ttodata.3

This a good VPN source

.TH IPSEC_TTODATA 3 "16 August 2003"
.\" RCSID $Id: ttodata.3,v 1.8 2004/04/09 18:00:37 mcr Exp $
.SH NAME
ipsec ttodata, datatot \- convert binary data bytes from and to text formats
.SH SYNOPSIS
.B "#include <freeswan.h>"
.sp
.B "const char *ttodata(const char *src, size_t srclen,"
.ti +1c
.B "int base, char *dst, size_t dstlen, size_t *lenp);"
.br
.B "const char *ttodatav(const char *src, size_t srclen,"
.ti +1c
.B "int base, char *dst, size_t dstlen, size_t *lenp,"
.ti +1c
.B "char *errp, size_t errlen, int flags);"
.br
.B "size_t datatot(const char *src, size_t srclen,"
.ti +1c
.B "int format, char *dst, size_t dstlen);"
.SH DESCRIPTION
.IR Ttodata ,
.IR ttodatav ,
and
.I datatot
convert arbitrary binary data (e.g. encryption or authentication keys)
from and to more-or-less human-readable text formats.
.PP
Currently supported formats are hexadecimal, base64, and characters.
.PP
A hexadecimal text value begins with a
.B 0x
(or
.BR 0X )
prefix and continues with two-digit groups
of hexadecimal digits (0-9, and a-f or A-F),
each group encoding the value of one binary byte, high-order digit first.
A single
.B _
(underscore)
between consecutive groups is ignored, permitting punctuation to improve 
readability; doing this every eight digits seems about right.
.PP
A base64 text value begins with a
.B 0s
(or
.BR 0S )
prefix 
and continues with four-digit groups of base64 digits (A-Z, a-z, 0-9, +, and /),
each group encoding the value of three binary bytes as described in
section 6.8 of RFC 2045.
If
.B flags
has the
.B TTODATAV_IGNORESPACE
bit on, blanks are ignore (after the prefix).
Note that the last one or two digits of a base64 group can be
.B =
to indicate that fewer than three binary bytes are encoded.
.PP
A character text value begins with a
.B 0t
(or
.BR 0T )
prefix
and continues with text characters, each being the value of one binary byte. 
.PP
All these functions basically copy data from
.I src
(whose size is specified by
.IR srclen )
to
.I dst
(whose size is specified by
.IR dstlen ),
doing the conversion en route.
If the result will not fit in
.IR dst ,
it is truncated;
under no circumstances are more than
.I dstlen
bytes of result written to
.IR dst .
.I Dstlen
can be zero, in which case
.I dst
need not be valid and no result bytes are written at all.
.PP
The
.I base
parameter of
.I ttodata
and
.I ttodatav
specifies what format the input is in;
normally it should be
.B 0
to signify that this gets figured out from the prefix.
Values of
.BR 16 ,
.BR 64 ,
and
.BR 256
respectively signify hexadecimal, base64, and character-text formats
without prefixes.
.PP
The
.I format
parameter of
.IR datatot ,
a single character used as a type code,
specifies which text format is wanted.
The value
.B 0
(not ASCII
.BR '0' ,
but a zero value) specifies a reasonable default.
Other currently-supported values are:
.RS 2
.TP 4
.B 'x'
continuous lower-case hexadecimal with a
.B 0x
prefix
.TP
.B 'h'
lower-case hexadecimal with a
.B 0x
prefix and a
.B _
every eight digits
.TP
.B ':'
lower-case hexadecimal with no prefix and a
.B :
(colon) every two digits
.TP
.B 16
lower-case hexadecimal with no prefix or
.B _
.TP
.B 's'
continuous base64 with a
.B 0s
prefix
.TP
.B 64
continuous base64 with no prefix
.RE
.PP
The default format is currently
.BR 'h' .
.PP
.I Ttodata
returns NULL for success and
a pointer to a string-literal error message for failure;
see DIAGNOSTICS.
On success,
if and only if
.I lenp
is non-NULL,
.B *lenp
is set to the number of bytes required to contain the full untruncated result.
It is the caller's responsibility to check this against
.I dstlen
to determine whether he has obtained a complete result.
The
.B *lenp
value is correct even if
.I dstlen
is zero, which offers a way to determine how much space would be needed
before having to allocate any.
.PP
.I Ttodatav
is just like
.I ttodata
except that in certain cases,
if
.I errp
is non-NULL,
the buffer pointed to by
.I errp
(whose length is given by
.IR errlen )
is used to hold a more detailed error message.
The return value is NULL for success,
and is either
.I errp
or a pointer to a string literal for failure.
If the size of the error-message buffer is
inadequate for the desired message,
.I ttodatav
will fall back on returning a pointer to a literal string instead.
The
.I freeswan.h
header file defines a constant
.B TTODATAV_BUF
which is the size of a buffer large enough for worst-case results.
.PP
The normal return value of
.IR datatot
is the number of bytes required
to contain the full untruncated result.
It is the caller's responsibility to check this against
.I dstlen
to determine whether he has obtained a complete result.
The return value is correct even if
.I dstlen
is zero, which offers a way to determine how much space would be needed
before having to allocate any.
A return value of
.B 0
signals a fatal error of some kind
(see DIAGNOSTICS).
.PP
A zero value for
.I srclen
in
.I ttodata
(but not
.IR datatot !)
is synonymous with
.BR strlen(src) .
A non-zero
.I srclen
in
.I ttodata
must not include the terminating NUL.
.PP
Unless
.I dstlen
is zero,
the result supplied by
.I datatot
is always NUL-terminated,
and its needed-size return value includes space for the terminating NUL.
.PP
Several obsolete variants of these functions
.RI ( atodata ,
.IR datatoa ,
.IR atobytes ,
and
.IR bytestoa )
are temporarily also supported.
.SH SEE ALSO
sprintf(3), ipsec_atoaddr(3)
.SH DIAGNOSTICS
Fatal errors in
.I ttodata
and
.I ttodatav
are:
unknown characters in the input;
unknown or missing prefix;
unknown base;
incomplete digit group;
non-zero padding in a base64 less-than-three-bytes digit group;
zero-length input.
.PP
Fatal errors in
.I datatot
are:
unknown format code;
zero-length input.
.SH HISTORY
Written for the FreeS/WAN project by Henry Spencer.
.SH BUGS
.I Datatot
should have a format code to produce character-text output.
.PP
The
.B 0s
and
.B 0t
prefixes are the author's inventions and are not a standard
of any kind.
They have been chosen to avoid collisions with existing practice
(some C implementations use
.B 0b
for binary)
and possible confusion with unprefixed hexadecimal.