/*
* Copyright (C) 2012 Square, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package okhttp3;
import java.net.
InetAddress;
import java.net.
UnknownHostException;
import java.util.
Arrays;
import java.util.
List;
/**
* A domain name service that resolves IP addresses for host names. Most applications will use the
* {@linkplain #SYSTEM system DNS service}, which is the default. Some applications may provide
* their own implementation to use a different DNS server, to prefer IPv6 addresses, to prefer IPv4
* addresses, or to force a specific known IP address.
*
* <p>Implementations of this interface must be safe for concurrent use.
*/
public interface
Dns {
/**
* A DNS that uses {@link InetAddress#getAllByName} to ask the underlying operating system to
* lookup IP addresses. Most custom {@link Dns} implementations should delegate to this instance.
*/
Dns SYSTEM = new
Dns() {
@
Override public
List<
InetAddress>
lookup(
String hostname) throws
UnknownHostException {
if (
hostname == null) throw new
UnknownHostException("hostname == null");
try {
return
Arrays.
asList(
InetAddress.
getAllByName(
hostname));
} catch (
NullPointerException e) {
UnknownHostException unknownHostException =
new
UnknownHostException("Broken system behaviour for dns lookup of " +
hostname);
unknownHostException.
initCause(
e);
throw
unknownHostException;
}
}
};
/**
* Returns the IP addresses of {@code hostname}, in the order they will be attempted by OkHttp. If
* a connection to an address fails, OkHttp will retry the connection with the next address until
* either a connection is made, the set of IP addresses is exhausted, or a limit is exceeded.
*/
List<
InetAddress>
lookup(
String hostname) throws
UnknownHostException;
}