VIS

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NAME

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

LIBRARY

Lb libbsd

SYNOPSIS

In vis.h (See libbsd(7) for include usage.) 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

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 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, Fa nextc , is only used when selecting the VIS_CSTYLE encoding format (explained below).

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 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 NUL 's Both forms 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 NUL ) Both forms return the number of characters in Fa dst (not including the trailing NUL ) The Fn stravis function allocates space dynamically to hold the string. The ``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 errno to 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.

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 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.

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 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 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 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 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 Fa nextc parameter is looked at to determine if a NUL character can be encoded as `\0' instead of `\000' If Fa 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, Fa dst must be four times the number of bytes processed from Fa src . But note that each multibyte character can be up to MB_LEN_MAX bytes so in terms of multibyte characters, Fa dst must be four times MB_LEN_MAX times the number of characters processed from Fa src .

ENVIRONMENT

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

ERRORS

The functions Fn nvis and Fn snvis will return 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 errno to:

Bq Er ENOSPC: The destination buffer size is not large enough to perform the conversion.

HISTORY

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

VIS