1LWRES_GETHOSTENT(3) BIND9 LWRES_GETHOSTENT(3)
2
6 lwres_gethostbyname, lwres_gethostbyname2, lwres_gethostbyaddr,
7 lwres_gethostent, lwres_sethostent, lwres_endhostent,
8 lwres_gethostbyname_r, lwres_gethostbyaddr_r, lwres_gethostent_r,
9 lwres_sethostent_r, lwres_endhostent_r - lightweight resolver get
10 network host entry
11
13 #include <lwres/netdb.h>
14 struct hostent * lwres_gethostbyname(const char *name);
16 struct hostent * lwres_gethostbyname2(const char *name, int af);
18 struct hostent * lwres_gethostbyaddr(const char *addr, int len,
20 int type);
21 struct hostent * lwres_gethostent(void);
23 void lwres_sethostent(int stayopen);
25 void lwres_endhostent(void);
27 struct hostent * lwres_gethostbyname_r(const char *name,
29 struct hostent *resbuf,
30 char *buf, int buflen,
31 int *error);
32 struct hostent * lwres_gethostbyaddr_r(const char *addr, int len,
34 int type,
35 struct hostent *resbuf,
36 char *buf, int buflen,
37 int *error);
38 struct hostent * lwres_gethostent_r(struct hostent *resbuf, char *buf,
40 int buflen, int *error);
41 void lwres_sethostent_r(int stayopen);
43 void lwres_endhostent_r(void);
45
47 These functions provide hostname-to-address and address-to-hostname
48 lookups by means of the lightweight resolver. They are similar to the
49 standard gethostent(3) functions provided by most operating systems.
50 They use a struct hostent which is usually defined in <namedb.h>.
51 struct hostent {
53 char *h_name; /* official name of host */
54 char **h_aliases; /* alias list */
55 int h_addrtype; /* host address type */
56 int h_length; /* length of address */
57 char **h_addr_list; /* list of addresses from name server */
58 };
59 #define h_addr h_addr_list[0] /* address, for backward compatibility */
60 The members of this structure are:
62 h_name
64 The official (canonical) name of the host.
65 h_aliases
67 A NULL-terminated array of alternate names (nicknames) for the
68 host.
69 h_addrtype
71 The type of address being returned — PF_INET or PF_INET6.
72 h_length
74 The length of the address in bytes.
75 h_addr_list
77 A NULL terminated array of network addresses for the host. Host
78 addresses are returned in network byte order.
79 For backward compatibility with very old software, h_addr is the first
81 address in h_addr_list.
82 lwres_gethostent(), lwres_sethostent(), lwres_endhostent(),
84 lwres_gethostent_r(), lwres_sethostent_r() and lwres_endhostent_r()
85 provide iteration over the known host entries on systems that provide
86 such functionality through facilities like /etc/hosts or NIS. The
87 lightweight resolver does not currently implement these functions; it
88 only provides them as stub functions that always return failure.
89 lwres_gethostbyname() and lwres_gethostbyname2() look up the hostname
91 name. lwres_gethostbyname() always looks for an IPv4 address while
92 lwres_gethostbyname2() looks for an address of protocol family af:
93 either PF_INET or PF_INET6 — IPv4 or IPV6 addresses respectively.
94 Successful calls of the functions return a struct hostentfor the name
95 that was looked up. NULL is returned if the lookups by
96 lwres_gethostbyname() or lwres_gethostbyname2() fail.
97 Reverse lookups of addresses are performed by lwres_gethostbyaddr().
99 addr is an address of length len bytes and protocol family type —
100 PF_INET or PF_INET6. lwres_gethostbyname_r() is a thread-safe function
101 for forward lookups. If an error occurs, an error code is returned in
102 *error. resbuf is a pointer to a struct hostent which is initialised
103 by a successful call to lwres_gethostbyname_r(). buf is a buffer of
104 length len bytes which is used to store the h_name, h_aliases, and
105 h_addr_list elements of the struct hostent returned in resbuf.
106 Successful calls to lwres_gethostbyname_r() return resbuf, which is a
107 pointer to the struct hostent it created.
108 lwres_gethostbyaddr_r() is a thread-safe function that performs a
110 reverse lookup of address addr which is len bytes long and is of
111 protocol family type — PF_INET or PF_INET6. If an error occurs, the
112 error code is returned in *error. The other function parameters are
113 identical to those in lwres_gethostbyname_r(). resbuf is a pointer to
114 a struct hostent which is initialised by a successful call to
115 lwres_gethostbyaddr_r(). buf is a buffer of length len bytes which is
116 used to store the h_name, h_aliases, and h_addr_list elements of the
117 struct hostent returned in resbuf. Successful calls to
118 lwres_gethostbyaddr_r() return resbuf, which is a pointer to the struct
119 hostent() it created.
120
122 The functions lwres_gethostbyname(), lwres_gethostbyname2(),
123 lwres_gethostbyaddr(), and lwres_gethostent() return NULL to indicate
124 an error. In this case the global variable lwres_h_errno will contain
125 one of the following error codes defined in <lwres/netdb.h>:
126 HOST_NOT_FOUND
128 The host or address was not found.
129 TRY_AGAIN
131 A recoverable error occurred, e.g., a timeout. Retrying the lookup
132 may succeed.
133 NO_RECOVERY
135 A non-recoverable error occurred.
136 NO_DATA
138 The name exists, but has no address information associated with it
139 (or vice versa in the case of a reverse lookup). The code
140 NO_ADDRESS is accepted as a synonym for NO_DATA for backwards
141 compatibility.
142 lwres_hstrerror(3) translates these error codes to suitable error
144 messages.
145 lwres_gethostent() and lwres_gethostent_r() always return NULL.
147 Successful calls to lwres_gethostbyname_r() and lwres_gethostbyaddr_r()
149 return resbuf, a pointer to the struct hostent that was initialised by
150 these functions. They return NULL if the lookups fail or if buf was too
151 small to hold the list of addresses and names referenced by the h_name,
152 h_aliases, and h_addr_list elements of the struct hostent. If buf was
153 too small, both lwres_gethostbyname_r() and lwres_gethostbyaddr_r() set
154 the global variable errno to ERANGE.
155
157 gethostent(3), lwres_getipnode(3), lwres_hstrerror(3)
158
160 lwres_gethostbyname(), lwres_gethostbyname2(), lwres_gethostbyaddr()
161 and lwres_endhostent() are not thread safe; they return pointers to
162 static data and provide error codes through a global variable.
163 Thread-safe versions for name and address lookup are provided by
164 lwres_gethostbyname_r(), and lwres_gethostbyaddr_r() respectively.
165 The resolver daemon does not currently support any non-DNS name
167 services such as /etc/hosts or NIS, consequently the above functions
168 don't, either.
169
171 Internet Systems Consortium, Inc.
172
174 Copyright © 2001, 2004, 2005, 2007, 2014-2016, 2018-2020 Internet
175 Systems Consortium, Inc. ("ISC")
176ISC 2007-06-18 LWRES_GETHOSTENT(3)