NAME
ipsec ttoaddr, tnatoaddr, addrtot - convert Internet addresses to and
from text
ipsec ttosubnet, subnettot - convert subnet/mask text form to and from
addresses
SYNOPSIS
#include <freeswan.h>
const char *ttoaddr(const char *src, size_t srclen,
int af, ip_address *addr);
const char *tnatoaddr(const char *src, size_t srclen,
int af, ip_address *addr);
size_t addrtot(const ip_address *addr, int format,
char *dst, size_t dstlen);
const char *ttosubnet(const char *src, size_t srclen,
int af, ip_subnet *dst);
size_t subnettot(const ip_subnet *sub, int format,
char *dst, size_t dstlen);
DESCRIPTION
Ttoaddr converts a text-string name or numeric address into a binary
address (in network byte order). Tnatoaddr does the same conversion,
but the only text forms it accepts are the ‘‘official’’ forms of
numeric address (dotted-decimal for IPv4, colon-hex for IPv6). Addrtot
does the reverse conversion, from binary address back to a text form.
Ttosubnet and subnettot do likewise for the ‘‘address/mask’’ form used
to write a specification of a subnet.
An IPv4 address is specified in text 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 text-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 applying addrtot to an IPv4
address is always complete and does not contain leading zeros.
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.
An IPv6 address is specified in text with colon-hex notation (e.g.
0:56:78ab:22:33:44:55:66), colon-hex with :: abbreviating at most one
subsequence of multiple zeros (e.g. 99:ab::54:068, which is synonymous
with 99:ab:0:0:0:0:54:68), or a DNS name to be looked up via
gethostbyname(3). The result of applying addrtot to an IPv6 address
will use :: abbreviation if possible, and will not contain leading
zeros.
The letters in hexadecimal may be uppercase or lowercase or any mixture
thereof.
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
gethostbyname2(3) is used, so with current DNS implementations, the
result when the name corresponds to more than one address is difficult
to predict. IPv4 name lookup resorts to getnetbyname(3) only if
gethostbyname2(3) fails.
A subnet specification is of the form network/mask. The network and
mask can be any form acceptable to ttoaddr. In addition, and
preferably, 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 in IPv4 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 or ::/0 in
IPv4 or IPv6 respectively.
Ttosubnet 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). Subnettot always generates the decimal-
integer-bit-count form of the mask, with no leading zeros.
The srclen parameter of ttoaddr and ttosubnet specifies the length of
the text 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 af parameter of ttoaddr and ttosubnet specifies the address family
of interest. It should be either AF_INET or AF_INET6.
The dstlen parameter of addrtot and subnettot 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, ADDRTOT_BUF and SUBNETTOT_BUF, which are the sizes
of buffers just large enough for worst-case results.
The format parameter of addrtot and subnettot specifies what format is
to be used for the conversion. The value 0 (not the character ’0’, but
a zero value) specifies a reasonable default, and is in fact the only
format currently available in subnettot. Addrtot also accepts format
values ’r’ (signifying a text form suitable for DNS reverse lookups,
e.g. 4.3.2.1.IN-ADDR.ARPA. for IPv4 and RFC 2874 format for IPv6),
and ’R’ (signifying an alternate reverse-lookup form, an error for IPv4
and RFC 1886 format for IPv6). Reverse-lookup names always end with a
‘‘.’’.
The text-to-binary functions return NULL for success and a pointer to a
string-literal error message for failure; see DIAGNOSTICS. The binary-
to-text 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 ttoaddr are: empty input; unknown address family;
attempt to allocate temporary storage for a very long name failed; name
lookup failed; syntax error in dotted-decimal or colon-hex form;
dotted-decimal or colon-hex component too large.
Fatal errors in ttosubnet are: no / in src; ttoaddr error in conversion
of network or mask; bit-count mask too big; mask non-contiguous.
Fatal errors in addrtot and subnettot 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.
Ttoaddr does not support the mixed colon-hex-dotted-decimal convention
used to embed an IPv4 address in an IPv6 address.
Addrtot always uses the :: abbreviation (which can appear only once in
an address) for the first sequence of multiple zeros in an IPv6
address. One can construct addresses (unlikely ones) in which this is
suboptimal.
Addrtot ’r’ conversion of an IPv6 address uses lowercase hexadecimal,
not the uppercase used in RFC 2874’s examples. It takes careful
reading of RFCs 2874, 2673, and 2234 to realize that lowercase is
technically legitimate here, and there may be software which botches
this and hence would have trouble with lowercase hex.
Possibly subnettot ought to recognize the %default case and generate
that string as its output. Currently it doesn’t.
It is barely possible that somebody, somewhere, might have a legitimate
use for non-contiguous subnet masks.
Getnetbyname(3) is a historical dreg.
Tnatoaddr probably should enforce completeness of dotted-decimal
addresses.
The restriction of text-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 text-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 = ttoaddr( /* ... */ );
if (error != NULL) {
/* something went wrong */
28 Sept 2001 IPSEC_TTOADDR(3)