Web3 Connection refused, help!

[simolus3]

Web3 Connection refused, help!

[liuyuejiang]

I found the problem. In ganache, in the setting, the server's host name is 127.0.0.0 initially, I switch to 0.0.0.0 and it works well!!! Probably, for geth node, the problem is rpcdomain property.
Thank you so much! Finally, I spend a whole night to solve this problem.

[simolus3]

Right, but the Android emulator will also setup a virtual network, so you can't reach your host through 0.0.0.0. You can use 10.0.2.2 though, as explained here.

[simolus3]

No, it wouldn't work on a real device. In that case you'd have to lookup the IP address of the host. Inside your local network it probably starts with 192.168, so you could use that address for devices inside your local network.

[liuyuejiang]

var privatekey = '0x6166244d506a4c1635e0a0723cda3780fa80462a869682xxxxxxxxxx';
var apiUrl = "http://10.0.0.47:8545"; //Replace with your API

var httpClient = new Client();
var ethClient = new Web3Client(apiUrl, httpClient);
// String data = await DefaultAssetBundle.of(context).loadString(
//     "assets/web3/8acd17e6f4fef86fdf75078d179ec2612fb354ae.json");
// final jsonResult = json.encode(data);

// Wallet wallet = Wallet.fromJson(data, "aa");
var credentials = Credentials.fromPrivateKeyHex(privatekey);

// Credentials unlocked = wallet.credentials;
EtherAmount balance = await ethClient.getBalance(credentials.address);
print(balance.getValueInUnit(EtherUnit.ether));

I tried to use both methods. It didn't work.

[simolus3]

If you try something like

var httpClient = new Client();
await httpClient.get('$apiUrl/');

before starting your ethClient. Does that also throw the exception?
If so, you might be missing the internet permission in your Flutter app. Maybe this helps?

[liuyuejiang]

If you try something like

var httpClient = new Client();
await httpClient.get('$apiUrl/');

before starting your ethClient. Does that also throw the exception?
If so, you might be missing the internet permission in your Flutter app. Maybe this helps?

It doesn't help when I add await httpClient.get('$apiUrl/');, the same exception.
This time I deployed my smart contract on ganache, when I tried to connect, it shows the same exception.
Could it be a problem with MacOS? Do I need to switch to Linux to deploy my smart contract?

[simolus3]

I don't think it's an issue with your operating system. Rather, the error indicates that your Flutter app is unable to reach the network.

Are you on Android? If so, try adding <uses-permission android:name="android.permission.INTERNET" /> to the AndroidManifest.xml in the android/app folder of your Flutter project.

[liuyuejiang]

I have already added the permission long long ago, the app can access the Internet well.
Do I need to provide other environment information?

[simolus3]

Hm, that's really weird.
But just to be sure, if you remove the web3dart related code of that snippet entirely and just try to make a request with the http package like this:

import "package:http/http.dart" as http;

await http.get("http://10.0.0.47:8545");

You do get the same problem, right?

I don't really get how your app can access the internet while still getting connection errors in web3dart. This library delegates all the work to the Client(), which is part of the http package. If you're making http requests elsewhere in your app, you're probably already using that package. It's weird how that works while there are errors in web3dart.

I'm not really familiar with MacOS unfortunately. I might be that there is a firewall blocking that port, even from the local network?

[liuyuejiang]

Hm, that's really weird.
But just to be sure, if you remove the web3dart related code of that snippet entirely and just try to make a request with the http package like this:

import "package:http/http.dart" as http;

await http.get("http://10.0.0.47:8545");

You do get the same problem, right?

I don't really get how your app can access the internet while still getting connection errors in web3dart. This library delegates all the work to the Client(), which is part of the http package. If you're making http requests elsewhere in your app, you're probably already using that package. It's weird how that works while there are errors in web3dart.

I'm not really familiar with MacOS unfortunately. I might be that there is a firewall blocking that port, even from the local network?

I do have these permissions, like:
<uses-permission android:name="android.permission.INTERNET" /> <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" /> <uses-permission android:name="android.permission.ACCESS_LOCATION_EXTRA_COMMANDS" /> <uses-permission android:name="android.permission.WAKE_LOCK" /> <uses-permission android:name="android.hardware.location.gps" /> <uses-permission android:name="android.permission.READ_PHONE_STATE"/> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

So, that's why confusing. I will try to use http tomorrow. Thank you, I will let you know.

[PeterTF656]

@simolus3 @liuyuejiang I am running into a very similar issue... In my case, my app runs fine on an ios simulator, but on an actual android device/emulator, it gives out E/flutter ( 6625): [ERROR:flutter/lib/ui/ui_dart_state.cc(199)] Unhandled Exception: SocketException: OS Error: Connection refused, errno = 111, address = 0.0.0.0, port = 51300, and I have added in the permission for android to access internet.

When I opened the dart dev tool, in the Network tab, the ws and http methods both showed pending.

Any help is appreciated...

[simolus3]

Why would you connect to 0.0.0.0? Surely there's no Ethereum node running on the actual emulator?

[PeterTF656]

Why would you connect to 0.0.0.0? Surely there's no Ethereum node running on the actual emulator?

Thank you sir for your quick reply. I used Ganache and I changed the server hostname to 0.0.0.0 - all interfaces

[PeterTF656]

Right, but the Android emulator will also setup a virtual network, so you can't reach your host through 0.0.0.0. You can use 10.0.2.2 though, as explained here.

Yes sir, It did work. Thank you! One more question, how about a real android device? Will it work with 10.0.2.2 Ganache?