i have the same problem ...
IBOOK:teste $ flutter pub get
Unhandled exception:
Bad state: Future already completed
#0 _AsyncCompleter.complete (dart:async/future_impl.dart:42:31)
#1 _NativeSocket.startConnect..connectNext. (dart:io-patch/socket_patch.dart:642:23)
#2 _NativeSocket.issueWriteEvent.issue (dart:io-patch/socket_patch.dart:1045:14)
#3 _NativeSocket.issueWriteEvent (dart:io-patch/socket_patch.dart:1052:12)
#4 _NativeSocket.multiplex (dart:io-patch/socket_patch.dart:1073:11)
#5 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12)
Running "flutter pub get" in teste...
pub get failed (255; #5 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:168:12))