Kotlin HTTP GET JSON field with timeouts

import java.net.HttpURLConnection
import java.net.URI

fun getJsonField(url: String, field: String): String? {
    val conn = URI(url).toURL().openConnection() as HttpURLConnection
    conn.connectTimeout = 3_000
    conn.readTimeout = 5_000
    val body = try {
        check(conn.responseCode in 200..299) { "HTTP ${conn.responseCode} for $url" }
        conn.inputStream.bufferedReader().use { it.readText() }
    } finally {
        conn.disconnect()
    }
    val keyAt = body.indexOf('"' + field + '"')
    if (keyAt < 0) return null
    val colonAt = body.indexOf(':', keyAt)
    if (colonAt < 0) return null
    val from = body.indexOf('"', colonAt + 1)
    val to = body.indexOf('"', from + 1)
    // minimal quoted-string scan; use a real JSON parser for nested data
    return if (from < 0 || to < 0) null else body.substring(from + 1, to)
}