1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2010-2021, VU University Amsterdam
    7                              SWI-Prolog Solutions b.v.
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
   13
   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
   16
   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
   19       the documentation and/or other materials provided with the
   20       distribution.
   21
   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   26    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   27    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   28    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   29    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   30    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   31    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   32    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   33    POSSIBILITY OF SUCH DAMAGE.
   34*/
   35
   36:- module(fastrw,
   37          [ fast_read/1,                % -Term
   38            fast_write/1,               % +Term
   39            fast_read/2,                % +Stream, -Term
   40            fast_write/2,               % +Stream, +Term
   41            fast_write_to_string/3      % +Term, -String, ?Tail
   42          ]).   43:- autoload(library(lists),[append/3]).   44
   45
   46/** <module> Fast reading and writing of terms
   47
   48This library provides the SICStus   and  Ciao library(fastrw) interface.
   49The idea behind this library  is  to   design  a  fast serialization for
   50Prolog  terms.  Ideally,  this  should    be   portable  between  Prolog
   51implementation. Unfortunately there is no   portably  binary term format
   52defined.
   53
   54The current implementation  is  based   on  PL_record_external(),  which
   55provides a binary representation of terms  that is processed efficiently
   56and can handle subterm sharing,  cycles   and  attributed  variables. In
   57other words, this library can handle any Prolog term except _blobs_ such
   58as stream handles, database references, etc. We   try to keep the format
   59compatible between versions, but this is   not guaranteed. Conversion is
   60always possible by reading a database  using   the  old version, dump it
   61using write_canonical/1 and read it into the new version.
   62
   63This library is built upon the following built in predicates:
   64
   65  - fast_term_serialized/2 translates between a term and its
   66  serialization as a byte string.
   67  - fast_read/2 and fast_write/2 read/write binary serializations.
   68
   69@tbd    Establish a portable binary format.
   70@compat The format is not compatible to SICStus/Ciao (which are not
   71        compatible either).  Future versions of this library might
   72        implement a different encoding.
   73@bug    The current implementation of fast_read/1 __is not safe__.
   74        It is guaranteed to safely read terms written using
   75        fast_write/1, but may crash on arbitrary input.  The
   76        implementation does perform some basic sanity checks,
   77        including validation of the magic start byte.
   78*/
   79
   80%!  fast_read(-Term)
   81%
   82%   The next term is read from current standard input and is unified
   83%   with Term. The syntax of the term   must  agree with fast_read /
   84%   fast_write format. If the end  of   the  input has been reached,
   85%   Term is unified with the term =end_of_file=.
   86
   87fast_read(Term) :-
   88    fast_read(current_input, Term).
   89
   90%!  fast_write(+Term)
   91%
   92%   Output Term in a way that   fast_read/1  and fast_read/2 will be
   93%   able to read it back.
   94
   95fast_write(Term) :-
   96    fast_write(current_output, Term).
   97
   98%!  fast_write_to_string(+Term, -String, ?Tail)
   99%
  100%   Perform a fast-write to the difference-slist String\Tail.
  101
  102fast_write_to_string(T, S, R) :-
  103    fast_term_serialized(T, String),
  104    string_codes(String, Codes),
  105    append(Codes, R, S)