[flutter_tool] Don't crash on a failure to write to std{out,err} (#49380)

packages/flutter_tools/lib/runner.dart

@@ -112,12 +112,12 @@ Future<int> _handleToolError(
     }
   } else {
     // We've crashed; emit a log report.
-    stderr.writeln();
+    safeStdioWrite(stderr, '\n');
 
     if (!reportCrashes) {
       // Print the stack trace on the bots - don't write a crash report.
-      stderr.writeln('$error');
-      stderr.writeln(stackTrace.toString());
+      safeStdioWrite(stderr, '$error\n');
+      safeStdioWrite(stderr, '$stackTrace\n');
       return _exit(1);
     }
 
@@ -138,9 +138,10 @@ Future<int> _handleToolError(
 
       return _exit(1);
     } catch (error) {
-      stderr.writeln(
+      safeStdioWrite(
+        stderr,
         'Unable to generate crash report due to secondary error: $error\n'
-            'please let us know at https://github.com/flutter/flutter/issues.',
+        'please let us know at https://github.com/flutter/flutter/issues.\n',
       );
       // Any exception throw here (including one thrown by `_exit()`) will
       // get caught by our zone's `onError` handler. In order to avoid an

packages/flutter_tools/lib/src/base/io.dart

@@ -253,6 +253,22 @@ Stream<List<int>> get stdin => globals.stdio.stdin;
 io.IOSink get stderr => globals.stdio.stderr;
 bool get stdinHasTerminal => globals.stdio.stdinHasTerminal;
 
+/// Writes [message] to [sink], falling back on [fallback] if the write
+/// throws any exception. The default fallback calls [print] on [message].
+void safeStdioWrite(io.IOSink sink, String message, {
+  void Function(String, dynamic, StackTrace) fallback,
+}) {
+  try {
+    sink.write(message);
+  } catch (err, stack) {
+    if (fallback == null) {
+      print(message);
+    } else {
+      fallback(message, err, stack);
+    }
+  }
+}
+
 // TODO(zra): Move pid and writePidFile into `ProcessInfo`.
 void writePidFile(String pidFile) {
   if (pidFile != null) {

packages/flutter_tools/lib/src/base/logger.dart

@@ -229,9 +229,9 @@ class StdoutLogger extends Logger {
       message = _terminal.bolden(message);
     }
     message = _terminal.color(message, color ?? TerminalColor.red);
-    _stdio.stderr.writeln(message);
+    writeToStdErr('$message\n');
     if (stackTrace != null) {
-      _stdio.stderr.writeln(stackTrace.toString());
+      writeToStdErr('$stackTrace\n');
     }
     _status?.resume();
   }
@@ -269,7 +269,12 @@ class StdoutLogger extends Logger {
 
   @protected
   void writeToStdOut(String message) {
-    _stdio.stdout.write(message);
+    safeStdioWrite(_stdio.stdout, message);
+  }
+
+  @protected
+  void writeToStdErr(String message) {
+    safeStdioWrite(_stdio.stderr, message);
   }
 
   @override
@@ -355,10 +360,10 @@ class WindowsStdoutLogger extends StdoutLogger {
   @override
   void writeToStdOut(String message) {
     // TODO(jcollins-g): wrong abstraction layer for this, move to [Stdio].
-    _stdio.stdout.write(message
-        .replaceAll('✗', 'X')
-        .replaceAll('✓', '√')
-    );
+    final String windowsMessage = message
+      .replaceAll('✗', 'X')
+      .replaceAll('✓', '√');
+    safeStdioWrite(_stdio.stdout, windowsMessage);
   }
 }
 
@@ -789,9 +794,13 @@ class SummaryStatus extends Status {
     super.start();
   }
 
+  void _writeToStdOut(String message) {
+    safeStdioWrite(_stdio.stdout, message);
+  }
+
   void _printMessage() {
     assert(!_messageShowingOnCurrentLine);
-    _stdio.stdout.write('${message.padRight(padding)}     ');
+    _writeToStdOut('${message.padRight(padding)}     ');
     _messageShowingOnCurrentLine = true;
   }
 
@@ -802,14 +811,14 @@ class SummaryStatus extends Status {
     }
     super.stop();
     writeSummaryInformation();
-    _stdio.stdout.write('\n');
+    _writeToStdOut('\n');
   }
 
   @override
   void cancel() {
     super.cancel();
     if (_messageShowingOnCurrentLine) {
-      _stdio.stdout.write('\n');
+      _writeToStdOut('\n');
     }
   }
 
@@ -822,16 +831,16 @@ class SummaryStatus extends Status {
   /// Examples: `    0.5s`, `   150ms`, ` 1,600ms`, `    3.1s (!)`
   void writeSummaryInformation() {
     assert(_messageShowingOnCurrentLine);
-    _stdio.stdout.write(elapsedTime.padLeft(_kTimePadding));
+    _writeToStdOut(elapsedTime.padLeft(_kTimePadding));
     if (seemsSlow) {
-      _stdio.stdout.write(' (!)');
+      _writeToStdOut(' (!)');
     }
   }
 
   @override
   void pause() {
     super.pause();
-    _stdio.stdout.write('\n');
+    _writeToStdOut('\n');
     _messageShowingOnCurrentLine = false;
   }
 }
@@ -894,8 +903,12 @@ class AnsiSpinner extends Status {
     _startSpinner();
   }
 
+  void _writeToStdOut(String message) {
+    safeStdioWrite(_stdio.stdout, message);
+  }
+
   void _startSpinner() {
-    _stdio.stdout.write(_clear); // for _callback to backspace over
+    _writeToStdOut(_clear); // for _callback to backspace over
     timer = Timer.periodic(const Duration(milliseconds: 100), _callback);
     _callback(timer);
   }
@@ -904,21 +917,21 @@ class AnsiSpinner extends Status {
     assert(this.timer == timer);
     assert(timer != null);
     assert(timer.isActive);
-    _stdio.stdout.write(_backspace);
+    _writeToStdOut(_backspace);
     ticks += 1;
     if (seemsSlow) {
       if (!timedOut) {
         timedOut = true;
-        _stdio.stdout.write('$_clear\n');
+        _writeToStdOut('$_clear\n');
       }
       if (slowWarningCallback != null) {
         _slowWarning = slowWarningCallback();
       } else {
         _slowWarning = _defaultSlowWarning;
       }
-      _stdio.stdout.write(_slowWarning);
+      _writeToStdOut(_slowWarning);
     }
-    _stdio.stdout.write('${_clearChar * spinnerIndent}$_currentAnimationFrame');
+    _writeToStdOut('${_clearChar * spinnerIndent}$_currentAnimationFrame');
   }
 
   @override
@@ -932,7 +945,7 @@ class AnsiSpinner extends Status {
   }
 
   void _clearSpinner() {
-    _stdio.stdout.write('$_backspace$_clear$_backspace');
+    _writeToStdOut('$_backspace$_clear$_backspace');
   }
 
   @override
@@ -1002,20 +1015,20 @@ class AnsiStatus extends AnsiSpinner {
   void _startStatus() {
     final String line = '${message.padRight(padding)}$_margin';
     _totalMessageLength = line.length;
-    _stdio.stdout.write(line);
+    _writeToStdOut(line);
   }
 
   @override
   void stop() {
     super.stop();
     writeSummaryInformation();
-    _stdio.stdout.write('\n');
+    _writeToStdOut('\n');
   }
 
   @override
   void cancel() {
     super.cancel();
-    _stdio.stdout.write('\n');
+    _writeToStdOut('\n');
   }
 
   /// Print summary information when a task is done.
@@ -1026,16 +1039,20 @@ class AnsiStatus extends AnsiSpinner {
   /// line before writing the elapsed time.
   void writeSummaryInformation() {
     if (multilineOutput) {
-      _stdio.stdout.write('\n${'$message Done'.padRight(padding)}$_margin');
+      _writeToStdOut('\n${'$message Done'.padRight(padding)}$_margin');
     }
-    _stdio.stdout.write(elapsedTime.padLeft(_kTimePadding));
+    _writeToStdOut(elapsedTime.padLeft(_kTimePadding));
     if (seemsSlow) {
-      _stdio.stdout.write(' (!)');
+      _writeToStdOut(' (!)');
     }
   }
 
   void _clearStatus() {
-    _stdio.stdout.write('${_backspaceChar * _totalMessageLength}${_clearChar * _totalMessageLength}${_backspaceChar * _totalMessageLength}');
+    _writeToStdOut(
+      '${_backspaceChar * _totalMessageLength}'
+      '${_clearChar * _totalMessageLength}'
+      '${_backspaceChar * _totalMessageLength}',
+    );
   }
 
   @override

packages/flutter_tools/lib/src/commands/daemon.dart

@@ -143,7 +143,7 @@ class Daemon {
     final dynamic id = request['id'];
 
     if (id == null) {
-      stderr.writeln('no id for request: $request');
+      safeStdioWrite(stderr, 'no id for request: $request\n');
       return;
     }
 
@@ -323,9 +323,9 @@ class DaemonDomain extends Domain {
           // capture the print output for testing.
           print(message.message);
         } else if (message.level == 'error') {
-          stderr.writeln(message.message);
+          safeStdioWrite(stderr, '${message.message}\n');
           if (message.stackTrace != null) {
-            stderr.writeln(message.stackTrace.toString().trimRight());
+            safeStdioWrite(stderr, '${message.stackTrace.toString().trimRight()}\n');
           }
         }
       } else {
@@ -872,7 +872,13 @@ Stream<Map<String, dynamic>> get stdinCommandStream => stdin
   });
 
 void stdoutCommandResponse(Map<String, dynamic> command) {
-  stdout.writeln('[${jsonEncodeObject(command)}]');
+  safeStdioWrite(
+    stdout,
+    '[${jsonEncodeObject(command)}]\n',
+    fallback: (String message, dynamic error, StackTrace stack) {
+      throwToolExit('Failed to write daemon command response to stdout: $error');
+    },
+  );
 }
 
 String jsonEncodeObject(dynamic object) {

packages/flutter_tools/lib/src/commands/shell_completion.dart

@@ -49,7 +49,8 @@ class ShellCompletionCommand extends FlutterCommand {
     }
 
     if (argResults.rest.isEmpty || argResults.rest.first == '-') {
-      stdout.write(generateCompletionScript(<String>['flutter']));
+      final String script = generateCompletionScript(<String>['flutter']);
+      safeStdioWrite(stdout, script);
       return FlutterCommandResult.warning();
     }
 

packages/flutter_tools/test/general.shard/base/logger_test.dart

@@ -5,12 +5,14 @@
 import 'dart:convert' show jsonEncode;
 
 import 'package:platform/platform.dart';
+import 'package:flutter_tools/src/base/io.dart';
 import 'package:flutter_tools/src/base/logger.dart';
 import 'package:flutter_tools/src/base/terminal.dart';
+import 'package:mockito/mockito.dart';
 import 'package:quiver/testing/async.dart';
 
 import '../../src/common.dart';
-import '../../src/mocks.dart';
+import '../../src/mocks.dart' as mocks;
 
 final Platform _kNoAnsiPlatform = FakePlatform.fromPlatform(const LocalPlatform())..stdoutSupportsAnsi = false;
 final String red = RegExp.escape(AnsiTerminal.red);
@@ -18,6 +20,9 @@ final String bold = RegExp.escape(AnsiTerminal.bold);
 final String resetBold = RegExp.escape(AnsiTerminal.resetBold);
 final String resetColor = RegExp.escape(AnsiTerminal.resetColor);
 
+class MockStdio extends Mock implements Stdio {}
+class MockStdout extends Mock implements Stdout {}
+
 void main() {
   group('AppContext', () {
     FakeStopwatch fakeStopWatch;
@@ -25,10 +30,11 @@ void main() {
     setUp(() {
       fakeStopWatch = FakeStopwatch();
     });
+
     testWithoutContext('error', () async {
       final BufferLogger mockLogger = BufferLogger(
         terminal: AnsiTerminal(
-          stdio: MockStdio(),
+          stdio: mocks.MockStdio(),
           platform: _kNoAnsiPlatform,
         ),
         outputPreferences: OutputPreferences.test(showColor: false),
@@ -51,7 +57,7 @@ void main() {
     testWithoutContext('ANSI colored errors', () async {
       final BufferLogger mockLogger = BufferLogger(
         terminal: AnsiTerminal(
-          stdio:  MockStdio(),
+          stdio:  mocks.MockStdio(),
           platform: FakePlatform()..stdoutSupportsAnsi = true,
         ),
         outputPreferences: OutputPreferences.test(showColor: true),
@@ -75,8 +81,40 @@ void main() {
     });
   });
 
+  testWithoutContext('Logger does not throw when stdio write throws', () async {
+    final MockStdio stdio = MockStdio();
+    final MockStdout stdout = MockStdout();
+    final MockStdout stderr = MockStdout();
+    bool stdoutThrew = false;
+    bool stderrThrew = false;
+    when(stdio.stdout).thenReturn(stdout);
+    when(stdio.stderr).thenReturn(stderr);
+    when(stdout.write(any)).thenAnswer((_) {
+      stdoutThrew = true;
+      throw 'Error';
+    });
+    when(stderr.write(any)).thenAnswer((_) {
+      stderrThrew = true;
+      throw 'Error';
+    });
+    final Logger logger = StdoutLogger(
+      terminal: AnsiTerminal(
+        stdio: stdio,
+        platform: _kNoAnsiPlatform,
+      ),
+      stdio: stdio,
+      outputPreferences: OutputPreferences.test(),
+      timeoutConfiguration: const TimeoutConfiguration(),
+      platform: FakePlatform(),
+    );
+    logger.printStatus('message');
+    logger.printError('error message');
+    expect(stdoutThrew, true);
+    expect(stderrThrew, true);
+  });
+
   group('Spinners', () {
-    MockStdio mockStdio;
+    mocks.MockStdio mockStdio;
     FakeStopwatch mockStopwatch;
     FakeStopwatchFactory stopwatchFactory;
     int called;
@@ -85,7 +123,7 @@ void main() {
 
     setUp(() {
       mockStopwatch = FakeStopwatch();
-      mockStdio = MockStdio();
+      mockStdio = mocks.MockStdio();
       called = 0;
       stopwatchFactory = FakeStopwatchFactory(mockStopwatch);
     });
@@ -375,14 +413,15 @@ void main() {
       });
     }
   });
+
   group('Output format', () {
-    MockStdio mockStdio;
+    mocks.MockStdio mockStdio;
     SummaryStatus summaryStatus;
     int called;
     final RegExp secondDigits = RegExp(r'[^\b]\b\b\b\b\b[0-9]+[.][0-9]+(?:s|ms)');
 
     setUp(() {
-      mockStdio = MockStdio();
+      mockStdio = mocks.MockStdio();
       called = 0;
       summaryStatus = SummaryStatus(
         message: 'Hello world',