gen/FreeBSD/unvis.3

   1 .\"     $NetBSD: unvis.3,v 1.27 2012/12/15 07:34:36 wiz Exp $
   2 .\"     $FreeBSD$
   3 .\"
   4 .\" Copyright (c) 1989, 1991, 1993
   5 .\"     The Regents of the University of California.  All rights reserved.
   6 .\"
   7 .\" Redistribution and use in source and binary forms, with or without
   8 .\" modification, are permitted provided that the following conditions
   9 .\" are met:
  10 .\" 1. Redistributions of source code must retain the above copyright
  11 .\"    notice, this list of conditions and the following disclaimer.
  12 .\" 2. Redistributions in binary form must reproduce the above copyright
  13 .\"    notice, this list of conditions and the following disclaimer in the
  14 .\"    documentation and/or other materials provided with the distribution.
  15 .\" 3. Neither the name of the University nor the names of its contributors
  16 .\"    may be used to endorse or promote products derived from this software
  17 .\"    without specific prior written permission.
  18 .\"
  19 .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
  20 .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  21 .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  22 .\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
  23 .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  24 .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  25 .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  26 .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  27 .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  28 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  29 .\" SUCH DAMAGE.
  30 .\"
  31 .\"     @(#)unvis.3     8.2 (Berkeley) 12/11/93
  32 .\"
  33 .Dd March 12, 2011
  34 .Dt UNVIS 3
  35 .Os
  36 .Sh NAME
  37 .Nm unvis ,
  38 .Nm strunvis
  39 .Nd decode a visual representation of characters
  40 .Sh LIBRARY
  41 .Lb libc
  42 .Sh SYNOPSIS
  43 .In vis.h
  44 .Ft int
  45 .Fn unvis "char *cp" "int c" "int *astate" "int flag"
  46 .Ft int
  47 .Fn strunvis "char *dst" "const char *src"
  48 .Ft int
  49 .Fn strnunvis "char *dst" "size_t dlen" "const char *src"
  50 .Ft int
  51 .Fn strunvisx "char *dst" "const char *src" "int flag"
  52 .Ft int
  53 .Fn strnunvisx "char *dst" "size_t dlen" "const char *src" "int flag"
  54 .Sh DESCRIPTION
  55 The
  56 .Fn unvis ,
  57 .Fn strunvis
  58 and
  59 .Fn strunvisx
  60 functions
  61 are used to decode a visual representation of characters, as produced
  62 by the
  63 .Xr vis 3
  64 function, back into
  65 the original form.
  66 .Pp
  67 The
  68 .Fn unvis
  69 function is called with successive characters in
  70 .Ar c
  71 until a valid sequence is recognized, at which time the decoded
  72 character is available at the character pointed to by
  73 .Ar cp .
  74 .Pp
  75 The
  76 .Fn strunvis
  77 function decodes the characters pointed to by
  78 .Ar src
  79 into the buffer pointed to by
  80 .Ar dst .
  81 The
  82 .Fn strunvis
  83 function simply copies
  84 .Ar src
  85 to
  86 .Ar dst ,
  87 decoding any escape sequences along the way,
  88 and returns the number of characters placed into
  89 .Ar dst ,
  90 or \-1 if an
  91 invalid escape sequence was detected.
  92 The size of
  93 .Ar dst
  94 should be equal to the size of
  95 .Ar src
  96 (that is, no expansion takes place during decoding).
  97 .Pp
  98 The
  99 .Fn strunvisx
 100 function does the same as the
 101 .Fn strunvis
 102 function,
 103 but it allows you to add a flag that specifies the style the string
 104 .Ar src
 105 is encoded with.
 106 Currently, the supported flags are:
 107 .Dv VIS_HTTPSTYLE
 108 and
 109 .Dv VIS_MIMESTYLE .
 110 .Pp
 111 The
 112 .Fn unvis
 113 function implements a state machine that can be used to decode an
 114 arbitrary stream of bytes.
 115 All state associated with the bytes being decoded is stored outside the
 116 .Fn unvis
 117 function (that is, a pointer to the state is passed in), so
 118 calls decoding different streams can be freely intermixed.
 119 To start decoding a stream of bytes, first initialize an integer to zero.
 120 Call
 121 .Fn unvis
 122 with each successive byte, along with a pointer
 123 to this integer, and a pointer to a destination character.
 124 The
 125 .Fn unvis
 126 function has several return codes that must be handled properly.
 127 They are:
 128 .Bl -tag -width UNVIS_VALIDPUSH
 129 .It Li \&0 No (zero)
 130 Another character is necessary; nothing has been recognized yet.
 131 .It Dv UNVIS_VALID
 132 A valid character has been recognized and is available at the location
 133 pointed to by
 134 .Fa cp .
 135 .It Dv UNVIS_VALIDPUSH
 136 A valid character has been recognized and is available at the location
 137 pointed to by
 138 .Fa cp ;
 139 however, the character currently passed in should be passed in again.
 140 .It Dv UNVIS_NOCHAR
 141 A valid sequence was detected, but no character was produced.
 142 This return code is necessary to indicate a logical break between characters.
 143 .It Dv UNVIS_SYNBAD
 144 An invalid escape sequence was detected, or the decoder is in an unknown state.
 145 The decoder is placed into the starting state.
 146 .El
 147 .Pp
 148 When all bytes in the stream have been processed, call
 149 .Fn unvis
 150 one more time with flag set to
 151 .Dv UNVIS_END
 152 to extract any remaining character (the character passed in is ignored).
 153 .Pp
 154 The
 155 .Fa flag
 156 argument is also used to specify the encoding style of the source.
 157 If set to
 158 .Dv VIS_HTTPSTYLE
 159 or
 160 .Dv VIS_HTTP1808 ,
 161 .Fn unvis
 162 will decode URI strings as specified in RFC 1808.
 163 If set to
 164 .Dv VIS_HTTP1866 ,
 165 .Fn unvis
 166 will decode entity references and numeric character references
 167 as specified in RFC 1866.
 168 If set to
 169 .Dv VIS_MIMESTYLE ,
 170 .Fn unvis
 171 will decode MIME Quoted-Printable strings as specified in RFC 2045.
 172 If set to
 173 .Dv VIS_NOESCAPE ,
 174 .Fn unvis
 175 will not decode
 176 .Ql \e
 177 quoted characters.
 178 .Pp
 179 The following code fragment illustrates a proper use of
 180 .Fn unvis .
 181 .Bd -literal -offset indent
 182 int state = 0;
 183 char out;
 184
 185 while ((ch = getchar()) != EOF) {
 186 again:
 187         switch(unvis(\*[Am]out, ch, \*[Am]state, 0)) {
 188         case 0:
 189         case UNVIS_NOCHAR:
 190                 break;
 191         case UNVIS_VALID:
 192                 (void)putchar(out);
 193                 break;
 194         case UNVIS_VALIDPUSH:
 195                 (void)putchar(out);
 196                 goto again;
 197         case UNVIS_SYNBAD:
 198                 errx(EXIT_FAILURE, "Bad character sequence!");
 199         }
 200 }
 201 if (unvis(\*[Am]out, '\e0', \*[Am]state, UNVIS_END) == UNVIS_VALID)
 202         (void)putchar(out);
 203 .Ed
 204 .Sh ERRORS
 205 The functions
 206 .Fn strunvis ,
 207 .Fn strnunvis ,
 208 .Fn strunvisx ,
 209 and
 210 .Fn strnunvisx
 211 will return \-1 on error and set
 212 .Va errno
 213 to:
 214 .Bl -tag -width Er
 215 .It Bq Er EINVAL
 216 An invalid escape sequence was detected, or the decoder is in an unknown state.
 217 .El
 218 .Pp
 219 In addition the functions
 220 .Fn strnunvis
 221 and
 222 .Fn strnunvisx
 223 will can also set
 224 .Va errno
 225 on error to:
 226 .Bl -tag -width Er
 227 .It Bq Er ENOSPC
 228 Not enough space to perform the conversion.
 229 .El
 230 .Sh SEE ALSO
 231 .Xr unvis 1 ,
 232 .Xr vis 1 ,
 233 .Xr vis 3
 234 .Rs
 235 .%A R. Fielding
 236 .%T Relative Uniform Resource Locators
 237 .%O RFC1808
 238 .Re
 239 .Sh HISTORY
 240 The
 241 .Fn unvis
 242 function
 243 first appeared in
 244 .Bx 4.4 .
 245 The
 246 .Fn strnunvis
 247 and
 248 .Fn strnunvisx
 249 functions appeared in OS X 10.12.
 250 .Sh BUGS
 251 The names
 252 .Dv VIS_HTTP1808
 253 and
 254 .Dv VIS_HTTP1866
 255 are wrong.
 256 Percent-encoding was defined in RFC 1738, the original RFC for URL.
 257 RFC 1866 defines HTML 2.0, an application of SGML, from which it
 258 inherits concepts of numeric character references and entity
 259 references.