xref: /dragonfly/lib/libc/net/getipnodebyname.3 (revision 2020c8fe) 
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30.\"     From: @(#)gethostbyname.3	8.4 (Berkeley) 5/25/95
31.\" $FreeBSD: src/lib/libc/net/getipnodebyname.3,v 1.18 2007/01/09 00:28:02 imp Exp $
32.\" $DragonFly: src/lib/libc/net/getipnodebyname.3,v 1.4 2007/11/23 23:16:36 swildner Exp $
33.\"
34.Dd August 6, 2004
35.Dt GETIPNODEBYNAME 3
36.Os
37.\"
38.Sh NAME
39.Nm getipnodebyname ,
40.Nm getipnodebyaddr ,
41.Nm freehostent
42.Nd nodename-to-address and address-to-nodename translation
43.\"
44.Sh LIBRARY
45.Lb libc
46.Sh SYNOPSIS
47.In sys/types.h
48.In sys/socket.h
49.In netdb.h
50.Ft "struct hostent *"
51.Fn getipnodebyname "const char *name" "int af" "int flags" "int *error_num"
52.Ft "struct hostent *"
53.Fn getipnodebyaddr "const void *src" "size_t len" "int af" "int *error_num"
54.Ft void
55.Fn freehostent "struct hostent *ptr"
56.\"
57.Sh DESCRIPTION
58The
59.Fn getipnodebyname
60and
61.Fn getipnodebyaddr
62functions are very similar to
63.Xr gethostbyname 3 ,
64.Xr gethostbyname2 3
65and
66.Xr gethostbyaddr 3 .
67The functions cover all the functionalities provided by the older ones,
68and provide better interface to programmers.
69The functions require additional arguments,
70.Fa af ,
71and
72.Fa flags ,
73for specifying address family and operation mode.
74The additional arguments allow programmer to get address for a nodename,
75for specific address family
76(such as
77.Dv AF_INET
78or
79.Dv AF_INET6 ) .
80The functions also require an additional pointer argument,
81.Fa error_num
82to return the appropriate error code,
83to support thread safe error code returns.
84.Pp
85The type and usage of the return value,
86.Li "struct hostent"
87is described in
88.Xr gethostbyname 3 .
89.Pp
90For
91.Fn getipnodebyname ,
92the
93.Fa name
94argument can be either a node name or a numeric address
95string
96(i.e., a dotted-decimal IPv4 address or an IPv6 hex address).
97The
98.Fa af
99argument specifies the address family, either
100.Dv AF_INET
101or
102.Dv AF_INET6 .
103The
104.Fa flags
105argument specifies the types of addresses that are searched for,
106and the types of addresses that are returned.
107We note that a special flags value of
108.Dv AI_DEFAULT
109(defined below)
110should handle most applications.
111That is, porting simple applications to use IPv6 replaces the call
112.Bd -literal -offset
113   hptr = gethostbyname(name);
114.Ed
115.Pp
116with
117.Bd -literal -offset
118   hptr = getipnodebyname(name, AF_INET6, AI_DEFAULT, &error_num);
119.Ed
120.Pp
121Applications desiring finer control over the types of addresses
122searched for and returned, can specify other combinations of the
123.Fa flags
124argument.
125.Pp
126A
127.Fa flags
128of
129.Li 0
130implies a strict interpretation of the
131.Fa af
132argument:
133.Bl -bullet
134.It
135If
136.Fa flags
137is 0 and
138.Fa af
139is
140.Dv AF_INET ,
141then the caller wants only IPv4 addresses.
142A query is made for
143.Li A
144records.
145If successful, the IPv4 addresses are returned and the
146.Li h_length
147member of the
148.Li hostent
149structure will be 4, else the function returns a
150.Dv NULL
151pointer.
152.It
153If
154.Fa flags
155is 0 and if
156.Fa af
157is
158.Li AF_INET6 ,
159then the caller wants only IPv6 addresses.
160A query is made for
161.Li AAAA
162records.
163If successful, the IPv6 addresses are returned and the
164.Li h_length
165member of the
166.Li hostent
167structure will be 16, else the function returns a
168.Dv NULL
169pointer.
170.El
171.Pp
172Other constants can be logically-ORed into the
173.Fa flags
174argument, to modify the behavior of the function.
175.Bl -bullet
176.It
177If the
178.Dv AI_V4MAPPED
179flag is specified along with an
180.Fa af
181of
182.Dv AF_INET6 ,
183then the caller will accept IPv4-mapped IPv6 addresses.
184That is, if no
185.Li AAAA
186records are found then a query is made for
187.Li A
188records and any found are returned as IPv4-mapped IPv6 addresses
189.Li ( h_length
190will be 16).
191The
192.Dv AI_V4MAPPED
193flag is ignored unless
194.Fa af
195equals
196.Dv AF_INET6 .
197.It
198The
199.Dv AI_V4MAPPED_CFG
200flag is exact same as the
201.Dv AI_V4MAPPED
202flag only if the kernel supports IPv4-mapped IPv6 address.
203.It
204If the
205.Dv AI_ALL
206flag is used in conjunction with the
207.Dv AI_V4MAPPED
208flag, and only used with the IPv6 address family.
209When
210.Dv AI_ALL
211is logically or'd with
212.Dv AI_V4MAPPED
213flag then the caller wants all addresses: IPv6 and IPv4-mapped IPv6.
214A query is first made for
215.Li AAAA
216records and if successful, the
217IPv6 addresses are returned.
218Another query is then made for
219.Li A
220records and any found are returned as IPv4-mapped IPv6 addresses.
221.Li h_length
222will be 16.
223Only if both queries fail does the function
224return a
225.Dv NULL
226pointer.
227This flag is ignored unless af equals
228AF_INET6.
229If both
230.Dv AI_ALL
231and
232.Dv AI_V4MAPPED
233are specified,
234.Dv AI_ALL
235takes precedence.
236.It
237The
238.Dv AI_ADDRCONFIG
239flag specifies that a query for
240.Li AAAA
241records
242should occur only if the node has at least one IPv6 source
243address configured and a query for
244.Li A
245records should occur only if the node has at least one IPv4 source address
246configured.
247.Pp
248For example, if the node has no IPv6 source addresses configured,
249and
250.Fa af
251equals AF_INET6, and the node name being looked up has both
252.Li AAAA
253and
254.Li A
255records, then:
256(a) if only
257.Dv AI_ADDRCONFIG
258is
259specified, the function returns a
260.Dv NULL
261pointer;
262(b) if
263.Dv AI_ADDRCONFIG
264|
265.Dv AI_V4MAPPED
266is specified, the
267.Li A
268records are returned as IPv4-mapped IPv6 addresses;
269.El
270.Pp
271The special flags value of
272.Dv AI_DEFAULT
273is defined as
274.Bd -literal -offset
275   #define  AI_DEFAULT  (AI_V4MAPPED_CFG | AI_ADDRCONFIG)
276.Ed
277.Pp
278We noted that the
279.Fn getipnodebyname
280function must allow the
281.Fa name
282argument to be either a node name or a literal address string
283(i.e., a dotted-decimal IPv4 address or an IPv6 hex address).
284This saves applications from having to call
285.Xr inet_pton 3
286to handle literal address strings.
287When the
288.Fa name
289argument is a literal address string,
290the
291.Fa flags
292argument is always ignored.
293.Pp
294There are four scenarios based on the type of literal address string
295and the value of the
296.Fa af
297argument.
298The two simple cases are when
299.Fa name
300is a dotted-decimal IPv4 address and
301.Fa af
302equals
303.Dv AF_INET ,
304or when
305.Fa name
306is an IPv6 hex address and
307.Fa af
308equals
309.Dv AF_INET6 .
310The members of the
311returned hostent structure are:
312.Li h_name
313points to a copy of the
314.Fa name
315argument,
316.Li h_aliases
317is a
318.Dv NULL
319pointer,
320.Li h_addrtype
321is a copy of the
322.Fa af
323argument,
324.Li h_length
325is either 4
326(for
327.Dv AF_INET )
328or 16
329(for
330.Dv AF_INET6 ) ,
331.Li h_addr_list[0]
332is a pointer to the 4-byte or 16-byte binary address,
333and
334.Li h_addr_list[1]
335is a
336.Dv NULL
337pointer.
338.Pp
339When
340.Fa name
341is a dotted-decimal IPv4 address and
342.Fa af
343equals
344.Dv AF_INET6 ,
345and
346.Dv AI_V4MAPPED
347is specified,
348an IPv4-mapped IPv6 address is returned:
349.Li h_name
350points to an IPv6 hex address containing the IPv4-mapped IPv6 address,
351.Li h_aliases
352is a
353.Dv NULL
354pointer,
355.Li h_addrtype
356is
357.Dv AF_INET6 ,
358.Li h_length
359is 16,
360.Li h_addr_list[0]
361is a pointer to the 16-byte binary address, and
362.Li h_addr_list[1]
363is a
364.Dv NULL
365pointer.
366.Pp
367It is an error when
368.Fa name
369is an IPv6 hex address and
370.Fa af
371equals
372.Dv AF_INET .
373The function's return value is a
374.Dv NULL
375pointer and the value pointed to by
376.Fa error_num
377equals
378.Dv HOST_NOT_FOUND .
379.Pp
380The
381.Fn getipnodebyaddr
382function
383takes almost the same argument as
384.Xr gethostbyaddr 3 ,
385but adds a pointer to return an error number.
386Additionally it takes care of IPv4-mapped IPv6 addresses,
387and IPv4-compatible IPv6 addresses.
388.Pp
389The
390.Fn getipnodebyname
391and
392.Fn getipnodebyaddr
393functions
394dynamically allocate the structure to be returned to the caller.
395The
396.Fn freehostent
397function
398reclaims memory region allocated and returned by
399.Fn getipnodebyname
400or
401.Fn getipnodebyaddr .
402.\"
403.Sh FILES
404.Bl -tag -width /etc/nsswitch.conf -compact
405.It Pa /etc/hosts
406.It Pa /etc/nsswitch.conf
407.It Pa /etc/resolv.conf
408.El
409.\"
410.Sh DIAGNOSTICS
411The
412.Fn getipnodebyname
413and
414.Fn getipnodebyaddr
415functions
416returns
417.Dv NULL
418on errors.
419The integer values pointed to by
420.Fa error_num
421may then be checked to see whether this is a temporary failure
422or an invalid or unknown host.
423The meanings of each error code are described in
424.Xr gethostbyname 3 .
425.\"
426.Sh SEE ALSO
427.Xr getaddrinfo 3 ,
428.Xr gethostbyaddr 3 ,
429.Xr gethostbyname 3 ,
430.Xr getnameinfo 3 ,
431.Xr hosts 5 ,
432.Xr nsswitch.conf 5 ,
433.Xr services 5 ,
434.Xr hostname 7 ,
435.Xr named 8
436.Rs
437.%A R. Gilligan
438.%A S. Thomson
439.%A J. Bound
440.%A W. Stevens
441.%T Basic Socket Interface Extensions for IPv6
442.%R RFC 2553
443.%D March 1999
444.Re
445.\"
446.Sh STANDARDS
447The
448.Fn getipnodebyname
449and
450.Fn getipnodebyaddr
451functions
452are documented in
453.Dq Basic Socket Interface Extensions for IPv6
454(RFC 2553).
455.\"
456.Sh HISTORY
457The implementation first appeared in KAME advanced networking kit.
458.\"
459.Sh BUGS
460The
461.Fn getipnodebyname
462and
463.Fn getipnodebyaddr
464functions
465do not handle scoped IPv6 address properly.
466If you use these functions,
467your program will not be able to handle scoped IPv6 addresses.
468For IPv6 address manipulation,
469.Fn getaddrinfo 3
470and
471.Fn getnameinfo 3
472are recommended.
473.Pp
474The text was shamelessly copied from RFC 2553.
475