fix(fetch): align Blob snapshot semantics

CHANGELOG.md

@@ -2,6 +2,8 @@
 
 - Added `Body.size` for exposing known body byte lengths without consuming the
   body.
+- Fixed `Blob` byte snapshot semantics so byte-backed parts and read buffers are
+  copied consistently across native, `dart:io`, and js wrappers.
 
 ## 0.5.0
 

lib/src/fetch/blob.js.dart

@@ -1,3 +1,5 @@
+import 'dart:typed_data';
+
 import 'package:block/block.dart' as block;
 import 'package:web/web.dart' as web;
 
@@ -25,10 +27,17 @@ class Blob extends native.Blob implements block.Block {
 
   static Object _normalizePart(native.BlobPart part) {
     return switch (part) {
-      final Blob blob => blob,
-      final native.Blob blob => blob,
+      final ByteBuffer buffer => Uint8List.fromList(buffer.asUint8List()),
+      final ByteData data => Uint8List.fromList(
+        data.buffer.asUint8List(data.offsetInBytes, data.lengthInBytes),
+      ),
+      final Uint8List bytes => Uint8List.fromList(bytes),
+      final List<int> bytes => Uint8List.fromList(bytes),
+      final String text => text,
+      final Blob blob => native.blobBacking(blob),
+      final native.Blob blob => native.blobBacking(blob),
       final web.Blob blob => blob,
-      _ => native.Blob([part]),
+      _ => native.blobBacking(native.Blob([part])),
     };
   }
 }

lib/src/fetch/blob.native.dart

@@ -41,10 +41,12 @@ class Blob implements block.Block {
   @override
   int get size => _host.size;
 
-  Future<Uint8List> bytes() => _host.arrayBuffer();
+  Future<Uint8List> bytes() => arrayBuffer();
 
   @override
-  Future<Uint8List> arrayBuffer() => _host.arrayBuffer();
+  Future<Uint8List> arrayBuffer() async {
+    return Uint8List.fromList(await _host.arrayBuffer());
+  }
 
   @override
   Future<String> text() => _host.text();
@@ -55,7 +57,13 @@ class Blob implements block.Block {
       throw ArgumentError.value(chunkSize, 'chunkSize', 'Must be > 0');
     }
 
-    return _host.stream(chunkSize: chunkSize);
+    return _stream(chunkSize);
+  }
+
+  Stream<Uint8List> _stream(int chunkSize) async* {
+    await for (final chunk in _host.stream(chunkSize: chunkSize)) {
+      yield Uint8List.fromList(chunk);
+    }
   }
 
   @override
@@ -74,8 +82,8 @@ class Blob implements block.Block {
     return switch (part) {
       final Blob blob => blob._host,
       final block.Block blockPart => blockPart,
-      final ByteBuffer buffer => ByteData.sublistView(buffer.asUint8List()),
-      final ByteData data => ByteData.sublistView(
+      final ByteBuffer buffer => Uint8List.fromList(buffer.asUint8List()),
+      final ByteData data => Uint8List.fromList(
         data.buffer.asUint8List(data.offsetInBytes, data.lengthInBytes),
       ),
       final Uint8List bytes => Uint8List.fromList(bytes),
@@ -90,6 +98,12 @@ class Blob implements block.Block {
   }
 }
 
+/// Returns the backing block for Blob-part normalization.
+///
+/// Platform wrappers use this to preserve Blob byte-sequence semantics without
+/// calling overridable read methods on Blob subclasses.
+block.Block blobBacking(Blob blob) => blob._host;
+
 /// Normalizes Blob/File MIME type inputs using the File API rules.
 String normalizeBlobType(String type) {
   StringBuffer? buffer;

test/blob_test.dart

@@ -0,0 +1,103 @@
+import 'dart:convert';
+import 'dart:typed_data';
+
+import 'package:ht/src/fetch/blob.dart' as platform_blob;
+import 'package:test/test.dart';
+
+void main() {
+  group('Blob', () {
+    test('snapshots byte parts at construction', () async {
+      final typedBytes = Uint8List.fromList(utf8.encode('ab'));
+      final bufferBytes = Uint8List.fromList(utf8.encode('cd'));
+      final dataBytes = Uint8List.fromList(utf8.encode('-ef-'));
+      final data = ByteData.sublistView(dataBytes, 1, 3);
+      final listBytes = <int>[...utf8.encode('gh')];
+
+      final blob = platform_blob.Blob(<platform_blob.BlobPart>[
+        typedBytes,
+        bufferBytes.buffer,
+        data,
+        listBytes,
+      ]);
+
+      typedBytes[0] = 'x'.codeUnitAt(0);
+      bufferBytes[0] = 'y'.codeUnitAt(0);
+      dataBytes[1] = 'z'.codeUnitAt(0);
+      listBytes[0] = 'w'.codeUnitAt(0);
+
+      expect(await blob.text(), 'abcdefgh');
+
+      final singleBufferBytes = Uint8List.fromList(utf8.encode('ij'));
+      final singleBufferBlob = platform_blob.Blob(<platform_blob.BlobPart>[
+        singleBufferBytes.buffer,
+      ]);
+      singleBufferBytes[0] = 'x'.codeUnitAt(0);
+      expect(await singleBufferBlob.text(), 'ij');
+
+      final singleDataBytes = Uint8List.fromList(utf8.encode('-kl-'));
+      final singleDataBlob = platform_blob.Blob(<platform_blob.BlobPart>[
+        ByteData.sublistView(singleDataBytes, 1, 3),
+      ]);
+      singleDataBytes[1] = 'y'.codeUnitAt(0);
+      expect(await singleDataBlob.text(), 'kl');
+    });
+
+    test('arrayBuffer and bytes return defensive copies', () async {
+      final blob = platform_blob.Blob(<platform_blob.BlobPart>[
+        Uint8List.fromList(utf8.encode('abc')),
+      ]);
+
+      final buffer = await blob.arrayBuffer();
+      buffer[0] = 'x'.codeUnitAt(0);
+
+      expect(await blob.text(), 'abc');
+
+      final bytes = await blob.bytes();
+      bytes[1] = 'y'.codeUnitAt(0);
+
+      expect(await blob.text(), 'abc');
+    });
+
+    test('stream chunks do not expose mutable backing', () async {
+      final blob = platform_blob.Blob(<platform_blob.BlobPart>[
+        Uint8List.fromList(utf8.encode('abcd')),
+      ]);
+
+      expect(() => blob.stream(chunkSize: 0), throwsArgumentError);
+
+      final chunks = await blob.stream(chunkSize: 2).toList();
+      chunks.first[0] = 'x'.codeUnitAt(0);
+
+      expect(await blob.text(), 'abcd');
+      expect(
+        await blob.stream(chunkSize: 2).map(utf8.decode).toList(),
+        <String>['ab', 'cd'],
+      );
+    });
+
+    test('Blob parts use Blob backing instead of read overrides', () async {
+      final blob = platform_blob.Blob(<platform_blob.BlobPart>[
+        _ReadOverridingBlob(),
+      ]);
+
+      expect(await blob.text(), 'base');
+    });
+  });
+}
+
+class _ReadOverridingBlob extends platform_blob.Blob {
+  _ReadOverridingBlob() : super(<platform_blob.BlobPart>['base'], 'text/plain');
+
+  @override
+  Future<Uint8List> arrayBuffer() async {
+    return Uint8List.fromList(utf8.encode('override'));
+  }
+
+  @override
+  Stream<Uint8List> stream({int chunkSize = 16 * 1024}) {
+    return Stream<Uint8List>.value(Uint8List.fromList(utf8.encode('override')));
+  }
+
+  @override
+  Future<String> text() async => 'override';
+}