HttpClient crashes when using lantern VPN on Ubuntu.

• Dart SDK Version (dart --version)
  Dart VM version: 2.5.0-dev.1.0 (Unknown timestamp) on “linux_x64”
• OS: Ubuntu 18.04
• Issue: flutter pub get error, reproduced by the following sample code.

Hi, Dart team,
I get an error when updating flutter sdk using flutter pub get. same issue as flutter/flutter#12301. I think the root cause may related to the dart:io package.

Here’s my analyze:

1. I set up a Dart Command line app and reproduced the error:

`
import “dart:io”;
void main() {
var google = “https://www.google.com/“;
var client2 = HttpClient();
// same crash
// client2.findProxy = (uri) {
// return “PROXY 127.0.0.1:45653”;
// };

// same crash
client2.findProxy = (url) {
return HttpClient.findProxyFromEnvironment(
url, environment: {“http_proxy”: “127.0.0.1:45653”, “https_proxy”: “127.0.0.1:45653”});
};

// no respond.
// client2.findProxy = HttpClient.findProxyFromEnvironment;
// no respond.
// client2.findProxy = null;

client2.getUrl(
Uri.parse(google))
.then((HttpClientRequest request) {
print(request.headers);
return request.close();
}).then((HttpClientResponse response) {
// Process the response.
print(response.headers);
});
}
`

2. Error message is:

Unhandled exception: NoSuchMethodError: The setter 'readEventsEnabled=' was called on null. Receiver: null Tried calling: readEventsEnabled=false #0 _rootHandleUncaughtError.<anonymous closure> (dart:async/zone.dart:1112:29) #1 _microtaskLoop (dart:async/schedule_microtask.dart:41:21) #2 _startMicrotaskLoop (dart:async/schedule_microtask.dart:50:5) #3 _runPendingImmediateCallback (dart:isolate-patch/isolate_patch.dart:116:13) #4 _RawReceivePortImpl._handleMessage (dart:isolate-patch/isolate_patch.dart:173:5)

3. VPN settings:

I think this may related to my VPN environment settings. The following parameters are set automatically by Lantern VPN software. https://github.com/getlantern/lantern
`lixiang@lixiang-TM1701:~$ env | grep proxy

https_proxy=http://127.0.0.1:45653/
http_proxy=http://127.0.0.1:45653/
no_proxy=localhost,127.0.0.0/8,::1
`

4. curl is working.

curl https://www.google.com

5. JAVA is working with proxy
   `
   package com.tony.builder;

import org.apache.http.HttpEntity;
import org.apache.http.HttpHost;
import org.apache.http.ParseException;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.IOException;

public class Main {

public static void main(String[] args) {
    String result = sendGet("http://www.google.com");
    System.out.println(result);
}

public static String sendGet(String url) {
    HttpHost proxy = new HttpHost("127.0.0.1", 45653, "http");

    RequestConfig defaultRequestConfig = RequestConfig.custom()
            .setProxy(proxy)
            .build();

    CloseableHttpClient httpclient = HttpClients.custom().setDefaultRequestConfig(defaultRequestConfig).build();

    HttpGet httpget = new HttpGet(url);
    CloseableHttpResponse response = null;
    try {
        response = httpclient.execute(httpget);
    } catch (IOException e1) {
        e1.printStackTrace();
    }
    String result = null;
    try {
        HttpEntity entity = response.getEntity();
        if (entity != null) {
            result = EntityUtils.toString(entity);
        }
    } catch (ParseException | IOException e) {
        e.printStackTrace();
    } finally {
        try {
            response.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    return result;
}

}
`

Any ideas or suggestion will be helpful, thanks.

@sgjesse https://github.com/sgjesse Maybe you have more ideas? thanks.