| UNVIS(3) | Library Functions Manual | UNVIS(3) | 
unvis, strunvis,
  strnunvis, strunvisx,
  strnunvisx —
#include <vis.h>
int
  
  unvis(char
    *cp, int c,
    int *astate,
    int flag);
int
  
  strunvis(char
    *dst, const char
    *src);
int
  
  strnunvis(char
    *dst, size_t dlen,
    const char *src);
int
  
  strunvisx(char
    *dst, const char
    *src, int
  flag);
int
  
  strnunvisx(char
    *dst, size_t dlen,
    const char *src,
    int flag);
unvis(), strunvis() and
  strunvisx() functions are used to decode a visual
  representation of characters, as produced by the
  vis(3) function, back into the
  original form.
The unvis() function is called with
    successive characters in c until a valid sequence is
    recognized, at which time the decoded character is available at the
    character pointed to by cp.
The strunvis() function decodes the
    characters pointed to by src into the buffer pointed
    to by dst. The strunvis()
    function simply copies src to
    dst, decoding any escape sequences along the way, and
    returns the number of characters placed into dst, or
    -1 if an invalid escape sequence was detected. The size of
    dst should be equal to the size of
    src (that is, no expansion takes place during
    decoding).
The strunvisx() and
    strnunvisx() functions do the same as the
    strunvis() and strnunvis()
    functions, but take a flag that specifies the style the string
    src is encoded with. The meaning of the flag is the
    same as explained below for unvis().
The unvis() function implements a state
    machine that can be used to decode an arbitrary stream of bytes. All state
    associated with the bytes being decoded is stored outside the
    unvis() function (that is, a pointer to the state is
    passed in), so calls decoding different streams can be freely intermixed. To
    start decoding a stream of bytes, first initialize an integer to zero. Call
    unvis() with each successive byte, along with a
    pointer to this integer, and a pointer to a destination character. The
    unvis() function has several return codes that must
    be handled properly. They are:
0
    (zero)UNVIS_VALIDUNVIS_VALIDPUSHUNVIS_NOCHARUNVIS_SYNBADWhen all bytes in the stream have been processed, call
    unvis() one more time with flag set to
    UNVIS_END to extract any remaining character (the
    character passed in is ignored).
The flag argument is also used to specify
    the encoding style of the source. If set to
    VIS_NOESCAPE unvis() will
    not decode backslash escapes. If set to
    VIS_HTTPSTYLE or
    VIS_HTTP1808, unvis() will
    decode URI strings as specified in RFC 1808. If set to
    VIS_HTTP1866, unvis() will
    decode entity references and numeric character references as specified in
    RFC 1866. If set to VIS_MIMESTYLE,
    unvis() will decode MIME Quoted-Printable strings as
    specified in RFC 2045. If set to VIS_NOESCAPE,
    unvis() will not decode
    ‘\’ quoted characters.
The following code fragment illustrates a proper use of
    unvis().
int state = 0;
char out;
while ((ch = getchar()) != EOF) {
again:
	switch(unvis(&out, ch, &state, 0)) {
	case 0:
	case UNVIS_NOCHAR:
		break;
	case UNVIS_VALID:
		(void)putchar(out);
		break;
	case UNVIS_VALIDPUSH:
		(void)putchar(out);
		goto again;
	case UNVIS_SYNBAD:
		errx(EXIT_FAILURE, "Bad character sequence!");
	}
}
if (unvis(&out, '\0', &state, UNVIS_END) == UNVIS_VALID)
	(void)putchar(out);
strunvis(),
  strnunvis(), strunvisx(), and
  strnunvisx() will return -1 on error and set
  errno to:
EINVAL]In addition the functions strnunvis() and
    strnunvisx() will can also set
    errno on error to:
ENOSPC]R. Fielding, Relative Uniform Resource Locators, RFC1808.
unvis() function first appeared in
  4.4BSD. The strnunvis() and
  strnunvisx() functions appeared in
  NetBSD 6.0.
VIS_HTTP1808 and
  VIS_HTTP1866 are wrong. Percent-encoding was defined
  in RFC 1738, the original RFC for URL. RFC 1866 defines HTML 2.0, an
  application of SGML, from which it inherits concepts of numeric character
  references and entity references.
| May 8, 2019 | NetBSD 9.3 |