unvis(), strunvis() -- decode visual representation of characters

SYNOPSIS

#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(), strvis() and strvisx() functions, 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 specified pointer. The strunvis() function decodes the characters at the specified source into the destination buffer.

The strunvis() function simply copies the source to the destination, decoding any escape sequences along the way, and returns the number of characters placed into the destination buffer, or -1 if an invalid escape sequence was detected. The size of the destination buffer should be equal to the size of the source buffer (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 the destination character. The unvis() function has several return codes that must be handled properly. They are:

0: Another character is necessary; nothing has been recognized yet.
UNVIS_VALID: A valid character has been recognized and is available at the specified location.
UNVIS_VALIDPUSH: A valid character has been recognized and is available at the specified location; however, the character currently passed in should be passed in again.
UNVIS_NOCHAR: A valid sequence was detected, but no character was produced. This return code is necessary to indicate a logical break between characters.
UNVIS_SYNBAD: An invalid escape sequence was detected, or the decoder is in an unknown state. The decoder is placed into the starting state.

When all bytes in the stream have been processed, call unvis() one more time with the 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:
		putchar(out);
		break;
	case UNVIS_VALIDPUSH:
		putchar(out);
		goto again;
	case UNVIS_SYNBAD:
		fprintf(stderr, "bad sequence!\n");
		exit(1);
	}
}
if (unvis(&out, (char)0, &state, UNVIS_END) == UNVIS_VALID)
	putchar(out);

PARAMETERS

cp: Pointer to stored character.
c: Character to parse for conversion
astate: Pointer to location in which state is stored
flag: Should be 0 until the end of the input stream, at which time a final call should be made with flag set to UNVIS_END
dst: Destination buffer for decoded characters.
dlen: Size in characters of dst buffer.
src: Buffer of characters to be converted.

RETURN VALUES

The unvis() function returns one of the state flags described above. The strunvis() function returns the number of characters stored to the destination buffer, or -1 on error.

On error, the functions strunvis(), strnunvis(), strunvisx(), and strnunvisx() will return -1 on error and set errno to:

EINVAL: An invalid escape sequence was detected, or the decoder is in an unknown state.

In addition the functions strnunvis() and strnunvisx() will can also set errno on error to:

ENOSPC: Not enough space to perform the conversion.

unvis(), strunvis()
decode visual representation of characters

Function

SYNOPSIS

DESCRIPTION

PARAMETERS

RETURN VALUES

CONFORMANCE

MULTITHREAD SAFETY LEVEL

PORTING ISSUES

AVAILABILITY

SEE ALSO

unvis(), strunvis() decode visual representation of characters

Function

unvis(), strunvis()
decode visual representation of characters