.\" .\" Copyright 1998 by the Massachusetts Institute of Technology. .\" .\" Permission to use, copy, modify, and distribute this .\" software and its documentation for any purpose and without .\" fee is hereby granted, provided that the above copyright .\" notice appear in all copies and that both that copyright .\" notice and this permission notice appear in supporting .\" documentation, and that the name of M.I.T. not be used in .\" advertising or publicity pertaining to distribution of the .\" software without specific, written prior permission. .\" M.I.T. makes no representations about the suitability of .\" this software for any purpose. It is provided "as is" .\" without express or implied warranty. .\" .TH ARES_GETADDRINFO 3 "4 November 2018" .SH NAME ares_getaddrinfo \- Initiate a host query by name and service .SH SYNOPSIS .nf .B #include .PP .B typedef void (*ares_addrinfo_callback)(void *\fIarg\fP, int \fIstatus\fP, .B int \fItimeouts\fP, struct ares_addrinfo *\fIresult\fP) .PP .B void ares_getaddrinfo(ares_channel \fIchannel\fP, const char *\fIname\fP, .B const char* \fIservice\fP, const struct ares_addrinfo_hints *\fIhints\fP, .B ares_addrinfo_callback \fIcallback\fP, void *\fIarg\fP) .fi .SH DESCRIPTION The .B ares_getaddrinfo function initiates a host query by name on the name service channel identified by .IR channel . The .I name and .I service parameters give the hostname and service as NULL-terminated C strings. The .I hints parameter is an .BR ares_addrinfo_hints structure: .PP .RS .EX struct ares_addrinfo_hints { int ai_flags; int ai_family; int ai_socktype; int ai_protocol; }; .EE .RE .TP .I ai_family Specifies desired address family. AF_UNSPEC means return both AF_INET and AF_INET6. .TP .I ai_socktype Specifies desired socket type, for example SOCK_STREAM or SOCK_DGRAM. Setting this to 0 means any type. .TP .I ai_protocol Setting this to 0 means any protocol. .TP .I ai_flags Specifies additional options, see below. .PP .TP 19 .B ARES_AI_NUMERICSERV If this option is set .I service field will be treated as a numeric value. .TP 19 .B ARES_AI_CANONNAME The ares_addrinfo structure will return a canonical names list. .TP 19 .B ARES_AI_NOSORT Result addresses will not be sorted and no connections to resolved addresses will be attempted. .TP 19 .B ARES_AI_ENVHOSTS Read hosts file path from the environment variable .I CARES_HOSTS . .PP When the query is complete or has failed, the ares library will invoke \fIcallback\fP. Completion or failure of the query may happen immediately, or may happen during a later call to \fIares_process(3)\fP, \fIares_destroy(3)\fP or \fIares_cancel(3)\fP. .PP The callback argument .I arg is copied from the .B ares_getaddrinfo argument .IR arg . The callback argument .I status indicates whether the query succeeded and, if not, how it failed. It may have any of the following values: .TP 19 .B ARES_SUCCESS The host lookup completed successfully. .TP 19 .B ARES_ENOTIMP The ares library does not know how to find addresses of type .IR family . .TP 19 .B ARES_ENOTFOUND The .I name was not found. .TP 19 .B ARES_ENOMEM Memory was exhausted. .TP 19 .B ARES_ECANCELLED The query was cancelled. .TP 19 .B ARES_EDESTRUCTION The name service channel .I channel is being destroyed; the query will not be completed. .PP On successful completion of the query, the callback argument .I result points to a .B struct ares_addrinfo which contains two linked lists, one with resolved addresses and another with canonical names. Also included is the official name of the host (analogous to gethostbyname() h_name). .PP .RS .EX struct ares_addrinfo { struct ares_addrinfo_cname *cnames; struct ares_addrinfo_node *nodes; char *name; }; .EE .RE .PP .I ares_addrinfo_node structure is similar to RFC3493 addrinfo, but without canonname and with extra ttl field. .RS .PP .EX struct ares_addrinfo_node { int ai_ttl; int ai_flags; int ai_family; int ai_socktype; int ai_protocol; ares_socklen_t ai_addrlen; struct sockaddr *ai_addr; struct ares_addrinfo_node *ai_next; }; .EE .RE .PP .I ares_addrinfo_cname structure is a linked list of CNAME records where .I ttl is a time to live .I alias is a label of the resource record and .I name is a value (canonical name) of the resource record. See RFC2181 10.1.1. CNAME terminology. .RS .PP .EX struct ares_addrinfo_cname { int ttl; char *alias; char *name; struct ares_addrinfo_cname *next; }; .EE .RE .PP The reserved memory has to be deleted by .B ares_freeaddrinfo. The result is sorted according to RFC6724 except: - Rule 3 (Avoid deprecated addresses) - Rule 4 (Prefer home addresses) - Rule 7 (Prefer native transport) Please note that the function will attempt a connection on each of the resolved addresses as per RFC6724. .SH AVAILABILITY This function was added in c-ares 1.16.0, released in March 2020. .SH SEE ALSO .BR ares_freeaddrinfo (3) .SH AUTHOR Christian Ammer .br Andrew Selivanov