How to get ip address from call object - kotlin

Question

I use Ktor for a backend service and I'd like to log incoming requests. I have the feature installed and everything is great but how I can obtain the remote IP address?
call.request.origin.remoteHost
I use this line but I get a hostname, not the IP. I use the standard getByName method from the InetAddress class to get the IP.
Is there a better way?

Answer 1

You can't do this with Ktor as it is not Ktor's job to resolve IP addresses from domains.
What you can use however is Java's InetAddress:
val url = "http://google.com";
val ip = Inet4Address.getByName(url);

Answer 2

Depends on how accurate you want this information to be.
If you read through Ktor code, you'll see that the remoteHost is actually set from the HTTP X-Forwarded-Host header.
From API documentation:
* NEVER use it for user authentication as it can be easily falsified (user can simply set some HTTP headers
* such as X-Forwarded-Host so you should NEVER rely on it in any security checks.
* If you are going to use it to create a back-connection please do it with care as an offender can easily
* use it to force you to connect to some host that is not intended to be connected to so that may cause
* serious consequences.
A better way might be to get the IP from the application engine itself. Unfortunately, the ApplicationCall itself is private, so you'll have to resort to reflection, which isn't optimal:
class RoutingApplicationCall(private val call: ApplicationCall,
Still, this is possible:
// Getting the private field through reflection
val f = context::class.memberProperties.find { it.name == "call" }
f?.let {
// Making it accessible
it.isAccessible = true
val w = it.getter.call(context) as NettyApplicationCall
// Getting the remote address
val ip: SocketAddress? = w.request.context.pipeline().channel().remoteAddress()
println("IP: $ip")
}