# Poco::Net

# class DNS

Library: Net
Package: NetCore
Header: Poco/Net/DNS.h

## Description

This class provides an interface to the domain name service.

An internal DNS cache is used to speed up name lookups.

## Member Summary

Member Functions: aierror, error, flushCache, hostByAddress, hostByName, hostName, lastError, reload, resolve, resolveOne, thisHost

## Enumerations

### HintFlag

DNS_HINT_NONE = 0

DNS_HINT_AI_PASSIVE = 0x00000001

Socket address will be used in bind() call

DNS_HINT_AI_CANONNAME = 0x00000002

Return canonical name in first ai_canonname

DNS_HINT_AI_NUMERICHOST = 0x00000004

Nodename must be a numeric address string

DNS_HINT_AI_NUMERICSERV = 0x00001000

Servicename must be a numeric port number

DNS_HINT_AI_ALL = 0x00000100

Query both IP6 and IP4 with AI_V4MAPPED

DNS_HINT_AI_ADDRCONFIG = 0x00000400

Resolution only if global address configured

DNS_HINT_AI_V4MAPPED = 0x00000800

On v6 failure, query v4 and convert to V4MAPPED format

## Member Functions

### flushCache

static void flushCache();

Deprecated. This function is deprecated and should no longer be used.

Flushes the internal DNS cache.

As of 1.4.2, the DNS cache is no longer used and this method does not do anything.

### hostByAddress

static HostEntry hostByAddress(
const IPAddress & address,
unsigned hintFlags = DNS_HINT_AI_CANONNAME | DNS_HINT_AI_ADDRCONFIG
);

Returns a HostEntry object containing the DNS information for the host with the given IP address. HintFlag argument is only used on platforms that have getaddrinfo().

Throws a HostNotFoundException if a host with the given name cannot be found.

Throws a DNSException in case of a general DNS error.

Throws an IOException in case of any other error.

### hostByName

static HostEntry hostByName(
const std::string & hostname,
unsigned hintFlags = DNS_HINT_AI_CANONNAME | DNS_HINT_AI_ADDRCONFIG
);

Returns a HostEntry object containing the DNS information for the host with the given name. HintFlag argument is only used on platforms that have getaddrinfo().

Throws a HostNotFoundException if a host with the given name cannot be found.

Throws a NoAddressFoundException if no address can be found for the hostname.

Throws a DNSException in case of a general DNS error.

Throws an IOException in case of any other error.

### hostName

static std::string hostName();

Returns the host name of this host.

### reload

static void reload();

Reloads the resolver configuration.

This method will call res_init() if the Net library has been compiled with -DPOCO_HAVE_LIBRESOLV. Otherwise it will do nothing.

### resolve

static HostEntry resolve(
const std::string & address
);

Returns a HostEntry object containing the DNS information for the host with the given IP address or host name.

Throws a HostNotFoundException if a host with the given name cannot be found.

Throws a NoAddressFoundException if no address can be found for the hostname.

Throws a DNSException in case of a general DNS error.

Throws an IOException in case of any other error.

### resolveOne

static IPAddress resolveOne(
const std::string & address
);

Convenience method that calls resolve(address) and returns the first address from the HostInfo.

### thisHost

static HostEntry thisHost();

Returns a HostEntry object containing the DNS information for this host.

Throws a HostNotFoundException if DNS information for this host cannot be found.

Throws a NoAddressFoundException if no address can be found for this host.

Throws a DNSException in case of a general DNS error.

Throws an IOException in case of any other error.

### aierror

static void aierror(
int code,
const std::string & arg
);

Throws an exception according to the getaddrinfo() error code.

### error

static void error(
int code,
const std::string & arg
);

Throws an exception according to the error code.

### lastError

static int lastError();

Returns the code of the last error.