WebView Asset PathHandler that returns contents of a zip archive.

ZipArchivePathHandler.kt

// Licensed under CC-0 terms. https://creativecommons.org/share-your-work/public-domain/cc0/

import java.io.ByteArrayInputStream
import java.io.ByteArrayOutputStream
import java.nio.ByteBuffer
import java.util.zip.ZipInputStream
import android.webkit.WebResourceResponse
import androidx.webkit.WebViewAssetLoader

// WebView Asset PathHandler that returns contents of a zip archive.
class ZipArchivePathHandler(private val zipArchiveBytes: ByteArray) : WebViewAssetLoader.PathHandler {

    override fun handle(path: String): WebResourceResponse? {
        val bs = ByteArrayInputStream(zipArchiveBytes)
        val zs = ZipInputStream(bs)
        while(true) {
            val entry = zs.nextEntry ?: break
            if (entry.name == path) {
                if (entry.size > Int.MAX_VALUE)
                    return WebResourceResponse("text/html", "utf-8", 500, "Internal Error", mapOf(), ByteArrayInputStream("Internal Error: compressed zip entry ${entry.name} has bloated size: ${entry.size}".toByteArray()))
                // huh, entry.size is not really available??
                val os = ByteArrayOutputStream(4096)
                val bytes = ByteArray(4096)
                while (true) {
                    val size = zs.read(bytes, 0, bytes.size)
                    if (size < 0)
                        break
                    os.write(bytes, 0, size)
                }
                return WebResourceResponse(
                    MimeTypeMap.getSingleton()
                        .getMimeTypeFromExtension(MimeTypeMap.getFileExtensionFromUrl(path)),
                    "utf-8",
                    ByteArrayInputStream(os.toByteArray()))
            }
        }
        return WebResourceResponse("text/html", "utf-8", 404, "Not Found", mapOf(), ByteArrayInputStream("Not found".toByteArray()))
    }
}