UNVIS(3) BSD Library Functions Manual UNVIS(3)

NAME
     uunnvviiss, ssttrruunnvviiss - decode a visual representation of characters

LLIIBBRRAARRYY
     Standard C Library (libc, -lc)

SYNOPSIS
     ##iinncclluuddee <>

     int
     uunnvviiss(char *cp, int c, int *astate, int flag);

     int
     ssttrruunnvviiss(char *dst, const char *src);

     int
     ssttrruunnvviissxx(char *dst, const char *src, int flag);

DESCRIPTION
     The uunnvviiss(), ssttrruunnvviiss() and ssttrruunnvviissxx() functions are used to decode a
     visual representation of characters, as produced by the vis(3) function,
     back into the original form.  Unvis 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.  Strunvis
     decodes the characters pointed to by src into the buffer pointed to by
     dst.

     The ssttrruunnvviiss() 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 ssttrruunnvviissxx() function does the same as the ssttrruunnvviiss() function, but it
     allows you to add a flag that specifies the style the string src is
     encoded with.  Currently, the only supported flag is VISHTTPSTYLE.

     The uunnvviiss() 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 uunnvviiss() 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 uunnvviiss() with each successive byte, along with a
     pointer to this integer, and a pointer to a destination character.  The
     uunnvviiss() function has several return codes that must be handled properly.
     They are:

     0 (zero)         Another character is necessary; nothing has been recog-
                      nized yet.

     UNVISVALID      A valid character has been recognized and is available
                      at the location pointed to by cp.

     UNVISVALIDPUSH  A valid character has been recognized and is available
                      at the location pointed to by cp; however, the character
                      currently passed in should be passed in again.

     UNVISNOCHAR     A valid sequence was detected, but no character was pro-
                      duced.  This return code is necessary to indicate a log-
                      ical break between characters.

     UNVISSYNBAD     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 uunnvviiss() one more
     time with flag set to UNVISEND 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 VISHTTPSTYLE, uunnvviiss() will decode URI strings as
     specified in RFC 1808.

     The following code fragment illustrates a proper use of uunnvviiss().

           int state = 0;
           char out;

           while ((ch = getchar()) != EOF) {
           again:
                   switch(unvis(&out, ch, &state, 0)) {
                   case 0:
                   case UNVISNOCHAR:
                           break;
                   case UNVISVALID:
                           (void) putchar(out);
                           break;
                   case UNVISVALIDPUSH:
                           (void) putchar(out);
                           goto again;
                   case UNVISSYNBAD:
                           (void)fprintf(stderr, "bad sequence!\n");
                   exit(1);
                   }
           }
           if (unvis(&out, (char)0, &state, UNVISEND) == UNVISVALID)
                   (void) putchar(out);

SEE ALSO
     vis(1), vis(3)

     R. Fielding, Relative Uniform Resource Locators, RFC1808.

HISTORY     The uunnvviiss() function first appeared in 4.4BSD.

BSD                            December 11, 1993                           BSD