feat(android): generate kotlin files at build time (#671)

* feat(android): generate kotlin files at build time

* changefile

* Update kotlin-files.md

* fix android ci

* Add option for extra code when generating files

* rerun build script when env changes

* change it to a class code, prepare var name for future additions

* Delete MainActivity.kt

* uppercase [skip ci]

* fix android detection

Co-authored-by: Lucas Nogueira <lucas@tauri.studio>

.changes/kotlin-files.md

@@ -0,0 +1,5 @@
+---
+"wry": "minor"
+---
+
+WRY will now generate the needed kotlin files at build time but you need to set `WRY_ANDROID_REVERSED_DOMAIN`, `WRY_ANDROID_APP_NAME_SNAKE_CASE` and `WRY_ANDROID_KOTLIN_FILES_OUT_DIR` env vars.

.github/workflows/build.yml

@@ -13,7 +13,15 @@ jobs:
           - { target: x86_64-unknown-linux-gnu, os: ubuntu-latest }
           - { target: x86_64-apple-darwin, os: macos-latest }
           - { target: aarch64-apple-ios, os: macos-latest }
-          - { target: aarch64-linux-android, os: ubuntu-latest }
+          - {
+              target: aarch64-linux-android,
+              os: ubuntu-latest,
+              env: {
+                WRY_ANDROID_REVERSED_DOMAIN: "app.tauri",
+                WRY_ANDROID_APP_NAME_SNAKE_CASE: "wry",
+                WRY_ANDROID_KOTLIN_FILES_OUT_DIR: "out",
+              }
+            }
 
     runs-on: ${{ matrix.platform.os }}
 
@@ -74,8 +82,16 @@ jobs:
             ${{ matrix.platform }}-stable-cargo-core-${{ hashFiles('Cargo.toml') }}
             ${{ matrix.platform }}-stable-cargo-core-
 
+      - name: create kotlin out dir
+        if: contains(matrix.platform.target, 'android')
+        run: mkdir out
+
       - name: build wry
         run: cargo build --features tray --target ${{ matrix.platform.target }}
+        env:
+          WRY_ANDROID_REVERSED_DOMAIN: ${{ matrix.platform.env.WRY_ANDROID_REVERSED_DOMAIN }}
+          WRY_ANDROID_APP_NAME_SNAKE_CASE: ${{ matrix.platform.env.WRY_ANDROID_APP_NAME_SNAKE_CASE }}
+          WRY_ANDROID_KOTLIN_FILES_OUT_DIR: ${{ matrix.platform.env.WRY_ANDROID_KOTLIN_FILES_OUT_DIR }}
 
       - name: build tests and examples
         shell: bash

README.md

@@ -123,6 +123,13 @@ WebView2 provided by Microsoft Edge Chromium is used. So wry supports Windows 7,
 
 We have experimental support of mobile ends. If you are interested in playing or hacking it, please follow this [note](https://hackmd.io/XIcEwk4GSxy8APZhSa0UnA?view).
 
+When building for Android, WRY generates kotlin files that are needed to run WRY on Android and you have to set the following environment variables:
+- `WRY_ANDROID_REVERSED_DOMAIN`
+- `WRY_ANDROID_APP_NAME_SNAKE_CASE`
+- `WRY_ANDROID_KOTLIN_FILES_OUT_DIR`
+
+You can skip setting these environment variables if you are using the WRY template from our [`cargo-mobile`](https://github.com/tauri-apps/cargo-mobile) fork.
+
 ## License
 
 Apache-2.0/MIT

build.rs

@@ -9,4 +9,61 @@ fn main() {
   if is_macos {
     println!("cargo:rustc-link-lib=framework=WebKit");
   }
+
+  let is_android = std::env::var("CARGO_CFG_TARGET_OS")
+    .map(|t| t == "android")
+    .unwrap_or_default();
+  if is_android {
+    use std::{fs, path::PathBuf};
+
+    fn env_var(var: &str) -> String {
+      std::env::var(var).expect(&format!(
+        " `{}` is not set, which is needed to generate the kotlin files for android.",
+        var
+      ))
+    }
+
+    println!("cargo:rerun-if-env-changed=WRY_ANDROID_REVERSED_DOMAIN");
+    println!("cargo:rerun-if-env-changed=WRY_ANDROID_APP_NAME_SNAKE_CASE");
+    println!("cargo:rerun-if-env-changed=WRY_ANDROID_KOTLIN_FILES_OUT_DIR");
+
+    let reversed_domain = env_var("WRY_ANDROID_REVERSED_DOMAIN");
+    let app_name_snake_case = env_var("WRY_ANDROID_APP_NAME_SNAKE_CASE");
+    let kotlin_out_dir = env_var("WRY_ANDROID_KOTLIN_FILES_OUT_DIR");
+
+    let kotlin_out_dir = PathBuf::from(kotlin_out_dir)
+      .canonicalize()
+      .expect("Failed to canonicalize path");
+    let kotlin_files =
+      fs::read_dir(PathBuf::from(env_var("CARGO_MANIFEST_DIR")).join("src/webview/android/kotlin"))
+        .expect("failed to read kotlin directory");
+
+    for file in kotlin_files {
+      let file = file.unwrap();
+
+      let class_extension_env = format!(
+        "WRY_{}_CLASS_EXTENSION",
+        file
+          .path()
+          .file_stem()
+          .unwrap()
+          .to_string_lossy()
+          .to_uppercase()
+      );
+
+      println!("cargo:rerun-if-env-changed={}", class_extension_env);
+
+      let content = fs::read_to_string(file.path())
+        .expect("failed to read kotlin file as string")
+        .replace("{{app-domain-reversed}}", &reversed_domain)
+        .replace("{{app-name-snake-case}}", &app_name_snake_case)
+        .replace(
+          "{{class-extension}}",
+          &std::env::var(&class_extension_env).unwrap_or_default(),
+        );
+
+      fs::write(kotlin_out_dir.join(file.file_name()), content)
+        .expect("Failed to write kotlin file");
+    }
+  }
 }

src/webview/android/kotlin/Ipc.kt

@@ -0,0 +1,20 @@
+package {{app-domain-reversed}}.{{app-name-snake-case}}
+
+import android.webkit.*
+
+class Ipc {
+    @JavascriptInterface
+    fun postMessage(message: String) {
+        this.ipc(message)
+    }
+
+    companion object {
+        init {
+            System.loadLibrary("{{app-name-snake-case}}")
+        }
+    }
+
+    private external fun ipc(message: String)
+
+    {{class-extension}}
+}

src/webview/android/kotlin/RustWebViewClient.kt

@@ -0,0 +1,36 @@
+package {{app-domain-reversed}}.{{app-name-snake-case}}
+
+import android.graphics.Bitmap
+import android.webkit.*
+
+class RustWebViewClient(initScripts: Array<String>): WebViewClient() {
+    private val initializationScripts: Array<String>
+
+    init {
+      initializationScripts = initScripts
+    }
+
+    override fun onPageStarted(view: WebView?, url: String?, favicon: Bitmap?) {
+        for (script in initializationScripts) {
+          view?.evaluateJavascript(script, null)
+        }
+        super.onPageStarted(view, url, favicon)
+    }
+
+    override fun shouldInterceptRequest(
+        view: WebView,
+        request: WebResourceRequest
+    ): WebResourceResponse? {
+        return handleRequest(request)
+    }
+
+    companion object {
+        init {
+            System.loadLibrary("{{app-name-snake-case}}")
+        }
+    }
+
+    private external fun handleRequest(request: WebResourceRequest): WebResourceResponse?
+
+    {{class-extension}}
+}

src/webview/android/kotlin/TauriActivity.kt

@@ -0,0 +1,73 @@
+package {{app-domain-reversed}}.{{app-name-snake-case}}
+
+import android.os.Bundle
+import androidx.appcompat.app.AppCompatActivity
+
+abstract class TauriActivity : AppCompatActivity() {
+  override fun onCreate(savedInstanceState: Bundle?) {
+        super.onCreate(savedInstanceState)
+        create(this)
+    }
+
+    override fun onStart() {
+        super.onStart()
+        start()
+    }
+
+    override fun onResume() {
+        super.onResume()
+        resume()
+    }
+
+    override fun onPause() {
+        super.onPause()
+        pause()
+    }
+
+    override fun onStop() {
+        super.onStop()
+        stop()
+    }
+
+    override fun onWindowFocusChanged(hasFocus: Boolean) {
+        super.onWindowFocusChanged(hasFocus)
+        focus(hasFocus)
+    }
+
+    override fun onSaveInstanceState(outState: Bundle) {
+        super.onSaveInstanceState(outState)
+        save()
+    }
+
+    override fun onDestroy() {
+        super.onDestroy()
+        destroy()
+    }
+
+    override fun onLowMemory() {
+        super.onLowMemory()
+        memory()
+    }
+
+    fun getAppClass(name: String): Class<*> {
+        return Class.forName(name)
+    }
+
+    companion object {
+        init {
+            System.loadLibrary("{{app-name-snake-case}}")
+        }
+    }
+
+    private external fun create(activity: TauriActivity)
+    private external fun start()
+    private external fun resume()
+    private external fun pause()
+    private external fun stop()
+    private external fun save()
+    private external fun destroy()
+    private external fun memory()
+    private external fun focus(focus: Boolean)
+
+    {{class-extension}}
+}