IPSEC_TTOADDR(3)					     Library Functions Manual						  IPSEC_TTOADDR(3)

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 geth-
       ostbyname(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  prefer-
       ably,  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 con-
       verted, 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  writ-
       ten, 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  func-
       tions, 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  signi-
       fying 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)