feat: add frame cryptor.

lib/src/e2ee.worker/crypto.dart

@@ -0,0 +1,94 @@
+import 'dart:async';
+import 'dart:typed_data';
+import 'dart:js_util' as jsutil;
+import 'dart:html' as html;
+
+import 'package:js/js.dart';
+
+@JS('Promise')
+class Promise<T> {
+  external factory Promise._();
+}
+
+@JS('Algorithm')
+class Algorithm {
+  external String get name;
+}
+
+@JS('crypto.subtle.encrypt')
+external Promise<ByteBuffer> encrypt(
+  dynamic algorithm,
+  html.CryptoKey key,
+  ByteBuffer data,
+);
+
+@JS('crypto.subtle.decrypt')
+external Promise<ByteBuffer> decrypt(
+  dynamic algorithm,
+  html.CryptoKey key,
+  ByteBuffer data,
+);
+
+@JS()
+@anonymous
+class AesGcmParams {
+  external factory AesGcmParams({
+    required String name,
+    required ByteBuffer iv,
+    ByteBuffer? additionalData,
+    int tagLength = 128,
+  });
+}
+
+ByteBuffer jsArrayBufferFrom(List<int> data) {
+  // Avoid copying if possible
+  if (data is Uint8List &&
+      data.offsetInBytes == 0 &&
+      data.lengthInBytes == data.buffer.lengthInBytes) {
+    return data.buffer;
+  }
+  // Copy
+  return Uint8List.fromList(data).buffer;
+}
+
+@JS('crypto.subtle.importKey')
+external Promise<html.CryptoKey> importKey(
+  String format,
+  ByteBuffer keyData,
+  dynamic algorithm,
+  bool extractable,
+  List<String> keyUsages,
+);
+
+@JS('crypto.subtle.exportKey')
+external Promise<ByteBuffer> exportKey(
+  String format,
+  html.CryptoKey key,
+);
+
+@JS('crypto.subtle.deriveKey')
+external Promise<html.CryptoKey> deriveKey(
+    dynamic algorithm,
+    html.CryptoKey baseKey,
+    dynamic derivedKeyAlgorithm,
+    bool extractable,
+    List<String> keyUsages);
+
+@JS('crypto.subtle.deriveBits')
+external Promise<ByteBuffer> deriveBits(
+  dynamic algorithm,
+  html.CryptoKey baseKey,
+  int length,
+);
+
+Future<html.CryptoKey> impportKeyFromRawData(List<int> secretKeyData,
+    {required String webCryptoAlgorithm,
+    required List<String> keyUsages}) async {
+  return jsutil.promiseToFuture<html.CryptoKey>(importKey(
+    'raw',
+    jsArrayBufferFrom(secretKeyData),
+    jsutil.jsify({'name': webCryptoAlgorithm}),
+    false,
+    keyUsages,
+  ));
+}