NAME
vis, nvis, strvis, stravis, strnvis, strvisx, strnvisx, strenvisx, svis, snvis, strsvis, strsnvis, strsvisx, strsnvisx, strsenvisx — visually encode charactersLIBRARY
library “libbsd”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 trailingNUL
); 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.
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:
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.
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 theLC_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 returnNULL
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.April 22, 2017 | Debian |