MISC: Support compression of save data (#1162)

* Use Compression Streams API instead of jszip or other libraries.
* Remove usage of base64 in the new binary format.
* Do not convert binary data to string and back. The type of save data is SaveData, it's either string (old base64 format) or Uint8Array (new binary format).
* Proper support for interacting with electron-related code. Electron-related code assumes that save data is in the base64 format.
* Proper support for other tools (DevMenu, pretty-save.js). Full support for DevMenu will be added in a follow-up PR. Check the comments in src\DevMenu\ui\SaveFileDev.tsx for details.

src/utils/SaveDataUtils.ts

@@ -0,0 +1,59 @@
+import { SaveData } from "../types";
+
+export abstract class SaveDataError extends Error {
+  constructor(message: string) {
+    super(message);
+    this.name = this.constructor.name;
+  }
+}
+
+export class UnsupportedSaveData extends SaveDataError {}
+
+export class InvalidSaveData extends SaveDataError {}
+
+export function canUseBinaryFormat(): boolean {
+  return "CompressionStream" in globalThis;
+}
+
+async function compress(dataString: string): Promise<Uint8Array> {
+  const compressedReadableStream = new Blob([dataString]).stream().pipeThrough(new CompressionStream("gzip"));
+  return new Uint8Array(await new Response(compressedReadableStream).arrayBuffer());
+}
+
+async function decompress(binaryData: Uint8Array): Promise<string> {
+  const decompressedReadableStream = new Blob([binaryData]).stream().pipeThrough(new DecompressionStream("gzip"));
+  const reader = decompressedReadableStream.pipeThrough(new TextDecoderStream("utf-8", { fatal: true })).getReader();
+  let result = "";
+  try {
+    for (let { value, done } = await reader.read(); !done; { value, done } = await reader.read()) {
+      result += value;
+    }
+  } catch (error) {
+    throw new InvalidSaveData(String(error));
+  }
+  return result;
+}
+
+export async function encodeJsonSaveString(jsonSaveString: string): Promise<SaveData> {
+  // Fallback to the base64 format if player's browser does not support Compression Streams API.
+  if (canUseBinaryFormat()) {
+    return await compress(jsonSaveString);
+  } else {
+    // The unescape(encodeURIComponent()) pair encodes jsonSaveString into a "binary string" suitable for btoa, despite
+    // seeming like a no-op at first glance.
+    // Ref: https://stackoverflow.com/a/57713220
+    return btoa(unescape(encodeURIComponent(jsonSaveString)));
+  }
+}
+
+/** Return json save string */
+export async function decodeSaveData(saveData: SaveData): Promise<string> {
+  if (saveData instanceof Uint8Array) {
+    if (!canUseBinaryFormat()) {
+      throw new UnsupportedSaveData("Your browser does not support Compression Streams API");
+    }
+    return await decompress(saveData);
+  } else {
+    return decodeURIComponent(escape(atob(saveData)));
+  }
+}