Fix theme file size calculation to improve upload batching reliability

Author: EvilGenius13

.changeset/short-owls-drop.md

@@ -0,0 +1,5 @@
+---
+'@shopify/theme': patch
+---
+
+Fix theme file size calculation to improve upload batching reliability

packages/theme/src/cli/utilities/theme-uploader.test.ts

@@ -437,6 +437,17 @@ describe('theme-uploader', () => {
   })
 
   test('should create batches for files when bulk upload request size limit is reached', async () => {
+    const originalByteLength = Buffer.byteLength
+    const byteLengthSpy = vi.spyOn(Buffer, 'byteLength')
+
+    // Mock the byte length to return the max batch bytesize
+    byteLengthSpy.mockImplementation((value: any, encoding?: BufferEncoding) => {
+      if (typeof value === 'string' && value === 'some_settings_data') {
+        return MAX_BATCH_BYTESIZE
+      }
+      return originalByteLength(value, encoding)
+    })
+
     // Given
     const remoteChecksums: Checksum[] = []
     const themeFileSystem = fakeThemeFileSystem(
@@ -448,7 +459,6 @@ describe('theme-uploader', () => {
             key: 'config/settings_data.json',
             checksum: '2',
             value: 'some_settings_data',
-            stats: {size: MAX_BATCH_BYTESIZE, mtime: 0},
           },
         ],
         ['config/settings_schema.json', {key: 'config/settings_schema.json', checksum: '3', value: 'settings_schema'}],
@@ -467,6 +477,8 @@ describe('theme-uploader', () => {
 
     // Then
     expect(bulkUploadThemeAssets).toHaveBeenCalledTimes(3)
+
+    byteLengthSpy.mockRestore()
   })
 
   test('should retry failed uploads', async () => {

packages/theme/src/cli/utilities/theme-uploader.ts

@@ -357,10 +357,14 @@ function calculateLocalChecksums(localThemeFileSystem: ThemeFileSystem): Checksu
   const checksums: ChecksumWithSize[] = []
 
   localThemeFileSystem.files.forEach((file, key) => {
+    // Text files: use UTF-8 byte count
+    // Binary files: use base64 length
+    const size = file.value ? Buffer.byteLength(file.value, 'utf8') : file.attachment?.length ?? 0
+
     checksums.push({
       key,
       checksum: file.checksum,
-      size: file.stats?.size ?? 0,
+      size,
     })
   })