diff --git a/pkg/_fe_analyzer_shared/lib/src/scanner/io.dart b/pkg/_fe_analyzer_shared/lib/src/scanner/io.dart
index f51fbd6069e..6269939a250 100644
--- a/pkg/_fe_analyzer_shared/lib/src/scanner/io.dart
+++ b/pkg/_fe_analyzer_shared/lib/src/scanner/io.dart
@@ -4,38 +4,14 @@
 
 library _fe_analyzer_shared.scanner.io;
 
-import 'dart:io' show File, RandomAccessFile;
+import 'dart:io' show File;
 
 import 'dart:typed_data' show Uint8List;
 
 Uint8List readBytesFromFileSync(Uri uri) {
-  RandomAccessFile file = new File.fromUri(uri).openSync();
-  Uint8List list;
-  try {
-    int length = file.lengthSync();
-    // +1 to have a 0 terminated list, see [Scanner].
-    list = new Uint8List(length + 1);
-    file.readIntoSync(list, /* start = */ 0, length);
-  } finally {
-    file.closeSync();
-  }
-  return list;
+  return new File.fromUri(uri).readAsBytesSync();
 }
 
-Future<Uint8List> readBytesFromFile(Uri uri,
-    {bool ensureZeroTermination = true}) async {
-  RandomAccessFile file = await new File.fromUri(uri).open();
-  Uint8List list;
-  try {
-    int length = await file.length();
-    // +1 to have a 0 terminated list, see [Scanner].
-    list = new Uint8List(ensureZeroTermination ? length + 1 : length);
-    int read = await file.readInto(list);
-    if (read != length) {
-      throw "Error reading file: ${uri}";
-    }
-  } finally {
-    await file.close();
-  }
-  return list;
+Future<Uint8List> readBytesFromFile(Uri uri) async {
+  return await new File.fromUri(uri).readAsBytes();
 }
diff --git a/pkg/_fe_analyzer_shared/lib/src/scanner/scanner.dart b/pkg/_fe_analyzer_shared/lib/src/scanner/scanner.dart
index f76528d47ed..7cb27907b3b 100644
--- a/pkg/_fe_analyzer_shared/lib/src/scanner/scanner.dart
+++ b/pkg/_fe_analyzer_shared/lib/src/scanner/scanner.dart
@@ -73,9 +73,6 @@ ScannerResult scan(Uint8List bytes,
     bool includeComments = false,
     LanguageVersionChanged? languageVersionChanged,
     bool allowLazyStrings = true}) {
-  if (bytes.last != 0) {
-    throw new ArgumentError("[bytes]: the last byte must be 0.");
-  }
   Scanner scanner = new Utf8BytesScanner(bytes,
       configuration: configuration,
       includeComments: includeComments,
diff --git a/pkg/_fe_analyzer_shared/lib/src/scanner/string_scanner.dart b/pkg/_fe_analyzer_shared/lib/src/scanner/string_scanner.dart
index 14b2e4b522b..366d5a3ca6f 100644
--- a/pkg/_fe_analyzer_shared/lib/src/scanner/string_scanner.dart
+++ b/pkg/_fe_analyzer_shared/lib/src/scanner/string_scanner.dart
@@ -139,8 +139,10 @@ class StringScanner extends AbstractScanner {
   }
 
   @override
-  // To preserve old behavior we only return true once advance has been out of
-  // bounds. This should probably change. It's at least used in tests
-  // (where the eof token has its offset reduced by one to 'fix' this.)
+  // This class used to enforce zero-terminated input, so we only return true
+  // once advance has been out of bounds.
+  // TODO(jensj): This should probably change.
+  // It's at least used in tests (where the eof token has its offset reduced
+  // by one to 'fix' this.)
   bool atEndOfFile() => scanOffset > _stringLengthMinusOne;
 }
diff --git a/pkg/_fe_analyzer_shared/lib/src/scanner/utf8_bytes_scanner.dart b/pkg/_fe_analyzer_shared/lib/src/scanner/utf8_bytes_scanner.dart
index 7ea5cc8047a..f842eaa1d03 100644
--- a/pkg/_fe_analyzer_shared/lib/src/scanner/utf8_bytes_scanner.dart
+++ b/pkg/_fe_analyzer_shared/lib/src/scanner/utf8_bytes_scanner.dart
@@ -33,11 +33,7 @@ import 'token_impl.dart'
  * that points to substrings.
  */
 class Utf8BytesScanner extends AbstractScanner {
-  /**
-   * The file content.
-   *
-   * The content is zero-terminated.
-   */
+  /// The raw file content.
   final Uint8List _bytes;
   final int _bytesLengthMinusOne;
 
@@ -86,15 +82,6 @@ class Utf8BytesScanner extends AbstractScanner {
    */
   int utf8Slack = 0;
 
-  /**
-   * Creates a new Utf8BytesScanner. The source file is expected to be a
-   * [Utf8BytesSourceFile] that holds a list of UTF-8 bytes. Otherwise the
-   * string text of the source file is decoded.
-   *
-   * The list of UTF-8 bytes [file.slowUtf8Bytes()] is expected to return an
-   * array whose last element is '0' to signal the end of the file. If this
-   * is not the case, the entire array is copied before scanning.
-   */
   Utf8BytesScanner(this._bytes,
       {ScannerConfiguration? configuration,
       bool includeComments = false,
@@ -104,7 +91,6 @@ class Utf8BytesScanner extends AbstractScanner {
         super(configuration, includeComments, languageVersionChanged,
             numberOfBytesHint: _bytes.length,
             allowLazyStrings: allowLazyStrings) {
-    assert(_bytes.last == 0);
     // Skip a leading BOM.
     if (containsBomAt(/* offset = */ 0)) {
       byteOffset += 3;
@@ -168,10 +154,11 @@ class Utf8BytesScanner extends AbstractScanner {
     } else {
       expectedHighBytes = 1; // Bad code unit.
     }
-    // TODO(jensj): Don't we need a bounds check here? Can't I crash this?
     int numBytes = 0;
     for (int i = 0; i < expectedHighBytes; i++) {
-      if (_bytes[byteOffset + i] < 0x80) {
+      int next = byteOffset + i;
+      if (next > _bytesLengthMinusOne) break;
+      if (_bytes[next] < 0x80) {
         break;
       }
       numBytes++;
@@ -300,5 +287,10 @@ class Utf8BytesScanner extends AbstractScanner {
   }
 
   @override
-  bool atEndOfFile() => byteOffset >= _bytesLengthMinusOne;
+  // This class used to require zero-terminated input, so we only return true
+  // once advance has been out of bounds.
+  // TODO(jensj): This should probably change.
+  // It's at least used in tests (where the eof token has its offset reduced
+  // by one to 'fix' this.)
+  bool atEndOfFile() => byteOffset > _bytesLengthMinusOne;
 }
diff --git a/pkg/_fe_analyzer_shared/test/scanner_benchmark.dart b/pkg/_fe_analyzer_shared/test/scanner_benchmark.dart
index d1102dc18af..6c39cb60daf 100644
--- a/pkg/_fe_analyzer_shared/test/scanner_benchmark.dart
+++ b/pkg/_fe_analyzer_shared/test/scanner_benchmark.dart
@@ -20,8 +20,6 @@ void main(List<String> args) {
       scanType = ScanType.string;
     } else if (arg == "--bytes") {
       scanType = ScanType.bytes;
-    } else if (arg == "--bytes0") {
-      scanType = ScanType.bytesWith0Byte;
     } else if (arg == "--stringtobytes") {
       scanType = ScanType.stringAsBytes;
     } else if (arg == "--count") {
@@ -41,8 +39,6 @@ void main(List<String> args) {
   String content = f.readAsStringSync();
   String contentZeroTerminated = content + '\x00';
   Uint8List contentBytes = f.readAsBytesSync();
-  Uint8List zeroTerminatedBytes = new Uint8List(contentBytes.length + 1);
-  zeroTerminatedBytes.setRange(0, contentBytes.length, contentBytes);
 
   int numErrors = 0;
   Stopwatch stopwatch = new Stopwatch()..start();
@@ -68,22 +64,7 @@ void main(List<String> args) {
       lengthProcessed = contentBytes.length;
       for (int i = 0; i < iterations; i++) {
         hasErrors = scan(
-          zeroTerminatedBytes,
-          configuration: new ScannerConfiguration(
-            enableExtensionMethods: true,
-            enableNonNullable: true,
-            enableTripleShift: true,
-          ),
-          includeComments: true,
-        ).hasErrors;
-      }
-    case ScanType.bytesWith0Byte:
-      lengthProcessed = contentBytes.length;
-      for (int i = 0; i < iterations; i++) {
-        Uint8List tmp = new Uint8List(contentBytes.length + 1);
-        tmp.setRange(0, contentBytes.length, contentBytes);
-        hasErrors = scan(
-          tmp,
+          contentBytes,
           configuration: new ScannerConfiguration(
             enableExtensionMethods: true,
             enableNonNullable: true,
@@ -134,7 +115,6 @@ void main(List<String> args) {
 enum ScanType {
   string("string characters"),
   bytes("bytes"),
-  bytesWith0Byte("bytes"),
   stringAsBytes("string characters as bytes"),
   countLfs("bytes");
 
diff --git a/pkg/build_integration/lib/file_system/multi_root.dart b/pkg/build_integration/lib/file_system/multi_root.dart
index 7b8a0488288..494f6efb2d2 100644
--- a/pkg/build_integration/lib/file_system/multi_root.dart
+++ b/pkg/build_integration/lib/file_system/multi_root.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:typed_data';
 
 // ignore: implementation_imports
 import 'package:front_end/src/api_unstable/build_integration.dart';
@@ -81,7 +82,7 @@ class MultiRootFileSystemEntity implements FileSystemEntity {
       (await delegate).existsAsyncIfPossible();
 
   @override
-  Future<List<int>> readAsBytes() async => (await delegate).readAsBytes();
+  Future<Uint8List> readAsBytes() async => (await delegate).readAsBytes();
 
   @override
   Future<List<int>> readAsBytesAsyncIfPossible() async =>
@@ -104,7 +105,7 @@ class MissingFileSystemEntity implements FileSystemEntity {
   Future<bool> existsAsyncIfPossible() => exists();
 
   @override
-  Future<List<int>> readAsBytes() =>
+  Future<Uint8List> readAsBytes() =>
       Future.error(FileSystemException(uri, 'File not found'));
 
   @override
diff --git a/pkg/build_integration/lib/file_system/single_root.dart b/pkg/build_integration/lib/file_system/single_root.dart
index bf3d17c1d7f..8c49c71d461 100644
--- a/pkg/build_integration/lib/file_system/single_root.dart
+++ b/pkg/build_integration/lib/file_system/single_root.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:typed_data';
+
 // ignore: implementation_imports
 import 'package:front_end/src/api_unstable/build_integration.dart';
 
@@ -68,7 +70,7 @@ class SingleRootFileSystemEntity implements FileSystemEntity {
       delegate.existsAsyncIfPossible();
 
   @override
-  Future<List<int>> readAsBytes() async => delegate.readAsBytes();
+  Future<Uint8List> readAsBytes() async => delegate.readAsBytes();
 
   @override
   Future<List<int>> readAsBytesAsyncIfPossible() async =>
diff --git a/pkg/compiler/lib/compiler_api.dart b/pkg/compiler/lib/compiler_api.dart
index bb05db919ad..2aea0939507 100644
--- a/pkg/compiler/lib/compiler_api.dart
+++ b/pkg/compiler/lib/compiler_api.dart
@@ -5,6 +5,7 @@
 library compiler;
 
 import 'dart:async';
+import 'dart:typed_data';
 
 import 'package:front_end/src/api_unstable/dart2js.dart' as fe;
 
@@ -107,11 +108,11 @@ abstract class CompilerInput {
   /// zero-terminated list of encoded bytes. If the input kind is
   /// `InputKind.binary` the resulting list is the raw bytes from the input
   /// source.
-  Future<Input<List<int>>> readFromUri(Uri uri,
+  Future<Input<Uint8List>> readFromUri(Uri uri,
       {InputKind inputKind = InputKind.UTF8});
 
   /// Register that [uri] should be an `InputKind.UTF8` input with the
-  /// given [source] as its zero-terminated list of contents.
+  /// given [source] of contents.
   ///
   /// If [uri] was read prior to this call, this registration has no effect,
   /// otherwise it is expected that a future [readFromUri] will return the
@@ -122,7 +123,7 @@ abstract class CompilerInput {
   /// of source files that may not be available on disk. By using these
   /// registered contents, dart2js will be able to provide accurate line/column
   /// information on an error.
-  void registerUtf8ContentsForDiagnostics(Uri uri, List<int> source);
+  void registerUtf8ContentsForDiagnostics(Uri uri, Uint8List source);
 }
 
 /// Output types used in `CompilerOutput.createOutputSink`.
diff --git a/pkg/compiler/lib/src/compiler.dart b/pkg/compiler/lib/src/compiler.dart
index 322932c63a6..898af4026a4 100644
--- a/pkg/compiler/lib/src/compiler.dart
+++ b/pkg/compiler/lib/src/compiler.dart
@@ -6,6 +6,7 @@ library dart2js.compiler_base;
 
 import 'dart:async' show Future;
 import 'dart:convert' show jsonEncode;
+import 'dart:typed_data';
 
 import 'package:compiler/src/universe/use.dart' show StaticUse;
 import 'package:front_end/src/api_unstable/dart2js.dart' as fe;
@@ -836,7 +837,7 @@ class Compiler {
     }
   }
 
-  Future<api.Input<List<int>>> callUserProvider(
+  Future<api.Input<Uint8List>> callUserProvider(
       Uri uri, api.InputKind inputKind) {
     try {
       return userProviderTask
diff --git a/pkg/compiler/lib/src/io/location_provider.dart b/pkg/compiler/lib/src/io/location_provider.dart
index 0f5f501c670..1efb0f56435 100644
--- a/pkg/compiler/lib/src/io/location_provider.dart
+++ b/pkg/compiler/lib/src/io/location_provider.dart
@@ -40,7 +40,7 @@ class LocationCollector extends CodeOutputListener implements LocationProvider {
   @override
   Location getLocation(int offset) {
     RangeError.checkValueInInterval(offset, 0, length, 'offset');
-    return Source(lineStarts, const <int>[], null, null)
+    return Source.emptySource(lineStarts, null, null)
         .getLocation(_dummyFile, offset);
   }
 
diff --git a/pkg/compiler/lib/src/io/mapped_file.dart b/pkg/compiler/lib/src/io/mapped_file.dart
index 8369871ca60..dc5f3a27f9d 100644
--- a/pkg/compiler/lib/src/io/mapped_file.dart
+++ b/pkg/compiler/lib/src/io/mapped_file.dart
@@ -11,34 +11,24 @@ import 'dart:typed_data';
 import 'package:compiler/src/source_file_provider.dart';
 import 'package:mmap/mmap.dart';
 
-Uint8List viewOfFile(String filename, bool zeroTerminated) {
+Uint8List viewOfFile(String filename) {
   final mappedFile = mmapFile(filename);
-  if (!zeroTerminated) {
-    return mappedFile.fileBytes;
-  }
-  if (mappedFile.hasZeroPadding) {
-    return mappedFile.fileBytesZeroTerminated;
-  }
-  // In the rare case we need a zero-terminated list and the file size
-  // is exactly page-aligned we need to allocate a new list with extra
-  // room for the terminating 0.
-  return Uint8List(mappedFile.fileLength + 1)
-    ..setRange(0, mappedFile.fileLength, mappedFile.fileBytes);
+  return mappedFile.fileBytes;
 }
 
 class MemoryMapSourceFileByteReader implements SourceFileByteReader {
   const MemoryMapSourceFileByteReader();
 
   @override
-  Uint8List getBytes(String filename, {bool zeroTerminated = true}) {
+  Uint8List getBytes(String filename) {
     if (supportsMMap) {
       try {
-        return viewOfFile(filename, zeroTerminated);
+        return viewOfFile(filename);
       } catch (e) {
-        return readAll(filename, zeroTerminated: zeroTerminated);
+        return readAll(filename);
       }
     } else {
-      return readAll(filename, zeroTerminated: zeroTerminated);
+      return readAll(filename);
     }
   }
 }
diff --git a/pkg/compiler/lib/src/io/source_file.dart b/pkg/compiler/lib/src/io/source_file.dart
index 5b03592c76b..48a51872e4b 100644
--- a/pkg/compiler/lib/src/io/source_file.dart
+++ b/pkg/compiler/lib/src/io/source_file.dart
@@ -15,7 +15,7 @@ import '../../compiler_api.dart' as api show Input, InputKind;
 
 /// Represents a file of source code. The content can be either a [String] or
 /// a UTF-8 encoded [List<int>] of bytes.
-abstract class SourceFile implements api.Input<List<int>>, LocationProvider {
+abstract class SourceFile implements api.Input<Uint8List>, LocationProvider {
   /// The absolute URI of the source file.
   @override
   Uri get uri;
@@ -28,11 +28,8 @@ abstract class SourceFile implements api.Input<List<int>>, LocationProvider {
   kernel.Source get kernelSource {
     // TODO(johnniwinther): Instead of creating a new Source object,
     // we should use the one provided by the front-end.
-    return _cachedKernelSource ??= kernel.Source(
-        lineStarts,
-        slowUtf8ZeroTerminatedBytes(),
-        uri /* TODO(jensj): What is the import URI? */,
-        uri)
+    return _cachedKernelSource ??= kernel.Source(lineStarts, utf8Bytes(),
+        uri /* TODO(jensj): What is the import URI? */, uri)
       ..cachedText = slowText();
   }
 
@@ -44,9 +41,8 @@ abstract class SourceFile implements api.Input<List<int>>, LocationProvider {
   /// The text content of the file represented as a String
   String slowText();
 
-  /// The content of the file represented as a UTF-8 encoded [List<int>],
-  /// terminated with a trailing 0 byte.
-  List<int> slowUtf8ZeroTerminatedBytes();
+  /// The content of the file represented as a UTF-8 encoded [Uint8List].
+  Uint8List utf8Bytes();
 
   /// The length of the string representation of this source file, i.e.,
   /// equivalent to [:slowText().length:], but faster.
@@ -169,40 +165,26 @@ abstract class SourceFile implements api.Input<List<int>>, LocationProvider {
   int get lines => lineStarts.length - 1;
 }
 
-List<int> _zeroTerminateIfNecessary(List<int> bytes) {
-  if (bytes.length > 0 && bytes.last == 0) return bytes;
-  List<int> result = Uint8List(bytes.length + 1);
-  result.setRange(0, bytes.length, bytes);
-  result[result.length - 1] = 0;
-  return result;
-}
-
 class Utf8BytesSourceFile extends SourceFile {
   @override
   final Uri uri;
 
   /// The UTF-8 encoded content of the source file.
-  final List<int> zeroTerminatedContent;
+  final Uint8List content;
 
   /// Creates a Utf8BytesSourceFile.
-  ///
-  /// If possible, the given [content] should be zero-terminated. If it isn't,
-  /// the constructor clones the content and adds a trailing 0.
-  Utf8BytesSourceFile(this.uri, List<int> content)
-      : this.zeroTerminatedContent = _zeroTerminateIfNecessary(content);
+  Utf8BytesSourceFile(this.uri, this.content) : assert(content.last != 0);
 
   @override
-  List<int> get data => zeroTerminatedContent;
+  Uint8List get data => content;
 
   @override
   String slowText() {
-    // Don't convert the trailing zero byte.
-    return utf8.decoder
-        .convert(zeroTerminatedContent, 0, zeroTerminatedContent.length - 1);
+    return utf8.decoder.convert(content);
   }
 
   @override
-  List<int> slowUtf8ZeroTerminatedBytes() => zeroTerminatedContent;
+  Uint8List utf8Bytes() => content;
 
   @override
   String slowSubstring(int start, int end) {
@@ -244,7 +226,7 @@ class StringSourceFile extends SourceFile {
       : this(Uri(path: filename), filename, text);
 
   @override
-  List<int> get data => utf8.encode(text);
+  Uint8List get data => utf8.encode(text);
 
   @override
   int get length => text.length;
@@ -255,8 +237,8 @@ class StringSourceFile extends SourceFile {
   String slowText() => text;
 
   @override
-  List<int> slowUtf8ZeroTerminatedBytes() {
-    return _zeroTerminateIfNecessary(utf8.encode(text));
+  Uint8List utf8Bytes() {
+    return utf8.encode(text);
   }
 
   @override
@@ -267,15 +249,15 @@ class StringSourceFile extends SourceFile {
 }
 
 /// Binary input data.
-class Binary implements api.Input<List<int>> {
+class Binary implements api.Input<Uint8List> {
   @override
   final Uri uri;
-  List<int>? _data;
+  Uint8List? _data;
 
-  Binary(this.uri, List<int> data) : _data = data;
+  Binary(this.uri, Uint8List data) : _data = data;
 
   @override
-  List<int> get data {
+  Uint8List get data {
     if (_data != null) return _data!;
     throw StateError("'get data' after 'release()'");
   }
diff --git a/pkg/compiler/lib/src/kernel/front_end_adapter.dart b/pkg/compiler/lib/src/kernel/front_end_adapter.dart
index 154b6783b14..16099115efc 100644
--- a/pkg/compiler/lib/src/kernel/front_end_adapter.dart
+++ b/pkg/compiler/lib/src/kernel/front_end_adapter.dart
@@ -7,6 +7,7 @@
 library compiler.kernel.front_end_adapter;
 
 import 'dart:async';
+import 'dart:typed_data';
 
 import 'package:front_end/src/api_unstable/dart2js.dart' as fe;
 
@@ -40,7 +41,7 @@ class _CompilerFileSystemEntity implements fe.FileSystemEntity {
 
   @override
   Future<String> readAsString() async {
-    api.Input<List<int>> input;
+    api.Input<Uint8List> input;
     try {
       input = await fs.inputProvider
           .readFromUri(uri, inputKind: api.InputKind.UTF8);
@@ -55,8 +56,8 @@ class _CompilerFileSystemEntity implements fe.FileSystemEntity {
   }
 
   @override
-  Future<List<int>> readAsBytes() async {
-    api.Input<List<int>> input;
+  Future<Uint8List> readAsBytes() async {
+    api.Input<Uint8List> input;
     try {
       input = await fs.inputProvider
           .readFromUri(uri, inputKind: api.InputKind.binary);
diff --git a/pkg/compiler/lib/src/phase/load_kernel.dart b/pkg/compiler/lib/src/phase/load_kernel.dart
index 8abee9fa91a..cf50c3dfb7b 100644
--- a/pkg/compiler/lib/src/phase/load_kernel.dart
+++ b/pkg/compiler/lib/src/phase/load_kernel.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:typed_data';
 
 import 'package:_js_interop_checks/src/transformations/static_interop_class_eraser.dart';
 import 'package:collection/collection.dart';
@@ -185,7 +186,7 @@ Future<_LoadFromKernelResult> _loadFromKernel(
   ir.Component component = ir.Component();
 
   Future<void> read(Uri uri) async {
-    api.Input<List<int>> input =
+    api.Input<Uint8List> input =
         await compilerInput.readFromUri(uri, inputKind: api.InputKind.binary);
     BinaryBuilder(input.data).readComponent(component);
   }
diff --git a/pkg/compiler/lib/src/serialization/task.dart b/pkg/compiler/lib/src/serialization/task.dart
index 7972516c754..3f841bc4611 100644
--- a/pkg/compiler/lib/src/serialization/task.dart
+++ b/pkg/compiler/lib/src/serialization/task.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:typed_data';
 
 import 'package:kernel/ast.dart' as ir;
 import 'package:kernel/binary/ast_from_binary.dart' as ir;
@@ -130,7 +131,7 @@ class SerializationTask extends CompilerTask {
     return await measureIoSubtask('deserialize closed world', () async {
       final uri = _options.dataUriForStage(CompilerStage.closedWorld);
       _reporter.log('Reading data from $uri');
-      api.Input<List<int>> dataInput =
+      api.Input<Uint8List> dataInput =
           await _provider.readFromUri(uri, inputKind: api.InputKind.binary);
       DataSourceReader source = DataSourceReader(
           BinaryDataSource(dataInput.data, stringInterner: _stringInterner),
@@ -167,7 +168,7 @@ class SerializationTask extends CompilerTask {
     return await measureIoSubtask('deserialize data', () async {
       final uri = _options.dataUriForStage(CompilerStage.globalInference);
       _reporter.log('Reading data from $uri');
-      api.Input<List<int>> dataInput =
+      api.Input<Uint8List> dataInput =
           await _provider.readFromUri(uri, inputKind: api.InputKind.binary);
       DataSourceReader source = DataSourceReader(
           BinaryDataSource(dataInput.data, stringInterner: _stringInterner),
@@ -234,7 +235,7 @@ class SerializationTask extends CompilerTask {
           '${_options.dataUriForStage(CompilerStage.codegenSharded)}$shard');
       await measureIoSubtask('deserialize codegen', () async {
         _reporter.log('Reading data from ${uri}');
-        api.Input<List<int>> dataInput =
+        api.Input<Uint8List> dataInput =
             await _provider.readFromUri(uri, inputKind: api.InputKind.binary);
         // TODO(36983): This code is extracted because there appeared to be a
         // memory leak for large buffer held by `source`.
@@ -251,7 +252,7 @@ class SerializationTask extends CompilerTask {
       JsBackendStrategy backendStrategy,
       JClosedWorld closedWorld,
       Uri uri,
-      api.Input<List<int>> dataInput,
+      api.Input<Uint8List> dataInput,
       Map<MemberEntity, Deferrable<CodegenResult>> results,
       bool useDeferredSourceReads,
       SourceLookup sourceLookup,
diff --git a/pkg/compiler/lib/src/source_file_provider.dart b/pkg/compiler/lib/src/source_file_provider.dart
index d79d6973f18..1aa20bcf459 100644
--- a/pkg/compiler/lib/src/source_file_provider.dart
+++ b/pkg/compiler/lib/src/source_file_provider.dart
@@ -17,7 +17,7 @@ import 'io/source_file.dart';
 import 'util/output_util.dart';
 
 abstract class SourceFileByteReader {
-  List<int> getBytes(String filename, {bool zeroTerminated = true});
+  Uint8List getBytes(String filename);
 }
 
 abstract class SourceFileProvider implements api.CompilerInput {
@@ -29,11 +29,11 @@ abstract class SourceFileProvider implements api.CompilerInput {
   final Set<Uri> _registeredUris = {};
   final Map<Uri, Uri> _mappedUris = {};
   final bool disableByteCache;
-  final Map<Uri, List<int>> _byteCache = {};
+  final Map<Uri, Uint8List> _byteCache = {};
 
   SourceFileProvider(this.byteReader, {this.disableByteCache = true});
 
-  Future<api.Input<List<int>>> readBytesFromUri(
+  Future<api.Input<Uint8List>> readBytesFromUri(
       Uri resourceUri, api.InputKind inputKind) {
     if (!resourceUri.isAbsolute) {
       resourceUri = cwd.resolveUri(resourceUri);
@@ -46,8 +46,8 @@ abstract class SourceFileProvider implements api.CompilerInput {
   }
 
   /// Adds [source] to the cache under the [resourceUri] key.
-  api.Input<List<int>> _sourceToFile(
-      Uri resourceUri, List<int> source, api.InputKind inputKind) {
+  api.Input<Uint8List> _sourceToFile(
+      Uri resourceUri, Uint8List source, api.InputKind inputKind) {
     switch (inputKind) {
       case api.InputKind.UTF8:
         return Utf8BytesSourceFile(resourceUri, source);
@@ -57,7 +57,7 @@ abstract class SourceFileProvider implements api.CompilerInput {
   }
 
   @override
-  void registerUtf8ContentsForDiagnostics(Uri resourceUri, List<int> source) {
+  void registerUtf8ContentsForDiagnostics(Uri resourceUri, Uint8List source) {
     if (!resourceUri.isAbsolute) {
       resourceUri = cwd.resolveUri(resourceUri);
     }
@@ -77,13 +77,12 @@ abstract class SourceFileProvider implements api.CompilerInput {
     return _registeredUris.add(uri);
   }
 
-  api.Input<List<int>> _readFromFileSync(Uri uri, api.InputKind inputKind) {
+  api.Input<Uint8List> _readFromFileSync(Uri uri, api.InputKind inputKind) {
     final resourceUri = _mappedUris[uri] ?? uri;
     assert(resourceUri.isScheme('file'));
-    List<int> source;
+    Uint8List source;
     try {
-      source = byteReader.getBytes(resourceUri.toFilePath(),
-          zeroTerminated: inputKind == api.InputKind.UTF8);
+      source = byteReader.getBytes(resourceUri.toFilePath());
     } on FileSystemException catch (ex) {
       String? message = ex.osError?.message;
       String detail = message != null ? ' ($message)' : '';
@@ -98,7 +97,7 @@ abstract class SourceFileProvider implements api.CompilerInput {
     return _sourceToFile(Uri.parse(relativizeUri(uri)), source, inputKind);
   }
 
-  api.Input<List<int>>? _readFromFileSyncOrNull(
+  api.Input<Uint8List>? _readFromFileSyncOrNull(
       Uri uri, api.InputKind inputKind) {
     try {
       return _readFromFileSync(uri, inputKind);
@@ -109,7 +108,7 @@ abstract class SourceFileProvider implements api.CompilerInput {
 
   /// Read [resourceUri] directly as a UTF-8 file. If reading fails, `null` is
   /// returned.
-  api.Input<List<int>>? readUtf8FromFileSyncForTesting(Uri resourceUri) {
+  api.Input<Uint8List>? readUtf8FromFileSyncForTesting(Uri resourceUri) {
     try {
       return _readFromFileSync(resourceUri, api.InputKind.UTF8);
     } catch (e) {
@@ -119,9 +118,9 @@ abstract class SourceFileProvider implements api.CompilerInput {
     }
   }
 
-  Future<api.Input<List<int>>> _readFromFile(
+  Future<api.Input<Uint8List>> _readFromFile(
       Uri resourceUri, api.InputKind inputKind) {
-    api.Input<List<int>> input;
+    api.Input<Uint8List> input;
     try {
       input = _readFromFileSync(resourceUri, inputKind);
     } catch (e) {
@@ -131,7 +130,7 @@ abstract class SourceFileProvider implements api.CompilerInput {
   }
 
   /// Get the bytes for a previously accessed UTF-8 [Uri].
-  api.Input<List<int>>? getUtf8SourceFile(Uri resourceUri) {
+  api.Input<Uint8List>? getUtf8SourceFile(Uri resourceUri) {
     if (!resourceUri.isAbsolute) {
       resourceUri = cwd.resolveUri(resourceUri);
     }
@@ -156,23 +155,13 @@ abstract class SourceFileProvider implements api.CompilerInput {
 class MemoryCopySourceFileByteReader implements SourceFileByteReader {
   const MemoryCopySourceFileByteReader();
   @override
-  List<int> getBytes(String filename, {bool zeroTerminated = true}) {
-    return readAll(filename, zeroTerminated: zeroTerminated);
+  Uint8List getBytes(String filename) {
+    return readAll(filename);
   }
 }
 
-Uint8List readAll(String filename, {bool zeroTerminated = true}) {
-  RandomAccessFile file = File(filename).openSync();
-  int length = file.lengthSync();
-  int bufferLength = length;
-  if (zeroTerminated) {
-    // +1 to have a 0 terminated list, see [Scanner].
-    bufferLength++;
-  }
-  var buffer = Uint8List(bufferLength);
-  file.readIntoSync(buffer, 0, length);
-  file.closeSync();
-  return buffer;
+Uint8List readAll(String filename) {
+  return File(filename).readAsBytesSync();
 }
 
 class CompilerSourceFileProvider extends SourceFileProvider {
@@ -182,7 +171,7 @@ class CompilerSourceFileProvider extends SourceFileProvider {
       : super(byteReader);
 
   @override
-  Future<api.Input<List<int>>> readFromUri(Uri uri,
+  Future<api.Input<Uint8List>> readFromUri(Uri uri,
           {api.InputKind inputKind = api.InputKind.UTF8}) =>
       readBytesFromUri(uri, inputKind);
 }
@@ -284,7 +273,7 @@ class FormattingDiagnosticHandler implements api.CompilerDiagnostics {
     if (uri == null) {
       print('${color(message)}');
     } else {
-      api.Input<List<int>>? file = provider.getUtf8SourceFile(uri);
+      api.Input<Uint8List>? file = provider.getUtf8SourceFile(uri);
       if (file is SourceFile && begin != null && end != null) {
         print(file.getLocationMessage(color(message), begin, end,
             colorize: color));
@@ -503,7 +492,7 @@ class BazelInputProvider extends SourceFileProvider {
   static Uri _resolve(String path) => Uri.base.resolve(path);
 
   @override
-  Future<api.Input<List<int>>> readFromUri(Uri uri,
+  Future<api.Input<Uint8List>> readFromUri(Uri uri,
       {api.InputKind inputKind = api.InputKind.UTF8}) async {
     var resolvedUri = uri;
     var path = uri.path;
@@ -517,7 +506,7 @@ class BazelInputProvider extends SourceFileProvider {
         }
       }
     }
-    api.Input<List<int>> result =
+    api.Input<Uint8List> result =
         await readBytesFromUri(resolvedUri, inputKind);
     if (uri != resolvedUri) {
       if (!resolvedUri.isAbsolute) {
@@ -548,7 +537,7 @@ class MultiRootInputProvider extends SourceFileProvider {
       {super.disableByteCache});
 
   @override
-  Future<api.Input<List<int>>> readFromUri(Uri uri,
+  Future<api.Input<Uint8List>> readFromUri(Uri uri,
       {api.InputKind inputKind = api.InputKind.UTF8}) async {
     var resolvedUri = uri;
     if (resolvedUri.isScheme(markerScheme)) {
@@ -562,7 +551,7 @@ class MultiRootInputProvider extends SourceFileProvider {
         }
       }
     }
-    api.Input<List<int>> result =
+    api.Input<Uint8List> result =
         await readBytesFromUri(resolvedUri, inputKind);
     _mappedUris[uri] = resolvedUri;
     return result;
diff --git a/pkg/compiler/lib/src/util/memory_source_file_helper.dart b/pkg/compiler/lib/src/util/memory_source_file_helper.dart
index 628f39f084e..ed50443b0b5 100644
--- a/pkg/compiler/lib/src/util/memory_source_file_helper.dart
+++ b/pkg/compiler/lib/src/util/memory_source_file_helper.dart
@@ -5,6 +5,7 @@
 library dart2js.test.memory_source_file_helper;
 
 import 'dart:async' show Future;
+import 'dart:typed_data';
 export 'dart:io' show Platform;
 
 import 'package:compiler/compiler_api.dart' as api;
@@ -26,7 +27,7 @@ class MemorySourceFileProvider extends CompilerSourceFileProvider {
   MemorySourceFileProvider(Map<String, dynamic> this.memorySourceFiles);
 
   @override
-  Future<api.Input<List<int>>> readBytesFromUri(
+  Future<api.Input<Uint8List>> readBytesFromUri(
       Uri resourceUri, api.InputKind inputKind) {
     if (!resourceUri.isScheme('memory')) {
       return super.readBytesFromUri(resourceUri, inputKind);
@@ -39,7 +40,7 @@ class MemorySourceFileProvider extends CompilerSourceFileProvider {
       return Future.error(Exception(
           'No such memory file $resourceUri in ${memorySourceFiles.keys}'));
     }
-    api.Input<List<int>> input;
+    api.Input<Uint8List> input;
     StringSourceFile? stringFile;
     registerUri(resourceUri);
     if (source is String) {
@@ -60,12 +61,12 @@ class MemorySourceFileProvider extends CompilerSourceFileProvider {
   }
 
   @override
-  Future<api.Input<List<int>>> readFromUri(Uri resourceUri,
+  Future<api.Input<Uint8List>> readFromUri(Uri resourceUri,
           {api.InputKind inputKind = api.InputKind.UTF8}) =>
       readBytesFromUri(resourceUri, inputKind);
 
   @override
-  api.Input<List<int>>? getUtf8SourceFile(Uri resourceUri) {
+  api.Input<Uint8List>? getUtf8SourceFile(Uri resourceUri) {
     var source = memorySourceFiles[resourceUri.path];
     if (source == null) return null;
     return source is String
diff --git a/pkg/compiler/test/deferred_loading/deferred_load_id_map_helper.dart b/pkg/compiler/test/deferred_loading/deferred_load_id_map_helper.dart
index 41afd5418e9..6d37a5dfdc8 100644
--- a/pkg/compiler/test/deferred_loading/deferred_load_id_map_helper.dart
+++ b/pkg/compiler/test/deferred_loading/deferred_load_id_map_helper.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:io' hide Link;
+import 'dart:typed_data';
 
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/compiler_api.dart';
@@ -54,7 +55,8 @@ Future<void> runTest(String testGroup, int shard, List<String> options,
         ],
         outputProvider: cfeCollector,
         beforeRun: (c) => compiler = c);
-    final cfeDill = cfeCollector.binaryOutputMap.values.first.list;
+    final cfeDill =
+        Uint8List.fromList(cfeCollector.binaryOutputMap.values.first.list);
     final dillInputFiles = {cfeFilename: cfeDill};
     final resultCollector = OutputCollector();
     final compilerResult = await runCompiler(
diff --git a/pkg/compiler/test/end_to_end/dill_loader_test.dart b/pkg/compiler/test/end_to_end/dill_loader_test.dart
index 4ee5c40a8f7..f85139d4d2f 100644
--- a/pkg/compiler/test/end_to_end/dill_loader_test.dart
+++ b/pkg/compiler/test/end_to_end/dill_loader_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:typed_data';
+
 import 'package:compiler/src/elements/names.dart';
 
 import 'package:compiler/src/util/memory_compiler.dart';
@@ -34,7 +36,7 @@ main() {
       ..setExitCodeOnProblem = true
       ..verify = true;
 
-    List<int> kernelBinary =
+    Uint8List kernelBinary =
         serializeComponent((await kernelForProgram(uri, options))!.component!);
     var compiler = compilerFor(
         entryPoint: uri,
diff --git a/pkg/compiler/test/end_to_end/modular_loader_test.dart b/pkg/compiler/test/end_to_end/modular_loader_test.dart
index c7ea04c7144..8e73444a54d 100644
--- a/pkg/compiler/test/end_to_end/modular_loader_test.dart
+++ b/pkg/compiler/test/end_to_end/modular_loader_test.dart
@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:typed_data';
+
 import 'package:compiler/src/elements/names.dart';
 
 import 'package:compiler/src/util/memory_compiler.dart';
@@ -77,7 +79,7 @@ main() {
 }
 
 /// Generate a component for a modular compilation unit.
-Future<List<int>> compileUnit(List<String> inputs, Map<String, dynamic> sources,
+Future<Uint8List> compileUnit(List<String> inputs, Map<String, dynamic> sources,
     {List<String> deps = const []}) async {
   var fs = MemoryFileSystem(_defaultDir);
   sources.forEach((name, data) {
diff --git a/pkg/compiler/test/serialization/serialization_diff_helper.dart b/pkg/compiler/test/serialization/serialization_diff_helper.dart
index 581c22860c0..094e2da4b3f 100644
--- a/pkg/compiler/test/serialization/serialization_diff_helper.dart
+++ b/pkg/compiler/test/serialization/serialization_diff_helper.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:io';
+import 'dart:typed_data';
 import 'package:compiler/compiler_api.dart' as api;
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/util/memory_compiler.dart';
@@ -36,7 +37,7 @@ Future<CompiledOutput> compileWithSerialization(
         options: options);
     Expect.isTrue(result.isSuccess);
     outputProvider.binaryOutputMap.forEach((fileName, binarySink) {
-      memorySourceFiles[fileName.path] = binarySink.list;
+      memorySourceFiles[fileName.path] = Uint8List.fromList(binarySink.list);
     });
     return outputProvider.clear();
   }
diff --git a/pkg/dev_compiler/lib/src/kernel/asset_file_system.dart b/pkg/dev_compiler/lib/src/kernel/asset_file_system.dart
index b92d314cc24..4925e858a34 100644
--- a/pkg/dev_compiler/lib/src/kernel/asset_file_system.dart
+++ b/pkg/dev_compiler/lib/src/kernel/asset_file_system.dart
@@ -5,6 +5,7 @@
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
+import 'dart:typed_data';
 
 import 'package:async/async.dart';
 import 'package:front_end/src/api_prototype/file_system.dart';
@@ -84,7 +85,7 @@ class AssetFileSystemEntity implements FileSystemEntity {
   Future<bool> existsAsyncIfPossible() => exists();
 
   @override
-  Future<List<int>> readAsBytes() async {
+  Future<Uint8List> readAsBytes() async {
     return _runWithClient((httpClient) async {
       var response = await httpClient.getUrl(uri);
       if (response.statusCode != HttpStatus.ok) {
diff --git a/pkg/front_end/lib/src/api_prototype/file_system.dart b/pkg/front_end/lib/src/api_prototype/file_system.dart
index 4d9030835d8..0d742313183 100644
--- a/pkg/front_end/lib/src/api_prototype/file_system.dart
+++ b/pkg/front_end/lib/src/api_prototype/file_system.dart
@@ -4,6 +4,8 @@
 
 library front_end.file_system;
 
+import 'dart:typed_data' show Uint8List;
+
 /// Abstract interface to file system operations.
 ///
 /// All front end interaction with the file system goes through this interface;
@@ -66,7 +68,7 @@ abstract class FileSystemEntity {
   /// If an error occurs while attempting to read the file (e.g. because no such
   /// file exists, or the entity is a directory), the future is completed with
   /// [FileSystemException].
-  Future<List<int>> readAsBytes();
+  Future<Uint8List> readAsBytes();
 
   /// Attempts to access this file system entity as a file and read its contents
   /// as raw bytes.
diff --git a/pkg/front_end/lib/src/api_prototype/language_version.dart b/pkg/front_end/lib/src/api_prototype/language_version.dart
index b5c73ad1ac7..2e36d55ac3a 100644
--- a/pkg/front_end/lib/src/api_prototype/language_version.dart
+++ b/pkg/front_end/lib/src/api_prototype/language_version.dart
@@ -68,7 +68,7 @@ Future<VersionAndPackageUri> languageVersionForUri(
     int? major;
     int? minor;
     if (fileUri != null) {
-      List<int>? rawBytes;
+      Uint8List? rawBytes;
       try {
         FileSystem fileSystem = context.options.fileSystem;
         rawBytes = await fileSystem.entityForUri(fileUri).readAsBytes();
@@ -76,10 +76,7 @@ Future<VersionAndPackageUri> languageVersionForUri(
         rawBytes = null;
       }
       if (rawBytes != null) {
-        Uint8List zeroTerminatedBytes = new Uint8List(rawBytes.length + 1);
-        zeroTerminatedBytes.setRange(0, rawBytes.length, rawBytes);
-
-        scan(zeroTerminatedBytes,
+        scan(rawBytes,
             includeComments: false,
             configuration: new ScannerConfiguration(), languageVersionChanged:
                 (Scanner scanner, LanguageVersionToken version) {
diff --git a/pkg/front_end/lib/src/api_prototype/memory_file_system.dart b/pkg/front_end/lib/src/api_prototype/memory_file_system.dart
index 0101274adf4..524a411ddcf 100644
--- a/pkg/front_end/lib/src/api_prototype/memory_file_system.dart
+++ b/pkg/front_end/lib/src/api_prototype/memory_file_system.dart
@@ -93,7 +93,7 @@ class MemoryFileSystemEntity implements FileSystemEntity {
 
   @override
   // Coverage-ignore(suite): Not run.
-  Future<List<int>> readAsBytes() {
+  Future<Uint8List> readAsBytes() {
     Uint8List? contents = _fileSystem._files[uri];
     if (contents == null) {
       return new Future.error(
diff --git a/pkg/front_end/lib/src/api_prototype/standard_file_system.dart b/pkg/front_end/lib/src/api_prototype/standard_file_system.dart
index f37ad1ee570..3ece5444600 100644
--- a/pkg/front_end/lib/src/api_prototype/standard_file_system.dart
+++ b/pkg/front_end/lib/src/api_prototype/standard_file_system.dart
@@ -5,6 +5,7 @@
 library front_end.standard_file_system;
 
 import 'dart:io' as io;
+import 'dart:typed_data';
 
 import '../base/file_system_dependency_tracker.dart';
 import 'file_system.dart';
@@ -90,7 +91,7 @@ class _IoFileSystemEntity implements FileSystemEntity {
   }
 
   @override
-  Future<List<int>> readAsBytes() {
+  Future<Uint8List> readAsBytes() {
     try {
       FileSystemDependencyTracker.recordDependency(tracker, uri);
       return new Future.value(new io.File.fromUri(uri).readAsBytesSync());
@@ -159,7 +160,7 @@ class DataFileSystemEntity implements FileSystemEntity {
   }
 
   @override
-  Future<List<int>> readAsBytes() {
+  Future<Uint8List> readAsBytes() {
     return new Future.value(uri.data!.contentAsBytes());
   }
 
diff --git a/pkg/front_end/lib/src/base/hybrid_file_system.dart b/pkg/front_end/lib/src/base/hybrid_file_system.dart
index 07e33b2a60a..b482ea18aaa 100644
--- a/pkg/front_end/lib/src/base/hybrid_file_system.dart
+++ b/pkg/front_end/lib/src/base/hybrid_file_system.dart
@@ -6,6 +6,8 @@
 /// sdk sources from disk.
 library front_end.src.hybrid_file_system;
 
+import 'dart:typed_data';
+
 import '../api_prototype/file_system.dart';
 import '../api_prototype/memory_file_system.dart';
 import '../api_prototype/standard_file_system.dart';
@@ -64,7 +66,7 @@ class HybridFileSystemEntity implements FileSystemEntity {
       (await delegate).existsAsyncIfPossible();
 
   @override
-  Future<List<int>> readAsBytes() async => (await delegate).readAsBytes();
+  Future<Uint8List> readAsBytes() async => (await delegate).readAsBytes();
 
   @override
   // Coverage-ignore(suite): Not run.
diff --git a/pkg/front_end/lib/src/base/incremental_compiler.dart b/pkg/front_end/lib/src/base/incremental_compiler.dart
index 9dbad217581..2b76e917b0d 100644
--- a/pkg/front_end/lib/src/base/incremental_compiler.dart
+++ b/pkg/front_end/lib/src/base/incremental_compiler.dart
@@ -6,6 +6,7 @@ library fasta.incremental_compiler;
 
 import 'dart:async' show Completer;
 import 'dart:convert' show JsonEncoder;
+import 'dart:typed_data';
 
 import 'package:_fe_analyzer_shared/src/scanner/abstract_scanner.dart'
     show ScannerConfiguration;
@@ -1219,7 +1220,7 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
       }
 
       for (Uri uri in builderUris) {
-        List<int>? previousSource = context.uriToSource[uri]?.source;
+        Uint8List? previousSource = context.uriToSource[uri]?.source;
         if (previousSource == null || previousSource.isEmpty) {
           recorderForTesting?.recordAdvancedInvalidationResult(
               AdvancedInvalidationResult.noPreviousSource);
diff --git a/pkg/front_end/lib/src/kernel/kernel_target.dart b/pkg/front_end/lib/src/kernel/kernel_target.dart
index f681f8432e9..d6bc23036e6 100644
--- a/pkg/front_end/lib/src/kernel/kernel_target.dart
+++ b/pkg/front_end/lib/src/kernel/kernel_target.dart
@@ -4,6 +4,8 @@
 
 library fasta.kernel_target;
 
+import 'dart:typed_data';
+
 import 'package:_fe_analyzer_shared/src/messages/severity.dart' show Severity;
 import 'package:kernel/ast.dart';
 import 'package:kernel/class_hierarchy.dart' show ClassHierarchy;
@@ -263,7 +265,7 @@ class KernelTarget {
   bool _hasAddedSources = false;
 
   void addSourceInformation(
-      Uri importUri, Uri fileUri, List<int> lineStarts, List<int> sourceCode) {
+      Uri importUri, Uri fileUri, List<int> lineStarts, Uint8List sourceCode) {
     Source source = new Source(lineStarts, sourceCode, importUri, fileUri);
     uriToSource[fileUri] = source;
     if (_hasAddedSources) {
@@ -271,8 +273,8 @@ class KernelTarget {
       // The sources have already been added to the component in [link] so we
       // have to add source directly here to create a consistent component.
       component?.uriToSource[fileUri] = excludeSource
-          ? new Source(source.lineStarts, const <int>[], source.importUri,
-              source.fileUri)
+          ? new Source.emptySource(
+              source.lineStarts, source.importUri, source.fileUri)
           : source;
     }
   }
@@ -869,8 +871,8 @@ class KernelTarget {
       uriToSource[uri] = excludeSource
           ?
           // Coverage-ignore(suite): Not run.
-          new Source(source.lineStarts, const <int>[], source.importUri,
-              source.fileUri)
+          new Source.emptySource(
+              source.lineStarts, source.importUri, source.fileUri)
           : source;
     }
 
diff --git a/pkg/front_end/lib/src/kernel/macro/macro.dart b/pkg/front_end/lib/src/kernel/macro/macro.dart
index 689fdadc5b0..b3050b91c4d 100644
--- a/pkg/front_end/lib/src/kernel/macro/macro.dart
+++ b/pkg/front_end/lib/src/kernel/macro/macro.dart
@@ -2,6 +2,9 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'dart:convert';
+import 'dart:typed_data';
+
 import 'package:_fe_analyzer_shared/src/macros/uri.dart';
 import 'package:_fe_analyzer_shared/src/scanner/scanner.dart';
 import 'package:kernel/ast.dart';
@@ -1307,14 +1310,16 @@ class MacroApplications {
 
       component.accept(new ReOffsetVisitor(reOffsetMaps));
 
-      ScannerResult scannerResult = scanString(source,
+      Uint8List sourceUtf8 = utf8.encode(source);
+
+      ScannerResult scannerResult = scan(sourceUtf8,
           configuration: new ScannerConfiguration(
               enableExtensionMethods: true,
               enableNonNullable: true,
               enableTripleShift: true,
               forAugmentationLibrary: true));
       _sourceLoader.target.addSourceInformation(augmentationImportUri,
-          augmentationFileUri, scannerResult.lineStarts, source.codeUnits);
+          augmentationFileUri, scannerResult.lineStarts, sourceUtf8);
       for (Uri intermediateAugmentationUri in intermediateAugmentationUris) {
         _sourceLoader.target
             .removeSourceInformation(intermediateAugmentationUri);
diff --git a/pkg/front_end/lib/src/source/source_library_builder.dart b/pkg/front_end/lib/src/source/source_library_builder.dart
index ca8c33a1e4b..f49ad984817 100644
--- a/pkg/front_end/lib/src/source/source_library_builder.dart
+++ b/pkg/front_end/lib/src/source/source_library_builder.dart
@@ -4,7 +4,8 @@
 
 library fasta.source_library_builder;
 
-import 'dart:convert' show jsonEncode;
+import 'dart:convert' show jsonEncode, utf8;
+import 'dart:typed_data';
 
 import 'package:_fe_analyzer_shared/src/field_promotability.dart';
 import 'package:_fe_analyzer_shared/src/flow_analysis/flow_analysis_operations.dart';
@@ -563,8 +564,9 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
         indexedLibrary: indexedLibrary,
         omittedTypes: omittedTypeDeclarationBuilders);
     addAugmentationLibrary(augmentationLibrary);
+    Uint8List sourceUtf8 = utf8.encode(source);
     loader.registerUnparsedLibrarySource(
-        augmentationLibrary.compilationUnit, source);
+        augmentationLibrary.compilationUnit, sourceUtf8);
     return augmentationLibrary;
   }
 
diff --git a/pkg/front_end/lib/src/source/source_loader.dart b/pkg/front_end/lib/src/source/source_loader.dart
index 1a9e6c46517..cf62a098b33 100644
--- a/pkg/front_end/lib/src/source/source_loader.dart
+++ b/pkg/front_end/lib/src/source/source_loader.dart
@@ -1002,9 +1002,6 @@ severity: $severity
         bytes = synthesizeSourceForMissingFile(compilationUnit.importUri, null);
       }
       if (bytes != null) {
-        Uint8List zeroTerminatedBytes = new Uint8List(bytes.length + 1);
-        zeroTerminatedBytes.setRange(0, bytes.length, bytes);
-        bytes = zeroTerminatedBytes;
         sourceBytes[fileUri] = bytes;
       }
     }
@@ -1012,7 +1009,7 @@ severity: $severity
     if (bytes == null) {
       // If it isn't found in the cache, read the file read from the file
       // system.
-      List<int> rawBytes;
+      Uint8List rawBytes;
       try {
         rawBytes = await fileSystem.entityForUri(fileUri).readAsBytes();
       } on FileSystemException catch (e) {
@@ -1022,9 +1019,7 @@ severity: $severity
         rawBytes =
             synthesizeSourceForMissingFile(compilationUnit.importUri, message);
       }
-      Uint8List zeroTerminatedBytes = new Uint8List(rawBytes.length + 1);
-      zeroTerminatedBytes.setRange(0, rawBytes.length, rawBytes);
-      bytes = zeroTerminatedBytes;
+      bytes = rawBytes;
       sourceBytes[fileUri] = bytes;
       byteCount += rawBytes.length;
     }
@@ -1063,8 +1058,6 @@ severity: $severity
     }, allowLazyStrings: allowLazyStrings);
     Token token = result.tokens;
     if (!suppressLexicalErrors) {
-      List<int> source = getSource(bytes);
-
       /// We use the [importUri] of the created [Library] and not the
       /// [importUri] of the [LibraryBuilder] since it might be an augmentation
       /// library which is not directly part of the output.
@@ -1087,7 +1080,7 @@ severity: $severity
         }
       }
       target.addSourceInformation(
-          importUri, compilationUnit.fileUri, result.lineStarts, source);
+          importUri, compilationUnit.fileUri, result.lineStarts, bytes);
     }
     compilationUnit.issuePostponedProblems();
     compilationUnit.markLanguageVersionFinal();
@@ -1142,11 +1135,8 @@ severity: $severity
   ///
   /// This is used for creating synthesized augmentation libraries.
   void registerUnparsedLibrarySource(
-      SourceCompilationUnit compilationUnit, String source) {
-    List<int> codeUnits = source.codeUnits;
-    Uint8List bytes = new Uint8List(codeUnits.length + 1);
-    bytes.setRange(0, codeUnits.length, codeUnits);
-    sourceBytes[compilationUnit.fileUri] = bytes;
+      SourceCompilationUnit compilationUnit, Uint8List source) {
+    sourceBytes[compilationUnit.fileUri] = source;
     _unparsedLibraries.addLast(compilationUnit);
   }
 
@@ -1239,16 +1229,6 @@ severity: $severity
     }
   }
 
-  List<int> getSource(List<int> bytes) {
-    // bytes is 0-terminated. We don't want that included.
-    if (bytes is Uint8List) {
-      return new Uint8List.view(
-          bytes.buffer, bytes.offsetInBytes, bytes.length - 1);
-    }
-    // Coverage-ignore(suite): Not run.
-    return bytes.sublist(0, bytes.length - 1);
-  }
-
   Future<Null> buildOutline(SourceCompilationUnit compilationUnit) async {
     Token tokens = await tokenize(compilationUnit);
     OutlineBuilder listener = compilationUnit.createOutlineBuilder();
diff --git a/pkg/front_end/lib/src/util/import_export_etc_helper.dart b/pkg/front_end/lib/src/util/import_export_etc_helper.dart
index cfe40243a30..8dafa92e44b 100644
--- a/pkg/front_end/lib/src/util/import_export_etc_helper.dart
+++ b/pkg/front_end/lib/src/util/import_export_etc_helper.dart
@@ -8,11 +8,11 @@ import 'dart:typed_data';
 import 'parser_ast.dart';
 import 'parser_ast_helper.dart';
 
-FileInfoHelper getFileInfoHelper(Uint8List zeroTerminatedBytes) {
+FileInfoHelper getFileInfoHelper(Uint8List rawBytes) {
   ImportExportPartLibraryHelperVisitor visitor =
       new ImportExportPartLibraryHelperVisitor();
   getAST(
-    zeroTerminatedBytes,
+    rawBytes,
     enableExtensionMethods: true,
     enableNonNullable: true,
     enableTripleShift: true,
@@ -24,9 +24,7 @@ FileInfoHelper getFileInfoHelper(Uint8List zeroTerminatedBytes) {
 
 FileInfoHelper getFileInfoHelperFromString(String source) {
   Uint8List rawBytes = utf8.encode(source);
-  Uint8List zeroTerminatedBytes = new Uint8List(rawBytes.length + 1);
-  zeroTerminatedBytes.setRange(0, rawBytes.length, rawBytes);
-  return getFileInfoHelper(zeroTerminatedBytes);
+  return getFileInfoHelper(rawBytes);
 }
 
 class FileInfoHelper {
diff --git a/pkg/front_end/lib/src/util/outline_extractor.dart b/pkg/front_end/lib/src/util/outline_extractor.dart
index 91015748478..f6237ce4418 100644
--- a/pkg/front_end/lib/src/util/outline_extractor.dart
+++ b/pkg/front_end/lib/src/util/outline_extractor.dart
@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:convert';
+import 'dart:typed_data';
 
 import 'package:_fe_analyzer_shared/src/parser/identifier_context.dart';
 import 'package:_fe_analyzer_shared/src/scanner/abstract_scanner.dart'
@@ -129,7 +130,7 @@ class _Processor {
       fileUri = uriTranslator.translate(importUri)!;
     }
     if (verbosityLevel >= 20) log("$fileUri");
-    final List<int> bytes =
+    final Uint8List bytes =
         await fileSystem.entityForUri(fileUri).readAsBytes();
     // TODO: Support updating the configuration; also default it to match
     // the package version.
@@ -142,7 +143,7 @@ class _Processor {
         textualOutline(bytes, configuration, enablePatterns: true);
     textualOutlineStopwatch.stop();
     if (outlined == null) throw "Textual outline returned null";
-    final List<int> bytes2 = utf8.encode(outlined);
+    final Uint8List bytes2 = utf8.encode(outlined);
     getAstStopwatch.start();
     List<Token> languageVersionsSeen = [];
     final ParserAstNode ast = getAST(bytes2,
diff --git a/pkg/front_end/lib/src/util/parser_ast.dart b/pkg/front_end/lib/src/util/parser_ast.dart
index 62b11916fe9..9c7d4973952 100644
--- a/pkg/front_end/lib/src/util/parser_ast.dart
+++ b/pkg/front_end/lib/src/util/parser_ast.dart
@@ -25,7 +25,7 @@ import 'parser_ast_helper.dart';
 // "assumed version" (from package config probably) which is then updated if
 // a language version is seen which will then implicitly answer these questions.
 CompilationUnitEnd getAST(
-  List<int> rawBytes, {
+  Uint8List rawBytes, {
   bool includeBody = true,
   bool includeComments = false,
   bool enableExtensionMethods = false,
@@ -35,16 +35,13 @@ CompilationUnitEnd getAST(
   List<Token>? languageVersionsSeen,
   List<int>? lineStarts,
 }) {
-  Uint8List bytes = new Uint8List(rawBytes.length + 1);
-  bytes.setRange(0, rawBytes.length, rawBytes);
-
   ScannerConfiguration scannerConfiguration = new ScannerConfiguration(
       enableExtensionMethods: enableExtensionMethods,
       enableNonNullable: enableNonNullable,
       enableTripleShift: enableTripleShift);
 
   Utf8BytesScanner scanner = new Utf8BytesScanner(
-    bytes,
+    rawBytes,
     includeComments: includeComments,
     configuration: scannerConfiguration,
     languageVersionChanged: (scanner, languageVersion) {
diff --git a/pkg/front_end/lib/src/util/textual_outline.dart b/pkg/front_end/lib/src/util/textual_outline.dart
index 89a7a4d46ea..443c278995f 100644
--- a/pkg/front_end/lib/src/util/textual_outline.dart
+++ b/pkg/front_end/lib/src/util/textual_outline.dart
@@ -421,7 +421,7 @@ class BoxedInt {
 //              "show A, B, C hide A show A" would be empty.
 
 String? textualOutline(
-  List<int> rawBytes,
+  Uint8List rawBytes,
   ScannerConfiguration configuration, {
   bool throwOnUnexpected = false,
   bool performModelling = false,
@@ -429,14 +429,11 @@ String? textualOutline(
   required bool enablePatterns,
   TextualOutlineInfoForTesting? infoForTesting,
 }) {
-  Uint8List bytes = new Uint8List(rawBytes.length + 1);
-  bytes.setRange(0, rawBytes.length, rawBytes);
-
   List<_Chunk> parsedChunks = <_Chunk>[];
 
   BoxedInt originalPosition = new BoxedInt(0);
 
-  Utf8BytesScanner scanner = new Utf8BytesScanner(bytes,
+  Utf8BytesScanner scanner = new Utf8BytesScanner(rawBytes,
       includeComments: false,
       configuration: configuration, languageVersionChanged:
           (Scanner scanner, LanguageVersionToken languageVersionToken) {
diff --git a/pkg/front_end/test/crashing_test_case_minimizer_impl.dart b/pkg/front_end/test/crashing_test_case_minimizer_impl.dart
index 2cac8ba10ac..c73fa95956b 100644
--- a/pkg/front_end/test/crashing_test_case_minimizer_impl.dart
+++ b/pkg/front_end/test/crashing_test_case_minimizer_impl.dart
@@ -2273,7 +2273,7 @@ class _FakeFileSystemEntity extends FileSystemEntity {
   Future<bool> existsAsyncIfPossible() => exists();
 
   @override
-  Future<List<int>> readAsBytes() {
+  Future<Uint8List> readAsBytes() {
     _ensureCachedIfOk();
     Uint8List? data = fs.data[uri];
     if (data == null) throw new FileSystemException(uri, "File doesn't exist.");
diff --git a/pkg/front_end/test/fasta/messages_suite.dart b/pkg/front_end/test/fasta/messages_suite.dart
index e4431da6fd1..abb2a2729b2 100644
--- a/pkg/front_end/test/fasta/messages_suite.dart
+++ b/pkg/front_end/test/fasta/messages_suite.dart
@@ -162,7 +162,7 @@ class MessageTestSuite extends ChainContext {
       List<String> formatSpellingMistakes(spell.SpellingResult spellResult,
           int offset, String message, String messageForDenyListed) {
         if (source == null) {
-          List<int> bytes = file.readAsBytesSync();
+          Uint8List bytes = file.readAsBytesSync();
           List<int> lineStarts = <int>[];
           int indexOf = 0;
           while (indexOf >= 0) {
diff --git a/pkg/front_end/test/fasta/testing/suite.dart b/pkg/front_end/test/fasta/testing/suite.dart
index 7c81ff79730..342b5740249 100644
--- a/pkg/front_end/test/fasta/testing/suite.dart
+++ b/pkg/front_end/test/fasta/testing/suite.dart
@@ -1882,7 +1882,7 @@ class _FakeFileSystemEntity extends FileSystemEntity {
       fs.data[uri] = null;
       return;
     }
-    fs.data[uri] = (await f.readAsBytes()) as Uint8List;
+    fs.data[uri] = await f.readAsBytes();
   }
 
   @override
@@ -1897,7 +1897,7 @@ class _FakeFileSystemEntity extends FileSystemEntity {
   Future<bool> existsAsyncIfPossible() => exists();
 
   @override
-  Future<List<int>> readAsBytes() async {
+  Future<Uint8List> readAsBytes() async {
     await _ensureCachedIfOk();
     Uint8List? data = fs.data[uri];
     if (data == null) throw new FileSystemException(uri, "File doesn't exist.");
diff --git a/pkg/front_end/test/fasta/textual_outline_suite.dart b/pkg/front_end/test/fasta/textual_outline_suite.dart
index ee077adb1f3..0823b853e1f 100644
--- a/pkg/front_end/test/fasta/textual_outline_suite.dart
+++ b/pkg/front_end/test/fasta/textual_outline_suite.dart
@@ -5,6 +5,7 @@
 library fasta.test.textual_outline_test;
 
 import 'dart:io';
+import 'dart:typed_data';
 
 import 'package:_fe_analyzer_shared/src/scanner/abstract_scanner.dart'
     show ScannerConfiguration;
@@ -110,7 +111,7 @@ class TextualOutline extends Step<TestDescription, TestDescription, Context> {
     Map<ExperimentalFlag, bool> experimentalFlagsExplicit =
         folderOptions.computeExplicitExperimentalFlags(const {});
 
-    List<int> bytes = new File.fromUri(description.uri).readAsBytesSync();
+    Uint8List bytes = new File.fromUri(description.uri).readAsBytesSync();
     for (bool modelled in [false, true]) {
       TextualOutlineInfoForTesting info = new TextualOutlineInfoForTesting();
       String? result = textualOutline(
diff --git a/pkg/front_end/test/fasta/util/parser_ast_test.dart b/pkg/front_end/test/fasta/util/parser_ast_test.dart
index 5cda7d350e4..09ca9fb7697 100644
--- a/pkg/front_end/test/fasta/util/parser_ast_test.dart
+++ b/pkg/front_end/test/fasta/util/parser_ast_test.dart
@@ -4,6 +4,7 @@
 
 import 'dart:convert';
 import 'dart:io';
+import 'dart:typed_data';
 
 import 'package:front_end/src/util/parser_ast.dart';
 import 'package:front_end/src/util/parser_ast_helper.dart';
@@ -33,7 +34,7 @@ void canParseTopLevelIshOfAllFrontendFiles() {
       if (!entry.path.endsWith(".dart")) continue;
       try {
         processed++;
-        List<int> data = entry.readAsBytesSync();
+        Uint8List data = entry.readAsBytesSync();
         CompilationUnitEnd ast = getAST(
           data,
           includeBody: true,
@@ -79,7 +80,7 @@ void canParseTopLevelIshOfAllFrontendFiles() {
 void testTopLevelStuff() {
   File file = new File.fromUri(
       base.resolve("parser_ast_test_data/top_level_stuff.txt"));
-  List<int> data = file.readAsBytesSync();
+  Uint8List data = file.readAsBytesSync();
   CompilationUnitEnd ast = getAST(data,
       includeBody: true,
       includeComments: true,
@@ -161,7 +162,7 @@ void testTopLevelStuff() {
 
 void testClassStuff() {
   File file = new File.fromUri(base.resolve("parser_ast_test_data/class.txt"));
-  List<int> data = file.readAsBytesSync();
+  Uint8List data = file.readAsBytesSync();
   CompilationUnitEnd ast = getAST(data,
       includeBody: true,
       includeComments: true,
@@ -245,7 +246,7 @@ void testClassStuff() {
 
 void testMixinStuff() {
   File file = new File.fromUri(base.resolve("parser_ast_test_data/mixin.txt"));
-  List<int> data = file.readAsBytesSync();
+  Uint8List data = file.readAsBytesSync();
   CompilationUnitEnd ast = getAST(data,
       includeBody: true,
       includeComments: true,
diff --git a/pkg/front_end/test/find_all_subclasses_tool.dart b/pkg/front_end/test/find_all_subclasses_tool.dart
index 3221148e7b4..613466c6870 100644
--- a/pkg/front_end/test/find_all_subclasses_tool.dart
+++ b/pkg/front_end/test/find_all_subclasses_tool.dart
@@ -25,13 +25,11 @@ Future<Set<Class>> getAllTokens() async {
 /// Compiles either a File or a Directory and finds all subtypes of (including)
 /// the specified [className] in a file containing [classFilename].
 Future<Set<Class>> findIn(
-    FileSystemEntity where, String className, String classFilename) async {
+    Directory where, String className, String classFilename) async {
   List<Uri> files = [];
-  if (where is File) {
-    files.add(where.uri);
-  } else if (where is Directory) {
-    for (FileSystemEntity subEntity in where.listSync(recursive: true)) {
-      if (subEntity is File) {
+  for (FileSystemEntity subEntity in where.listSync(recursive: true)) {
+    if (subEntity is File) {
+      if (subEntity.path.toLowerCase().endsWith(".dart")) {
         files.add(subEntity.uri);
       }
     }
diff --git a/pkg/front_end/test/lint_suite.dart b/pkg/front_end/test/lint_suite.dart
index 3a2e35887c0..c6c9aa6e22f 100644
--- a/pkg/front_end/test/lint_suite.dart
+++ b/pkg/front_end/test/lint_suite.dart
@@ -65,7 +65,7 @@ class LintTestDescription extends TestDescription {
 }
 
 class LintTestCache {
-  List<int>? rawBytes;
+  Uint8List? rawBytes;
   late List<int> lineStarts;
   Source? source;
   Token? firstToken;
@@ -133,12 +133,7 @@ class LintStep extends Step<LintTestDescription, LintTestDescription, Context> {
       LintTestDescription description, Context context) async {
     if (description.cache.rawBytes == null) {
       File f = new File.fromUri(description.uri);
-      description.cache.rawBytes = f.readAsBytesSync();
-
-      Uint8List bytes = new Uint8List(description.cache.rawBytes!.length + 1);
-      bytes.setRange(
-          0, description.cache.rawBytes!.length, description.cache.rawBytes!);
-
+      Uint8List bytes = description.cache.rawBytes = f.readAsBytesSync();
       Utf8BytesScanner scanner = new Utf8BytesScanner(
         bytes,
         configuration: const ScannerConfiguration(
diff --git a/pkg/front_end/test/parser_suite.dart b/pkg/front_end/test/parser_suite.dart
index 00edba90bdd..c60766e67e5 100644
--- a/pkg/front_end/test/parser_suite.dart
+++ b/pkg/front_end/test/parser_suite.dart
@@ -153,7 +153,7 @@ class ParserAstStep extends Step<TestDescription, TestDescription, Context> {
       TestDescription description, Context context) {
     Uri uri = description.uri;
     File f = new File.fromUri(uri);
-    List<int> rawBytes = f.readAsBytesSync();
+    Uint8List rawBytes = f.readAsBytesSync();
     ParserAstNode ast = getAST(rawBytes);
     if (ast.what != "CompilationUnit") {
       throw "Expected a single element for 'CompilationUnit' "
@@ -181,7 +181,7 @@ class ListenerStep extends Step<TestDescription, TestDescription, Context> {
     Token firstToken = scanUri(uri, shortName, lineStarts: lineStarts);
 
     File f = new File.fromUri(uri);
-    List<int> rawBytes = f.readAsBytesSync();
+    Uint8List rawBytes = f.readAsBytesSync();
     Source source = new Source(lineStarts, rawBytes, uri, uri);
     String shortNameId = "${suiteName}/${shortName}";
     ParserTestListenerWithMessageFormatting parserTestListener =
@@ -240,7 +240,7 @@ class IntertwinedStep extends Step<TestDescription, TestDescription, Context> {
         scanUri(description.uri, description.shortName, lineStarts: lineStarts);
 
     File f = new File.fromUri(description.uri);
-    List<int> rawBytes = f.readAsBytesSync();
+    Uint8List rawBytes = f.readAsBytesSync();
     Source source =
         new Source(lineStarts, rawBytes, description.uri, description.uri);
 
@@ -416,7 +416,7 @@ Token scanUri(Uri uri, String shortName, {List<int>? lineStarts}) {
   }
 
   File f = new File.fromUri(uri);
-  List<int> rawBytes = f.readAsBytesSync();
+  Uint8List rawBytes = f.readAsBytesSync();
 
   return scanRawBytes(rawBytes, config, lineStarts);
 }
@@ -427,12 +427,9 @@ bool shouldAllowPatterns(String shortName) {
 }
 
 Token scanRawBytes(
-    List<int> rawBytes, ScannerConfiguration config, List<int>? lineStarts) {
-  Uint8List bytes = new Uint8List(rawBytes.length + 1);
-  bytes.setRange(0, rawBytes.length, rawBytes);
-
-  Utf8BytesScanner scanner =
-      new Utf8BytesScanner(bytes, includeComments: true, configuration: config);
+    Uint8List rawBytes, ScannerConfiguration config, List<int>? lineStarts) {
+  Utf8BytesScanner scanner = new Utf8BytesScanner(rawBytes,
+      includeComments: true, configuration: config);
   Token firstToken = scanner.tokenize();
   if (lineStarts != null) {
     lineStarts.addAll(scanner.lineStarts);
diff --git a/pkg/front_end/test/parser_test_listener_creator.dart b/pkg/front_end/test/parser_test_listener_creator.dart
index e009af9574f..472a297a97e 100644
--- a/pkg/front_end/test/parser_test_listener_creator.dart
+++ b/pkg/front_end/test/parser_test_listener_creator.dart
@@ -27,12 +27,9 @@ String generateTestListener(Uri repoDir) {
   final StringBuffer out = new StringBuffer();
   File f = new File.fromUri(
       repoDir.resolve("pkg/_fe_analyzer_shared/lib/src/parser/listener.dart"));
-  List<int> rawBytes = f.readAsBytesSync();
-
-  Uint8List bytes = new Uint8List(rawBytes.length + 1);
-  bytes.setRange(0, rawBytes.length, rawBytes);
-
-  Utf8BytesScanner scanner = new Utf8BytesScanner(bytes, includeComments: true);
+  Uint8List rawBytes = f.readAsBytesSync();
+  Utf8BytesScanner scanner =
+      new Utf8BytesScanner(rawBytes, includeComments: true);
   Token firstToken = scanner.tokenize();
 
   out.write(r"""
diff --git a/pkg/front_end/test/parser_test_parser_creator.dart b/pkg/front_end/test/parser_test_parser_creator.dart
index 3afa436ac1d..a181c22d406 100644
--- a/pkg/front_end/test/parser_test_parser_creator.dart
+++ b/pkg/front_end/test/parser_test_parser_creator.dart
@@ -27,12 +27,9 @@ String generateTestParser(Uri repoDir) {
   StringBuffer out = new StringBuffer();
   File f = new File.fromUri(repoDir
       .resolve("pkg/_fe_analyzer_shared/lib/src/parser/parser_impl.dart"));
-  List<int> rawBytes = f.readAsBytesSync();
-
-  Uint8List bytes = new Uint8List(rawBytes.length + 1);
-  bytes.setRange(0, rawBytes.length, rawBytes);
-
-  Utf8BytesScanner scanner = new Utf8BytesScanner(bytes, includeComments: true);
+  Uint8List rawBytes = f.readAsBytesSync();
+  Utf8BytesScanner scanner =
+      new Utf8BytesScanner(rawBytes, includeComments: true);
   Token firstToken = scanner.tokenize();
 
   out.write(r"""
diff --git a/pkg/front_end/test/scanner_fasta_test.dart b/pkg/front_end/test/scanner_fasta_test.dart
index 12afe4e332a..474d94859b6 100644
--- a/pkg/front_end/test/scanner_fasta_test.dart
+++ b/pkg/front_end/test/scanner_fasta_test.dart
@@ -29,10 +29,8 @@ void main() {
   });
 }
 
-Uint8List encodeAsNullTerminatedUtf8(String source) {
-  final sourceBytes = utf8.encode(source);
-  return Uint8List(sourceBytes.length + 1)
-    ..setRange(0, sourceBytes.length, sourceBytes);
+Uint8List encodeAsUtf8(String source) {
+  return utf8.encode(source);
 }
 
 @reflectiveTest
@@ -46,8 +44,7 @@ class ScannerTest_Fasta_FuzzTestAPI {
     expect(result.hasErrors, isFalse);
     expect(result.tokens.type, same(Keyword.CLASS));
 
-    // UTF8 encode source with trailing zero
-    Uint8List bytes = encodeAsNullTerminatedUtf8(source);
+    Uint8List bytes = encodeAsUtf8(source);
 
     result = usedForFuzzTesting.scan(bytes);
     expect(result.hasErrors, isFalse);
@@ -60,7 +57,7 @@ class ScannerTest_Fasta_UTF8 extends ScannerTest_Fasta {
   @override
   Token scanWithListener(String source, ErrorListener listener,
       {ScannerConfiguration? configuration}) {
-    var bytes = encodeAsNullTerminatedUtf8(source);
+    var bytes = encodeAsUtf8(source);
     var result =
         scan(bytes, configuration: configuration, includeComments: true);
     var token = result.tokens;
@@ -103,10 +100,10 @@ class ScannerTest_Fasta_UTF8 extends ScannerTest_Fasta {
     }
 
     for (int byte0 = 1; byte0 <= 0xFF; ++byte0) {
-      Uint8List bytes = Uint8List(2)..[0] = byte0;
+      Uint8List bytes = Uint8List(1)..[0] = byte0;
       scanBytes(bytes);
       for (int byte1 = 1; byte1 <= 0xFF; ++byte1) {
-        Uint8List bytes = Uint8List(3)
+        Uint8List bytes = Uint8List(2)
           ..[0] = byte0
           ..[1] = byte1;
         scanBytes(bytes);
@@ -708,7 +705,7 @@ class ScannerTest_Fasta_Direct_UTF8 extends ScannerTest_Fasta_Direct {
   @override
   ScannerResult scanSource(source,
       {bool includeComments = true, bool? enableTripleShift}) {
-    Uint8List encoded = encodeAsNullTerminatedUtf8(source);
+    Uint8List encoded = encodeAsUtf8(source);
 
     ScannerConfiguration? configuration;
     if (enableTripleShift == true) {
diff --git a/pkg/front_end/test/spelling_test_base.dart b/pkg/front_end/test/spelling_test_base.dart
index af250e4d73f..adf89e3ca5f 100644
--- a/pkg/front_end/test/spelling_test_base.dart
+++ b/pkg/front_end/test/spelling_test_base.dart
@@ -73,13 +73,10 @@ class SpellTest extends Step<TestDescription, TestDescription, SpellContext> {
   Future<Result<TestDescription>> run(
       TestDescription description, SpellContext context) async {
     File f = new File.fromUri(description.uri);
-    List<int> rawBytes = f.readAsBytesSync();
-
-    Uint8List bytes = new Uint8List(rawBytes.length + 1);
-    bytes.setRange(0, rawBytes.length, rawBytes);
+    Uint8List rawBytes = f.readAsBytesSync();
 
     Utf8BytesScanner scanner =
-        new Utf8BytesScanner(bytes, includeComments: true);
+        new Utf8BytesScanner(rawBytes, includeComments: true);
     Token firstToken = scanner.tokenize();
     Token? token = firstToken;
 
diff --git a/pkg/front_end/test/utils/kernel_chain.dart b/pkg/front_end/test/utils/kernel_chain.dart
index a853be4021d..abc53e1f353 100644
--- a/pkg/front_end/test/utils/kernel_chain.dart
+++ b/pkg/front_end/test/utils/kernel_chain.dart
@@ -334,12 +334,8 @@ class ErrorCommentChecker
     File f = new File.fromUri(uri);
     if (!f.existsSync()) return const {};
     Uint8List rawBytes = f.readAsBytesSync();
-
-    Uint8List bytes = new Uint8List(rawBytes.length + 1);
-    bytes.setRange(0, rawBytes.length, rawBytes);
-
     Utf8BytesScanner scanner = new Utf8BytesScanner(
-      bytes,
+      rawBytes,
       configuration: const ScannerConfiguration(
           enableExtensionMethods: true,
           enableNonNullable: true,
@@ -354,7 +350,7 @@ class ErrorCommentChecker
 
     Token? token = firstToken;
     Token? previousToken;
-    Source lineStartsHelper = new Source(lineStarts, const [], null, null);
+    Source lineStartsHelper = new Source.emptySource(lineStarts, null, null);
     Map<int, List<CommentToken>> linesToComments = {};
     while (token != null && !token.isEof) {
       CommentToken? precedingComments = token.precedingComments;
diff --git a/pkg/front_end/tool/_fasta/parser_ast_helper_creator.dart b/pkg/front_end/tool/_fasta/parser_ast_helper_creator.dart
index f00ac6b6250..6925c04751a 100644
--- a/pkg/front_end/tool/_fasta/parser_ast_helper_creator.dart
+++ b/pkg/front_end/tool/_fasta/parser_ast_helper_creator.dart
@@ -27,12 +27,9 @@ String generateAstHelper(Uri repoDir) {
   StringBuffer out = new StringBuffer();
   File f = new File.fromUri(
       repoDir.resolve("pkg/_fe_analyzer_shared/lib/src/parser/listener.dart"));
-  List<int> rawBytes = f.readAsBytesSync();
-
-  Uint8List bytes = new Uint8List(rawBytes.length + 1);
-  bytes.setRange(0, rawBytes.length, rawBytes);
-
-  Utf8BytesScanner scanner = new Utf8BytesScanner(bytes, includeComments: true);
+  Uint8List rawBytes = f.readAsBytesSync();
+  Utf8BytesScanner scanner =
+      new Utf8BytesScanner(rawBytes, includeComments: true);
   Token firstToken = scanner.tokenize();
 
   out.write(r"""
diff --git a/pkg/front_end/tool/dart_doctest_impl.dart b/pkg/front_end/tool/dart_doctest_impl.dart
index cb92db7c6e0..b7833d54821 100644
--- a/pkg/front_end/tool/dart_doctest_impl.dart
+++ b/pkg/front_end/tool/dart_doctest_impl.dart
@@ -530,16 +530,13 @@ List<Test> extractTests(Uint8List rawBytes, Uri uriForReporting) {
 }
 
 Token scanRawBytes(Uint8List rawBytes, {List<int>? lineStarts}) {
-  Uint8List bytes = new Uint8List(rawBytes.length + 1);
-  bytes.setRange(0, rawBytes.length, rawBytes);
-
   ScannerConfiguration scannerConfiguration = new ScannerConfiguration(
       enableExtensionMethods: true,
       enableNonNullable: true,
       enableTripleShift: true);
 
   Utf8BytesScanner scanner = new Utf8BytesScanner(
-    bytes,
+    rawBytes,
     includeComments: true,
     configuration: scannerConfiguration,
     languageVersionChanged: (scanner, languageVersion) {
diff --git a/pkg/front_end/tool/incremental_perf.dart b/pkg/front_end/tool/incremental_perf.dart
index 7a48c302744..b70d8c6c07a 100644
--- a/pkg/front_end/tool/incremental_perf.dart
+++ b/pkg/front_end/tool/incremental_perf.dart
@@ -44,6 +44,7 @@ library front_end.tool.incremental_perf;
 
 import 'dart:convert';
 import 'dart:io' hide FileSystemEntity;
+import 'dart:typed_data';
 
 import 'package:args/args.dart';
 import 'package:front_end/src/api_prototype/front_end.dart';
@@ -255,7 +256,7 @@ class OverlayFileSystemEntity implements FileSystemEntity {
       (await delegate).existsAsyncIfPossible();
 
   @override
-  Future<List<int>> readAsBytes() async => (await delegate).readAsBytes();
+  Future<Uint8List> readAsBytes() async => (await delegate).readAsBytes();
 
   @override
   Future<List<int>> readAsBytesAsyncIfPossible() async =>
diff --git a/pkg/front_end/tool/perf.dart b/pkg/front_end/tool/perf.dart
index ef56c6adb99..252a277a787 100644
--- a/pkg/front_end/tool/perf.dart
+++ b/pkg/front_end/tool/perf.dart
@@ -212,11 +212,7 @@ Set<Source> scanReachableFiles(Uri entryUri) {
 /// Loads the file contents of all [files] as bytes.
 Set<Uint8List> loadFileContentsAsBytes(Set<Source> files) {
   return files.map((Source source) {
-    final bytes = utf8.encode(source.contents.data);
-    // CFE needs files to e 0-terminated.
-    return Uint8List(bytes.length + 1)
-      ..setRange(0, bytes.length, bytes)
-      ..[bytes.length] = 0;
+    return utf8.encode(source.contents.data);
   }).toSet();
 }
 
diff --git a/pkg/frontend_server/lib/src/binary_protocol.dart b/pkg/frontend_server/lib/src/binary_protocol.dart
index d08ca71940d..c9993162288 100644
--- a/pkg/frontend_server/lib/src/binary_protocol.dart
+++ b/pkg/frontend_server/lib/src/binary_protocol.dart
@@ -189,7 +189,7 @@ class _FileSystemEntity implements fe.FileSystemEntity {
   Future<bool> existsAsyncIfPossible() => exists();
 
   @override
-  Future<List<int>> readAsBytes() async {
+  Future<Uint8List> readAsBytes() async {
     final Uint8List? storedBytes = _fileSystem._dills[uri];
     if (storedBytes != null) {
       return storedBytes;
diff --git a/pkg/kernel/lib/ast.dart b/pkg/kernel/lib/ast.dart
index 75330b1785c..5137c85dc2e 100644
--- a/pkg/kernel/lib/ast.dart
+++ b/pkg/kernel/lib/ast.dart
@@ -66,6 +66,7 @@ library kernel.ast;
 
 import 'dart:collection' show ListBase;
 import 'dart:convert' show utf8;
+import 'dart:typed_data';
 
 import 'package:_fe_analyzer_shared/src/type_inference/nullability_suffix.dart';
 import 'package:_fe_analyzer_shared/src/type_inference/type_analyzer_operations.dart'
@@ -14826,10 +14827,11 @@ class _ChildReplacer extends Transformer {
 }
 
 class Source {
+  static final Uint8List _emptySource = new Uint8List(0);
   final List<int>? lineStarts;
 
   /// A UTF8 encoding of the original source file.
-  final List<int> source;
+  final Uint8List source;
 
   final Uri? importUri;
 
@@ -14841,6 +14843,9 @@ class Source {
 
   Source(this.lineStarts, this.source, this.importUri, this.fileUri);
 
+  Source.emptySource(this.lineStarts, this.importUri, this.fileUri)
+      : source = _emptySource;
+
   /// Return the text corresponding to [line] which is a 1-based line
   /// number. The returned line contains no line separators.
   String? getTextLine(int line) {
diff --git a/pkg/kernel/lib/binary/ast_to_binary.dart b/pkg/kernel/lib/binary/ast_to_binary.dart
index 96bb985f1f9..7c37cbc5b57 100644
--- a/pkg/kernel/lib/binary/ast_to_binary.dart
+++ b/pkg/kernel/lib/binary/ast_to_binary.dart
@@ -879,8 +879,8 @@ class BinaryPrinter implements Visitor<void>, BinarySink {
           !(includeSources &&
               _sourcesFromRealImplementation.length > i &&
               _sourcesFromRealImplementation[i] == true)) {
-        source = new Source(
-            <int>[], const <int>[], source?.importUri, source?.fileUri);
+        source =
+            new Source.emptySource(<int>[], source?.importUri, source?.fileUri);
       }
 
       String uriAsString = "$uri";
diff --git a/pkg/kernel/test/load_concat_dill_keeps_source_test.dart b/pkg/kernel/test/load_concat_dill_keeps_source_test.dart
index 5ed31de5dd1..5ea17720d9d 100644
--- a/pkg/kernel/test/load_concat_dill_keeps_source_test.dart
+++ b/pkg/kernel/test/load_concat_dill_keeps_source_test.dart
@@ -40,7 +40,7 @@ void main() {
   cPartial1.uriToSource[uri1] =
       new Source([42, 2 * 42], utf8.encode("source #1"), uri1, uri1);
   cPartial1.uriToSource[uri2] =
-      new Source([43, 3 * 43], const <int>[], uri1, uri1);
+      new Source.emptySource([43, 3 * 43], uri1, uri1);
   List<int> partial1Serialized = serialize(cPartial1);
   expectSource(partial1Serialized, true, false);
 
@@ -48,7 +48,7 @@ void main() {
     ..setMainMethodAndMode(null, false, NonNullableByDefaultCompiledMode.Strong)
     ..libraries.add(library2);
   cPartial2.uriToSource[uri1] =
-      new Source([42, 2 * 42], const <int>[], uri1, uri1);
+      new Source.emptySource([42, 2 * 42], uri1, uri1);
   cPartial2.uriToSource[uri2] =
       new Source([43, 3 * 43], utf8.encode("source #2"), uri1, uri1);
   List<int> partial2Serialized = serialize(cPartial2);
diff --git a/pkg/vm/lib/http_filesystem.dart b/pkg/vm/lib/http_filesystem.dart
index 59664943056..ed77bf1b64d 100644
--- a/pkg/vm/lib/http_filesystem.dart
+++ b/pkg/vm/lib/http_filesystem.dart
@@ -4,6 +4,7 @@
 
 import 'dart:async';
 import 'dart:io' as io;
+import 'dart:typed_data';
 
 import 'package:front_end/src/api_unstable/vm.dart';
 
@@ -42,7 +43,7 @@ class HttpFileSystemEntity implements FileSystemEntity {
   Future<bool> existsAsyncIfPossible() => exists();
 
   @override
-  Future<List<int>> readAsBytes() async {
+  Future<Uint8List> readAsBytes() async {
     return connectAndRun((io.HttpClient httpClient) async {
       io.HttpClientRequest request = await httpClient.getUrl(uri);
       io.HttpClientResponse response = await request.close();
@@ -51,7 +52,7 @@ class HttpFileSystemEntity implements FileSystemEntity {
         throw new FileSystemException(uri, response.toString());
       }
       List<List<int>> list = await response.toList();
-      return list.expand((list) => list).toList();
+      return new Uint8List.fromList(list.expand((list) => list).toList());
     });
   }