.TH IPSEC_ATOSA 3 "11 June 2001"
.SH NAME
ipsec atosa, satoa \- convert IPsec Security Association IDs to and from ASCII
.SH SYNOPSIS
.B "#include <freeswan.h>
.sp
.B "const char *atosa(const char *src, size_t srclen,"
.ti +1c
.B "struct sa_id *sa);
.br
.B "size_t satoa(struct sa_id sa, int format,"
.ti +1c
.B "char *dst, size_t dstlen);"
.sp
.B "struct sa_id {"
.ti +1c
.B "struct in_addr dst;"
.ti +1c
.B "ipsec_spi_t spi;"
.ti +1c
.B "int proto;"
.br
.B "};"
.SH DESCRIPTION
These functions are obsolete; see
.IR ipsec_ttosa (3)
for their replacements.
.PP
.I Atosa
converts an ASCII Security Association (SA) specifier into an
.B sa_id
structure (containing
a destination-host address
in network byte order,
an SPI number in network byte order, and
a protocol code).
.I Satoa
does the reverse conversion, back to an ASCII SA specifier.
.PP
An SA is specified in ASCII with a mail-like syntax, e.g.
.BR esp507@1.2.3.4 .
An SA specifier contains
a protocol prefix (currently
.BR ah ,
.BR esp ,
or
.BR tun ),
an unsigned integer SPI number,
and an IP address.
The SPI number can be decimal or hexadecimal
(with
.B 0x
prefix), as accepted by
.IR ipsec_atoul (3).
The IP address can be any form accepted by
.IR ipsec_atoaddr (3),
e.g. dotted-decimal address or DNS name.
.PP
As a special case, the SA specifier
.B %passthrough
signifies the special SA used to indicate that packets should be
passed through unaltered.
(At present, this is a synonym for
.BR tun0x0@0.0.0.0 ,
but that is subject to change without notice.)
This form is known to both
.I atosa
and
.IR satoa ,
so the internal form of
.B %passthrough
is never visible.
.PP
The
.B <freeswan.h>
header file supplies the
.B sa_id
structure, as well as a data type
.B ipsec_spi_t
which is an unsigned 32-bit integer.
(There is no consistency between kernel and user on what such a type
is called, hence the header hides the differences.)
.PP
The protocol code uses the same numbers that IP does.
For user convenience, given the difficulty in acquiring the exact set of
protocol names used by the kernel,
.B <freeswan.h>
defines the names
.BR SA_ESP ,
.BR SA_AH ,
and
.B SA_IPIP
to have the same values as the kernel names
.BR IPPROTO_ESP ,
.BR IPPROTO_AH ,
and
.BR IPPROTO_IPIP .
.PP
The
.I srclen
parameter of
.I atosa
specifies the length of the ASCII string pointed to by
.IR src ;
it is an error for there to be anything else
(e.g., a terminating NUL) within that length.
As a convenience for cases where an entire NUL-terminated string is
to be converted,
a
.I srclen
value of
.B 0
is taken to mean
.BR strlen(src) .
.PP
The
.I dstlen
parameter of
.I satoa
specifies the size of the
.I dst
parameter;
under no circumstances are more than
.I dstlen
bytes written to
.IR dst .
A result which will not fit is truncated.
.I Dstlen
can be zero, in which case
.I dst
need not be valid and no result is written,
but the return value is unaffected;
in all other cases, the (possibly truncated) result is NUL-terminated.
The
.I freeswan.h
header file defines a constant,
.BR SATOA_BUF ,
which is the size of a buffer just large enough for worst-case results.
.PP
The
.I format
parameter of
.I satoa
specifies what format is to be used for the conversion.
The value
.B 0
(not the ASCII character
.BR '0' ,
but a zero value)
specifies a reasonable default
(currently
lowercase protocol prefix, lowercase hexadecimal SPI, dotted-decimal address).
The value
.B d
causes the SPI to be generated in decimal instead.
.PP
.I Atosa
returns
.B NULL
for success and
a pointer to a string-literal error message for failure;
see DIAGNOSTICS.
.I Satoa
returns
.B 0
for a failure, and otherwise
always returns the size of buffer which would 
be needed to
accommodate the full conversion result, including terminating NUL;
it is the caller's responsibility to check this against the size of
the provided buffer to determine whether truncation has occurred.
.SH SEE ALSO
ipsec_atoul(3), ipsec_atoaddr(3), inet(3)
.SH DIAGNOSTICS
Fatal errors in
.I atosa
are:
empty input;
input too small to be a legal SA specifier;
no
.B @
in input;
unknown protocol prefix;
conversion error in
.I atoul
or
.IR atoaddr .
.PP
Fatal errors in
.I satoa
are:
unknown format; unknown protocol code.
.SH HISTORY
Written for the FreeS/WAN project by Henry Spencer.
.SH BUGS
The
.B tun
protocol code is a FreeS/WANism which may eventually disappear.
.PP
The restriction of ASCII-to-binary error reports to literal strings
(so that callers don't need to worry about freeing them or copying them)
does limit the precision of error reporting.
.PP
The ASCII-to-binary error-reporting convention lends itself
to slightly obscure code,
because many readers will not think of NULL as signifying success.
A good way to make it clearer is to write something like:
.PP
.RS
.nf
.B "const char *error;"
.sp
.B "error = atoaddr( /* ... */ );"
.B "if (error != NULL) {"
.B "        /* something went wrong */"
.fi
.RE