Provided by: libbsd-dev_0.12.1-1build1_amd64 bug

NAME

     vis, nvis, strvis, stravis, strnvis, strvisx, strnvisx, strenvisx, svis, snvis, strsvis,
     strsnvis, strsvisx, strsnvisx, strsenvisx — visually encode characters

LIBRARY

     Utility functions from BSD systems (libbsd, -lbsd)

SYNOPSIS

     #include <vis.h>
     (See libbsd(7) for include usage.)

     char *
     vis(char *dst, int c, int flag, int nextc);

     char *
     nvis(char *dst, size_t dlen, int c, int flag, int nextc);

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

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

     int
     strnvis(char *dst, size_t dlen, const char *src, int flag);

     int
     strvisx(char *dst, const char *src, size_t len, int flag);

     int
     strnvisx(char *dst, size_t dlen, const char *src, size_t len, int flag);

     int
     strenvisx(char *dst, size_t dlen, const char *src, size_t len, int flag, int *cerr_ptr);

     char *
     svis(char *dst, int c, int flag, int nextc, const char *extra);

     char *
     snvis(char *dst, size_t dlen, int c, int flag, int nextc, const char *extra);

     int
     strsvis(char *dst, const char *src, int flag, const char *extra);

     int
     strsnvis(char *dst, size_t dlen, const char *src, int flag, const char *extra);

     int
     strsvisx(char *dst, const char *src, size_t len, int flag, const char *extra);

     int
     strsnvisx(char *dst, size_t dlen, const char *src, size_t len, int flag, const char *extra);

     int
     strsenvisx(char *dst, size_t dlen, const char *src, size_t len, int flag, const char *extra,
         int *cerr_ptr);

DESCRIPTION

     The vis() function copies into dst a string which represents the character c.  If c needs no
     encoding, it is copied in unaltered.  The string is null terminated, and a pointer to the
     end of the string is returned.  The maximum length of any encoding is four bytes (not
     including the trailing NUL); thus, when encoding a set of characters into a buffer, the size
     of the buffer should be four times the number of bytes encoded, plus one for the trailing
     NUL.  The flag parameter is used for altering the default range of characters considered for
     encoding and for altering the visual representation.  The additional character, nextc, is
     only used when selecting the VIS_CSTYLE encoding format (explained below).

     The strvis(), stravis(), strnvis(), strvisx(), and strnvisx() functions copy into dst a
     visual representation of the string src.  The strvis() and strnvis() functions encode
     characters from src up to the first NUL.  The strvisx() and strnvisx() functions encode
     exactly len characters from src (this is useful for encoding a block of data that may
     contain NUL's).  Both forms NUL terminate dst.  The size of dst must be four times the
     number of bytes encoded from src (plus one for the NUL).  Both forms return the number of
     characters in dst (not including the trailing NUL).  The stravis() function allocates space
     dynamically to hold the string.  The “n” versions of the functions also take an additional
     argument dlen that indicates the length of the dst buffer.  If dlen is not large enough to
     fit the converted string then the strnvis() and strnvisx() functions return -1 and set errno
     to ENOSPC.  The strenvisx() function takes an additional argument, cerr_ptr, that is used to
     pass in and out a multibyte conversion error flag.  This is useful when processing single
     characters at a time when it is possible that the locale may be set to something other than
     the locale of the characters in the input data.

     The functions svis(), snvis(), strsvis(), strsnvis(), strsvisx(), strsnvisx(), and
     strsenvisx() correspond to vis(), nvis(), strvis(), strnvis(), strvisx(), strnvisx(), and
     strenvisx() but have an additional argument extra, pointing to a NUL terminated list of
     characters.  These characters will be copied encoded or backslash-escaped into dst.  These
     functions are useful e.g. to remove the special meaning of certain characters to shells.

     The encoding is a unique, invertible representation composed entirely of graphic characters;
     it can be decoded back into the original form using the unvis(3bsd), strunvis(3bsd) or
     strnunvis(3bsd) functions.

     There are two parameters that can be controlled: the range of characters that are encoded
     (applies only to vis(), nvis(), strvis(), strnvis(), strvisx(), and strnvisx()), and the
     type of representation used.  By default, all non-graphic characters, except space, tab, and
     newline are encoded (see isgraph(3)).  The following flags alter this:

     VIS_DQ      Also encode double quotes

     VIS_GLOB    Also encode the magic characters (‘*’, ‘?’, ‘[’, and ‘#’) recognized by glob(3).

     VIS_SHELL   Also encode the meta characters used by shells (in addition to the glob
                 characters): (‘'’, ‘`’, ‘"’, ‘;’, ‘&’, ‘<’, ‘>’, ‘(’, ‘)’, ‘|’, ‘]’, ‘\’, ‘$’,
                 ‘!’, ‘^’, and ‘~’).

     VIS_SP      Also encode space.

     VIS_TAB     Also encode tab.

     VIS_NL      Also encode newline.

     VIS_WHITE   Synonym for VIS_SP | VIS_TAB | VIS_NL.

     VIS_META    Synonym for VIS_WHITE | VIS_GLOB | VIS_SHELL.

     VIS_SAFE    Only encode “unsafe” characters.  Unsafe means control characters which may
                 cause common terminals to perform unexpected functions.  Currently this form
                 allows space, tab, newline, backspace, bell, and return — in addition to all
                 graphic characters — unencoded.

     (The above flags have no effect for svis(), snvis(), strsvis(), strsnvis(), strsvisx(), and
     strsnvisx().  When using these functions, place all graphic characters to be encoded in an
     array pointed to by extra.  In general, the backslash character should be included in this
     array, see the warning on the use of the VIS_NOSLASH flag below).

     There are six forms of encoding.  All forms use the backslash character ‘\’ to introduce a
     special sequence; two backslashes are used to represent a real backslash, except
     VIS_HTTPSTYLE that uses ‘%’, or VIS_MIMESTYLE that uses ‘=’.  These are the visual formats:

     (default)   Use an ‘M’ to represent meta characters (characters with the 8th bit set), and
                 use caret ‘^’ to represent control characters (see iscntrl(3)).  The following
                 formats are used:

                 \^C    Represents the control character ‘C’.  Spans characters ‘\000’ through
                        ‘\037’, and ‘\177’ (as ‘\^?’).

                 \M-C   Represents character ‘C’ with the 8th bit set.  Spans characters ‘\241’
                        through ‘\376’.

                 \M^C   Represents control character ‘C’ with the 8th bit set.  Spans characters
                        ‘\200’ through ‘\237’, and ‘\377’ (as ‘\M^?’).

                 \040   Represents ASCII space.

                 \240   Represents Meta-space.

     VIS_CSTYLE  Use C-style backslash sequences to represent standard non-printable characters.
                 The following sequences are used to represent the indicated characters:

                       \a — BEL (007)
                       \b — BS (010)
                       \f — NP (014)
                       \n — NL (012)
                       \r — CR (015)
                       \s — SP (040)
                       \t — HT (011)
                       \v — VT (013)
                       \0 — NUL (000)

                 When using this format, the nextc parameter is looked at to determine if a NUL
                 character can be encoded as ‘\0’ instead of ‘\000’.  If nextc is an octal digit,
                 the latter representation is used to avoid ambiguity.

                 Non-printable characters without C-style backslash sequences use the default
                 representation.

     VIS_OCTAL   Use a three digit octal sequence.  The form is ‘\ddd’ where d represents an
                 octal digit.

     VIS_CSTYLE | VIS_OCTAL
                 Same as VIS_CSTYLE except that non-printable characters without C-style
                 backslash sequences use a three digit octal sequence.

     VIS_HTTPSTYLE
                 Use URI encoding as described in RFC 1738.  The form is ‘%xx’ where x represents
                 a lower case hexadecimal digit.

     VIS_MIMESTYLE
                 Use MIME Quoted-Printable encoding as described in RFC 2045, only don't break
                 lines and don't handle CRLF.  The form is ‘=XX’ where X represents an upper case
                 hexadecimal digit.

     There is one additional flag, VIS_NOSLASH, which inhibits the doubling of backslashes and
     the backslash before the default format (that is, control characters are represented by ‘^C’
     and meta characters as ‘M-C’).  With this flag set, the encoding is ambiguous and non-
     invertible.

MULTIBYTE CHARACTER SUPPORT

     These functions support multibyte character input.  The encoding conversion is influenced by
     the setting of the LC_CTYPE environment variable which defines the set of characters that
     can be copied without encoding.

     If VIS_NOLOCALE is set, processing is done assuming the C locale and overriding any other
     environment settings.

     When 8-bit data is present in the input, LC_CTYPE must be set to the correct locale or to
     the C locale.  If the locales of the data and the conversion are mismatched, multibyte
     character recognition may fail and encoding will be performed byte-by-byte instead.

     As noted above, dst must be four times the number of bytes processed from src.  But note
     that each multibyte character can be up to MB_LEN_MAX bytes so in terms of multibyte
     characters, dst must be four times MB_LEN_MAX times the number of characters processed from
     src.

ENVIRONMENT

     LC_CTYPE  Specify the locale of the input data.  Set to C if the input data locale is
               unknown.

ERRORS

     The functions nvis() and snvis() will return NULL and the functions strnvis(), strnvisx(),
     strsnvis(), and strsnvisx(), will return -1 when the dlen destination buffer size is not
     enough to perform the conversion while setting errno to:

     [ENOSPC]  The destination buffer size is not large enough to perform the conversion.

SEE ALSO

     unvis(1), vis(1), glob(3), unvis(3bsd)

     T. Berners-Lee, Uniform Resource Locators (URL), RFC 1738.

     Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies,
     RFC 2045.

HISTORY

     The vis(), strvis(), and strvisx() functions first appeared in 4.4BSD.  The svis(),
     strsvis(), and strsvisx() functions appeared in NetBSD 1.5.  The buffer size limited
     versions of the functions (nvis(), strnvis(), strnvisx(), snvis(), strsnvis(), and
     strsnvisx()) appeared in NetBSD 6.0 and FreeBSD 9.2.  Multibyte character support was added
     in NetBSD 7.0 and FreeBSD 9.2.