.\" $OpenBSD: gethostbyname.3,v 1.22 2004/03/14 18:05:37 jmc Exp $ .\" .\" Copyright (c) 1983, 1987, 1991, 1993 .\" The Regents of the University of California. All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the University nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .Dd March 13, 1997 .Dt GETHOSTBYNAME 3 .Os .Sh NAME .Nm dnsres_init , .Nm dnsres_gethostbyname , .Nm dnsres_gethostbyname2 , .Nm dnsres_gethostbyaddr , .Nm dnsres_getaddrinfo .Nd non blocking DNS resolving library .Sh SYNOPSIS .Fd #include .Fd #include .Fd #include .Fd #include .Ft int .Fn dnsres_init "struct dnsres *_resp" .Ft void .Fn dnsres_gethostbyname "struct dnsres *res" "const char *name" "void (*cb)(struct hostent *hp, int error, void *arg)" "void *arg" .Ft void .Fn dnsres_gethostbyname2 "struct dnsres *res" "const char *name" "int af" "void (*cb)(struct hostent *hp, int error, void *arg)" "void *arg" .Ft void .Fn dnsres_gethostbyaddr "struct dnsres *res" "const char *addr" "int len" "int af" "void (*cb)(struct hostent *hp, int error, void *arg)" "void *arg" .Ft void .Fn dnsres_getaddrinfo "struct dnsres *res" "const char *hostname" "const char *servname" "const struct addrinfo *hints" "void (*cb)(struct addrinfo *ai, int res, void *arg)" "void *arg" .Sh DESCRIPTION The .Fn dnsres_init is used to initialize the .Nm dnsres library. If you are developing a multi-threaded application, you need one .Va struct dnsres per thread. .Pp The .Fn dnsres_gethostbyname , .Fn dnsres_gethostbyname2 and .Fn dnsres_gethostbyaddr functions each call their provided callback function with a pointer to an object with the following structure describing an internet host referenced by name or by address, respectively. This structure contains either information obtained from the name server (i.e., .Xr resolver 3 and .Xr named 8 ) , broken-out fields from a line in .Pa /etc/hosts , or database entries supplied by the .Xr yp 8 system. .Xr resolv.conf 5 describes how the particular database is chosen. .Bd -literal struct dnsres_hostent { char *h_name; /* official name of host */ char **h_aliases; /* alias list */ int h_addrtype; /* host address type */ int h_length; /* length of address */ char **h_addr_list; /* list of addresses from name server */ }; .Ed .Pp The members of this structure are: .Bl -tag -width h_addr_list .It Fa h_name Official name of the host. .It Fa h_aliases A NULL-terminated array of alternate names for the host. .It Fa h_addrtype The type of address being returned. .It Fa h_length The length, in bytes, of the address. .It Fa h_addr_list A zero-terminated array of network addresses for the host. Host addresses are returned in network byte order. .It Fa h_addr The first address in .Fa h_addr_list ; this is for backward compatibility. .El .Pp The function .Fn dnsres_gethostbyname will search for the named host in the current domain and its parents using the search lookup semantics detailed in .Xr resolv.conf 5 and .Xr hostname 7 . .Pp .Fn dnsres_gethostbyname2 is an advanced form of .Fn gethostbyname which allows lookups in address families other than .Dv AF_INET . Currently, the only supported address family besides .Dv AF_INET is .Dv AF_INET6 . .Pp The .Fn dnsres_gethostbyaddr function will search for the specified address of length .Fa len in the address family .Fa af . The only address family currently supported is .Dv AF_INET . .Pp The .Fn dnsres_getaddrinfo function is used to get a list of IP addresses and port numbers for host hostname and service servname. .Sh ENVIRONMENT .Bl -tag -width HOSTALIASES .It HOSTALIASES A file containing local host aliases. See .Xr hostname 7 for more information. .It RES_OPTIONS A list of options to override the resolver's internal defaults. See .Xr resolver 3 for more information. .El .Sh FILES .Bl -tag -width /etc/resolv.conf -compact .It Pa /etc/hosts .It Pa /etc/resolv.conf .El .Sh DIAGNOSTICS Error return status from .Fn dnsres_gethostbyname , .Fn dnsres_gethostbyname2 , and .Fn dnsres_gethostbyaddr is indicated by a null pointer passed to the callback function. The integer .Va dr_errno may then be checked in .Va struct dnsres to see whether this is a temporary failure or an invalid or unknown host. .Pp The variable .Va h_errno can have the following values: .Bl -tag -width DNSRES_HOST_NOT_FOUND .It Dv DNSRES_HOST_NOT_FOUND No such host is known. .It Dv DNSRES_TRY_AGAIN This is usually a temporary error and means that the local server did not receive a response from an authoritative server. A retry at some later time may succeed. .It Dv DNSRES_NO_RECOVERY Some unexpected server failure was encountered. This is a non-recoverable error. .It Dv DNSRES_NO_DATA The requested name is valid but does not have an IP address; this is not a temporary error. This means that the name is known to the name server but there is no address associated with this name. Another type of request to the name server using this domain name will result in an answer; for example, a mail-forwarder may be registered for this domain. .It Dv DNSRES_NETDB_INTERNAL An internal error occurred. This may occurs when an address family other than .Dv AF_INET or .Dv AF_INET6 is specified or when a resource is unable to be allocated. .It Dv DNSRES_NETDB_SUCCESS The function completed successfully. .El .Sh SEE ALSO .Xr getnameinfo 3 , .Xr resolver 3 , .Xr hosts 5 , .Xr resolv.conf 5 , .Xr hostname 7 , .Xr named 8 .Sh HISTORY The .Fn herror function appeared in .Bx 4.3 . The .Fn endhostent , .Fn gethostbyaddr , .Fn gethostbyname , .Fn gethostent , and .Fn sethostent functions appeared in .Bx 4.2 . .Sh CAVEATS If the search routines in .Xr resolv.conf 5 decide to read the .Pa /etc/hosts file, .Fn gethostent and other functions will read the next line of the file, re-opening the file if necessary. .Pp The .Fn sethostent function opens and/or rewinds the file .Pa /etc/hosts . If the .Fa stayopen argument is non-zero, the file will not be closed after each call to .Fn gethostbyname , .Fn gethostbyname2 , or .Fn gethostbyaddr . .Pp The .Fn endhostent function closes the file. .Sh AUTHORS The .Nm dnsres library was hacked together by Niels Provos. Heavy use was made of the exisiting BSD resolver library.