How to Build a Super Simple HTTP Proxy in Kotlin in just 20 lines of code

Kotlin makes server-side development concise yet powerful. Here is a basic HTTP proxy server in Kotlin in less than 20 lines of code.

First we import the required packages:

import io.ktor.server.engine.*
import io.ktor.server.netty.*
import io.ktor.http.*
import io.ktor.client.*
import io.ktor.client.request.*

The ktor server package provides the API for the proxy server, ktor client to make requests, and ktor http for dealing with HTTP connections.

Next we create an embedded server:

embeddedServer(Netty, port = 8080) {
  // routing code
}.start(wait = true)

Inside the routing configuration we handle GET requests:

get("/") {
  // proxy logic
}

To proxy the request we:

Extract the target URL from the request path

val url = call.request.path().substring(1)

Make a GET request to the URL

val response = client.get<String>(url)

Return the proxied response

call.respond(response)

Here is the full HTTP proxy in Kotlin:

import io.ktor.server.engine.*
import io.ktor.server.netty.*
// other imports

fun main() {
  embeddedServer(Netty, port = 8080) {
    get("/") {
      val url = call.request.path().substring(1)
      val response = client.get<String>(url)
      call.respond(response)
    }
  }.start(wait = true)
}

This shows how concise and expressive an HTTP proxy can be in Kotlin using its coroutines and ktor library.

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How to Build a Super Simple HTTP Proxy in Kotlin in just 20 lines of code

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