Flutter (attach) expects NO_PROXY Environment Variable to be comma separated list on Windows.

@rakeshdn commented on Jul 26, 2020, 12:17 AM UTC:

While launching a flutter app from Android Studio , the flutter attach stage failed
with a HttpException complaining about a failure to upgrade to websocket for connection
to Dart observatory url on the loopback address 127.0.0.1
The end result is that flutter inspector,outline and performance tabs remain blank
and hot reload buttons stay disabled.

To get this to work ( unfortunately after wasting two days searching forums and trying many things.. )
I had to change NO_PROXY windows system environment variable value from
127.0.0.1;localhost to
127.0.0.1,localhost.
Windows convention is to separate tokens with semicolons rather than commas.
So this is likely to break other windows applications.

Note that Flutter doctor -v is happy with either comma or semicolon, and does not report any issues.

The root cause of problem could be the hard coded "," in code below (from http_impl.dart)
being new to Flutter and Dart, I am not even sure whether the code below is being used....

static String _findProxyFromEnvironment(
      Uri url, Map<String, String> environment) {
    checkNoProxy(String option) {
      if (option == null) return null;
      Iterator<String> names = option.split(",").map((s) => s.trim()).iterator;

Other related issues: (but not Windows specific)
flutter/flutter#25112
flutter/flutter#16875
flutter/flutter#52096

My tool chain version details below.

Microsoft Windows [Version 10.0.18362.836]
(c) 2019 Microsoft Corporation. All rights reserved.

C:\Users\sesa319166\AndroidStudioProjects\mi_card_flutter>flutter doctor -v
[√] Flutter (Channel @U, v1.17.5, on Microsoft Windows [Version 10.0.18362.836], locale en-GB)
• Flutter version 1.17.5 at C:\flsdk\flutter
• Framework revision 8af6b2f (4 weeks ago), 2020-06-30 12:53:55 -0700
• Engine revision ee76268252
• Dart version 2.8.4

[√] Android toolchain - develop for Android devices (Android SDK version 30.0.1)
• Android SDK at C:\Users\sesa319166\AppData\Local\Android\sdk
• Platform android-30, build-tools 30.0.1
• Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)
• All Android licenses accepted.

[√] Android Studio (version 4.0)
• Android Studio at C:\Program Files\Android\Android Studio
• Flutter plugin version 47.1.2
• Dart plugin version 193.7361
• Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[√] VS Code (version 1.47.2)
• VS Code at C:\Users\sesa319166\AppData\Local\Programs\Microsoft VS Code
• Flutter extension version 3.10.1

[√] Proxy Configuration
• HTTP_PROXY is set
• NO_PROXY is 127.0.0.1,localhost
• NO_PROXY contains 127.0.0.1
• NO_PROXY contains localhost

[√] Connected device (1 available)
• Android SDK built for x86 64 • emulator-5554 • android-x64 • Android 8.0.0 (API 26) (emulator)

• No issues found!

This issue was moved by helin24 from flutter/flutter-intellij#4716.

@helin24 commented on Jul 27, 2020, 3:25 AM UTC:

Thanks for this report! I'm not sure if this is an IDE issue or a Flutter issue. The lines you mentioned are in Flutter, but I also see urllib.py in the plugin, which includes:

    # check if the host ends with any of the DNS suffixes
    no_proxy_list = [proxy.strip() for proxy in no_proxy.split(',')]

Are you able to run flutter attach in the CLI or in VSCode?

@rakeshdn commented on Jul 27, 2020, 10:05 AM UTC:

Once I change no_proxy to be comma separated (or override it using set noproxy=127.0.0.1 within the shell) I can run flutter attach from CLI. I am not using VSCode for development at the moment. Thanks.

@helin24 commented on Jul 27, 2020, 3:43 PM UTC:

Okay, thanks for the detail. I suspect if the CLI doesn't work until you change your NO_PROXY comma, then this should be moved to the flutter repo.

[jonahwilliams]

This is an issue with Dart's http implementation.

[TahaTesser]

Hi @rakeshdn
From the above comment, the issue is related to http plugin rather than to Flutter itself. Please open the issue in the dedicated repository.
Closing, as this isn't an issue with Flutter itself.
If you disagree, please write in the comments,
providing your flutter doctor -v, your flutter run -v, your pubspec.yaml
a minimal reproducible code sample that does not use 3rd party plugins,
and I will reopen it.

Thank you

[github-actions]

This thread has been automatically locked since there has not been any recent activity after it was closed. If you are still experiencing a similar issue, please open a new bug, including the output of flutter doctor -v and a minimal reproduction of the issue.