NAME
ipsec atoaddr, addrtoa - convert Internet addresses to and from ASCII
ipsec atosubnet, subnettoa - convert subnet/mask ASCII form to and from
addresses
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 */
11 June 2001