[VM/Service] Include newline in the stdout service event.

TEST=new test added

Bug:54582
Change-Id: I5e8d3aab19c37353a12e3a0a65edbb954d52bb4b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/346084
Reviewed-by: Ben Konyi <bkonyi@google.com>
Commit-Queue: Siva Annamalai <asiva@google.com>

pkg/vm_service/test/capture_stdio_test.dart

@@ -37,11 +37,11 @@ var tests = <IsolateTest>[
       // initial stream subscription. Wait for the initial sentinel before
       // executing test logic.
       if (!started) {
-        started = output == 'start';
+        started = output == 'start\n';
         return;
       }
       expect(event.kind, EventKind.kWriteEvent);
-      expect(output, 'stdout');
+      expect(output, 'stdout\n');
       await stdoutSub.cancel();
       await service.streamCancel(EventStreams.kStdout);
       completer.complete();
@@ -57,7 +57,7 @@ var tests = <IsolateTest>[
     stdoutSub = service.onStdoutEvent.listen((event) async {
       expect(event.kind, EventKind.kWriteEvent);
       final decoded = utf8.decode(base64Decode(event.bytes!));
-      expect(decoded, 'print');
+      expect(decoded, 'print\n');
       await service.streamCancel(EventStreams.kStdout);
       await stdoutSub.cancel();
       completer.complete();

pkg/vm_service/test/stdio_newline_test.dart

@@ -0,0 +1,53 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// 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:async';
+import 'dart:convert';
+import 'dart:developer';
+
+import 'package:test/test.dart';
+import 'package:vm_service/vm_service.dart';
+
+import 'common/service_test_common.dart';
+import 'common/test_helper.dart';
+
+void test() {
+  print('started');
+  debugger();
+  print('lf1\ntrail');
+}
+
+var tests = <IsolateTest>[
+  hasStoppedAtBreakpoint,
+  (VmService service, IsolateRef isolateRef) async {
+    print('At breakpoint');
+    final completer = Completer<void>();
+    late StreamSubscription stdoutSub;
+    bool started = false;
+    stdoutSub = service.onStdoutEvent.listen((event) async {
+      final output = utf8.decode(base64Decode(event.bytes!));
+      // DDS buffers log history and sends each entry as an event upon the
+      // initial stream subscription. Wait for the initial sentinel before
+      // executing test logic.
+      if (!started) {
+        started = output == 'started\n';
+        return;
+      }
+      expect(output, 'lf1\ntrail\n');
+      await stdoutSub.cancel();
+      await service.streamCancel(EventStreams.kStdout);
+      completer.complete();
+    });
+    await service.streamListen(EventStreams.kStdout);
+    await service.resume(isolateRef.id!);
+    await completer.future;
+  },
+];
+
+Future<void> main(args) => runIsolateTests(
+      args,
+      tests,
+      'stdio_newline_test.dart',
+      testeeConcurrent: test,
+    );

runtime/bin/builtin_natives.cc

@@ -89,7 +89,8 @@ void FUNCTION_NAME(Builtin_PrintString)(Dart_NativeArguments args) {
   if (Dart_IsError(result)) {
     Dart_PropagateError(result);
   }
-  uint8_t* chars = Dart_ScopeAllocate(length + 1);
+  intptr_t new_length = length + 1;
+  uint8_t* chars = Dart_ScopeAllocate(new_length);
   ASSERT(chars != nullptr);
   result = Dart_CopyUTF8EncodingOfString(str, chars, length);
   if (Dart_IsError(result)) {
@@ -98,13 +99,13 @@ void FUNCTION_NAME(Builtin_PrintString)(Dart_NativeArguments args) {
   chars[length] = '\n';
 
   // Uses fwrite to support printing NUL bytes.
-  intptr_t res = fwrite(chars, 1, length + 1, stdout);
-  ASSERT(res == (length + 1));
+  intptr_t res = fwrite(chars, 1, new_length, stdout);
+  ASSERT(res == new_length);
   fflush(stdout);
   if (ShouldCaptureStdout()) {
     // For now we report print output on the Stdout stream.
     const char* res =
-        Dart_ServiceSendDataEvent("Stdout", "WriteEvent", chars, length);
+        Dart_ServiceSendDataEvent("Stdout", "WriteEvent", chars, new_length);
     ASSERT(res == nullptr);
   }
 }