This commit is contained in:
Martin Willi
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.TH IPSEC_ATOADDR 3 "11 June 2001"
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.\" RCSID $Id: atoaddr.3,v 1.1 2004/03/15 20:35:25 as Exp $
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.SH NAME
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ipsec atoaddr, addrtoa \- convert Internet addresses to and from ASCII
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.br
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ipsec atosubnet, subnettoa \- convert subnet/mask ASCII form to and from addresses
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.SH SYNOPSIS
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.B "#include <freeswan.h>
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.sp
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.B "const char *atoaddr(const char *src, size_t srclen,"
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.ti +1c
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.B "struct in_addr *addr);"
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.br
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.B "size_t addrtoa(struct in_addr addr, int format,"
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.ti +1c
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.B "char *dst, size_t dstlen);"
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.sp
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.B "const char *atosubnet(const char *src, size_t srclen,"
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.ti +1c
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.B "struct in_addr *addr, struct in_addr *mask);"
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.br
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.B "size_t subnettoa(struct in_addr addr, struct in_addr mask,"
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.ti +1c
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.B "int format, char *dst, size_t dstlen);"
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.SH DESCRIPTION
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These functions are obsolete; see
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.IR ipsec_ttoaddr (3)
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for their replacements.
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.PP
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.I Atoaddr
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converts an ASCII name or dotted-decimal address into a binary address
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(in network byte order).
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.I Addrtoa
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does the reverse conversion, back to an ASCII dotted-decimal address.
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.I Atosubnet
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and
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.I subnettoa
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do likewise for the ``address/mask'' ASCII form used to write a
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specification of a subnet.
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.PP
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An address is specified in ASCII as a
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dotted-decimal address (e.g.
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.BR 1.2.3.4 ),
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an eight-digit network-order hexadecimal number with the usual C prefix (e.g.
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.BR 0x01020304 ,
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which is synonymous with
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.BR 1.2.3.4 ),
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an eight-digit host-order hexadecimal number with a
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.B 0h
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prefix (e.g.
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.BR 0h01020304 ,
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which is synonymous with
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.B 1.2.3.4
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on a big-endian host and
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.B 4.3.2.1
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on a little-endian host),
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a DNS name to be looked up via
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.IR gethostbyname (3),
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or an old-style network name to be looked up via
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.IR getnetbyname (3).
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.PP
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A dotted-decimal address may be incomplete, in which case
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ASCII-to-binary conversion implicitly appends
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as many instances of
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.B .0
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as necessary to bring it up to four components.
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The components of a dotted-decimal address are always taken as
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decimal, and leading zeros are ignored.
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For example,
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.B 10
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is synonymous with
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.BR 10.0.0.0 ,
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and
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.B 128.009.000.032
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is synonymous with
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.BR 128.9.0.32
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(the latter example is verbatim from RFC 1166).
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The result of
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.I addrtoa
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is always complete and does not contain leading zeros.
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.PP
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The letters in
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a hexadecimal address may be uppercase or lowercase or any mixture thereof.
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Use of hexadecimal addresses is
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.B strongly
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.BR discouraged ;
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they are included only to save hassles when dealing with
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the handful of perverted programs which already print
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network addresses in hexadecimal.
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.PP
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DNS names may be complete (optionally terminated with a ``.'')
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or incomplete, and are looked up as specified by local system configuration
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(see
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.IR resolver (5)).
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The
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.I h_addr
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value returned by
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.IR gethostbyname (3)
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is used,
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so with current DNS implementations,
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the result when the name corresponds to more than one address is
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difficult to predict.
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Name lookup resorts to
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.IR getnetbyname (3)
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only if
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.IR gethostbyname (3)
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fails.
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.PP
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A subnet specification is of the form \fInetwork\fB/\fImask\fR.
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The
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.I network
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and
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.I mask
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can be any form acceptable to
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.IR atoaddr .
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In addition, the
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.I mask
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can be a decimal integer (leading zeros ignored) giving a bit count,
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in which case
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it stands for a mask with that number of high bits on and all others off
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(e.g.,
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.B 24
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means
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.BR 255.255.255.0 ).
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In any case, the mask must be contiguous
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(a sequence of high bits on and all remaining low bits off).
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As a special case, the subnet specification
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.B %default
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is a synonym for
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.BR 0.0.0.0/0 .
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.PP
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.I Atosubnet
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ANDs the mask with the address before returning,
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so that any non-network bits in the address are turned off
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(e.g.,
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.B 10.1.2.3/24
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is synonymous with
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.BR 10.1.2.0/24 ).
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.I Subnettoa
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generates the decimal-integer-bit-count
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form of the mask,
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with no leading zeros,
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unless the mask is non-contiguous.
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.PP
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The
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.I srclen
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parameter of
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.I atoaddr
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and
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.I atosubnet
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specifies the length of the ASCII string pointed to by
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.IR src ;
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it is an error for there to be anything else
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(e.g., a terminating NUL) within that length.
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As a convenience for cases where an entire NUL-terminated string is
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to be converted,
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a
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.I srclen
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value of
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.B 0
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is taken to mean
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.BR strlen(src) .
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.PP
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The
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.I dstlen
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parameter of
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.I addrtoa
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and
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.I subnettoa
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specifies the size of the
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.I dst
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parameter;
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under no circumstances are more than
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.I dstlen
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bytes written to
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.IR dst .
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A result which will not fit is truncated.
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.I Dstlen
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can be zero, in which case
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.I dst
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need not be valid and no result is written,
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but the return value is unaffected;
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in all other cases, the (possibly truncated) result is NUL-terminated.
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The
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.I freeswan.h
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header file defines constants,
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.B ADDRTOA_BUF
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and
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.BR SUBNETTOA_BUF ,
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which are the sizes of buffers just large enough for worst-case results.
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.PP
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The
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.I format
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parameter of
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.I addrtoa
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and
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.I subnettoa
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specifies what format is to be used for the conversion.
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The value
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.B 0
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(not the ASCII character
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.BR '0' ,
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but a zero value)
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specifies a reasonable default,
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and is in fact the only format currently available.
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This parameter is a hedge against future needs.
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.PP
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The ASCII-to-binary functions return NULL for success and
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a pointer to a string-literal error message for failure;
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see DIAGNOSTICS.
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The binary-to-ASCII functions return
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.B 0
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for a failure, and otherwise
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always return the size of buffer which would
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be needed to
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accommodate the full conversion result, including terminating NUL;
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it is the caller's responsibility to check this against the size of
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the provided buffer to determine whether truncation has occurred.
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.SH SEE ALSO
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inet(3)
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.SH DIAGNOSTICS
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Fatal errors in
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.I atoaddr
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are:
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empty input;
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attempt to allocate temporary storage for a very long name failed;
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name lookup failed;
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syntax error in dotted-decimal form;
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dotted-decimal component too large to fit in 8 bits.
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.PP
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Fatal errors in
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.I atosubnet
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are:
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no
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.B /
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in
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.IR src ;
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.I atoaddr
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error in conversion of
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.I network
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or
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.IR mask ;
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bit-count mask too big;
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mask non-contiguous.
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.PP
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Fatal errors in
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.I addrtoa
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and
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.I subnettoa
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are:
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unknown format.
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.SH HISTORY
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Written for the FreeS/WAN project by Henry Spencer.
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.SH BUGS
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The interpretation of incomplete dotted-decimal addresses
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(e.g.
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.B 10/24
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means
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.BR 10.0.0.0/24 )
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differs from that of some older conversion
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functions, e.g. those of
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.IR inet (3).
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The behavior of the older functions has never been
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particularly consistent or particularly useful.
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.PP
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Ignoring leading zeros in dotted-decimal components and bit counts
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is arguably the most useful behavior in this application,
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but it might occasionally cause confusion with the historical use of leading
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zeros to denote octal numbers.
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.PP
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It is barely possible that somebody, somewhere,
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might have a legitimate use for non-contiguous subnet masks.
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.PP
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.IR Getnetbyname (3)
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is a historical dreg.
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.PP
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The restriction of ASCII-to-binary error reports to literal strings
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(so that callers don't need to worry about freeing them or copying them)
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does limit the precision of error reporting.
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.PP
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The ASCII-to-binary error-reporting convention lends itself
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to slightly obscure code,
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because many readers will not think of NULL as signifying success.
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A good way to make it clearer is to write something like:
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.PP
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.RS
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.nf
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.B "const char *error;"
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.sp
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.B "error = atoaddr( /* ... */ );"
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.B "if (error != NULL) {"
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.B " /* something went wrong */"
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.fi
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.RE
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