gen/FreeBSD/vis.3

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  31 .\"     @(#)vis.3       8.1 (Berkeley) 6/9/93
  32 .\"
  33 .Dd February 19, 2013
  34 .Dt VIS 3
  35 .Os
  36 .Sh NAME
  37 .Nm vis ,
  38 .Nm nvis ,
  39 .Nm strvis ,
  40 .Nm strnvis ,
  41 .Nm strvisx ,
  42 .Nm strnvisx ,
  43 .Nm strenvisx ,
  44 .Nm svis ,
  45 .Nm snvis ,
  46 .Nm strsvis ,
  47 .Nm strsnvis ,
  48 .Nm strsvisx ,
  49 .Nm strsnvisx ,
  50 .Nm strsenvisx
  51 .Nd visually encode characters
  52 .Sh LIBRARY
  53 .Lb libc
  54 .Sh SYNOPSIS
  55 .In vis.h
  56 .Ft char *
  57 .Fn vis "char *dst" "int c" "int flag" "int nextc"
  58 .Ft char *
  59 .Fn nvis "char *dst" "size_t dlen" "int c" "int flag" "int nextc"
  60 .Ft int
  61 .Fn strvis "char *dst" "const char *src" "int flag"
  62 .Ft int
  63 .Fn strnvis "char *dst" "size_t dlen" "const char *src" "int flag"
  64 .Ft int
  65 .Fn strvisx "char *dst" "const char *src" "size_t len" "int flag"
  66 .Ft int
  67 .Fn strnvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag"
  68 .Ft int
  69 .Fn strenvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag" "int *cerr_ptr"
  70 .Ft char *
  71 .Fn svis "char *dst" "int c" "int flag" "int nextc" "const char *extra"
  72 .Ft char *
  73 .Fn snvis "char *dst" "size_t dlen" "int c" "int flag" "int nextc" "const char *extra"
  74 .Ft int
  75 .Fn strsvis "char *dst" "const char *src" "int flag" "const char *extra"
  76 .Ft int
  77 .Fn strsnvis "char *dst" "size_t dlen" "const char *src" "int flag" "const char *extra"
  78 .Ft int
  79 .Fn strsvisx "char *dst" "const char *src" "size_t len" "int flag" "const char *extra"
  80 .Ft int
  81 .Fn strsnvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag" "const char *extra"
  82 .Ft int
  83 .Fn strsenvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag" "const char *extra" "int *cerr_ptr"
  84 .Sh DESCRIPTION
  85 The
  86 .Fn vis
  87 function
  88 copies into
  89 .Fa dst
  90 a string which represents the character
  91 .Fa c .
  92 If
  93 .Fa c
  94 needs no encoding, it is copied in unaltered.
  95 The string is null terminated, and a pointer to the end of the string is
  96 returned.
  97 The maximum length of any encoding is four
  98 bytes (not including the trailing
  99 .Dv NUL ) ;
 100 thus, when
 101 encoding a set of characters into a buffer, the size of the buffer should
 102 be four times the number of bytes encoded, plus one for the trailing
 103 .Dv NUL .
 104 The flag parameter is used for altering the default range of
 105 characters considered for encoding and for altering the visual
 106 representation.
 107 The additional character,
 108 .Fa nextc ,
 109 is only used when selecting the
 110 .Dv VIS_CSTYLE
 111 encoding format (explained below).
 112 .Pp
 113 The
 114 .Fn strvis ,
 115 .Fn strnvis ,
 116 .Fn strvisx ,
 117 and
 118 .Fn strnvisx
 119 functions copy into
 120 .Fa dst
 121 a visual representation of
 122 the string
 123 .Fa src .
 124 The
 125 .Fn strvis
 126 and
 127 .Fn strnvis
 128 functions encode characters from
 129 .Fa src
 130 up to the
 131 first
 132 .Dv NUL .
 133 The
 134 .Fn strvisx
 135 and
 136 .Fn strnvisx
 137 functions encode exactly
 138 .Fa len
 139 characters from
 140 .Fa src
 141 (this
 142 is useful for encoding a block of data that may contain
 143 .Dv NUL Ns 's ) .
 144 Both forms
 145 .Dv NUL
 146 terminate
 147 .Fa dst .
 148 The size of
 149 .Fa dst
 150 must be four times the number
 151 of bytes encoded from
 152 .Fa src
 153 (plus one for the
 154 .Dv NUL ) .
 155 Both
 156 forms return the number of characters in
 157 .Fa dst
 158 (not including the trailing
 159 .Dv NUL ) .
 160 The
 161 .Dq Nm n
 162 versions of the functions also take an additional argument
 163 .Fa dlen
 164 that indicates the length of the
 165 .Fa dst
 166 buffer.
 167 If
 168 .Fa dlen
 169 is not large enough to fit the converted string then the
 170 .Fn strnvis
 171 and
 172 .Fn strnvisx
 173 functions return \-1 and set
 174 .Va errno
 175 to
 176 .Dv ENOSPC .
 177 The
 178 .Fn strenvisx
 179 function takes an additional argument,
 180 .Fa cerr_ptr ,
 181 that is used to pass in and out a multibyte conversion error flag.
 182 This is useful when processing single characters at a time when
 183 it is possible that the locale may be set to something other
 184 than the locale of the characters in the input data.
 185 .Pp
 186 The functions
 187 .Fn svis ,
 188 .Fn snvis ,
 189 .Fn strsvis ,
 190 .Fn strsnvis ,
 191 .Fn strsvisx ,
 192 .Fn strsnvisx ,
 193 and
 194 .Fn strsenvisx
 195 correspond to
 196 .Fn vis ,
 197 .Fn nvis ,
 198 .Fn strvis ,
 199 .Fn strnvis ,
 200 .Fn strvisx ,
 201 .Fn strnvisx ,
 202 and
 203 .Fn strenvisx
 204 but have an additional argument
 205 .Fa extra ,
 206 pointing to a
 207 .Dv NUL
 208 terminated list of characters.
 209 These characters will be copied encoded or backslash-escaped into
 210 .Fa dst .
 211 These functions are useful e.g. to remove the special meaning
 212 of certain characters to shells.
 213 .Pp
 214 The encoding is a unique, invertible representation composed entirely of
 215 graphic characters; it can be decoded back into the original form using
 216 the
 217 .Xr unvis 3 ,
 218 .Xr strunvis 3
 219 or
 220 .Xr strnunvis 3
 221 functions.
 222 .Pp
 223 There are two parameters that can be controlled: the range of
 224 characters that are encoded (applies only to
 225 .Fn vis ,
 226 .Fn nvis ,
 227 .Fn strvis ,
 228 .Fn strnvis ,
 229 .Fn strvisx ,
 230 and
 231 .Fn strnvisx ) ,
 232 and the type of representation used.
 233 By default, all non-graphic characters,
 234 except space, tab, and newline are encoded (see
 235 .Xr isgraph 3 ) .
 236 The following flags
 237 alter this:
 238 .Bl -tag -width VIS_WHITEX
 239 .It Dv VIS_GLOB
 240 Also encode the magic characters
 241 .Ql ( * ,
 242 .Ql \&? ,
 243 .Ql \&[
 244 and
 245 .Ql # )
 246 recognized by
 247 .Xr glob 3 .
 248 .It Dv VIS_SP
 249 Also encode space.
 250 .It Dv VIS_TAB
 251 Also encode tab.
 252 .It Dv VIS_NL
 253 Also encode newline.
 254 .It Dv VIS_WHITE
 255 Synonym for
 256 .Dv VIS_SP
 257 \&|
 258 .Dv VIS_TAB
 259 \&|
 260 .Dv VIS_NL .
 261 .It Dv VIS_SAFE
 262 Only encode
 263 .Dq unsafe
 264 characters.
 265 Unsafe means control characters which may cause common terminals to perform
 266 unexpected functions.
 267 Currently this form allows space, tab, newline, backspace, bell, and
 268 return \(em in addition to all graphic characters \(em unencoded.
 269 .El
 270 .Pp
 271 (The above flags have no effect for
 272 .Fn svis ,
 273 .Fn snvis ,
 274 .Fn strsvis ,
 275 .Fn strsnvis ,
 276 .Fn strsvisx ,
 277 and
 278 .Fn strsnvisx .
 279 When using these functions, place all graphic characters to be
 280 encoded in an array pointed to by
 281 .Fa extra .
 282 In general, the backslash character should be included in this array, see the
 283 warning on the use of the
 284 .Dv VIS_NOSLASH
 285 flag below).
 286 .Pp
 287 There are four forms of encoding.
 288 All forms use the backslash character
 289 .Ql \e
 290 to introduce a special
 291 sequence; two backslashes are used to represent a real backslash,
 292 except
 293 .Dv VIS_HTTPSTYLE
 294 that uses
 295 .Ql % ,
 296 or
 297 .Dv VIS_MIMESTYLE
 298 that uses
 299 .Ql = .
 300 These are the visual formats:
 301 .Bl -tag -width VIS_CSTYLE
 302 .It (default)
 303 Use an
 304 .Ql M
 305 to represent meta characters (characters with the 8th
 306 bit set), and use caret
 307 .Ql ^
 308 to represent control characters (see
 309 .Xr iscntrl 3 ) .
 310 The following formats are used:
 311 .Bl -tag -width xxxxx
 312 .It Dv \e^C
 313 Represents the control character
 314 .Ql C .
 315 Spans characters
 316 .Ql \e000
 317 through
 318 .Ql \e037 ,
 319 and
 320 .Ql \e177
 321 (as
 322 .Ql \e^? ) .
 323 .It Dv \eM-C
 324 Represents character
 325 .Ql C
 326 with the 8th bit set.
 327 Spans characters
 328 .Ql \e241
 329 through
 330 .Ql \e376 .
 331 .It Dv \eM^C
 332 Represents control character
 333 .Ql C
 334 with the 8th bit set.
 335 Spans characters
 336 .Ql \e200
 337 through
 338 .Ql \e237 ,
 339 and
 340 .Ql \e377
 341 (as
 342 .Ql \eM^? ) .
 343 .It Dv \e040
 344 Represents
 345 .Tn ASCII
 346 space.
 347 .It Dv \e240
 348 Represents Meta-space.
 349 .El
 350 .Pp
 351 .It Dv VIS_CSTYLE
 352 Use C-style backslash sequences to represent standard non-printable
 353 characters.
 354 The following sequences are used to represent the indicated characters:
 355 .Bd -unfilled -offset indent
 356 .Li \ea Tn  \(em BEL No (007)
 357 .Li \eb Tn  \(em BS No (010)
 358 .Li \ef Tn  \(em NP No (014)
 359 .Li \en Tn  \(em NL No (012)
 360 .Li \er Tn  \(em CR No (015)
 361 .Li \es Tn  \(em SP No (040)
 362 .Li \et Tn  \(em HT No (011)
 363 .Li \ev Tn  \(em VT No (013)
 364 .Li \e0 Tn  \(em NUL No (000)
 365 .Ed
 366 .Pp
 367 When using this format, the
 368 .Fa nextc
 369 parameter is looked at to determine if a
 370 .Dv NUL
 371 character can be encoded as
 372 .Ql \e0
 373 instead of
 374 .Ql \e000 .
 375 If
 376 .Fa nextc
 377 is an octal digit, the latter representation is used to
 378 avoid ambiguity.
 379 .It Dv VIS_OCTAL
 380 Use a three digit octal sequence.
 381 The form is
 382 .Ql \eddd
 383 where
 384 .Em d
 385 represents an octal digit.
 386 .It Dv VIS_HTTPSTYLE
 387 Use URI encoding as described in RFC 1738.
 388 The form is
 389 .Ql %xx
 390 where
 391 .Em x
 392 represents a lower case hexadecimal digit.
 393 .It Dv VIS_MIMESTYLE
 394 Use MIME Quoted-Printable encoding as described in RFC 2045, only don't
 395 break lines and don't handle CRLF.
 396 The form is
 397 .Ql =XX
 398 where
 399 .Em X
 400 represents an upper case hexadecimal digit.
 401 .El
 402 .Pp
 403 There is one additional flag,
 404 .Dv VIS_NOSLASH ,
 405 which inhibits the
 406 doubling of backslashes and the backslash before the default
 407 format (that is, control characters are represented by
 408 .Ql ^C
 409 and
 410 meta characters as
 411 .Ql M-C ) .
 412 With this flag set, the encoding is
 413 ambiguous and non-invertible.
 414 .Sh MULTIBYTE CHARACTER SUPPORT
 415 These functions support multibyte character input.
 416 The encoding conversion is influenced by the setting of the
 417 .Ev LC_CTYPE
 418 environment variable which defines the set of characters
 419 that can be copied without encoding.
 420 .Pp
 421 When 8-bit data is present in the input,
 422 .Ev LC_CTYPE
 423 must be set to the correct locale or to the C locale.
 424 If the locales of the data and the conversion are mismatched,
 425 multibyte character recognition may fail and encoding will be performed
 426 byte-by-byte instead.
 427 .Pp
 428 As noted above,
 429 .Fa dst
 430 must be four times the number of bytes processed from
 431 .Fa src .
 432 But note that each multibyte character can be up to
 433 .Dv MB_LEN_MAX
 434 bytes
 435 .\" (see
 436 .\" .Xr multibyte 3 )
 437 so in terms of multibyte characters,
 438 .Fa dst
 439 must be four times
 440 .Dv MB_LEN_MAX
 441 times the number of characters processed from
 442 .Fa src .
 443 .Sh ENVIRONMENT
 444 .Bl -tag -width ".Ev LC_CTYPE"
 445 .It Ev LC_CTYPE
 446 Specify the locale of the input data.
 447 Set to C if the input data locale is unknown.
 448 .El
 449 .Sh ERRORS
 450 The functions
 451 .Fn nvis
 452 and
 453 .Fn snvis
 454 will return
 455 .Dv NULL
 456 and the functions
 457 .Fn strnvis ,
 458 .Fn strnvisx ,
 459 .Fn strsnvis ,
 460 and
 461 .Fn strsnvisx ,
 462 will return \-1 when the
 463 .Fa dlen
 464 destination buffer size is not enough to perform the conversion while
 465 setting
 466 .Va errno
 467 to:
 468 .Bl -tag -width ".Bq Er ENOSPC"
 469 .It Bq Er ENOSPC
 470 The destination buffer size is not large enough to perform the conversion.
 471 .El
 472 .Sh SEE ALSO
 473 .Xr unvis 1 ,
 474 .Xr vis 1 ,
 475 .Xr glob 3 ,
 476 .\" .Xr multibyte 3 ,
 477 .Xr unvis 3
 478 .Rs
 479 .%A T. Berners-Lee
 480 .%T Uniform Resource Locators (URL)
 481 .%O "RFC 1738"
 482 .Re
 483 .Rs
 484 .%T "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies"
 485 .%O "RFC 2045"
 486 .Re
 487 .Sh HISTORY
 488 The
 489 .Fn vis ,
 490 .Fn strvis ,
 491 and
 492 .Fn strvisx
 493 functions first appeared in
 494 .Bx 4.4 .
 495 The
 496 .Fn svis ,
 497 .Fn strsvis ,
 498 .Fn strsvisx
 499 .Fn nvis ,
 500 .Fn strnvis ,
 501 .Fn strnvisx ,
 502 .Fn snvis ,
 503 .Fn strsnvis
 504 and
 505 .Fn strsnvisx
 506 functions as well as multibyte character support were added in OS X 10.12.