbol, int flags)
{ memfile *mf = PL_blob_data(symbol, NULL, NULL);

  Sfprintf(s, "<memory_file>(%p)", mf);
  return TRUE;
}


static PL_blob_t memfile_blob =
{ PL_BLOB_MAGIC,
  PL_BLOB_NOCOPY,
  "memory_file",
  release_memfile_symbol,
  compare_memfile_symbols,
  write_memfile_symbol,
  acquire_memfile_symbol
};


static int
unify_memfile(term_t handle, memfile *mf)
{ if ( PL_unify_blob(handle, mf, sizeof(*mf), &memfile_blob) )
    return TRUE;

  if ( !PL_is_variable(handle) )
    return PL_uninstantiation_error(handle);

  return FALSE;					/* (resource) error */
}


static int
get_memfile(term_t handle, memfile **mfp)
{ PL_blob_t *type;
  void *data;

  if ( PL_get_blob(handle, &data, NULL, &type) && type == &memfile_blob)
  { memfile *mf = data;

    assert(mf->magic == MEMFILE_MAGIC);
    LOCK(mf);

    if ( mf->symbol )
    { *mfp = mf;

      return TRUE;
    }

    UNLOCK(mf);
    PL_permission_error("access", "freed_memory_file", handle);
    return FALSE;
  }

  return PL_type_error("memory_file", handle);
}


static void
release_memfile(memfile *mf)
{ UNLOCK(mf);
}


static void
empty_memory_file(memfile *m)
{ if ( m->data )
    free(m->data);

  m->encoding     = ENC_UTF8;
  m->data         = NULL;
  m->end          = 0;
  m->gap_start    = 0;
  m->gap_size     = 0;
  m->char_count   = NOSIZE;
  m->pcache.valid = 0;
  m->here         = 0;
}


static foreign_t
new_memory_file(term_t handle)
{ memfile *m = calloc(1, sizeof(*m));

  if ( !m )
    return PL_resource_error("memory");

  m->magic    = MEMFILE_MAGIC;
  m->encoding = ENC_UTF8;
  m->data     = NULL;
  m->atom     = 0;
  m->symbol   = 0;
  m->stream   = NULL;
#ifdef O_PLMT
  pthread_mutex_init(&m->mutex, NULL);
#endif

  if ( unify_memfile(handle, m) )
    return TRUE;

  destroy_memory_file(m);
  return FALSE;
}


static void
clean_memory_file(memfile *m)
{ if ( m->stream )
  { Sclose(m->stream);
    m->stream = NULL;
  }
  if ( m->atom )
  { PL_unregister_atom(m->atom);
    m->atom = 0;
    m->data = NULL;
  } else if ( m->data )
  { free(m->data);
    m->data = NULL;
  }
}


static int
destroy_memory_file(memfile *m)
{ clean_memory_file(m);
#ifdef O_PLMT
  pthread_mutex_destroy(&m->mutex);
#endif
  m->magic = MEMFILE_CMAGIC;
  free(m);

  return TRUE;
}


static foreign_t
free_memory_file(term_t handle)
{ memfile *m;

  if ( get_memfile(handle, &m) )
  { m->symbol = 0;
    clean_memory_file(m);
    release_memfile(m);
    return TRUE;
  }

  return FALSE;
}

		 /*******************************
		 *	     CHECKING		*
		 *******************************/

#define ISUTF8_CB(c)  (((c)&0xc0) == 0x80) /* Is continuation byte */

#ifdef O_SECURE

#define CONT(in,i)   (assert(ISUTF8_CB(in[i])),1)
#define IS_UTF8_2BYTE(in) \
	((in[0]&0xe0) == 0xc0 && CONT(in,1))
#define IS_UTF8_3BYTE(in) \
	((in[0]&0xf0) == 0xe0 && CONT(in,1)&&CONT(in,2))
#define IS_UTF8_4BYTE(in) \
	((in[0]&0xf8) == 0xf0 && CONT(in,1)&&CONT(in,2)&&CONT(in,3))
#define IS_UTF8_5BYTE(in) \
	((in[0]&0xfc) == 0xf8 && CONT(in,1)&&CONT(in,2)&&CONT(in,3)&&CONT(in,4))
#define IS_UTF8_6BYTE(in) \
	((in[0]&0xfe) == 0xfc && CONT(in,1)&&CONT(in,2)&&CONT(in,3)&&CONT(in,4)&&CONT(in,5))

static size_t
check_utf8_seq(char *s, size_t len)
{ size_t count = 0;
  size_t skip;

  while(len > 0)
  { if ( (*s&0x80) )
    {      if ( IS_UTF8_2BYTE(s) ) skip = 2;
      else if ( IS_UTF8_3BYTE(s) ) skip = 3;
      else if ( IS_UTF8_4BYTE(s) ) skip = 4;
      else if ( IS_UTF8_5BYTE(s) ) skip = 5;
      else if ( IS_UTF8_6BYTE(s) ) skip = 6;
      else assert(0);
    } else
      skip = 1;

    assert(len >= skip);
    len -= skip;
    s   += skip;

    count++;
  }

  return count;
}


static void
check_memfile(memfile *mf)
{ size_t count = 0;

  count += check_utf8_seq(&mf->data[0],                          mf->gap_start);
  count += check_utf8_seq(&mf->data[mf->gap_start+mf->gap_size],
			  mf->end-(mf->gap_size+mf->gap_start));

  assert(mf->char_count == NOSIZE || mf->char_count == count);
}

#else /*O_SECURE*/

#define check_memfile(mf) (void)0

#endif /*O_SECURE*/

		 /*******************************
		 *	 STREAM FUNCTIONS	*
		 *******************************/

#define CHECK_MEMFILE(m) \
	if ( m->magic != MEMFILE_MAGIC ) \
	{ errno = EINVAL; \
	  return -1; \
	}

static ssize_t
read_memfile(void *handle, char *buf, size_t size)
{ memfile *m = handle;
  size_t done = 0;

  CHECK_MEMFILE(m);
  if ( m->here < m->gap_start )
  { size_t before_gap = m->gap_start - m->here;
    if ( size <= before_gap )
    { memcpy(buf, &m->data[m->here], size);
      m->here += size;
      return size;
    } else
    { memcpy(buf, &m->data[m->here], before_gap);
      m->here += before_gap;
      done = before_gap;
    }
  }

  /* we are now after the gap */
  { size_t left = size - done;
    size_t start = m->here + m->gap_size;
    size_t avail = m->end - start;

    if ( avail < left )
    { left = avail;
      size = done + avail;
    }
    m->here += left;
    memcpy(&buf[done], &m->data[start], left);
    return size;
  }
}


static size_t
memfile_nextsize(size_t needed)
{ size_t size = 512;

  while ( size < needed )
    size *= 2;

  return size;
}


static int
ensure_gap_size(memfile *m, size_t size)
{ if ( m->gap_size < size )
  { size_t nextsize = memfile_nextsize(m->end+(size-m->gap_size));
    void *ptr;

    if ( m->data )
      ptr = realloc(m->data, nextsize);
    else
      ptr = malloc(nextsize);

    if ( ptr != NULL )
    { size_t after_gap = m->end - (m->gap_start + m->gap_size);

      m->data = ptr;
      memmove(&m->data[nextsize-after_gap], &m->data[m->end-after_gap], after_gap);
      m->gap_size += nextsize - m->end;
      m->end = nextsize;
    } else
    { return -1;
    }
  }

  return 0;
}


static void
move_gap_to(memfile *m, size_t to)
{ assert(to <= m->end - m->gap_size);

  if ( to != m->gap_start )
  { if ( to > m->gap_start )		/* move forwards */
    { memmove(&m->data[m->gap_start],
	      &m->data[m->gap_start+m->gap_size],
	      to - m->gap_start);
      m->gap_start = to;
    } else				/* move backwards */
    { memmove(&m->data[to+m->gap_size],
	      &m->data[to],
	      m->gap_start - to);
      m->gap_start = to;
    }
  }
}


static ssize_t
write_memfile(void *handle, char *buf, size_t size)
{ memfile *m = handle;
  int rc;

  CHECK_MEMFILE(m);
  if ( size > 0 )
  { m->char_count = NOSIZE;		/* TBD: Dynamically update? */
    if ( m->gap_start < m->pcache.byte_count )
      m->pcache.valid = 0;

    if ( m->mode == ATOM_update )
    { size_t start = m->gap_start + m->gap_size;
      size_t after = m->end - start;

      if ( size > after )
      { if ( (rc=ensure_gap_size(m, size-after)) != 0 )
	  return rc;
	m->gap_size -= size-after;
      }
      memmove(&m->data[m->gap_start], buf, size);
      m->gap_start += size;
    } else
    { if ( (rc=ensure_gap_size(m, size)) != 0 )
	return rc;
      memcpy(&m->data[m->gap_start], buf, size);
      m->gap_start += size;
      m->gap_size  -= size;
    }
  }

  return size;
}

static int64_t
seek64_memfile(void *handle, int64_t offset, int whence)
{ memfile *m = handle;

  CHECK_MEMFILE(m);
  switch(whence)
  { case SIO_SEEK_SET:
      break;
    case SIO_SEEK_CUR:
      offset += m->here;
      break;
    case SIO_SEEK_END:
      offset = (m->end-m->gap_size) - offset;
      break;
    default:
      errno = EINVAL;
      return -1;
  }
  if ( offset < 0 || offset > (m->end - m->gap_size) )
  { errno = EINVAL;
    return -1;
  }

  if ( (m->stream->flags & SIO_INPUT) )	/* reading */
  { m->here = offset;
  } else
  { move_gap_to(m, offset);
  }

  return offset;
}

static long
seek_memfile(void *handle, long offset, int whence)
{ return (long)seek64_memfile(handle, (int64_t)offset, whence);
}

static int
close_memfile(void *handle)
{ memfile *m = handle;

  CHECK_MEMFILE(m);
  m->stream = NULL;
  m->mode = 0;
  if ( m->free_on_close )
    clean_memory_file(m);
  PL_unregister_atom(m->symbol);

  return 0;
}


IOFUNCTIONS memfile_functions =
{ read_memfile,
  write_memfile,
  seek_memfile,
  close_memfile,
  NULL,					/* control */
  seek64_memfile
};


static foreign_t
alreadyOpen(term_t handle, const char *op)
{ return pl_error(NULL, 0, "already open",
		  ERR_PERMISSION, handle, op, "memory_file");
}


static struct encname
{ IOENC  code;
  atom_t *name;
} encoding_names[] =
{ { ENC_UNKNOWN,     &ATOM_unknown },
  { ENC_OCTET,       &ATOM_octet },
  { ENC_ASCII,       &ATOM_ascii },
  { ENC_ISO_LATIN_1, &ATOM_iso_latin_1 },
  { ENC_ANSI,	     &ATOM_text },
  { ENC_UTF8,        &ATOM_utf8 },
  { ENC_UNICODE_BE,  &ATOM_unicode_be },
  { ENC_UNICODE_LE,  &ATOM_unicode_le },
  { ENC_WCHAR,	     &ATOM_wchar_t },
  { ENC_UNKNOWN,     NULL },
};


static IOENC
atom_to_encoding(atom_t a)
{ struct encname *en;

  for(en=encoding_names; en->name; en++)
  { if ( *en->name == a )
      return en->code;
  }

  return ENC_UNKNOWN;
}


static int
get_encoding(term_t t, IOENC *enc)
{ atom_t en;

  if ( PL_get_atom(t, &en) )
  { IOENC encoding;

    if ( (encoding = atom_to_encoding(en)) == ENC_UNKNOWN )
      return pl_error(NULL, 0, NULL, ERR_DOMAIN, t, "encoding");

    *enc = encoding;
    return TRUE;
  }

  return pl_error(NULL, 0, NULL, ERR_TYPE, t, "encoding");
}


static foreign_t
open_memory_file4(term_t handle, term_t mode, term_t stream, term_t options)
{ memfile *m;
  int rc;

  if ( get_memfile(handle, &m) )
  { int flags = SIO_FBUF|SIO_RECORDPOS|SIO_NOMUTEX;
    atom_t iom;
    IOSTREAM *fd;
    IOENC encoding;
    int free_on_close = FALSE;

    if ( m->stream )
    { rc = alreadyOpen(handle, "open");
      goto out;
    }
    if ( !PL_get_atom(mode, &iom) )
    { rc = pl_error("open_memory_file", 3, NULL, ERR_ARGTYPE, 2,
		    mode, "io_mode");
      goto out;
    }

    encoding = m->encoding;

    if ( options )
    { term_t tail = PL_copy_term_ref(options);
      term_t head = PL_new_term_ref();

      while(PL_get_list(tail, head, tail))
      { size_t arity;
	atom_t name;

	if ( PL_get_name_arity(head, &name, &arity) && arity == 1 )
	{ term_t arg = PL_new_term_ref();

	  _PL_get_arg(1, head, arg);
	  if ( name == ATOM_encoding )
	  { if ( !get_encoding(arg, &encoding) )
	    { rc = FALSE;
	      goto out;
	    }
	  } else if ( name == ATOM_free_on_close )
	  { if ( !PL_get_bool(arg, &free_on_close) )
	    { rc = pl_error("open_memory_file", 4, NULL, ERR_TYPE,
			    arg, "boolean");
	      goto out;
	    }
	  }
	} else
	{ rc = pl_error("open_memory_file", 4, NULL, ERR_TYPE, head, "option");
	  goto out;
	}
      }
      if ( !PL_get_nil(tail) )
      { rc = pl_error("open_memory_file", 4, NULL, ERR_TYPE, tail, "list");
	goto out;
      }
    }

    if ( iom == ATOM_write  || iom == ATOM_append ||
	 iom == ATOM_update || iom == ATOM_insert )
    { flags |= SIO_OUTPUT;
      if ( m->atom )
      { rc = pl_error("open_memory_file", 3, "read only",
		      ERR_PERMISSION, handle, "modify", "memory_file");
	goto out;
      }

      if ( iom == ATOM_write )
      { empty_memory_file(m);
	m->encoding   = encoding;
      } else
      { if ( m->encoding != encoding )
	{ rc = pl_error("open_memory_file", 3, "inconsistent encoding",
			ERR_PERMISSION, handle, PL_atom_chars(iom), "memory_file");
	  goto out;
	}
	if ( iom == ATOM_append )
	{ move_gap_to(m, m->end - m->gap_size);
	} else
	{ move_gap_to(m, 0);
	}
      }

    } else if ( iom == ATOM_read )
    { flags |= SIO_INPUT;
      m->free_on_close = free_on_close;
      m->here = 0;
    } else
    { rc = pl_error("open_memory_file", 3, NULL, ERR_DOMAIN,
		    mode, "io_mode");
      goto out;
    }

    if ( encoding != ENC_OCTET )
      flags |= SIO_TEXT;

    if ( !(fd = Snew(m, flags, &memfile_functions)) )
    { rc = pl_error("open_memory_file", 3, NULL, ERR_ERRNO, errno,
		    "create", "memory_file", handle);
      goto out;
    }

    if ( (rc=PL_unify_stream(stream, fd)) )
    { fd->encoding = encoding;
      fd->newline = SIO_NL_POSIX;
      m->stream = fd;
      m->mode = iom;
      PL_register_atom(m->symbol);
    } else
    { Sclose(fd);
    }

  out:
    release_memfile(m);
  } else
    rc = FALSE;

  return rc;
}


static foreign_t
open_memory_file(term_t handle, term_t mode, term_t stream)
{ return open_memory_file4(handle, mode, stream, 0);
}


static int
get_size_mf(memfile *m, IOENC encoding, size_t *sizep)
{ size_t size;

  if ( m->char_count != NOSIZE && encoding == m->encoding )
  { size = m->char_count;
  } else
  { size = m->end - m->gap_size;

    switch( encoding )
    { case ENC_ISO_LATIN_1:
      case ENC_OCTET:
      case ENC_ASCII:
	break;
      case ENC_UNICODE_BE:
      case ENC_UNICODE_LE:
	size /= 2;
        break;
      case ENC_WCHAR:
	size /= sizeof(wchar_t);
        break;
      case ENC_UTF8:
      { size_t gap_end = m->gap_start+m->gap_size;
	size = ( PL_utf8_strlen(m->data, m->gap_start) +
		 PL_utf8_strlen(&m->data[gap_end], m->end-gap_end)
	       );  /* assumes UTF-8 sequences are not broken over the gap */
	break;
      }
      default:
	assert(0);
        return FALSE;
    }

    if ( encoding == m->encoding )
      m->char_count = size;
  }

  *sizep = size;
  return TRUE;
}



static foreign_t
size_memory_file(term_t handle, term_t sizeh, term_t encoding)
{ memfile *m;
  int rc;

  if ( get_memfile(handle, &m) )
  { size_t size;
    IOENC size_enc;

    if ( m->stream && !m->atom )
    { rc = alreadyOpen(handle, "size");
      goto out;
    }

    if ( encoding )
    { if ( !get_encoding(encoding, &size_enc) )
      { rc = FALSE;
	goto out;
      }
    } else
      size_enc = m->encoding;

    rc = ( get_size_mf(m, size_enc, &size) &&
	   PL_unify_int64(sizeh, size)
	 );
  out:
    release_memfile(m);
  } else
    rc = FALSE;

  return rc;
}


static foreign_t
size_memory_file2(term_t handle, term_t size)
{ return size_memory_file(handle, size, 0);
}


static foreign_t
size_memory_file3(term_t handle, term_t size, term_t encoding)
{ return size_memory_file(handle, size, encoding);
}


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
utf8_position_memory_file(+MF, -Here, -Size)

Given  MF  is  a  UTF-8  encoded  memory   file,  unify  here  with  the
byte-position of the read-pointer and Size with   the  total size of the
memory file in bytes. This is a bit hacky predicate, but the information
is easily available at low cost, while it is very valuable for producing
answers  in  content-length  computation  of    the   HTTP  server.  See
http_wrapper.pl
- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - */

static foreign_t
utf8_position(term_t handle, term_t here, term_t size)
{ memfile *m;
  int rc;

  if ( get_memfile(handle, &m) )
  { if ( m->encoding != ENC_UTF8 )
    { rc = pl_error(NULL, 0, "no UTF-8 encoding",
		    ERR_PERMISSION, handle, "utf8_position", "memory_file");
      goto out;
    }
    if ( !PL_unify_integer(size, m->end - m->gap_size) )
    { rc = FALSE;
      goto out;
    }

    if ( m->stream )
    { IOPOS *op = m->stream->position;
      long p;

      m->stream->position = NULL;
      p = Stell(m->stream);
      m->stream->position = op;

      rc = PL_unify_integer(here, p);
    } else
      rc = PL_unify_integer(here, 0);

  out:
    release_memfile(m);
  } else
    rc = FALSE;

  return rc;
}


static foreign_t
atom_to_memory_file(term_t atom, term_t handle)
{ atom_t a;

  if ( PL_get_atom(atom, &a) )
  { memfile *m = calloc(1, sizeof(*m));

    if ( !m )
      return pl_error(NULL, 0, NULL, ERR_ERRNO, errno,
		      "create", "memory_file", handle);

    m->atom = a;
    PL_register_atom(m->atom);
    m->magic = MEMFILE_MAGIC;

    if ( (m->data = (char *)PL_atom_nchars(a, &m->char_count)) )
    { m->encoding  = ENC_ISO_LATIN_1;
      m->end       = m->char_count;
      m->gap_start = m->end;
    } else if ( (m->data = (char *)PL_atom_wchars(a, &m->char_count)) )
    { m->encoding = ENC_WCHAR;
      m->end = m->char_count * sizeof(wchar_t);
      m->gap_start = m->end;
    } else if ( PL_blob_data(a, &m->char_count, NULL) )
    { m->data = PL_blob_data(a, &m->end, NULL);
      m->encoding = ENC_OCTET;
      m->char_count = m->end;
      m->gap_start  = m->end;
    }

#ifdef O_PLMT
    pthread_mutex_init(&m->mutex, NULL);
#endif

    if ( unify_memfile(handle, m) )
    { return TRUE;
    } else
    { destroy_memory_file(m);
      return FALSE;
    }
  } else
  { return pl_error(NULL, 0, NULL, ERR_ARGTYPE, 1,
		    atom, "atom");
  }
}

		 /*******************************
		 *	  DIRECT EXCHANGE	*
		 *******************************/

static int
can_modify_memory_file(term_t handle, memfile *mf)
{ if ( mf->atom )
    return pl_error(NULL, 0, "read only",
		    ERR_PERMISSION, handle, "modify", "memory_file");
  if ( mf->stream )
    return alreadyOpen(handle, "modify");

  return TRUE;
}


/* Get the byte offset for a character
*/

static char *
utf8_skip_char(const char *in, const char *e)
{ if ( !(in[0]&0x80) )
  { return (char*)in+1;
  } else
  { in++;
    while ( in < e && ISUTF8_CB(in[0]) )
      in++;
    return (char*)in;
  }
}


/* Skip chars forward from a byte position, returning the new
   byte position in the memory file or NOSIZE if we would skip
   outside the limits of the memory file.  Returns:

     OUTOFRANGE if memfile is too small
     FALSE      if the encoding is not supported
     TRUE       if ok
*/

#define OUTOFRANGE -1

static int
mf_skip(memfile *mf, IOENC encoding, size_t from, size_t chars, size_t *end)
{ size_t to;

  switch(encoding)
  { case ENC_OCTET:
    case ENC_ASCII:
    case ENC_ISO_LATIN_1:
      to = from+chars;
      break;
    case ENC_UTF8:
    { const char *start, *s, *e;
      const size_t chars0 = (from == 0 ? chars : NOSIZE);

      if ( from == 0 &&
	   (mf->pcache.valid & V_CHARCOUNT) &&
	   chars >= mf->pcache.char_count )
      { from   = mf->pcache.byte_count;
	chars -= mf->pcache.char_count;
      }

      if ( from < mf->gap_start )
      { start = s = &mf->data[from];
	e = &mf->data[mf->gap_start];

	while(chars>0 && s<e)
	{ chars--;
	  s = utf8_skip_char(s, e);
	}
	from += s - start;
	if ( chars == 0 )
	{ utf8_out:
	  if ( chars0 != NOSIZE )
	  { mf->pcache.char_count = chars0;
	    mf->pcache.byte_count = from;
	    mf->pcache.valid |= V_CHARCOUNT;
	  }
	  *end = from;
	  return TRUE;
	}
	assert(s == e);
      }

      start = s = &mf->data[mf->gap_size+from];
      e = &mf->data[mf->end];
      while(chars>0 && s<e)
      { chars--;
	s = utf8_skip_char(s, e);
      }
      from += s - start;
      if ( chars == 0 )
	goto utf8_out;
      goto outofrange;
    }
    case ENC_UNICODE_BE:
    case ENC_UNICODE_LE:
      to = from + 2*chars;
      break;
    case ENC_WCHAR:
      to = from + sizeof(wchar_t) * chars;
      break;
    default:
      return PL_representation_error("encoding");
  }

  if ( to > mf->end - mf->gap_size )
  { outofrange:
    *end = mf->end - mf->gap_size;
    return OUTOFRANGE;
  }

  *end = to;
  return TRUE;
}


static int
get_offset(term_t where, memfile *mf, IOENC encoding, size_t *pos)
{ size_t p;

  if ( PL_get_size_ex(where, &p) )
  { int rc = mf_skip(mf, encoding, 0, p, pos);

    if ( rc != OUTOFRANGE )
      return rc;

    return PL_domain_error("offset", where);
  }

  return FALSE;
}


static foreign_t
insert_memory_file(term_t handle, term_t where, term_t data)
{ memfile *m;
  int rc;

  if ( get_memfile(handle, &m) )
  { size_t pos;
    int flags = CVT_ALL|CVT_WRITEQ|CVT_EXCEPTION;

    if ( can_modify_memory_file(handle, m) &&
	 get_offset(where, m, m->encoding, &pos) )
    { move_gap_to(m, pos);
      switch(m->encoding)
      { case ENC_OCTET:
	case ENC_ASCII:
	case ENC_ISO_LATIN_1:
	case ENC_ANSI:
	case ENC_UTF8:
	{ size_t len;
	  char *buf;
	  int rep = ( m->encoding == ENC_UTF8 ? REP_UTF8 :
		      m->encoding == ENC_ANSI ? REP_MB :
						REP_ISO_LATIN_1
		    );

	  if ( (rc=PL_get_nchars(data, &len, &buf, flags|rep)) )
	  { if ( write_memfile(m, buf, len) < 0 )
	      rc = PL_resource_error("memory");
	    check_memfile(m);
	  }
	  break;
	}
	case ENC_WCHAR:
	{ size_t len;
	  wchar_t *buf;

	  if ( (rc=PL_get_wchars(data, &len, &buf, flags)) )
	  { if ( write_memfile(m, (void*)buf, len*sizeof(wchar_t)) < 0 )
	      rc = PL_resource_error("memory");
	  }
	  break;
	}
	default:
	  rc = PL_representation_error("encoding");
      }
    } else
      rc = FALSE;

    release_memfile(m);
  } else
    rc = FALSE;

  return rc;
}


static foreign_t
delete_memory_file(term_t handle, term_t where, term_t len)
{ memfile *m;
  int rc;

  if ( get_memfile(handle, &m) )
  { size_t pos, end;
    size_t l;

    if ( can_modify_memory_file(handle, m) &&
	 get_offset(where, m, m->encoding, &pos) &&
	 PL_get_size_ex(len, &l) &&
	 mf_skip(m, m->encoding, pos, l, &end) != FALSE )
    { if ( end > pos )
      { if ( pos < m->pcache.byte_count )
	  m->pcache.valid = 0;

	move_gap_to(m, pos);
	m->gap_size += end-pos;
	m->char_count = NOSIZE;
      }
      rc = TRUE;
    } else
      rc = FALSE;

    release_memfile(m);
  } else
    rc = FALSE;

  return rc;
}


static foreign_t
mf_to_text(term_t handle, memfile *m, size_t from, size_t len,
	   term_t atom, term_t encoding, int flags)
{ IOENC enc;
  size_t start, end;

  if ( m->stream && (m->stream->flags & SIO_OUTPUT))
    return alreadyOpen(handle, "to_atom");

  if ( encoding )
  { if ( !get_encoding(encoding, &enc) )
      return FALSE;
  } else
    enc = m->encoding;

  if ( from == NOSIZE )
  { start = 0;
  } else
  { if ( mf_skip(m, enc, 0, from, &start) != TRUE )
      return FALSE;
  }

  if ( len == NOSIZE )
  { end = m->end - m->gap_size;
  } else
  { if ( mf_skip(m, enc, start, len, &end) != TRUE )
      return FALSE;
  }

  if ( m->data )
  { size_t len = end-start;
    const char *data;

    if ( start <= m->gap_start && end <= m->gap_start )
    { data = &m->data[start];
    } else if ( start >= m->gap_start+m->gap_size )
    { data = &m->data[m->gap_size + (start-m->gap_start)];
    } else
    { move_gap_to(m, end);
      data = &m->data[start];
    }

    switch(enc)
    { case ENC_ISO_LATIN_1:
      case ENC_OCTET:
	return PL_unify_chars(atom, flags, len, data);
      case ENC_WCHAR:
	return PL_unify_wchars(atom, flags,
			       len/sizeof(wchar_t),
			       (pl_wchar_t*)data);
      case ENC_UTF8:
	return PL_unify_chars(atom, flags|REP_UTF8, len, data);
      default:
	assert(0);
    }
  } else
    return PL_unify_chars(atom, flags, 0, "");

  return FALSE;
}


static foreign_t
memory_file_to_text(term_t handle, term_t text, term_t encoding, int flags)
{ memfile *mf;
  int rc;

  if ( get_memfile(handle, &mf) )
  { rc = mf_to_text(handle, mf, NOSIZE, NOSIZE, text, encoding, flags);
    release_memfile(mf);
  } else
    rc = FALSE;

  return rc;
}


static foreign_t
memory_file_to_atom2(term_t handle, term_t atom)
{ return memory_file_to_text(handle, atom, 0, PL_ATOM);
}


static foreign_t
memory_file_to_atom3(term_t handle, term_t atom, term_t encoding)
{ return memory_file_to_text(handle, atom, encoding, PL_ATOM);
}


static foreign_t
memory_file_to_codes2(term_t handle, term_t atom)
{ return memory_file_to_text(handle, atom, 0, PL_CODE_LIST);
}


static foreign_t
memory_file_to_codes3(term_t handle, term_t atom, term_t encoding)
{ return memory_file_to_text(handle, atom, encoding, PL_CODE_LIST);
}


static foreign_t
memory_file_to_string2(term_t handle, term_t atom)
{ return memory_file_to_text(handle, atom, 0, PL_STRING);
}


static foreign_t
memory_file_to_string3(term_t handle, term_t atom, term_t encoding)
{ return memory_file_to_text(handle, atom, encoding, PL_STRING);
}


static int
get_size_or_var(term_t t, size_t *sp)
{ if ( PL_is_variable(t) )
  { *sp = NOSIZE;
    return TRUE;
  }

  return PL_get_size_ex(t, sp);
}


static foreign_t
memory_file_substring(term_t handle,
		      term_t before, term_t len, term_t after,
		      term_t string)
{ memfile *mf;
  int rc;

  if ( (rc=get_memfile(handle, &mf)) )
  { size_t b, l, a, size;

    if ( get_size_or_var(before, &b) &&
	 get_size_or_var(len, &l) &&
	 get_size_or_var(after, &a) &&
	 get_size_mf(mf, mf->encoding, &size) )
    { if ( b != NOSIZE && l != NOSIZE )
      { rc = ( mf_to_text(handle, mf, b, l, string, 0, PL_STRING) &&
	       PL_unify_int64(after, size-(b+l)) );
      } else if ( b != NOSIZE && a != NOSIZE )
      {	rc = ( mf_to_text(handle, mf, b, size-(b+a), string, 0, PL_STRING) &&
	       PL_unify_int64(len, size-(b+a)) );
      } else if ( l != NOSIZE && a != NOSIZE )
      { rc = ( mf_to_text(handle, mf, size-(l+a), l, string, 0, PL_STRING) &&
	       PL_unify_int64(before, size-(l+a)) );
      } else
      { rc = PL_instantiation_error(b != NOSIZE ? before : len);
      }
    } else
      rc = FALSE;

    release_memfile(mf);
  }

  return rc;
}

/* skip lines from a given byte-offset, returning the byte-offset
   for the beginning of the next line and the logical character
   count that belongs to that.
*/

static int
skip_lines(memfile *mf, size_t from, size_t lines,
	   size_t *startp, size_t *chcountp)
{ const char *start, *s, *e;
  size_t chcount = 0;

  if ( lines == 0 )
  { *startp = from;
    *chcountp = 0;
    return TRUE;
  }

  if ( from < mf->gap_start )
  { start = s = mf->data+from;
    e = &mf->data[mf->gap_start];
  } else
  { after_gap:
    start = s = &mf->data[mf->gap_size+from];
    e = &mf->data[mf->end];
  }

  switch(mf->encoding)
  { case ENC_OCTET:
    case ENC_ASCII:
    case ENC_ISO_LATIN_1:
      while( s < e )
      { if ( *s++ == '\n' )
	{ if ( --lines == 0 )
	  { *startp   = from + (s-start) + 1;
	    *chcountp = chcount + (s-start) + 1;
	    return TRUE;
	  }
	}
      }
      chcount += e-s;
      break;
    case ENC_UTF8:
      while( s < e )
      { chcount++;
	if ( *s == '\n' )
	{ if ( --lines == 0 )
	  { *startp   = from + (s-start) + 1;
	    *chcountp = chcount;
	    return TRUE;
	  }
	}
	s = utf8_skip_char(s, e);
      }
      break;
    case ENC_WCHAR:
    { const wchar_t *ws = (const wchar_t*)s;
      const wchar_t *we = (const wchar_t*)e;
      const wchar_t *wstart = ws;

      while( ws < we )
      { if ( *ws++ == '\n' )
	{ if ( --lines == 0 )
	  { *startp   = from + (ws-wstart) + 1;
	    *chcountp = chcount + (ws-wstart) + 1;
	    return TRUE;
	  }
	}
      }
      chcount += we-ws;
      break;
    }
    default:
      return PL_representation_error("encoding");
  }

  if ( from < mf->gap_start )
  { from = mf->gap_start;
    goto after_gap;
  }

  *startp   = mf->end;
  *chcountp = chcount;

  return OUTOFRANGE;
}


/** memory_file_line_position(+MF, +Line, +LinePos, -Offset) is det.
    memory_file_line_position(+MF, -Line, -LinePos, +Offset) is det.

True when Offset is the character offset for Line:LinePos.
*/

static foreign_t
memory_file_line_position(term_t handle,
			  term_t line, term_t linepos, term_t offset)
{ memfile *mf;
  int rc;

  if ( get_memfile(handle, &mf) )
  { size_t l, lp, o;

    if ( get_size_or_var(line, &l) &&
	 get_size_or_var(linepos, &lp) &&
	 get_size_or_var(offset, &o) )
    { if ( l != NOSIZE && lp != NOSIZE )
      { size_t lstart, nstart;
	size_t chcount;
	size_t linelen;

	if ( l == 0 )
	{ rc = PL_domain_error("not_less_than_one", line);
	  goto out;
	}
	l--;

	if (     skip_lines(mf, 0,      l, &lstart, &chcount)  == TRUE &&
	     (rc=skip_lines(mf, lstart, 1, &nstart, &linelen)) != FALSE &&
	     (lp < linelen || (lp == linelen && rc == OUTOFRANGE)) )
	  rc = PL_unify_int64(offset, chcount+lp);
	else
	  rc = FALSE;
      } else if ( o != NOSIZE )
      { size_t chcount = 0;
	size_t lstart = 0;
	size_t line_count = 1;

	do
	{ size_t linelen;

	  if ( (rc=skip_lines(mf, lstart, 1, &lstart, &linelen)) != FALSE )
	  { if (  chcount + linelen > o ||
		 (chcount + linelen == o && rc == OUTOFRANGE)
	       )
	    { rc = ( PL_unify_int64(line, line_count) &&
		     PL_unify_int64(linepos, o-chcount) );
	      goto out;
	    }
	  }
	  line_count++;
	  chcount += linelen;
	} while(chcount < o && rc == TRUE);

	rc = FALSE;
      } else
      { rc = PL_instantiation_error(offset);
      }
    } else
      rc = FALSE;

  out:
    release_memfile(mf);
  } else
    rc = FALSE;

  return rc;
}


#define MKATOM(n) ATOM_ ## n = PL_new_atom(#n);

install_t
install_memfile()
{ MKATOM(encoding);
  MKATOM(unknown);
  MKATOM(octet);
  MKATOM(ascii);
  MKATOM(iso_latin_1);
  MKATOM(text);
  MKATOM(utf8);
  MKATOM(unicode_be);
  MKATOM(unicode_le);
  MKATOM(wchar_t);
  MKATOM(read);
  MKATOM(write);
  MKATOM(append);
  MKATOM(update);
  MKATOM(insert);
  MKATOM(free_on_close);

  PL_register_foreign("new_memory_file",	   1, new_memory_file,	      0);
  PL_register_foreign("free_memory_file",	   1, free_memory_file,	      0);
  PL_register_foreign("size_memory_file",	   2, size_memory_file2,      0);
  PL_register_foreign("size_memory_file",	   3, size_memory_file3,      0);
  PL_register_foreign("open_memory_file",	   3, open_memory_file,	      0);
  PL_register_foreign("open_memory_file",	   4, open_memory_file4,      0);
  PL_register_foreign("atom_to_memory_file",	   2, atom_to_memory_file,    0);
  PL_register_foreign("memory_file_to_atom",	   2, memory_file_to_atom2,   0);
  PL_register_foreign("memory_file_to_codes",	   2, memory_file_to_codes2,  0);
  PL_register_foreign("memory_file_to_string",	   2, memory_file_to_string2, 0);
  PL_register_foreign("memory_file_to_atom",	   3, memory_file_to_atom3,   0);
  PL_register_foreign("memory_file_to_codes",	   3, memory_file_to_codes3,  0);
  PL_register_foreign("memory_file_to_string",	   3, memory_file_to_string3, 0);
  PL_register_foreign("utf8_position_memory_file", 3, utf8_position,	      0);
  PL_register_foreign("insert_memory_file",	   3, insert_memory_file,     0);
  PL_register_foreign("delete_memory_file",	   3, delete_memory_file,     0);
  PL_register_foreign("memory_file_substring",     5, memory_file_substring,  0);
  PL_register_foreign("memory_file_line_position", 4, memory_file_line_position, 0);
}