NAME¶
ipsec_ttoaddr, ipsec_tnatoaddr, ipsec_addrtot, ipsec_ttosubnet, ipsec_subnettot
- convert Internet addresses and Subnet masks to and from text
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 */