[flutter_tools] Unhandled String exception when VM service connection closes before HTTP header completion (HttpException) #191178

Summary

In Flutter 3.47.0 telemetry, an unhandled String exception during VM Service connection establishment emerged as a top crash signature.

During application launch or debugger attach, if the remote socket resets before HTTP headers are received, dart:io throws HttpException. The connection error was formatted as a raw String and passed to Completer.completeError(), which bypassed on Exception catch blocks in callers and crashed the tool.

Telemetry Profile

• Release: Flutter 3.47.0 (Top 10 crasher)
• Signature: String-3df63b7a

Error Output

String: failed to connect to http://127.0.0.1:63745/TjwUKCgX5S8=/ HttpException: Connection closed before full header was received, uri = http://127.0.0.1:63745/TjwUKCgX5S8=/ws

Root Cause

1. In packages/flutter_tools/lib/src/vmservice.dart, _defaultOpenChannel only caught WebSocketException and SocketException for retries, omitting io.HttpException. Transient socket resets during handshake failed immediately without retries.
2. In packages/flutter_tools/lib/src/resident_runner.dart (FlutterDevice.connect), connection failures were passed to completer.completeError('failed to connect to $vmServiceUri $e', st) as a raw String.
3. Callers (ColdRunner, HotRunner) use on Exception catch (...), which does not catch String, allowing the error to propagate unhandled to the top level.

Proposed Fix

• Add on io.HttpException to _defaultOpenChannel retry loop in vmservice.dart.
• Complete error completers in FlutterDevice.connect with typed Exception objects instead of String.
• Track isConnecting and error state on stream closure in ResidentRunner.connect.