ktor httpclient: how to send request to specific ip address?

Question

I have DNS address which contains several ip addresses. It's possible to send request for each address using ktor http-client?

For classic curl it can be made usin --resolve option:

    curl https://host  --resolve "host:443:127.0.0.1"
    curl https://host  --resolve "host:443:127.0.0.2"

Answer 1

You can use Ktor's OkHttp engine to configure an underlying OkHttpClient to use a DNS service that resolves a specified host to a custom IP address. Unfortunately, if you want to provide multiple IP addresses for the same host you have to create a separate client instance for each IP address. Here is an example:

import io.ktor.client.HttpClient
import io.ktor.client.engine.okhttp.OkHttp
import io.ktor.client.request.get
import okhttp3.Dns
import okhttp3.OkHttpClient
import java.net.Inet4Address
import java.net.InetAddress

suspend fun main() {
    val okHttpClient = OkHttpClient.Builder()
        .dns(HostsDns(mapOf("example.com" to "127.0.0.1")))
        .build()

    val client = HttpClient(OkHttp) {
        engine {
            preconfigured = okHttpClient
        }
    }

    client.get("http://example.com")
}

class HostsDns(private val map: Map<String, String>) : Dns {
    override fun lookup(hostname: String): List<InetAddress> {
        val ip = map[hostname]
        return if (ip != null) listOf(Inet4Address.getByName(ip)) else Dns.Companion.SYSTEM.lookup(hostname)
    }
}