[mob] Simplify APIs for compress -> encrypt & vice versa (#2524)

## Description

## Tests

mobile/lib/services/machine_learning/file_ml/remote_fileml_service.dart

@@ -1,6 +1,4 @@
 import "dart:async";
-import "dart:convert";
-import "dart:io";
 
 import "package:computer/computer.dart";
 import "package:flutter/foundation.dart" show Uint8List;
@@ -11,8 +9,8 @@ import "package:photos/models/file/file.dart";
 import 'package:photos/services/machine_learning/file_ml/file_ml.dart';
 import "package:photos/services/machine_learning/file_ml/files_ml_data_response.dart";
 import "package:photos/services/machine_learning/file_ml/remote_embedding.dart";
-import "package:photos/utils/crypto_util.dart";
 import "package:photos/utils/file_download_util.dart";
+import "package:photos/utils/gzip.dart";
 import "package:shared_preferences/shared_preferences.dart";
 
 class RemoteFileMLService {
@@ -36,22 +34,18 @@ class RemoteFileMLService {
   }) async {
     fileML.putClipIfNotNull(clipEmbedding);
     fileML.putFaceIfNotNull(faceEmbedding);
-    final encryptionKey = getFileKey(file);
-    final embeddingJSON = jsonEncode(fileML.remoteRawData);
-    final compressedData = gzipUInt8List(utf8.encode(embeddingJSON));
-    final encryptedEmbedding =
-        await CryptoUtil.encryptChaCha(compressedData, encryptionKey);
-    final encryptedData =
-        CryptoUtil.bin2base64(encryptedEmbedding.encryptedData!);
-    final header = CryptoUtil.bin2base64(encryptedEmbedding.header!);
+    final ChaChaEncryptionResult encryptionResult = await gzipAndEncryptJson(
+      fileML.remoteRawData,
+      getFileKey(file),
+    );
     try {
       final _ = await _dio.put(
         "/embeddings",
         data: {
           "fileID": file.uploadedFileID!,
           "model": 'ggml-clip',
-          "encryptedEmbedding": encryptedData,
-          "decryptionHeader": header,
+          "encryptedEmbedding": encryptionResult.encData,
+          "decryptionHeader": encryptionResult.header,
         },
       );
     } catch (e, s) {
@@ -125,39 +119,21 @@ class RemoteFileMLService {
   }
 }
 
-Uint8List ungzipUint8List(Uint8List compressedData) {
-  final codec = GZipCodec();
-  final List<int> decompressedList = codec.decode(compressedData);
-  return Uint8List.fromList(decompressedList);
-}
-
-// gzipUInt8List
-Uint8List gzipUInt8List(Uint8List data) {
-  final codec = GZipCodec();
-  final compressedData = codec.encode(data);
-  return Uint8List.fromList(compressedData);
-}
-
 Future<Map<int, RemoteFileML>> _decryptFileMLComputer(
   Map<String, dynamic> args,
 ) async {
   final result = <int, RemoteFileML>{};
   final inputs = args["inputs"] as List<EmbeddingsDecoderInput>;
   for (final input in inputs) {
-    final decryptArgs = <String, dynamic>{};
-    decryptArgs["source"] =
-        CryptoUtil.base642bin(input.embedding.encryptedEmbedding);
-    decryptArgs["key"] = input.decryptionKey;
-    decryptArgs["header"] =
-        CryptoUtil.base642bin(input.embedding.decryptionHeader);
-    final embeddingData = chachaDecryptData(decryptArgs);
-    final unzippedData = ungzipUint8List(embeddingData);
-    final decodedJson = jsonDecode(utf8.decode(unzippedData));
-    final RemoteFileML decodedEmbedding = RemoteFileML.fromRemote(
-      input.embedding.fileID,
-      decodedJson as Map<String, dynamic>,
+    final decodedJson = decryptAndUnzipJsonSync(
+      input.decryptionKey,
+      encryptedData: input.embedding.encryptedEmbedding,
+      header: input.embedding.decryptionHeader,
+    );
+    result[input.embedding.fileID] = RemoteFileML.fromRemote(
+      input.embedding.fileID,
+      decodedJson,
     );
-    result[input.embedding.fileID] = decodedEmbedding;
   }
   return result;
 }

mobile/lib/utils/gzip.dart

@@ -0,0 +1,84 @@
+import "dart:convert";
+import "dart:io";
+
+import "package:computer/computer.dart";
+import "package:flutter/foundation.dart";
+import "package:photos/utils/crypto_util.dart";
+
+class ChaChaEncryptionResult {
+  final String encData;
+  final String header;
+
+  ChaChaEncryptionResult({
+    required this.encData,
+    required this.header,
+  });
+}
+
+Uint8List _unGzipUInt8List(Uint8List compressedData) {
+  final codec = GZipCodec();
+  final List<int> decompressedList = codec.decode(compressedData);
+  return Uint8List.fromList(decompressedList);
+}
+
+// gzipUInt8List
+Uint8List _gzipUInt8List(Uint8List data) {
+  final codec = GZipCodec();
+  final compressedData = codec.encode(data);
+  return Uint8List.fromList(compressedData);
+}
+
+Map<String, dynamic> decryptAndUnzipJsonSync(
+  Uint8List key, {
+  required String encryptedData,
+  required String header,
+}) {
+  final decryptedData = chachaDecryptData({
+    "source": CryptoUtil.base642bin(encryptedData),
+    "key": key,
+    "header": CryptoUtil.base642bin(header),
+  });
+  final decompressedData = _unGzipUInt8List(decryptedData);
+  final json = utf8.decode(decompressedData);
+  return jsonDecode(json);
+}
+
+// zipJsonAndEncryptSync performs all operations synchronously, on a single isolate.
+ChaChaEncryptionResult gzipAndEncryptJsonSync(
+  Map<String, dynamic> jsonData,
+  Uint8List key,
+) {
+  final json = utf8.encode(jsonEncode(jsonData));
+  final compressedJson = _gzipUInt8List(Uint8List.fromList(json));
+  final encryptedData = chachaEncryptData({
+    "source": compressedJson,
+    "key": key,
+  });
+  return ChaChaEncryptionResult(
+    encData: CryptoUtil.bin2base64(encryptedData.encryptedData!),
+    header: CryptoUtil.bin2base64(encryptedData.header!),
+  );
+}
+
+Future<ChaChaEncryptionResult> gzipAndEncryptJson(
+  Map<String, dynamic> jsonData,
+  Uint8List key,
+) async {
+  final Computer computer = Computer.shared();
+  final response =
+      await computer.compute<Map<String, dynamic>, ChaChaEncryptionResult>(
+    _gzipAndEncryptJsonSync,
+    param: {
+      "jsonData": jsonData,
+      "key": key,
+    },
+    taskName: "gzipAndEncryptJson",
+  );
+  return response;
+}
+
+ChaChaEncryptionResult _gzipAndEncryptJsonSync(
+  Map<String, dynamic> args,
+) {
+  return gzipAndEncryptJsonSync(args["jsonData"], args["key"]);
+}