Ubuntu Manpage: ipsec_ttoaddr, ipsec_tnatoaddr, ipsec_addrtot, ipsec_ttosubnet, ipsec_subnettot

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.

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 */