Свойство protocolVersion
Версия HTTP-протокола, используемого в запросе, либо "1.0", либо "1.1".
Реализация
String get protocolVersion;
© 2012 the Dart project authors
Licensed under the BSD 3-Clause "New" or "Revised" License.
https://api.dart.dev/stable/2.18.5/dart-io/HttpRequest/protocolVersion.html
