decompress .json.zstd fetched by getSaveData

src/services/SaveParserBackendService.ts

@@ -3,6 +3,7 @@ import type { SaveUploadConfig } from '@/config/AppConfig'
 import { GameEnum } from '@/config/games'
 import { packSaveForUpload, StageCallback } from '@/lib/saveArchive/client'
 import { OriginalFileType } from '@/lib/saveArchive/messages'
+import { createZstdDecompressStream } from '@/lib/saveArchive/zstdStream'
 
 export interface UploadSaveResponse {
     id: string
@@ -86,7 +87,12 @@ export class SaveParserBackendService {
         return await response.json()
     }
 
-    // Fetches the fully parsed data for a save once its parsing is done.
+    /**
+     * Fetches the fully parsed data for a save once its parsing is done.
+     *
+     * The backend stores and serves that data as zstd compressed json, so the
+     * body is decompressed on the way in rather than read as text first.
+     */
     async getSaveData(id: string): Promise<Record<string, unknown>> {
         const url = `${this.API_BASE}/getSaveData?id=${encodeURIComponent(id)}`
         const response = await fetch(url)
@@ -97,8 +103,16 @@ export class SaveParserBackendService {
                     (await getBodyTextOrEmpty(response))
             )
         }
+        // A body is only missing on a response that cannot carry one, which a
+        // successful getSaveData never is.
+        if (!response.body) {
+            throw new Error('Failed to get parsed save: response has no body')
+        }
 
-        return await response.json()
+        // Decompresses as the bytes arrive, so the compressed json is never
+        // held whole; only the parsed object stays in memory.
+        const json = response.body.pipeThrough(createZstdDecompressStream())
+        return await new Response(json).json()
     }
 
     /**