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.\"     @(#)vis.3	8.1 (Berkeley) 6/9/93
.\"
.Dd April 22, 2017
.Dt VIS 3
.Os
.Sh NAME
.Nm vis ,
.Nm nvis ,
.Nm strvis ,
.Nm stravis ,
.Nm strnvis ,
.Nm strvisx ,
.Nm strnvisx ,
.Nm strenvisx ,
.Nm svis ,
.Nm snvis ,
.Nm strsvis ,
.Nm strsnvis ,
.Nm strsvisx ,
.Nm strsnvisx ,
.Nm strsenvisx
.Nd visually encode characters
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In vis.h
.Ft char *
.Fn vis "char *dst" "int c" "int flag" "int nextc"
.Ft char *
.Fn nvis "char *dst" "size_t dlen" "int c" "int flag" "int nextc"
.Ft int
.Fn strvis "char *dst" "const char *src" "int flag"
.Ft int
.Fn stravis "char **dst" "const char *src" "int flag"
.Ft int
.Fn strnvis "char *dst" "size_t dlen" "const char *src" "int flag"
.Ft int
.Fn strvisx "char *dst" "const char *src" "size_t len" "int flag"
.Ft int
.Fn strnvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag"
.Ft int
.Fn strenvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag" "int *cerr_ptr"
.Ft char *
.Fn svis "char *dst" "int c" "int flag" "int nextc" "const char *extra"
.Ft char *
.Fn snvis "char *dst" "size_t dlen" "int c" "int flag" "int nextc" "const char *extra"
.Ft int
.Fn strsvis "char *dst" "const char *src" "int flag" "const char *extra"
.Ft int
.Fn strsnvis "char *dst" "size_t dlen" "const char *src" "int flag" "const char *extra"
.Ft int
.Fn strsvisx "char *dst" "const char *src" "size_t len" "int flag" "const char *extra"
.Ft int
.Fn strsnvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag" "const char *extra"
.Ft int
.Fn strsenvisx "char *dst" "size_t dlen" "const char *src" "size_t len" "int flag" "const char *extra" "int *cerr_ptr"
.Sh DESCRIPTION
The
.Fn vis
function
copies into
.Fa dst
a string which represents the character
.Fa c .
If
.Fa 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
.Dv 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
.Dv 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,
.Fa nextc ,
is only used when selecting the
.Dv VIS_CSTYLE
encoding format (explained below).
.Pp
The
.Fn strvis ,
.Fn stravis ,
.Fn strnvis ,
.Fn strvisx ,
and
.Fn strnvisx
functions copy into
.Fa dst
a visual representation of
the string
.Fa src .
The
.Fn strvis
and
.Fn strnvis
functions encode characters from
.Fa src
up to the
first
.Dv NUL .
The
.Fn strvisx
and
.Fn strnvisx
functions encode exactly
.Fa len
characters from
.Fa src
(this
is useful for encoding a block of data that may contain
.Dv NUL Ns 's ) .
Both forms
.Dv NUL
terminate
.Fa dst .
The size of
.Fa dst
must be four times the number
of bytes encoded from
.Fa src
(plus one for the
.Dv NUL ) .
Both
forms return the number of characters in
.Fa dst
(not including the trailing
.Dv NUL ) .
The
.Fn stravis
function allocates space dynamically to hold the string.
The
.Dq Nm n
versions of the functions also take an additional argument
.Fa dlen
that indicates the length of the
.Fa dst
buffer.
If
.Fa dlen
is not large enough to fit the converted string then the
.Fn strnvis
and
.Fn strnvisx
functions return \-1 and set
.Va errno
to
.Dv ENOSPC .
The
.Fn strenvisx
function takes an additional argument,
.Fa 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.
.Pp
The functions
.Fn svis ,
.Fn snvis ,
.Fn strsvis ,
.Fn strsnvis ,
.Fn strsvisx ,
.Fn strsnvisx ,
and
.Fn strsenvisx
correspond to
.Fn vis ,
.Fn nvis ,
.Fn strvis ,
.Fn strnvis ,
.Fn strvisx ,
.Fn strnvisx ,
and
.Fn strenvisx
but have an additional argument
.Fa extra ,
pointing to a
.Dv NUL
terminated list of characters.
These characters will be copied encoded or backslash-escaped into
.Fa dst .
These functions are useful e.g. to remove the special meaning
of certain characters to shells.
.Pp
The encoding is a unique, invertible representation composed entirely of
graphic characters; it can be decoded back into the original form using
the
.Xr unvis 3 ,
.Xr strunvis 3
or
.Xr strnunvis 3
functions.
.Pp
There are two parameters that can be controlled: the range of
characters that are encoded (applies only to
.Fn vis ,
.Fn nvis ,
.Fn strvis ,
.Fn strnvis ,
.Fn strvisx ,
and
.Fn strnvisx ) ,
and the type of representation used.
By default, all non-graphic characters,
except space, tab, and newline are encoded (see
.Xr isgraph 3 ) .
The following flags
alter this:
.Bl -tag -width VIS_WHITEX
.It Dv VIS_DQ
Also encode double quotes
.It Dv VIS_GLOB
Also encode the magic characters
.Ql ( * ,
.Ql \&? ,
.Ql \&[ ,
and
.Ql # )
recognized by
.Xr glob 3 .
.It Dv VIS_SHELL
Also encode the meta characters used by shells (in addition to the glob
characters):
.Ql ( ' ,
.Ql ` ,
.Ql \&" ,
.Ql \&; ,
.Ql & ,
.Ql < ,
.Ql > ,
.Ql \&( ,
.Ql \&) ,
.Ql \&| ,
.Ql \&] ,
.Ql \e ,
.Ql $ ,
.Ql \&! ,
.Ql \&^ ,
and
.Ql ~ ) .
.It Dv VIS_SP
Also encode space.
.It Dv VIS_TAB
Also encode tab.
.It Dv VIS_NL
Also encode newline.
.It Dv VIS_WHITE
Synonym for
.Dv VIS_SP | VIS_TAB | VIS_NL .
.It Dv VIS_META
Synonym for
.Dv VIS_WHITE | VIS_GLOB | VIS_SHELL .
.It Dv VIS_SAFE
Only encode
.Dq 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 \(em in addition to all graphic characters \(em unencoded.
.El
.Pp
(The above flags have no effect for
.Fn svis ,
.Fn snvis ,
.Fn strsvis ,
.Fn strsnvis ,
.Fn strsvisx ,
and
.Fn strsnvisx .
When using these functions, place all graphic characters to be
encoded in an array pointed to by
.Fa extra .
In general, the backslash character should be included in this array, see the
warning on the use of the
.Dv VIS_NOSLASH
flag below).
.Pp
There are six forms of encoding.
All forms use the backslash character
.Ql \e
to introduce a special
sequence; two backslashes are used to represent a real backslash,
except
.Dv VIS_HTTPSTYLE
that uses
.Ql % ,
or
.Dv VIS_MIMESTYLE
that uses
.Ql = .
These are the visual formats:
.Bl -tag -width VIS_CSTYLE
.It (default)
Use an
.Ql M
to represent meta characters (characters with the 8th
bit set), and use caret
.Ql ^
to represent control characters (see
.Xr iscntrl 3 ) .
The following formats are used:
.Bl -tag -width xxxxx
.It Dv \e^C
Represents the control character
.Ql C .
Spans characters
.Ql \e000
through
.Ql \e037 ,
and
.Ql \e177
(as
.Ql \e^? ) .
.It Dv \eM-C
Represents character
.Ql C
with the 8th bit set.
Spans characters
.Ql \e241
through
.Ql \e376 .
.It Dv \eM^C
Represents control character
.Ql C
with the 8th bit set.
Spans characters
.Ql \e200
through
.Ql \e237 ,
and
.Ql \e377
(as
.Ql \eM^? ) .
.It Dv \e040
Represents
.Tn ASCII
space.
.It Dv \e240
Represents Meta-space.
.El
.It Dv VIS_CSTYLE
Use C-style backslash sequences to represent standard non-printable
characters.
The following sequences are used to represent the indicated characters:
.Bd -unfilled -offset indent
.Li \ea Tn  \(em BEL No (007)
.Li \eb Tn  \(em BS No (010)
.Li \ef Tn  \(em NP No (014)
.Li \en Tn  \(em NL No (012)
.Li \er Tn  \(em CR No (015)
.Li \es Tn  \(em SP No (040)
.Li \et Tn  \(em HT No (011)
.Li \ev Tn  \(em VT No (013)
.Li \e0 Tn  \(em NUL No (000)
.Ed
.Pp
When using this format, the
.Fa nextc
parameter is looked at to determine if a
.Dv NUL
character can be encoded as
.Ql \e0
instead of
.Ql \e000 .
If
.Fa nextc
is an octal digit, the latter representation is used to
avoid ambiguity.
.Pp
Non-printable characters without C-style
backslash sequences use the default representation.
.It Dv VIS_OCTAL
Use a three digit octal sequence.
The form is
.Ql \eddd
where
.Em d
represents an octal digit.
.It Dv VIS_CSTYLE \&| Dv VIS_OCTAL
Same as
.Dv VIS_CSTYLE
except that non-printable characters without C-style
backslash sequences use a three digit octal sequence.
.It Dv VIS_HTTPSTYLE
Use URI encoding as described in RFC 1738.
The form is
.Ql %xx
where
.Em x
represents a lower case hexadecimal digit.
.It Dv 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
.Ql =XX
where
.Em X
represents an upper case hexadecimal digit.
.El
.Pp
There is one additional flag,
.Dv VIS_NOSLASH ,
which inhibits the
doubling of backslashes and the backslash before the default
format (that is, control characters are represented by
.Ql ^C
and
meta characters as
.Ql M-C ) .
With this flag set, the encoding is
ambiguous and non-invertible.
.Sh MULTIBYTE CHARACTER SUPPORT
These functions support multibyte character input.
The encoding conversion is influenced by the setting of the
.Ev LC_CTYPE
environment variable which defines the set of characters
that can be copied without encoding.
.Pp
If
.Dv VIS_NOLOCALE
is set, processing is done assuming the C locale and overriding
any other environment settings.
.Pp
When 8-bit data is present in the input,
.Ev 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.
.Pp
As noted above,
.Fa dst
must be four times the number of bytes processed from
.Fa src .
But note that each multibyte character can be up to
.Dv MB_LEN_MAX
bytes
.\" (see
.\" .Xr multibyte 3 )
so in terms of multibyte characters,
.Fa dst
must be four times
.Dv MB_LEN_MAX
times the number of characters processed from
.Fa src .
.Sh ENVIRONMENT
.Bl -tag -width ".Ev LC_CTYPE"
.It Ev LC_CTYPE
Specify the locale of the input data.
Set to C if the input data locale is unknown.
.El
.Sh ERRORS
The functions
.Fn nvis
and
.Fn snvis
will return
.Dv NULL
and the functions
.Fn strnvis ,
.Fn strnvisx ,
.Fn strsnvis ,
and
.Fn strsnvisx ,
will return \-1 when the
.Fa dlen
destination buffer size is not enough to perform the conversion while
setting
.Va errno
to:
.Bl -tag -width ".Bq Er ENOSPC"
.It Bq Er ENOSPC
The destination buffer size is not large enough to perform the conversion.
.El
.Sh SEE ALSO
.Xr unvis 1 ,
.Xr vis 1 ,
.Xr glob 3 ,
.\" .Xr multibyte 3 ,
.Xr unvis 3
.Rs
.%A T. Berners-Lee
.%T Uniform Resource Locators (URL)
.%O "RFC 1738"
.Re
.Rs
.%T "Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies"
.%O "RFC 2045"
.Re
.Sh HISTORY
The
.Fn vis ,
.Fn strvis ,
and
.Fn strvisx
functions first appeared in
.Bx 4.4 .
The
.Fn svis ,
.Fn strsvis ,
.Fn strsvisx
.Fn nvis ,
.Fn strnvis ,
.Fn strnvisx ,
.Fn snvis ,
.Fn strsnvis
and
.Fn strsnvisx
functions as well as multibyte character support were added in OS X 10.12.