The Fn 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 Fn strunvis function decodes the characters pointed to by src into the buffer pointed to by dst The Fn 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 Fn strunvisx function does the same as the Fn 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 Fn 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 Fn 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 Fn unvis with each successive byte, along with a pointer to this integer, and a pointer to a destination character. The Fn unvis function has several return codes that must be handled properly. They are:
When all bytes in the stream have been processed, call Fn unvis one more time with flag set to UNVIS_END to extract any remaining character (the character passed in is ignored).
The Fa flag argument is also used to specify the encoding style of the source. If set to VIS_HTTPSTYLE or VIS_HTTP1808 Fn unvis will decode URI strings as specified in RFC 1808. If set to VIS_HTTP1866 Fn unvis will decode entity references and numeric character references as specified in RFC 1866. If set to VIS_MIMESTYLE Fn unvis will decode MIME Quoted-Printable strings as specified in RFC 2045. If set to VIS_NOESCAPE Fn unvis will not decode `\' quoted characters.
The following code fragment illustrates a proper use of Fn 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);
In addition the functions Fn strnunvis and Fn strnunvisx will can also set errno on error to: