UNVIS(3) | Library Functions Manual | UNVIS(3) |
unvis
, strunvis
,
strnunvis
, strunvisx
,
strnunvisx
— decode a visual
representation of characters
Standard C Library (libc, -lc)
#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);
The
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
()
function does the same as the strunvis
() function,
but it allows you to add a flag that specifies the style the string
src is encoded with. Currently, the supported flags
are: VIS_HTTPSTYLE
and
VIS_MIMESTYLE
.
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_VALID
UNVIS_VALIDPUSH
UNVIS_NOCHAR
UNVIS_SYNBAD
When 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_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);
The functions 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.
The unvis
() function first appeared in
4.4BSD. The strnunvis
() and
strnunvisx
() functions appeared in OS X 10.12.
The names 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.
March 12, 2011 | macOS 14.6 |