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)  2016, VU University Amsterdam
   7    All rights reserved.
   8
   9    Redistribution and use in source and binary forms, with or without
  10    modification, are permitted provided that the following conditions
  11    are met:
  12
  13    1. Redistributions of source code must retain the above copyright
  14       notice, this list of conditions and the following disclaimer.
  15
  16    2. Redistributions in binary form must reproduce the above copyright
  17       notice, this list of conditions and the following disclaimer in
  18       the documentation and/or other materials provided with the
  19       distribution.
  20
  21    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  22    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  23    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
  24    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
  25    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
  26    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
  27    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
  28    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
  29    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  30    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
  31    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
  32    POSSIBILITY OF SUCH DAMAGE.
  33*/
  34
  35:- module(hash_stream,
  36          [ open_hash_stream/3,         % +OrgStream, -HashStream, +Options
  37            stream_hash/2               % +HashStream, -Hash
  38          ]).
  39:- use_foreign_library(foreign(hashstream)).
  40:- predicate_options(open_hash_stream/3, 3,
  41                     [ close_parent(boolean),
  42                       algorithm(oneof([md5,sha1,sha224,sha256,sha384,sha512]))
  43                     ]).
  44
  45/** <module> Maintain a hash on a stream
  46
  47This library defines a filter stream that   maintains a hash of the data
  48that passes through the stream. It can be   used  to compute the hash of
  49input data while it is being processed.   This is notably interesting if
  50data is processed from a socket as it avoids the need for collecting the
  51data first in a temporary file.
  52
  53A typical processing sequence  is   illustrated  below,  where process/2
  54somehow processed the data  and  save_result/3   records  the  result as
  55obtained from `URL` with content digest `SHA256` its `Result`.
  56
  57  ```
  58      ...,
  59      http_open(URL, In0, []),
  60      open_hash_stream(In0, In, [algorithm(sha256)]),
  61      process(In, Result),
  62      stream_hash(In, SHA256),
  63      close(In),
  64      save_result(URL, SHA256, Result)
  65  ```
  66
  67This library can also be used to compute   the hash for the content of a
  68file. The advantage is that this code doesn't rely on external tools. It
  69is considerably faster for short files, but considerably slower on large
  70files because Prolog I/O  is  based   on  character  streams rather than
  71blocks.
  72
  73  ```
  74  file_hash(Algorithm, File, Hash) :-
  75      setup_call_cleanup(
  76          open(File, read, In0, [type(binary)]),
  77          setup_call_cleanup(
  78              open_hash_stream(In0, In,
  79                               [ algorithm(Algorithm),
  80                                 close_parent(false)
  81                               ]),
  82              ( setup_call_cleanup(
  83                    open_null_stream(Null),
  84                    copy_stream_data(In, Null),
  85                    close(Null)),
  86                stream_hash(In, Hash)
  87              ),
  88              close(In)),
  89          close(In0)).
  90  ```
  91
  92@see    In addition to this hash library, SWI-Prolog provides
  93        library(md5), library(sha) and hash functions through
  94        library(crypto), part of the `ssl` package.
  95*/
  96
  97%!  open_hash_stream(+OrgStream, -HashStream, +Options) is det.
  98%
  99%   Open a filter stream on  OrgStream   that  maintains a hash. The
 100%   hash can be retrieved at any  time using stream_hash/2. Provided
 101%   options:
 102%
 103%     - algorithm(+Algorithm)
 104%     One of `md5`, `sha1`, `sha224`, `sha256`, `sha384` or
 105%     `sha512`. Default is `sha1`.
 106%     - close_parent(+Bool)
 107%     If `true` (default), closing the filter stream also closes the
 108%     original (parent) stream.
 109
 110
 111%!  stream_hash(+HashStream, -Digest:atom) is det.
 112%
 113%   Unify Digest with a hash for  the   bytes  send  to or read from
 114%   HashStream. Note that  the  hash  is   computed  on  the  stream
 115%   buffers. If the stream is an output  stream, it is first flushed
 116%   and the Digest represents the hash   at the current location. If
 117%   the stream is an input stream the  Digest represents the hash of
 118%   the processed input including the already buffered data.