Develop Reference

Flutter "Connection Refused" (errno=111) when trying to send an http get request to from physical device to pc

I built a flutter app which communicates with a web server that I wrote with flask. Everything works as intended without any errors if I use a virtual device. As soon as I try it in release mode on a physical device I get problems when it comes to the communication with the server
The only thing that I changed when using a physical device is the ip. I use 10.0.2.2 on the virtual device and my computers ip4 adress - that I get with ipconfig in windows 10 - on the physical device
Both devices are in the same network connected to the same router
Internet Permission is enabled in the AndroidManifest for all modes (Debug, Main, Profile)
I even disabled the firewall
The line that causes the issue is
await http.get(url).timeout(Duration(seconds: 15), onTimeout: () {
// Handle timeout
// This entire thing is in a try-catch block in an async function
});
In debug mode on the physical device when the HTTP get request is sent VSCode immediately says
Exception has occurred.
SocketException (SocketException: OS Error: Connection refused, errno = 111, address = 192.168.178.20, port = 43378)
First Question: Why Port 43378? Is that the port the HTTP request is sent to? Because when I run the flask app it says:
Running on http://127.0.0.1:5000/
Could that be the issue? I would have expected the exception to say the port is 5000 as declared in the URL. Or do I have to change something with how I set up the flask app? Currently it is the development server because I am still testing before I pay money and deploy
However I hope I didnt forget any important information. Any advice on what could be wrong or how to debug here is highly aprecciated

Pass an Uri object to http.get func. Uri classes let you specify the port as Documentation https://api.dart.dev/stable/2.12.0/dart-core/Uri-class.html

Call localhost API within react native ( android device : connected through local)

Have created a simple GET API using node.js and trying to consume it within my expo-react native project using axios/fetch.
The GET API is called whenever user clicks on submit button.
Submit -> http://localhost:port/api
However, when I am trying to test the feature on my android device by connecting the device through datacable and selecting "local" connect type in expo, the API call always falls under exception.
When I tried to log the exception, the exception is printed empty.
I double checked the API and it works fine when tested through postman.
I tried replacing localhost url with my-Ip (http://IP:port/api) and also with 127.0.0.1/127.0.2.2 (http://127.0.0.1:port/api , http://127.0.2.2:port/api) , but nothing seems to make the API call a success.
When I replaced the localhost URL with Facebook's network sample API, the application worked just fine. So, there is no issue with the API calling method.
Also, tried adding the port to windows inbound firewall request but that didn't work too.
Can someone help me out with this ?

You must call the API from your local IP address. To get your local IP, just do the following:
If you are on Ubuntu 16.04:
ifconfig | grep 192
If you are on Ubuntu 18.04:
ip -c a | grep 192
Your local IP address will probably be something like 192.168.0.XXX.

yes, i also had this problem until use my Local IP (example: http://192.168.1.55:port) instead 127.0.0.1
please see this answer

Good day,
This is working
I use my machine's IP the Ethernet adapter Ethernet 2: IPV4 Address
And allow my port on firewall both Inbound and outbound rules

cannot connect server when is in android phone

I'm working on a google cardboard project (Unity that will run on android phone)
I created a server in the Unity program that opens like this:
TcpListener listener = new TcpListener(IPAddress.Any, port);
listener.Start();
TcpListener client = listener.AcceptTcpClient();
Everything on backgroundworkers and nice things.
Then I connect from another piece of code running in a PC (WPF C# code). If Im running both programs in the PC I can connect flawlessly but when I compile for android and move the server to the phone, I cannot connect to it from the PC
When I try to perform:
host = Dns.GetHostEntry("192.168.1.8");
I get: Unknown host
The IP is correct (I made the server in the phone show it on screen, and I can ping to it) I think the problem is more related to the thing being in a different machine than to the fat that it is compiled for android but nevertheless.. here you have the full story.
Any help ?

Not sure what it was becauseI moved to UDP messages, and now it works.

QTcpServer - Unsupported Socket Operation on Android

I am trying to start a server on Android using QTcpServer with Qt 5.3.1 but the server does not start and I get "Unsupported Socket Operation". It works fine on Windows.
Code below:
void StartListening()
{
QHostAddress hostAddress;
hostAddress.setAddress(QString("localhost"));
hostAddress.toIPv4Address();
quint16 portNumber = 9878;
server->setMaxPendingConnections(1);
server->setProxy(QNetworkProxy::NoProxy);
if (server->listen(hostAddress, portNumber))
{
// Ok
}
else
{
Debug("Server did not start. " + server->errorString());
}
}
server->errorString() returns "Unsupported Socket Operation when it runs on Android
Isn't this supported by Qt Android or am I doing something wrong?
Thx

OK! I worked it out.
The problem is with this line:
hostAddress.setAddress(QString("localhost"));
If I replace "localhost" with "127.0.0.1", the server starts fine but no one outside the "device the server is running on" can connect to it. This means, let's say your network is using 192.168.1.xx and your Android device has the following IP address: 192.168.1.2. If you start the server with "127.0.0.1" on your Android device which has an IP address: "192.168.1.2" and then using your PC with an IP address 192.168.1.3 you do telnet 192.168.1.2 9878 it will fail to connect!
So then I decided to start the server by specifying the IP address of the Android device: 192.168.1.2
hostAddress.setAddress(QString("192.168.1.2"));
Voila! That works too! The server starts and I can connect from outside the device! For example if I do telnet 192.168.1.2 9878 from my PC while the server is started on Android, it connects! So all I need to do now is replace the hard coded IP address with the actual IP address of the device! I think QNetworkInterface::allInterfaces() or something like that will give me the ability to get the default IP address.
So just use the actual IP address of the network card rather than localhost or 127.0.0.1 and all should be Ok. All working now.

Bluecove on PC cannot detect connected android (galaxy tab 7.0)

I use this code
luugiathuy.com/2011/02/android-java-bluetooth/
The server side is the PC
the client is the device, with the app based on bluetooth chat example
The device (galaxy tab 7.0) can establish connection with the PC.
However the PC server (written in java and bluecove) did nothing, as nothing is connected.
The loop for trying to find connected device is
while(true) {
try {
System.out.println("waiting for connection...");
connection = notifier.acceptAndOpen();
Thread processThread = new Thread(new ProcessConnectionThread(connection));
processThread.start();
} catch (Exception e) {
e.printStackTrace();
return;
}
Output on PC:
uuid: 0000110100001000800000805f9b34fb
waiting for connection...
EDIT: source downloadhttps://github.com/luugiathuy/Remote-Bluetooth-Android

Same issue I got when I was trying in linux. But the reason (still not sure) when you run the bluetooth android application without turning on the Java server using bluecove, It will try to connect with the already installed bluetooth software. You may see the bluetooth icon asking for granting access to the mobile device.
To solve this, I just changed the uuid in the server and application (say from 1103 to 1101 and vice versa) and then started the server first and then the android application. Java server part started listening.
The reason I think may be the uuid when it did not found the bluecove stack service server, it got connected to the device server listening on same uuid. So after changing the uuid and making sure that the server is running before launching the android application should solve the issue.
If you are getting connected to the bluetooth system application and not to the Java bluecove server,
1) First change the uuid both server and android application.
2) Second make sure your server is running and listening on same uuid.
3) Launch the android application which try to communicate on same rfcomm connection uuid.
Server part code I took from : http://www.jsr82.com/jsr-82-sample-spp-server-and-client/
Library : http://code.google.com/p/bluecove/downloads/list

Yes, it happens with me too, I suggest you to fire following commend on shell, when it shows waiting for connection.
hcitool cc 58:C3:8B:D7:FA:F4
here 58:C3:8B:D7:FA:F4 is my device's bluetooth address, which should be replaced by your device's bluetooth address.
To get your device's bluetooth address, just start bluetooth in your device with discoverable mode and execute hcitool scan command, it will display all the active device with their name and bluetooth address.
Well you may run the above hcitool cc 58:C3:8B:D7:FA:F4 command via Java code as follows,
try
{
Process p=Runtime.getRuntime().exec("hcitool cc 58:C3:8B:D7:FA:F4");
}
catch ( Exception e )
{
}

The output from your program says it listens on UUID 0x1101. Is that true? The sample you reference shows it listening on a different UUID. Its Service Class Id is 0x04c6093b and is set as follows:
34 UUID uuid = new UUID(80087355); // "04c6093b-0000-1000-8000-00805f9b34fb"
35 String url = "btspp://localhost:" + uuid.toString() + ";name=RemoteBluetooth";
36 notifier = (StreamConnectionNotifier)Connector.open(url);
The two need to match on client and server.