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       ipsec_atoaddr,	ipsec_addrtoa,	 ipsec_atosubnet,   ipsec_subnettoa  -	convert  Internet
       addresses and Subnet masks to and from ASCII

       #include <libreswan.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);

       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., an eight-
       digit network-order hexadecimal number with the usual C prefix (e.g.  0x01020304, which is
       synonymous  with,  an eight-digit host-order hexadecimal number with a 0h prefix
       (e.g.  0h01020304, which is synonymous with on a big-endian host and on	a
       little-endian host), a DNS name to be looked up via gethostbyname(3), or an old-style net-
       work 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, and is synony-
       mous with (the latter example is verbatim from RFC 1166).  The result of  addr-
       toa 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  has-
       sles  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  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

       Atosubnet ANDs the mask with the address before returning, so that any non-network bits in
       the address are turned off (e.g., is synonymous with	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  trun-
       cated)  result  is  NUL-terminated.   The libreswan.h header file defines constants, ADDR-
       TOA_BUF and SUBNETTOA_BUF, which are the sizes of buffers just large enough for worst-case

       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  rea-
       sonable	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  accommo-
       date  the  full conversion result, including terminating NUL; it is the caller's responsi-
       bility to check this against the size of the provided buffer to determine whether  trunca-
       tion has occurred.


       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.

       Written for the FreeS/WAN project by Henry Spencer.

       The interpretation of incomplete dotted-decimal addresses (e.g.	10/24 means
       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-con-
       tiguous 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

       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 			 IPSEC_ATOADDR(3)
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