AdBlockWebViewClient.kt

package au.sj.sparrow.adblockwebview

import android.webkit.WebResourceRequest
import android.webkit.WebResourceResponse
import android.webkit.WebView
import android.webkit.WebViewClient
import okhttp3.HttpUrl
import java.io.ByteArrayInputStream

/**
 * Created by vorobei on 04/08/2018
 * @param blacklist - hash set of domains we want to block
 */
class AdBlockWebViewClient(var blacklist: HashSet<String> = HashSet()) : WebViewClient() {

    private val loadedUrls = HashMap<String, Boolean>()

    override fun shouldInterceptRequest(view: WebView?, request: WebResourceRequest?): WebResourceResponse? {
        val ad: Boolean
        val url = request?.url.toString()
        if (!loadedUrls.containsKey(url)) {
            ad = isAd(url)
            loadedUrls[url] = ad
        } else {
            ad = loadedUrls[url] ?: false
        }

        return if (ad) createEmptyResourse()
        else super.shouldInterceptRequest(view, request)
    }

    private fun createEmptyResourse(): WebResourceResponse {
        return WebResourceResponse("text/plain", "utf-8", ByteArrayInputStream("".toByteArray()))
    }

    private fun isAd(url: String): Boolean {
        val httpUrl = HttpUrl.parse(url)
        return isAdHost(httpUrl?.host() ?: "")
    }

    private fun isAdHost(host: String): Boolean {
        if (host.isEmpty()) return false
        val index = host.indexOf(".")
        return index >= 0 && (blacklist.contains(host) ||
                index + 1 < host.length && isAdHost(host.substring(index + 1)))
    }
}