WebView.postUrl with additionalHttpHeaders via extension

WebView.extension.kt

fun WebView.postUrl(url: String, postData: ByteArray, additionalHttpHeaders: MutableMap<String, String>) {

    val savedWebViewClient = if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
        webViewClient
    }
    else {
        getLegacyWebViewClient()
    }

    webViewClient = object : WebViewClient() {

        @Suppress("DEPRECATION")
        override fun shouldInterceptRequest(view: WebView, requestUrl: String): WebResourceResponse? {

            if (requestUrl != url) {
                if (savedWebViewClient != null) {
                    webViewClient = savedWebViewClient
                }
                return savedWebViewClient?.shouldInterceptRequest(view, requestUrl)
            }

            Log.d("WebViewClient", "(url) post \"${postData.decodeToString()}\" to ${requestUrl}")
            val httpsUrl = URL(requestUrl)
            val conn: HttpsURLConnection = httpsUrl.openConnection() as HttpsURLConnection
            conn.requestMethod = "POST"
            for ((key, value) in additionalHttpHeaders) {
                conn.addRequestProperty(key, value)
            }

            val os = conn.outputStream
            os.write(postData)
            os.close()

            val responseCode = conn.responseCode
            Log.d("WebViewClient", "responseCode = ${responseCode} ${conn.contentType}")
            try {
                val response = conn.inputStream.readBytes().decodeToString()
                if (savedWebViewClient != null) {
                    webViewClient = savedWebViewClient
                }
                view.post {
                    view.loadData(response, conn.contentType, conn.contentEncoding)
                }
            }
            catch (ex: Exception) {
                return null
            }

            return WebResourceResponse(null, null, null)
        }

        @RequiresApi(Build.VERSION_CODES.LOLLIPOP)
        override fun shouldInterceptRequest(view: WebView, request: WebResourceRequest): WebResourceResponse? {
            val requestUrl = request.url!!.toString()

            if (!request.isForMainFrame || request.method != "POST" || requestUrl != url) {
                if (savedWebViewClient != null) {
                    view.post {
                        webViewClient = savedWebViewClient
                    }
                }
                return savedWebViewClient?.shouldInterceptRequest(view, request)
            }

            Log.d("WebViewClient", "(request) ${request.method} \"${postData.decodeToString()}\" to ${requestUrl}")

            val httpsUrl = URL(requestUrl)
            val conn: HttpsURLConnection = httpsUrl.openConnection() as HttpsURLConnection
            conn.requestMethod = "POST"
            for ((key, value) in request.requestHeaders) {
                conn.addRequestProperty(key, value)
            }
            for ((key, value) in additionalHttpHeaders) {
                conn.addRequestProperty(key, value)
            }

            val os = conn.outputStream
            os.write(postData)
            os.close()

            val responseCode = conn.responseCode
            Log.d("WebViewClient", "responseCode=${responseCode} ${conn.contentType}")
            view.post {
                if (savedWebViewClient != null) {
                    webViewClient = savedWebViewClient
                }
            }

            val responseHeaders = mutableMapOf<String, String>()

            for ((key, list) in conn.headerFields) {
                if (key != null && list != null && list.size >= 1) {
                    responseHeaders[key] = list.get(0)
                }
            }
            // typical conn.contentType is "text/html; charset=UTF-8"; conn.contentEncoding is less reliable
            return WebResourceResponse(
                    conn.contentType.substringBefore(";"),
                    conn.contentType.substringAfter("charset=", "UTF-8"),
                    conn.responseCode,
                    conn.responseMessage,
                    responseHeaders,
                    conn.inputStream)
        }

        @Suppress("DEPRECATION")
        override fun shouldOverrideUrlLoading(view: WebView, url: String?): Boolean {
            if (savedWebViewClient == null) {
                return false
            }
            return savedWebViewClient.shouldOverrideUrlLoading(view, url)
        }

        @RequiresApi(Build.VERSION_CODES.N)
        override fun shouldOverrideUrlLoading(view: WebView, request: WebResourceRequest): Boolean {
            if (savedWebViewClient == null) {
                return false
            }
            return savedWebViewClient.shouldOverrideUrlLoading(view, request)
        }

        override fun onPageStarted(view: WebView, url: String?, favicon: Bitmap?) {
            if (savedWebViewClient != null) {
                view.post {
                    webViewClient = savedWebViewClient
                }
                savedWebViewClient.onPageStarted(view, url, favicon)
            }
        }

        override fun onPageFinished(view: WebView, url: String?) {
            Log.w("WebViewClient", "unexpected: onPageFinished ${url}")
        }

        override fun onLoadResource(view: WebView, url: String?) {
            Log.w("WebViewClient", "unexpected: onLoadResource ${url}")
        }

        override fun onPageCommitVisible(view: WebView, url: String?) {
            Log.w("WebViewClient", "unexpected: onPageCommitVisible ${url}")
        }

        override fun onTooManyRedirects(view: WebView, cancelMsg: Message, continueMsg: Message?) {
            Log.w("WebViewClient", "unexpected: onTooManyRedirects ${url}")
            if (savedWebViewClient != null) {
                view.post {
                    webViewClient = savedWebViewClient
                }
                savedWebViewClient.onPageStarted(view, url, favicon)
            }
            else {
                super.onTooManyRedirects(view, cancelMsg, continueMsg)
            }
        }

        @Suppress("DEPRECATION")
        override fun onReceivedError(view: WebView, errorCode: Int, description: String?, failingUrl: String?) {
            Log.i("WebViewClient", "onReceivedError ${url}")
            if (savedWebViewClient != null) {
                view.post {
                    webViewClient = savedWebViewClient
                }
                savedWebViewClient.onReceivedError(view, errorCode, description, failingUrl)
            }
            else {
                super.onReceivedError(view, errorCode, description, failingUrl)
            }
        }

        @RequiresApi(Build.VERSION_CODES.M)
        override fun onReceivedError(view: WebView, request: WebResourceRequest, error: WebResourceError) {
            Log.i("WebViewClient", "onReceivedError ${request.url}")
            if (savedWebViewClient != null) {
                view.post {
                    webViewClient = savedWebViewClient
                }
                savedWebViewClient.onReceivedError(view, request, error)
            }
            else {
                super.onReceivedError(view, request, error)
            }
        }

        @RequiresApi(Build.VERSION_CODES.M)
        override fun onReceivedHttpError(view: WebView, request: WebResourceRequest, errorResponse: WebResourceResponse?) {
            Log.i("WebViewClient", "onReceivedHttpError ${request.url}")
            if (savedWebViewClient != null) {
                view.post {
                    webViewClient = savedWebViewClient
                }
                savedWebViewClient.onReceivedHttpError(view, request, errorResponse)
            }
            else {
                super.onReceivedHttpError(view, request, errorResponse)
            }
        }

        override fun onFormResubmission(view: WebView, dontResend: Message, resend: Message?) {
            Log.i("WebViewClient", "onFormResubmission")
            if (savedWebViewClient != null) {
                view.post {
                    webViewClient = savedWebViewClient
                }
                savedWebViewClient.onFormResubmission(view, dontResend, resend)
            }
            else {
                super.onFormResubmission(view, dontResend, resend)
            }
        }

        override fun doUpdateVisitedHistory(view: WebView, url: String?, isReload: Boolean) {
            Log.i("WebViewClient", "doUpdateVisitedHistory")
            if (savedWebViewClient != null) {
                view.post {
                    webViewClient = savedWebViewClient
                }
                savedWebViewClient.doUpdateVisitedHistory(view, url, isReload)
            }
            else {
                super.doUpdateVisitedHistory(view, url, isReload)
            }
        }
    }

    postUrl(url, postData)
}

fun WebView.getLegacyWebViewClient(): WebViewClient? {
    try {

        val mProviderField = javaClass.getDeclaredField("mProvider")
        mProviderField.isAccessible = true
        val mProvider = mProviderField.get(this)
        if (mProvider != null) {
            val mContentsClientAdapterField = mProvider.javaClass.getDeclaredField("mContentsClientAdapter")
            mContentsClientAdapterField.isAccessible = true
            val mContentsClientAdapter = mContentsClientAdapterField.get(mProvider)
            if (mContentsClientAdapter != null) {
                val mWebViewClientField = mContentsClientAdapter.javaClass.getDeclaredField("mWebViewClient")
                mWebViewClientField.isAccessible = true
                val mWebViewClient = mWebViewClientField.get(mContentsClientAdapter)
                Log.i("WebViewClient", "getLegacyWebViewClient ${mWebViewClient}")
                return mWebViewClient as WebViewClient
            }
        }
        Log.i("WebViewClient", "getLegacyWebViewClient null")
    }
    catch (ex: Throwable) {
        Log.w("WebViewClient", "getLegacyWebViewClient failed", ex)
    }
    return null
}