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/*
* 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 okhttp3.Dns.Companion.SYSTEM
/**
* A domain name service that resolves IP addresses for host names. Most applications will use the
* [system DNS service][SYSTEM], 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.
*
* Implementations of this interface must be safe for concurrent use.
*/
interface Dns {
/**
* Returns the IP addresses of `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.
*/
@Throws(UnknownHostException::class)
fun lookup(hostname: String): List
companion object {
/**
* A DNS that uses [InetAddress.getAllByName] to ask the underlying operating system to
* lookup IP addresses. Most custom [Dns] implementations should delegate to this instance.
*/
@JvmField
val SYSTEM: Dns = DnsSystem()
private class DnsSystem : Dns {
override fun lookup(hostname: String): List {
try {
return InetAddress.getAllByName(hostname).toList()
} catch (e: NullPointerException) {
throw UnknownHostException("Broken system behaviour for dns lookup of $hostname").apply {
initCause(e)
}
}
}
}
}
}