NAME¶
ipsec_atoaddr, ipsec_addrtoa, ipsec_atosubnet, ipsec_subnettoa - convert
Internet addresses and Subnet masks to and from ASCII
SYNOPSIS¶
#include <freeswan.h>
const char *atoaddr(const char *src, size_t srclen, struct in_addr
*addr);
size_t addrtoa(struct in_addr addr, int format, char *dst, size_t
dstlen);
const char *atosubnet(const char *src, size_t srclen, struct in_addr
*addr, struct in_addr *mask);
size_t subnettoa(struct in_addr addr, struct in_addr mask, int format,
char *dst, size_t dstlen);
DESCRIPTION¶
These functions are obsolete; see
ipsec_ttoaddr(3) for their
replacements.
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
freeswan.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.
SEE ALSO¶
inet(3)
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.
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.
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.
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:
const char *error;
error = atoaddr( /* ... */ );
if (error != NULL) {
/* something went wrong */