document and improve the webview api

downloader-plugin/build.gradle.kts

@@ -7,7 +7,7 @@ plugins {
 
 android {
     namespace = "app.revanced.manager.plugin.downloader"
-    compileSdk = 34
+    compileSdk = 35
 
     defaultConfig {
         minSdk = 26

downloader-plugin/src/main/java/app/revanced/manager/plugin/downloader/webview/API.kt

@@ -5,6 +5,8 @@ import android.os.Bundle
 import android.os.Parcelable
 import app.revanced.manager.plugin.downloader.DownloaderScope
 import app.revanced.manager.plugin.downloader.GetResult
+import app.revanced.manager.plugin.downloader.GetScope
+import app.revanced.manager.plugin.downloader.Scope
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.ExperimentalCoroutinesApi
@@ -14,32 +16,49 @@ import kotlinx.coroutines.withContext
 import kotlinx.parcelize.Parcelize
 import java.net.HttpURLConnection
 import java.net.URI
+import kotlin.properties.Delegates
 
 internal typealias PageLoadCallback<T> = suspend WebViewCallbackScope<T>.(url: String) -> Unit
 internal typealias DownloadCallback<T> = suspend WebViewCallbackScope<T>.(url: String, mimeType: String, userAgent: String) -> Unit
 internal typealias ReadyCallback<T> = suspend WebViewCallbackScope<T>.() -> Unit
 
 @Parcelize
-data class DownloadUrl(val url: String, val mimeType: String, val userAgent: String) : Parcelable {
+/**
+ * A data class for storing a download
+ */
+data class DownloadUrl(val url: String, val userAgent: String?) : Parcelable {
+    /**
+     * Converts this into a [app.revanced.manager.plugin.downloader.DownloadResult].
+     */
     fun toResult() = with(URI.create(url).toURL().openConnection() as HttpURLConnection) {
         useCaches = false
         allowUserInteraction = false
-        setRequestProperty("User-Agent", userAgent)
+        userAgent?.let { setRequestProperty("User-Agent", it) }
+
         connectTimeout = 10_000
         connect()
+
         inputStream to getHeaderField("Content-Length").toLong()
     }
 }
 
-interface WebViewCallbackScope<T : Parcelable> {
-    suspend fun finish(result: GetResult<T>?)
+interface WebViewCallbackScope<T> : Scope {
+    /**
+     * Finishes the activity and returns the [result].
+     */
+    suspend fun finish(result: T)
+
+    /**
+     * Tells the WebView to load the specified [url].
+     */
     suspend fun load(url: String)
 }
 
-class WebViewScope<T : Parcelable> internal constructor(
+class WebViewScope<T> internal constructor(
     coroutineScope: CoroutineScope,
-    setResult: (GetResult<T>?) -> Unit
-) {
+    private val scopeImpl: Scope,
+    setResult: (T) -> Unit
+) : Scope by scopeImpl {
     private var onPageLoadCallback: PageLoadCallback<T> = {}
     private var onDownloadCallback: DownloadCallback<T> = { _, _, _ -> }
     private var onReadyCallback: ReadyCallback<T> =
@@ -76,8 +95,8 @@ class WebViewScope<T : Parcelable> internal constructor(
         }
     }
 
-    private val callbackScope = object : WebViewCallbackScope<T> {
-        override suspend fun finish(result: GetResult<T>?) {
+    private val callbackScope = object : WebViewCallbackScope<T>, Scope by scopeImpl {
+        override suspend fun finish(result: T) {
             setResult(result)
             // Tell the WebViewActivity to finish
             webView.let { withContext(Dispatchers.IO) { it.finish() } }
@@ -89,38 +108,66 @@ class WebViewScope<T : Parcelable> internal constructor(
 
     }
 
-    fun onDownload(block: DownloadCallback<T>) {
+    /**
+     * Called when the WebView attempts to navigate to a downloadable file.
+     */
+    fun download(block: DownloadCallback<T>) {
         onDownloadCallback = block
     }
 
-    fun onPageLoad(block: PageLoadCallback<T>) {
+    /**
+     * Called when the WebView finishes loading a page.
+     */
+    fun pageLoad(block: PageLoadCallback<T>) {
         onPageLoadCallback = block
     }
 
-    fun onReady(block: ReadyCallback<T>) {
+    /**
+     * Called when the WebView is ready. This should always call [WebViewCallbackScope.load].
+     */
+    fun ready(block: ReadyCallback<T>) {
         onReadyCallback = block
     }
 }
 
-fun <T : Parcelable> DownloaderScope<T>.webView(block: WebViewScope<T>.(packageName: String, version: String?) -> Unit) =
-    get { pkgName, version ->
-        var result: GetResult<T>? = null
+@JvmInline
+private value class Container<U>(val value: U)
 
+private suspend fun <T> GetScope.runWebView(title: String, block: WebViewScope<T>.() -> Unit) =
     coroutineScope {
-            val scope = WebViewScope(this) { result = it }
-            scope.block(pkgName, version)
+        var result by Delegates.notNull<Container<T>>()
+
+        val scope = WebViewScope<T>(this@coroutineScope, this@runWebView) { result = Container(it) }
+        scope.block()
+
+        // Start the webview activity and wait until it finishes
         requestStartActivity(Intent().apply {
             putExtras(Bundle().apply {
                 putBinder(WebViewActivity.BINDER_KEY, scope.binder)
-                    val pm = context.packageManager
-                    val label = pm.getPackageInfo(pluginPackageName, 0).applicationInfo.loadLabel(pm).toString()
-                    putString(WebViewActivity.TITLE_KEY, label)
+                putString(WebViewActivity.TITLE_KEY, title)
             })
             setClassName(
                 hostPackageName,
                 WebViewActivity::class.qualifiedName!!
             )
         })
+
+        result.value
+    }
+
+/**
+ * Implements [DownloaderScope.get] using an [android.webkit.WebView]. Event handlers are defined in the provided [block].
+ * The activity will keep running until it is cancelled or an event handler calls [WebViewCallbackScope.finish].
+ *
+ * @param title The title that will be shown in the WebView activity. The default value is the plugin application label.
+ */
+fun <T : Parcelable> DownloaderScope<T>.webView(
+    title: String = context.applicationInfo.loadLabel(
+        context.packageManager
+    ).toString(),
+    block: WebViewScope<GetResult<T>?>.(packageName: String, version: String?) -> Unit
+) = get { pkgName, version ->
+    runWebView(title) {
+        block(pkgName, version)
     }
-        result
 }

example-downloader-plugin/build.gradle.kts

@@ -9,12 +9,12 @@ android {
     val packageName = "app.revanced.manager.plugin.downloader.example"
 
     namespace = packageName
-    compileSdk = 34
+    compileSdk = 35
 
     defaultConfig {
         applicationId = packageName
         minSdk = 26
-        targetSdk = 34
+        targetSdk = 35
         versionCode = 1
         versionName = "1.0"
     }

example-downloader-plugin/src/main/java/app/revanced/manager/plugin/downloader/example/ExamplePlugin.kt

@@ -54,11 +54,15 @@ val installedAppDownloader = downloader<DownloadUrl> {
             build().toString()
         }
 
-        onDownload { url, mimeType, userAgent ->
-            finish(DownloadUrl(url, mimeType, userAgent) to version)
+        download { url, _, userAgent ->
+            finish(DownloadUrl(url, userAgent) to version)
         }
 
-        onReady {
+        pageLoad { url ->
+            println(url)
+        }
+
+        ready {
             load(startUrl)
         }
     }