MISC: Support importing Steam Cloud save file manually (#2583)

electron/saveDataBinaryFormat.js

@@ -1,13 +1,68 @@
 // The 2 magic bytes of the gzip header plus the mandatory compression type of DEFLATE
-const magicBytes = [0x1f, 0x8b, 0x08];
+const magicBytesOfDeflateGzip = new Uint8Array([0x1f, 0x8b, 0x08]);
+// Base64-encoded string of magicBytesOfDeflateGzip
+const base64EncodingOfMagicBytes = encodeBytesToBase64String(magicBytesOfDeflateGzip);
+// Convert the base64-encoded string to a byte array
+const byteArrayOfBase64EncodingOfMagicBytes = Uint8Array.from(base64EncodingOfMagicBytes, (c) => c.charCodeAt(0));
 
+/**
+ * @param {Uint8Array} bytes
+ * @returns {string}
+ */
+function encodeBytesToBase64String(bytes) {
+  let binaryString = "";
+  for (let i = 0; i < bytes.length; i++) {
+    binaryString += String.fromCharCode(bytes[i]);
+  }
+  return btoa(binaryString);
+}
+
+/**
+ * @param {Uint8Array} bytes
+ * @returns {Uint8Array}
+ */
+function decodeBase64BytesToBytes(bytes) {
+  let base64String = "";
+  for (let i = 0; i < bytes.length; i++) {
+    base64String += String.fromCharCode(bytes[i]);
+  }
+  const decodedBinaryString = atob(base64String);
+  const result = new Uint8Array(decodedBinaryString.length);
+  for (let i = 0; i < decodedBinaryString.length; i++) {
+    result[i] = decodedBinaryString.charCodeAt(i);
+  }
+  return result;
+}
+
+/**
+ * @param {string | Uint8Array} rawData
+ * @returns {boolean}
+ */
 function isBinaryFormat(rawData) {
-  for (let i = 0; i < magicBytes.length; ++i) {
-    if (magicBytes[i] !== rawData[i]) {
+  for (let i = 0; i < magicBytesOfDeflateGzip.length; ++i) {
+    if (magicBytesOfDeflateGzip[i] !== rawData[i]) {
       return false;
     }
   }
   return true;
 }
 
-module.exports = { isBinaryFormat };
+/**
+ * The Steam Cloud save file is a base64-encoded gz file.
+ *
+ * @param {string | Uint8Array} rawData
+ * @returns {boolean}
+ */
+function isSteamCloudFormat(rawData) {
+  if (typeof rawData === "string") {
+    return rawData.startsWith(base64EncodingOfMagicBytes);
+  }
+  for (let i = 0; i < byteArrayOfBase64EncodingOfMagicBytes.length; ++i) {
+    if (byteArrayOfBase64EncodingOfMagicBytes[i] !== rawData[i]) {
+      return false;
+    }
+  }
+  return true;
+}
+
+module.exports = { encodeBytesToBase64String, decodeBase64BytesToBytes, isBinaryFormat, isSteamCloudFormat };