guile/libguile/vports.c

/* Copyright 1995-1996,1998-2003,2006,2009-2011,2013,2018
     Free Software Foundation, Inc.

   This file is part of Guile.

   Guile 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.

   Guile 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 Guile.  If not, see
   <https://www.gnu.org/licenses/>.  */




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

#include <assert.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>

#include "boolean.h"
#include "chars.h"
#include "eval.h"
#include "fports.h"
#include "gsubr.h"
#include "numbers.h"
#include "ports-internal.h"
#include "ports.h"
#include "strings.h"
#include "vectors.h"

#include "vports.h"




/* {Ports - soft ports}
 * 
 */

static scm_t_port_type *scm_soft_port_type;

#define ENCODE_BUF_SIZE 10

struct soft_port {
  SCM write_char;
  SCM write_string;
  SCM flush;
  SCM read_char;
  SCM close;
  SCM input_waiting;
  uint8_t encode_buf[ENCODE_BUF_SIZE];
  size_t encode_cur;
  size_t encode_end;
};


/* Sadly it seems that most code expects there to be no write buffering
   at all.  */
static void
soft_port_get_natural_buffer_sizes (SCM port, size_t *read_size,
                                    size_t *write_size)
{
  *write_size = 1;
}

static size_t
soft_port_write (SCM port, SCM src, size_t start, size_t count)
{
  struct soft_port *stream = (void *) SCM_STREAM (port);
  signed char * ptr = SCM_BYTEVECTOR_CONTENTS (src) + start;

  scm_call_1 (stream->write_string,
              scm_from_port_stringn ((char *) ptr, count, port));

  /* Backwards compatibility.  */
  if (scm_is_true (stream->flush))
    scm_call_0 (stream->flush);

  return count;
}

/* places a single char in the input buffer.  */
static size_t
soft_port_read (SCM port, SCM dst, size_t start, size_t count)
{
  size_t written;
  struct soft_port *stream = (void *) SCM_STREAM (port);
  signed char *dst_ptr = SCM_BYTEVECTOR_CONTENTS (dst) + start;

  /* A character can be more than one byte, but we don't have a
     guarantee that there is more than one byte in the read buffer.  So,
     use an intermediate buffer.  Terrible.  This whole facility should
     be (re)designed.  */
  if (stream->encode_cur == stream->encode_end)
    {
      SCM ans;
      char *str;
      size_t len;

      ans = scm_call_0 (stream->read_char);
      if (scm_is_false (ans) || SCM_EOF_OBJECT_P (ans))
        return 0;
      SCM_ASSERT (SCM_CHARP (ans), ans, SCM_ARG1, "soft_port_read");

      /* It's possible to make a fast path here, but it would be fastest
         if the read procedure could fill its buffer directly.  */
      str = scm_to_port_stringn (scm_string (scm_list_1 (ans)), &len, port);
      assert (len > 0 && len <= ENCODE_BUF_SIZE);
      stream->encode_cur = 0;
      stream->encode_end = len;
      memcpy (stream->encode_buf, str, len);
      free (str);
    }

  for (written = 0;
       written < count && stream->encode_cur < stream->encode_end;
       written++, stream->encode_cur++)
    dst_ptr[written] = stream->encode_buf[stream->encode_cur];

  return written;
}


static void
soft_port_close (SCM port)
{
  struct soft_port *stream = (void *) SCM_STREAM (port);
  if (scm_is_true (stream->close))
    scm_call_0 (stream->close);
}


static int 
soft_port_input_waiting (SCM port)
{
  struct soft_port *stream = (void *) SCM_STREAM (port);
  if (scm_is_true (stream->input_waiting))
    return scm_to_int (scm_call_0 (stream->input_waiting));
  /* Default is such that char-ready? for soft ports returns #t, as it
     did before this extension was implemented. */
  return 1;
}



SCM_DEFINE (scm_make_soft_port, "make-soft-port", 2, 0, 0,
           (SCM pv, SCM modes),
	    "Return a port capable of receiving or delivering characters as\n"
	    "specified by the @var{modes} string (@pxref{File Ports,\n"
	    "open-file}).  @var{pv} must be a vector of length 5 or 6.  Its\n"
	    "components are as follows:\n"
	    "\n"
	    "@enumerate 0\n"
	    "@item\n"
	    "procedure accepting one character for output\n"
	    "@item\n"
	    "procedure accepting a string for output\n"
	    "@item\n"
	    "thunk for flushing output\n"
	    "@item\n"
	    "thunk for getting one character\n"
	    "@item\n"
	    "thunk for closing port (not by garbage collection)\n"
	    "@item\n"
	    "(if present and not @code{#f}) thunk for computing the number of\n"
	    "characters that can be read from the port without blocking.\n"
	    "@end enumerate\n"
	    "\n"
	    "For an output-only port only elements 0, 1, 2, and 4 need be\n"
	    "procedures.  For an input-only port only elements 3 and 4 need\n"
	    "be procedures.  Thunks 2 and 4 can instead be @code{#f} if\n"
	    "there is no useful operation for them to perform.\n"
	    "\n"
	    "If thunk 3 returns @code{#f} or an @code{eof-object}\n"
	    "(@pxref{Input, eof-object?, ,r5rs, The Revised^5 Report on\n"
	    "Scheme}) it indicates that the port has reached end-of-file.\n"
	    "For example:\n"
	    "\n"
	    "@lisp\n"
	    "(define stdout (current-output-port))\n"
	    "(define p (make-soft-port\n"
	    "           (vector\n"
	    "            (lambda (c) (write c stdout))\n"
	    "            (lambda (s) (display s stdout))\n"
	    "            (lambda () (display \".\" stdout))\n"
	    "            (lambda () (char-upcase (read-char)))\n"
	    "            (lambda () (display \"@@\" stdout)))\n"
	    "           \"rw\"))\n"
	    "\n"
	    "(write p p) @result{} #<input-output: soft 8081e20>\n"
	    "@end lisp")
#define FUNC_NAME s_scm_make_soft_port
{
  int vlen;
  struct soft_port *stream;

  SCM_VALIDATE_VECTOR (1, pv);
  vlen = SCM_SIMPLE_VECTOR_LENGTH (pv);
  SCM_ASSERT ((vlen == 5) || (vlen == 6), pv, 1, FUNC_NAME);
  SCM_VALIDATE_STRING (2, modes);

  stream = scm_gc_typed_calloc (struct soft_port);
  stream->write_char = SCM_SIMPLE_VECTOR_REF (pv, 0);
  stream->write_string = SCM_SIMPLE_VECTOR_REF (pv, 1);
  stream->flush = SCM_SIMPLE_VECTOR_REF (pv, 2);
  stream->read_char = SCM_SIMPLE_VECTOR_REF (pv, 3);
  stream->close = SCM_SIMPLE_VECTOR_REF (pv, 4);
  stream->input_waiting =
    vlen == 6 ? SCM_SIMPLE_VECTOR_REF (pv, 5) : SCM_BOOL_F;

  return scm_c_make_port (scm_soft_port_type, scm_i_mode_bits (modes),
                          (scm_t_bits) stream);
}
#undef FUNC_NAME


static scm_t_port_type *
scm_make_sfptob ()
{
  scm_t_port_type *ptob = scm_make_port_type ("soft", soft_port_read,
                                              soft_port_write);

  scm_set_port_close (ptob, soft_port_close);
  scm_set_port_needs_close_on_gc (ptob, 1);
  scm_set_port_get_natural_buffer_sizes (ptob,
                                         soft_port_get_natural_buffer_sizes);
  scm_set_port_input_waiting (ptob, soft_port_input_waiting);

  return ptob;
}

void
scm_init_vports ()
{
  scm_soft_port_type = scm_make_sfptob ();

#include "vports.x"
}