ipsec_atoaddr (3) - Linux Manuals
ipsec_atoaddr: convert Internet addresses and Subnet masks to and from ASCII
NAME
ipsec_atoaddr, ipsec_addrtoa, ipsec_atosubnet, ipsec_subnettoa - convert Internet addresses and Subnet masks to and from ASCIISYNOPSIS
#include <libreswan.h>
const char *atoaddr(const char *src, size_t srclen,
const char *atosubnet(const char *src, size_t srclen,
Atoaddr
converts an ASCII name or dotted-decimal address into a binary address
(in network byte order).
Addrtoa
does the reverse conversion, back to an ASCII dotted-decimal address.
Atosubnet
and
subnettoa
do likewise for the ``address/mask'' ASCII form used to write a
specification of a subnet.
An address is specified in ASCII as a
dotted-decimal address (e.g.
1.2.3.4),
an eight-digit network-order hexadecimal number with the usual C prefix (e.g.
0x01020304,
which is synonymous with
1.2.3.4),
an eight-digit host-order hexadecimal number with a
0h
prefix (e.g.
0h01020304,
which is synonymous with
1.2.3.4
on a big-endian host and
4.3.2.1
on a little-endian host),
a DNS name to be looked up via
gethostbyname(3),
or an old-style network name to be looked up via
getnetbyname(3).
A dotted-decimal address may be incomplete, in which case
ASCII-to-binary conversion implicitly appends
as many instances of
.0
as necessary to bring it up to four components.
The components of a dotted-decimal address are always taken as
decimal, and leading zeros are ignored.
For example,
10
is synonymous with
10.0.0.0,
and
128.009.000.032
is synonymous with
128.9.0.32
(the latter example is verbatim from RFC 1166).
The result of
addrtoa
is always complete and does not contain leading zeros.
The letters in
a hexadecimal address may be uppercase or lowercase or any mixture thereof.
Use of hexadecimal addresses is
strongly
discouraged;
they are included only to save hassles when dealing with
the handful of perverted programs which already print
network addresses in hexadecimal.
DNS names may be complete (optionally terminated with a ``.'')
or incomplete, and are looked up as specified by local system configuration
(see
resolver(5)).
The
h_addr
value returned by
gethostbyname(3)
is used,
so with current DNS implementations,
the result when the name corresponds to more than one address is
difficult to predict.
Name lookup resorts to
getnetbyname(3)
only if
gethostbyname(3)
fails.
A subnet specification is of the form network/mask.
The
network
and
mask
can be any form acceptable to
atoaddr.
In addition, the
mask
can be a decimal integer (leading zeros ignored) giving a bit count,
in which case
it stands for a mask with that number of high bits on and all others off
(e.g.,
24
means
255.255.255.0).
In any case, the mask must be contiguous
(a sequence of high bits on and all remaining low bits off).
As a special case, the subnet specification
%default
is a synonym for
0.0.0.0/0.
Atosubnet
ANDs the mask with the address before returning,
so that any non-network bits in the address are turned off
(e.g.,
10.1.2.3/24
is synonymous with
10.1.2.0/24).
Subnettoa
generates the decimal-integer-bit-count
form of the mask,
with no leading zeros,
unless the mask is non-contiguous.
The
srclen
parameter of
atoaddr
and
atosubnet
specifies the length of the ASCII string pointed to by
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
srclen
value of
0
is taken to mean
strlen(src).
The
dstlen
parameter of
addrtoa
and
subnettoa
specifies the size of the
dst
parameter;
under no circumstances are more than
dstlen
bytes written to
dst.
A result which will not fit is truncated.
Dstlen
can be zero, in which case
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
libreswan.h
header file defines constants,
ADDRTOA_BUF
and
SUBNETTOA_BUF,
which are the sizes of buffers just large enough for worst-case results.
The
format
parameter of
addrtoa
and
subnettoa
specifies what format is to be used for the conversion.
The value
0
(not the ASCII character
'0',
but a zero value)
specifies a reasonable default,
and is in fact the only format currently available.
This parameter is a hedge against future needs.
The ASCII-to-binary functions return NULL for success and
a pointer to a string-literal error message for failure;
see DIAGNOSTICS.
The binary-to-ASCII functions return
0
for a failure, and otherwise
always return 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.
Fatal errors in
atosubnet
are:
no
/
in
src;
atoaddr
error in conversion of
network
or
mask;
bit-count mask too big;
mask non-contiguous.
Fatal errors in
addrtoa
and
subnettoa
are:
unknown format.
Ignoring leading zeros in dotted-decimal components and bit counts
is arguably the most useful behavior in this application,
but it might occasionally cause confusion with the historical use of leading
zeros to denote octal numbers.
It is barely possible that somebody, somewhere,
might have a legitimate use for non-contiguous subnet masks.
Getnetbyname(3)
is a historical dreg.
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.
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:
size_t addrtoa(struct in_addr addr, int format,
size_t subnettoa(struct in_addr addr, struct in_addr mask,
DESCRIPTION
These functions are obsolete; see
ipsec_ttoaddr(3)
for their replacements.
DIAGNOSTICS
Fatal errors in
atoaddr
are:
empty input;
attempt to allocate temporary storage for a very long name failed;
name lookup failed;
syntax error in dotted-decimal form;
dotted-decimal component too large to fit in 8 bits.
HISTORY
Written for the FreeS/WAN project by Henry Spencer.
BUGS
The interpretation of incomplete dotted-decimal addresses
(e.g.
10/24
means
10.0.0.0/24)
differs from that of some older conversion
functions, e.g. those of
inet(3).
The behavior of the older functions has never been
particularly consistent or particularly useful.
const char *error;
error = atoaddr( /* ... */ );
if (error != NULL) {
/* something went wrong */