This man page describes the getdns library, the general concepts behind the API and some of the common elements of the public interface to the library. Each of the public entry points and more complex data types are captured in separate man pages.
getdns is modern asynchronous DNS API intended to be useful to application developers and operating system distributors as a way of making all types of DNS information easily available in many types of programs. The major features of this new API are:
Each of the entry points is offered with both asynchronous and synchronous signatures. The asynchronous functions rely on event handling and callback via libevent.
Functions are thread safe.
.LP
A context structure maintains DNS query and response data and is used to maintain state during calls to the public entry points.
.SHEXTENSIONS
Applications may populate an extension dictionary when making a call to the public entry points. To use an extension add it to the extension dictionary prior to making the call to the public entry point and set the value depending on the behavior you expect. These extensions include:
.HP3
dnssec_return_status (int)
Set to GETDNS_EXTENSION_TRUE to include the DNSSEC status for each DNS record in the replies_tree
.HP3
dnssec_return_only_secure (int)
Set to GETDNS_EXTENSION_TRUE to cause only records that the API can validate as secure withe DNSSEC to be returned in the
.Ireplies_tree
and
.Ireplies_fulllists
.HP3
dnssec_return_supporting_responses (int)
Set to GETDNS_EXTENSION_TRUE to cause the set of additional DNSSEC-related records needed for validation to be returned in the response object as the list named
.Iadditional_dnssec
at the top level of the response object
.HP3
return_both_v4_and_v6 (int)
Set to GETDNS_EXTENSION_TRUE to cause the results of both A and AAAA records for the queried name to be included in the response object.
.HP3
add_opt_parameters (dict)
TBD (complicated)
.HP3
add_warning_for_bad_dns
Set to GETDNS_EXTENSION_TRUE to cause each reply in the
.Ireplies_tree
to contain an additional name whose data type is a list,
.Ibad_dns
which contains zero or more ints that indicate the types of bad DNS found in the reply.
.RS6
.br
GETDNS_BAD_DNS_CNAME_IN_TARGET: query type does not allow a CNAME pointed to a CNAME
.br
GETDNS_BAD_DNS_ALL_NUMERIC_LABEL: one or more labels is all numeric
.br
GETDNS_BAD_DNS_CNAME_RETURNED_FOR_OTHER_TYPE: query type for other than CNAME returned a CNAME
.RE
.HP3
specify_class (int)
Set to the DNS class number (other than Internet (IN) class desired in query.
.HP3
return_api_information (int)
Set to GETDNS_EXTENSION_TRUE to add the following to the top level of the response object:
.RS6
.br
.Iversion_string
(bindata) : the version string for this version of the getdns API
.br
.Iimplementation_string
(bindata) : string set by this library's implementer as a build or version indicator
.br
.Iresolver_type
(int) : GETDNS_CONTEXT_RECURSING or GETDNS_CONTEXT_STUB depending on how the context is configured
.br
.Iall_context
(dict) : includes names from the context, use with
.Igetdns_pretty_print_dict
(3) for debugging
.RE
.HP3
return_call_debugging (int)
Set to GETDNS_EXTENSION_TRUE to add the name
.Icall_debugging
(list) to the top level of the response object that includes a dict for each call made to the API. TBD: more detail
The callback function contains a pointer to a response object. A response
object is always a dict. The response object always contains at least three
names: replies_full (a list) and replies_tree (a list), and status (an int).
replies_full is a list of DNS replies (each is bindata) as they appear on the
wire. replies_tree is a list of DNS replies (each is a dict) with the various
part of the reply parsed out. status is a status code for the query.
.LP
Because the API might be extended in the future, a response object might also
contain names other than replies_full, replies_tree, and status. Similarly, any
of the dicts described here might be extended in later versions of the API.
Thus, an application using the API must not assume that it knows all possible
names in a dict.
.LP
The following lists the status codes for response objects. Note that, if the
status is that there are no responses for the query, the lists in replies_full
and replies_tree will have zero length.
.HP3
.BGETDNS_RESPSTATUS_GOOD
At least one response was returned
.HP3
.BGETDNS_RESPSTATUS_NO_NAME
Queries for the name yielded all negative responses
.HP3
.BGETDNS_RESPSTATUS_ALL_TIMEOUT
All queries for the name timed out
.HP3
.BGETDNS_RESPSTATUS_NO_SECURE_ANSWERS
The context setting for getting only secure responses was specified, and at least one DNS response was received, but no DNS response was determined to be secure through DNSSEC.
.LP
The top level of replies_tree can optionally have the following names: canonical_name (a bindata), intermediate_aliases (a list), answer_ipv4_address (a bindata), answer_ipv6_address (a bindata), and answer_type (an int).
.LP
The value of canonical_name is the name that the API used for its lookup. It is
in FQDN presentation format. The values in the intermediate_aliases list are
domain names from any CNAME or unsynthesized DNAME found when resolving the
original query. The list might have zero entries if there were no CNAMEs in the
path. These may be useful, for example, for name comparisons when following the
rules in RFC 6125. The value of answer_ipv4_address and answer_ipv6_address
are the addresses of the server from which the answer was received. The value
of answer_type is the type of name service that generated the response. The
values are:
.RS3
GETDNS_NAMETYPE_DNS
Normal DNS (RFC 1035)
GETDNS_NAMETYPE_WINS
The WINS name service (some reference needed)
.RE
.LP
If the call was getdns_address or getdns_address_sync, the top level of
replies_tree has an additional name, just_address_answers (a list). The value
of just_address_answers is a list that contains all of the A and AAAA records
from the answer sections of any of the replies, in the order they appear in the
replies. Each item in the list is a dict with at least two names: address_type
(whose value is a bindata; it is currently either "IPv4" or "IPv6") and
address_data (whose value is a bindata). Note that the
dnssec_return_only_secure extension affects what will appear in the
just_address_answers list. If the DNS returns other
address types, those types will appear in this list as well.
.LP
The API can make service discovery through SRV records easier. If the call was
getdns_service or getdns_service_sync, the top level of replies_tree has an
additional name, srv_addresses (a list). The list is ordered by priority and
weight based on the weighting algorithm in RFC 2782, lowest priority value
first. Each element of the list is dict has at least two names: port and
domain_name. If the API was able to determine the address of the target domain
name (such as from its cache or from the Additional section of responses), the
dict for an element will also contain address_type (whose value is a bindata;
it is currently either "IPv4" or "IPv6") and address_data (whose value is a
bindata). Note that the dnssec_return_only_secure extension affects what will
appear in the srv_addresses list.
.SHStructureofDNSreplies_tree
.LP
The names in each entry in the the replies_tree list for DNS responses include
header (a dict), question (a dict), answer (a list), authority (a list), and
additional (a list), corresponding to the sections in the DNS message format.
The answer, authority, and additional lists each contain zero or more dicts,
with each dict in each list representing a resource record.
.LP
The names in the header dict are all the fields from Section 4.1.1. of RFC
