perf(browser): reuse decoded single-chunk upload buffers (#18960)

src/main/browser/browser-client-upload-transfer.test.ts

@@ -1,4 +1,4 @@
-import { describe, expect, it } from 'vitest'
+import { describe, expect, it, vi } from 'vitest'
 
 import type { BrowserClientHostCommandEvent } from '../../shared/browser-client-host-protocol'
 import {
@@ -102,3 +102,38 @@ describe('readBrowserClientUploadPaths', () => {
     )
   })
 })
+
+it.each([0, 1, 128 * 1024])(
+  'avoids recopying 16 single-chunk uploads of %i bytes',
+  async (size) => {
+    const source = Buffer.alloc(size, 171)
+    const response = {
+      contentBase64: source.toString('base64'),
+      bytesRead: size,
+      totalBytes: size,
+      eof: true
+    }
+    const remotePaths = Array.from({ length: 16 }, (_, i) => `file-${i}.bin`)
+    const request = vi.fn(async () => response)
+    const concat = vi.spyOn(Buffer, 'concat')
+    let copies = 0
+    let files: Awaited<ReturnType<typeof fetchBrowserClientUploadFiles>>
+    try {
+      files = await fetchBrowserClientUploadFiles({ request, event, remotePaths })
+      copies = concat.mock.calls.length
+    } finally {
+      concat.mockRestore()
+    }
+    expect(copies).toBe(0)
+    expect(request).toHaveBeenCalledTimes(16)
+    expect(files.map((file) => file.remotePath)).toEqual(remotePaths)
+    for (const file of files) {
+      expect(file.contents).toEqual(source)
+    }
+    if (size > 0) {
+      files[0].contents[0] = 0
+      expect(files[1].contents[0]).toBe(171)
+      expect(source[0]).toBe(171)
+    }
+  }
+)

src/main/browser/browser-client-upload-transfer.ts

@@ -74,7 +74,7 @@ export async function fetchBrowserClientUploadFiles(options: {
         throw new Error('browser_client_upload_transfer_stalled')
       }
     }
-    files.push({ remotePath, contents: Buffer.concat(chunks) })
+    files.push({ remotePath, contents: chunks.length === 1 ? chunks[0] : Buffer.concat(chunks) })
   }
   return files
 }