1.\" $NetBSD: unvis.3,v 1.30 2019/05/08 15:37:41 bad Exp $ 2.\" 3.\" Copyright (c) 1989, 1991, 1993 4.\" The Regents of the University of California. All rights reserved. 5.\" 6.\" Redistribution and use in source and binary forms, with or without 7.\" modification, are permitted provided that the following conditions 8.\" are met: 9.\" 1. Redistributions of source code must retain the above copyright 10.\" notice, this list of conditions and the following disclaimer. 11.\" 2. Redistributions in binary form must reproduce the above copyright 12.\" notice, this list of conditions and the following disclaimer in the 13.\" documentation and/or other materials provided with the distribution. 14.\" 3. Neither the name of the University nor the names of its contributors 15.\" may be used to endorse or promote products derived from this software 16.\" without specific prior written permission. 17.\" 18.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 19.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 20.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 21.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 22.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 23.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 24.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 25.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 26.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 27.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 28.\" SUCH DAMAGE. 29.\" 30.\" @(#)unvis.3 8.2 (Berkeley) 12/11/93 31.\" 32.Dd May 8, 2019 33.Dt UNVIS 3 34.Os 35.Sh NAME 36.Nm unvis , 37.Nm strunvis , 38.Nm strnunvis , 39.Nm strunvisx , 40.Nm strnunvisx 41.Nd decode a visual representation of characters 42.Sh LIBRARY 43.Lb libc 44.Sh SYNOPSIS 45.In vis.h 46.Ft int 47.Fn unvis "char *cp" "int c" "int *astate" "int flag" 48.Ft int 49.Fn strunvis "char *dst" "const char *src" 50.Ft int 51.Fn strnunvis "char *dst" "size_t dlen" "const char *src" 52.Ft int 53.Fn strunvisx "char *dst" "const char *src" "int flag" 54.Ft int 55.Fn strnunvisx "char *dst" "size_t dlen" "const char *src" "int flag" 56.Sh DESCRIPTION 57The 58.Fn unvis , 59.Fn strunvis 60and 61.Fn strunvisx 62functions 63are used to decode a visual representation of characters, as produced 64by the 65.Xr vis 3 66function, back into 67the original form. 68.Pp 69The 70.Fn unvis 71function is called with successive characters in 72.Ar c 73until a valid sequence is recognized, at which time the decoded 74character is available at the character pointed to by 75.Ar cp . 76.Pp 77The 78.Fn strunvis 79function decodes the characters pointed to by 80.Ar src 81into the buffer pointed to by 82.Ar dst . 83The 84.Fn strunvis 85function simply copies 86.Ar src 87to 88.Ar dst , 89decoding any escape sequences along the way, 90and returns the number of characters placed into 91.Ar dst , 92or \-1 if an 93invalid escape sequence was detected. 94The size of 95.Ar dst 96should be equal to the size of 97.Ar src 98(that is, no expansion takes place during decoding). 99.Pp 100The 101.Fn strunvisx 102and 103.Fn strnunvisx 104functions do the same as the 105.Fn strunvis 106and 107.Fn strnunvis 108functions, 109but take a flag that specifies the style the string 110.Ar src 111is encoded with. 112The meaning of the flag is the same as explained below for 113.Fn unvis . 114.Pp 115The 116.Fn unvis 117function implements a state machine that can be used to decode an 118arbitrary stream of bytes. 119All state associated with the bytes being decoded is stored outside the 120.Fn unvis 121function (that is, a pointer to the state is passed in), so 122calls decoding different streams can be freely intermixed. 123To start decoding a stream of bytes, first initialize an integer to zero. 124Call 125.Fn unvis 126with each successive byte, along with a pointer 127to this integer, and a pointer to a destination character. 128The 129.Fn unvis 130function has several return codes that must be handled properly. 131They are: 132.Bl -tag -width UNVIS_VALIDPUSH 133.It Li \&0 No (zero) 134Another character is necessary; nothing has been recognized yet. 135.It Dv UNVIS_VALID 136A valid character has been recognized and is available at the location 137pointed to by 138.Fa cp . 139.It Dv UNVIS_VALIDPUSH 140A valid character has been recognized and is available at the location 141pointed to by 142.Fa cp ; 143however, the character currently passed in should be passed in again. 144.It Dv UNVIS_NOCHAR 145A valid sequence was detected, but no character was produced. 146This return code is necessary to indicate a logical break between characters. 147.It Dv UNVIS_SYNBAD 148An invalid escape sequence was detected, or the decoder is in an unknown state. 149The decoder is placed into the starting state. 150.El 151.Pp 152When all bytes in the stream have been processed, call 153.Fn unvis 154one more time with flag set to 155.Dv UNVIS_END 156to extract any remaining character (the character passed in is ignored). 157.Pp 158The 159.Fa flag 160argument is also used to specify the encoding style of the source. 161If set to 162.Dv VIS_NOESCAPE 163.Fn unvis 164will not decode backslash escapes. 165If set to 166.Dv VIS_HTTPSTYLE 167or 168.Dv VIS_HTTP1808 , 169.Fn unvis 170will decode URI strings as specified in RFC 1808. 171If set to 172.Dv VIS_HTTP1866 , 173.Fn unvis 174will decode entity references and numeric character references 175as specified in RFC 1866. 176If set to 177.Dv VIS_MIMESTYLE , 178.Fn unvis 179will decode MIME Quoted-Printable strings as specified in RFC 2045. 180If set to 181.Dv VIS_NOESCAPE , 182.Fn unvis 183will not decode 184.Ql \e 185quoted characters. 186.Pp 187The following code fragment illustrates a proper use of 188.Fn unvis . 189.Bd -literal -offset indent 190int state = 0; 191char out; 192 193while ((ch = getchar()) != EOF) { 194again: 195 switch(unvis(&out, ch, &state, 0)) { 196 case 0: 197 case UNVIS_NOCHAR: 198 break; 199 case UNVIS_VALID: 200 (void)putchar(out); 201 break; 202 case UNVIS_VALIDPUSH: 203 (void)putchar(out); 204 goto again; 205 case UNVIS_SYNBAD: 206 errx(EXIT_FAILURE, "Bad character sequence!"); 207 } 208} 209if (unvis(&out, '\e0', &state, UNVIS_END) == UNVIS_VALID) 210 (void)putchar(out); 211.Ed 212.Sh ERRORS 213The functions 214.Fn strunvis , 215.Fn strnunvis , 216.Fn strunvisx , 217and 218.Fn strnunvisx 219will return \-1 on error and set 220.Va errno 221to: 222.Bl -tag -width Er 223.It Bq Er EINVAL 224An invalid escape sequence was detected, or the decoder is in an unknown state. 225.El 226.Pp 227In addition the functions 228.Fn strnunvis 229and 230.Fn strnunvisx 231will can also set 232.Va errno 233on error to: 234.Bl -tag -width Er 235.It Bq Er ENOSPC 236Not enough space to perform the conversion. 237.El 238.Sh SEE ALSO 239.Xr unvis 1 , 240.Xr vis 1 , 241.Xr vis 3 242.Rs 243.%A R. Fielding 244.%T Relative Uniform Resource Locators 245.%O RFC1808 246.Re 247.Sh HISTORY 248The 249.Fn unvis 250function 251first appeared in 252.Bx 4.4 . 253The 254.Fn strnunvis 255and 256.Fn strnunvisx 257functions appeared in 258.Nx 6.0 259and 260.Fx 9.2 . 261.Sh BUGS 262The names 263.Dv VIS_HTTP1808 264and 265.Dv VIS_HTTP1866 266are wrong. 267Percent-encoding was defined in RFC 1738, the original RFC for URL. 268RFC 1866 defines HTML 2.0, an application of SGML, from which it 269inherits concepts of numeric character references and entity 270references. 271