1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--                    G N A T . D E C O D E _ S T R I N G                   --
6--                                                                          --
7--                                 S p e c                                  --
8--                                                                          --
9--                     Copyright (C) 2007-2013, AdaCore                     --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32--  This generic package provides utility routines for converting from an
33--  encoded string to a corresponding Wide_String or Wide_Wide_String value
34--  using a specified encoding convention, which is supplied as the generic
35--  parameter. UTF-8 is handled especially efficiently, and if the encoding
36--  method is known at compile time to be WCEM_UTF8, then the instantiation
37--  is specialized to handle only the UTF-8 case and exclude code for the
38--  other encoding methods. The package also provides positioning routines
39--  for skipping encoded characters in either direction, and for validating
40--  strings for correct encodings.
41
42--  Note: this package is only about decoding sequences of 8-bit characters
43--  into corresponding 16-bit Wide_String or 32-bit Wide_Wide_String values.
44--  It knows nothing at all about the character encodings being used for the
45--  resulting Wide_Character and Wide_Wide_Character values. Most often this
46--  will be Unicode/ISO-10646 as specified by the Ada RM, but this package
47--  does not make any assumptions about the character coding. See also the
48--  packages Ada.Wide_[Wide_]Characters.Unicode for unicode specific functions.
49
50--  In particular, in the case of UTF-8, all valid UTF-8 encodings, as listed
51--  in table 3.6 of the Unicode Standard, version 6.2.0, are recognized as
52--  legitimate. This includes the full range 16#0000_0000# .. 16#03FF_FFFF#.
53--  This includes codes in the range 16#D800# - 16#DFFF#. These codes all
54--  have UTF-8 encoding sequences that are well-defined (e.g. the encoding for
55--  16#D800# is ED A0 80). But these codes do not correspond to defined Unicode
56--  characters and are thus considered to be "not well-formed" (see table 3.7
57--  of the Unicode Standard). If you need to exclude these codes, you must do
58--  that manually, e.g. use Decode_Wide_Character/Decode_Wide_String and check
59--  that the resulting code(s) are not in this range.
60
61--  Note on the use of brackets encoding (WCEM_Brackets). The brackets encoding
62--  method is ambiguous in the context of this package, since there is no way
63--  to tell if ["1234"] is eight unencoded characters or one encoded character.
64--  In the context of Ada sources, any sequence starting [" must be the start
65--  of an encoding (since that sequence is not valid in Ada source otherwise).
66--  The routines in this package use the same approach. If the input string
67--  contains the sequence [" then this is assumed to be the start of a brackets
68--  encoding sequence, and if it does not match the syntax, an error is raised.
69--  In the case of the Prev functions, a sequence ending with "] is assumed to
70--  be a valid brackets sequence, and an error is raised if it is not.
71
72with System.WCh_Con;
73
74generic
75   Encoding_Method : System.WCh_Con.WC_Encoding_Method;
76
77package GNAT.Decode_String is
78   pragma Pure;
79
80   function Decode_Wide_String (S : String) return Wide_String;
81   pragma Inline (Decode_Wide_String);
82   --  Decode the given String, which is encoded using the indicated coding
83   --  method, returning the corresponding decoded Wide_String value. If S
84   --  contains a character code that cannot be represented with the given
85   --  encoding, then Constraint_Error is raised.
86
87   procedure Decode_Wide_String
88     (S      : String;
89      Result : out Wide_String;
90      Length : out Natural);
91   --  Similar to the above function except that the result is stored in the
92   --  given Wide_String variable Result, starting at Result (Result'First). On
93   --  return, Length is set to the number of characters stored in Result. The
94   --  caller must ensure that Result is long enough (an easy choice is to set
95   --  the length equal to the S'Length, since decoding can never increase the
96   --  string length). If the length of Result is insufficient Constraint_Error
97   --  will be raised.
98
99   function Decode_Wide_Wide_String (S : String) return Wide_Wide_String;
100   --  Same as above function but for Wide_Wide_String output
101
102   procedure Decode_Wide_Wide_String
103     (S      : String;
104      Result : out Wide_Wide_String;
105      Length : out Natural);
106   --  Same as above procedure, but for Wide_Wide_String output
107
108   function Validate_Wide_String (S : String) return Boolean;
109   --  This function inspects the string S to determine if it contains only
110   --  valid encodings corresponding to Wide_Character values using the
111   --  given encoding. If a call to Decode_Wide_String (S) would return
112   --  without raising Constraint_Error, then Validate_Wide_String will
113   --  return True. If the call would have raised Constraint_Error, then
114   --  Validate_Wide_String will return False.
115
116   function Validate_Wide_Wide_String (S : String) return Boolean;
117   --  Similar to Validate_Wide_String, except that it succeeds if the string
118   --  contains only encodings corresponding to Wide_Wide_Character values.
119
120   procedure Decode_Wide_Character
121     (Input  : String;
122      Ptr    : in out Natural;
123      Result : out Wide_Character);
124   pragma Inline (Decode_Wide_Character);
125   --  This is a lower level procedure that decodes a single character using
126   --  the given encoding method. The encoded character is stored in Input,
127   --  starting at Input (Ptr). The resulting output character is stored in
128   --  Result, and on return Ptr is updated past the input character or
129   --  encoding sequence. Constraint_Error will be raised if the input has
130   --  has a character that cannot be represented using the given encoding,
131   --  or if Ptr is outside the bounds of the Input string.
132
133   procedure Decode_Wide_Wide_Character
134     (Input  : String;
135      Ptr    : in out Natural;
136      Result : out Wide_Wide_Character);
137   pragma Inline (Decode_Wide_Wide_Character);
138   --  Same as above procedure but with Wide_Wide_Character input
139
140   procedure Next_Wide_Character (Input : String; Ptr : in out Natural);
141   pragma Inline (Next_Wide_Character);
142   --  This procedure examines the input string starting at Input (Ptr), and
143   --  advances Ptr past one character in the encoded string, so that on return
144   --  Ptr points to the next encoded character. Constraint_Error is raised if
145   --  an invalid encoding is encountered, or the end of the string is reached
146   --  or if Ptr is less than String'First on entry, or if the character
147   --  skipped is not a valid Wide_Character code.
148
149   procedure Prev_Wide_Character (Input : String; Ptr : in out Natural);
150   --  This procedure is similar to Next_Encoded_Character except that it moves
151   --  backwards in the string, so that on return, Ptr is set to point to the
152   --  previous encoded character. Constraint_Error is raised if the start of
153   --  the string is encountered. It is valid for Ptr to be one past the end
154   --  of the string for this call (in which case on return it will point to
155   --  the last encoded character).
156   --
157   --  Note: it is not generally possible to do this function efficiently with
158   --  all encodings, the current implementation is only efficient for the case
159   --  of UTF-8 (Encoding_Method = WCEM_UTF8) and Brackets (Encoding_Method =
160   --  WCEM_Brackets). For all other encodings, we work by starting at the
161   --  beginning of the string and moving forward till Ptr is reached, which
162   --  is correct but slow.
163   --
164   --  Note: this routine assumes that the sequence prior to Ptr is correctly
165   --  encoded, it does not have a defined behavior if this is not the case.
166
167   procedure Next_Wide_Wide_Character (Input : String; Ptr : in out Natural);
168   pragma Inline (Next_Wide_Wide_Character);
169   --  Similar to Next_Wide_Character except that codes skipped must be valid
170   --  Wide_Wide_Character codes.
171
172   procedure Prev_Wide_Wide_Character (Input : String; Ptr : in out Natural);
173   --  Similar to Prev_Wide_Character except that codes skipped must be valid
174   --  Wide_Wide_Character codes.
175
176end GNAT.Decode_String;
177