Develop Reference

python client cant connect to java server

im trying to talk between my java app and python client. But it cant seem to connect.
I am not sure if it is because of a wrong IP-adress. Because i read somewhere that you can use the IP of the PC to connect to the virtual device, but i also used the 10.0.x.x address of the virtual device which also doesnt seem to work. In IntelliJ my code does seem to work, only not with the app.
my python client code:
import socket
HOST = "172.20.10.12"
PORT = 8080
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.connect((HOST, PORT))
print('connected')
sock.sendall(b'Hello!')
data = sock.recv(1024)
print("1", data, '\n')
sock.sendall(b'Bye\n')
data = sock.recv(1024)
print("2", data, '\n')
print("Socket closed")
sock.close()
And this is the receiving side of my app: StartReceive.java:
package com.example.test;
import java.io.IOException;
class StartReceive implements Runnable {
#Override
public void run() {
try {
Receive.startReceive();
} catch (IOException e) {
e.printStackTrace();
}
}
}
My receive.java:
public class Receive {
static String fromClient;
static String toClient;
public static void startReceive() throws IOException {
ServerSocket server = new ServerSocket(8080);
System.out.println("wait for connection on port 8080");
boolean run = true;
while (run) {
Socket client = server.accept();
System.out.println("got connection on port 8080");
BufferedReader in = new BufferedReader(new InputStreamReader(client.getInputStream()));
PrintWriter out = new PrintWriter(client.getOutputStream(), true);
fromClient = in.readLine();
System.out.println("received: " + fromClient);
if (fromClient != null) {
toClient = "message is received on server";
System.out.println("send: message is received");
out.println(toClient);
fromClient = in.readLine();
System.out.println("received: " + fromClient);
if (fromClient.equals("Bye")) {
toClient = "bye received on server";
System.out.println("send: bye received on server");
out.println(toClient);
client.close();
run = false;
System.out.println("socket closed");
}
}
}
}
}
And then i call it in my mainactivity like this:

To debug the connection issue, first try and set the IP to "localhost" on the client.
You might also usefully print server.getInetAddress() on the server side. It's possible you're not listening on the specific address that your client wanted to connect to.
I would debug this as follows:
Run the server
On the server PC, type the command 'netstat -a -p tcp' (this is Windows, right) and look for something you recognize as the server. The "virtual android device" must show up on the physical PC, since the physical PC is the thing that is physically connected to the physical network.
Try and connect to that server using some utility or other; I prefer telnet. 'telnet '. You should at least see your server's "connected" message on the server console output.
If this all goes well, you now know the server is basically functional.
Once your client is connected, you have a further bug:
You are sending 6 bytes, no newline.
sock.sendall(b'Hello!')
You are expecting to receive data terminated by a newline.
fromClient = in.readLine();
Your receiver is still waiting for the end of the line.

Arduino RP2040 (client) - Python (server) through WiFi

I am trying to connect my Arduino Nano Connect RP2040 with my machine using Python (3.8.8). I want to use WiFi communication protocol and I am currently working on a client-server socket.
Since I am not so familiar with this communication protocol I am following this thread which looks to perform good results. Of course, this thread talks about Ethernet and I am readapting using WiFiNina library which has been developed by Arduino in order to use the module.
Here the code I am running on Arduino:
#include <SPI.h>
#include <WiFiNINA.h>
#include <ArduinoJson.h>
// Enter a MAC address and IP address for your controller below.
// The IP address will be dependent on your local network:
byte mac[] = {
0x08, 0x3A, 0xF2, 0xB1, 0x9D, 0xE0 };
IPAddress ip(192,168,43,98);
// Enter the IP address of the server you're connecting to:
IPAddress server(192,168,0,4);
// Initialize the WiFi client library
// with the IP address and port of the server
WiFiClient client;
char ssid[] = "xxxxx"; // the name of your network
char username[] = "xxxxxxx";
char pass[] = "xxxxxxx";
void setup() {
// start the Wifi connection:
WiFi.beginEnterprise(ssid, username, pass);
// Open serial communications and wait for port to open:
Serial.begin(9600);
while (!Serial) {
; // wait for serial port to connect. Needed for Leonardo only
}
// give the Ethernet shield a second to initialize:
delay(1000);
Serial.println("connecting...");
// if you get a connection, report back via serial:
if (client.connect(server, 13380)) {
Serial.println("connected");
}
else {
// if you didn't get a connection to the server:
Serial.println("connection failed");
}
}
void loop()
{
//JSON stuff
StaticJsonBuffer<200> jsonBuffer;
JsonObject& root = jsonBuffer.createObject();
root["sensor"] = "gps";
root["time"] = 42;
JsonArray& data = root.createNestedArray("data");
data.add(48.756080);
data.add(2.302038);
char json[100];
root.printTo(json);
Serial.print(json);
// if there are incoming bytes available
// from the server, read them and print them:
if (client.available()) {
char c = client.read();
Serial.print(c);
}
// as long as there are bytes in the serial queue,
// read them and send them out the socket if it's open:
if (client.connected()) {
client.print(json);
}
// if the server's disconnected, stop the client:
if (!client.connected()) {
Serial.println();
Serial.println("disconnecting.");
client.stop();
// do nothing:
while(true);
}
}
I have used some functions from WiFiNina (for example .beginEnterprise() in order to connect Arduino to the network).
For what server concerns, here the code in Python:
import socket
import sys
import json
# host = '127.0.0.1'
host = '192.168.0.4'
port = 13380
address = (host, port)
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind(address)
server_socket.listen(5)
# server_socket.connect(address)
print ("waiting for a connection . . .")
conn, address = server_socket.accept()
print ("Connection established: "), address
while True:
output = conn.recv(84048);
if output.strip() == "disconnect":
conn.close()
sys.exit("Disconnect message received - terminate the connection")
conn.send("dack")
elif output:
print(output)
data = json.load(output)
print(data)
I am not interested in sending JSON data, like I have already mentioned I am just readapt the code in thread. I actually need to send data in real-time, but step-by-step :-)
The problem is that I cannot establish the connection between Arduino (client) and Python (server).
From server part, I actually got this error:
Traceback (most recent call last):
File "server_arduino.py", line 18, in <module>
server_socket.bind(address)
OSError: [WinError 10049] The requested address is not valid in its context
For some reasons which I actually did not understand yet, if I would change host in 127.0.0.1 (following suggestions here) the server part starts to work, and it stucks in waiting for a connection . . . printed in my console, because it needs a client to connect.
At this stage, running my Arduino code I got this:
connecting...
connection failed
{"sensor":"gps","time":42,"data":[48.75608,2.302038]}
disconnecting.
So, it does mean to me that I was able to connect to WiFi, but not to server.
Does anyone give me any suggestions?
I know I am really beginner and any suggestions would be really appreciated.

Socket server between Unity and Raspberry doesn't connect

So I am trying to send data from the raspberry pi to unity.
I trying to create socket server to do so.
I can get the socket server running on the raspberry pi and can also look at the port with netstat -tulpn | grep :5005 in the terminal on the machine where the python script is running.
I also tried it on my mac and it also showed up as a TCP-server.
However when I try to connect to the same port and ip via Unity or on another machine it doesn't work. I also can't seem to find the port when listing all of the ports with netstat.
Unity spits out a "Connection refused" error.
Here is the code in Unity in C#
using UnityEngine;
using System.Collections;
using System;
using System.IO;
using System.Net.Sockets;
public class ClientSocket : MonoBehaviour
{
bool socketReady = false;
TcpClient mySocket;
public NetworkStream theStream;
StreamWriter theWriter;
StreamReader theReader;
public String Host = "192.168.8.137";
public Int32 Port = 5005;
void Start()
{
setupSocket();
TextMessage("SocketTest");
}
public void setupSocket()
{ // Socket setup here
try
{
mySocket = new TcpClient(Host, Port);
theStream = mySocket.GetStream();
theWriter = new StreamWriter(theStream);
theReader = new StreamReader(theStream);
socketReady = true;
}
catch (Exception e)
{
Debug.Log("Socket error:" + e); // catch any exceptions
}
}
public void TextMessage(string message)
{
if (socketReady == true)
{
theWriter.Write(message);
theWriter.Flush();
}
}
}
here is the code in python, which should be running on the raspberry pi.
import socket
import sys
backlog = 1
size = 1024
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind(('192.168.8.137', 5005))
s.listen(1)
try:
print ("is waiting")
client, address = s.accept()
while 1:
data = client.recv(size)
if data:
print (data)
finally:
print("closing socket")
cient.close()
s.close()
I'm new to socket servers, but I really trying to accomplish a connection here.
Thanks for reading!

am pretty sure you need to encode the data that you about to send in c# TcpClient
adding an example from my final project:
string data = "Hello Server!"; //the message in string (important it will be string)
byte[] msg = Encoding.Unicode.GetBytes(data); //encoded the message using unicode (utf-16)
NetworkStream stream = client.GetStream(); //get the tcp client stream
stream.Write(msg, 0, msg.Length); //write the message to the stream
and in the server you suppose to have something like that:
msg = clnt.recv(1024) #reciving the data
msg = msg.decode("utf-16") #decoding the data
print(msg) #printing the data
and i think thats it
and i would recommend using port above 10000 because most of the ports can be used

C# communication with Python - No connection could be made because the target machine actively refused it

I'm trying to set up communication through a TCP/IP connection and are having problems with connecting the C# client to the Python Server.
It throws a SocketException:
System.Net.Sockets.SocketException: No connection could be made because the target machine actively refused it
I'm pretty sure that it is happening at the line where it tries to connect to the Python server: sender.Connect(remoteEP);
What I've tried
Before I used the IPv4 protocol and Pythons socket.AF_INET but I discovered that it seems like that my parsing of the IP Address in C# makes it an IPv6 address so that's what I'm using now but that didn't resolve the problem.
I also tried using IPAddress.Parse(ip) instead of getting the host first with Dns.GetHostEntry(ip) but that didn't seem to do anything.
The code
The C# code:
using UnityEngine;
using System;
using System.Net;
using System.Net.Sockets;
using System.Collections;
using System.Text;
public class PyCommunicator : MonoBehaviour {
private string ip = "::1"; // Localhost
private int port = 14654;
public string dataStringToSend
{
get { return dataStringToSend; }
set { dataStringToSend = value; }
}
private void Start()
{
StartCoroutine(RequestServerCoroutine());
}
IEnumerator RequestServerCoroutine()
{
while (true)
{
RequestServer();
yield return new WaitForSecondsRealtime(10);
}
}
public void RequestServer()
{
byte[] bytes = new byte[1024]; // 1 KiloByte
try
{
// Connect to a Remote server,
// and get host IP Address that is used to establish a connection.
// In this case, we get one IP address of localhost that is IPv6 : ::1
// If a host has multiple addresses, you will get a list of addresses
IPHostEntry host = Dns.GetHostEntry(ip);
IPAddress ipAddress = host.AddressList[0];
IPEndPoint remoteEP = new IPEndPoint(ipAddress, port);
// Create a TCP/IP socket.
Socket sender = new Socket(AddressFamily.InterNetworkV6,
SocketType.Stream, ProtocolType.Tcp);
// Connect the socket to the remote endpoint. Catch any errors.
try
{
// Connect to Remote EndPoint
sender.Connect(remoteEP);
Debug.Log("Successfully established a connection between Unity and Python.");
// Encode the data string into a byte array.
dataStringToSend = "Test from C#";
if (dataStringToSend != "")
{
byte[] msg = Encoding.ASCII.GetBytes(dataStringToSend);
// Send the data through the socket.
int bytesSent = sender.Send(msg);
// Reset.
dataStringToSend = "";
}
// Receive the response from the remote device.
int bytesRec = sender.Receive(bytes);
Debug.LogFormat("Echoed test = {0}",
Encoding.ASCII.GetString(bytes, 0, bytesRec));
// Release the socket.
sender.Shutdown(SocketShutdown.Both);
sender.Close();
}
catch (ArgumentNullException ane)
{
Debug.LogFormat("ArgumentNullException: {0}", ane.ToString());
}
catch (SocketException se)
{
Debug.LogFormat("SocketException: {0}", se.ToString());
}
catch (Exception e)
{
Debug.LogFormat("Unexpected exception: {0}", e.ToString());
}
}
catch (Exception e)
{
Debug.LogFormat("Exception from setup: {0}", e.ToString());
}
}
}
The C# code was taken from this link from the client section and modified for my own use.
Python code:
import socket
from time import sleep
class Communicator():
def __init__(self, ip, port):
self.ip = ip
self.port = port
self.data_to_send = None
self.socket = None
self.socket_conn = None
self.socket_addr = None
# Start listening right away.
self.start()
def start(self):
"""Start listening and accept connection."""
self.socket = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
self.socket.bind((self.ip, self.port))
# Begin listening for 1 connection.
self.socket.listen(1)
print("Socket is listening on ip (" + str(self.ip) + ") and port " + str(self.port))
self.socket_conn, self.socket_addr = self.socket.accept()
print("Connection between Unity and Python established. Unity-C# is at: " + str(self.socket_addr))
sleep(5) # TESTING PURPOSES
# Receive.
result = ""
chunk_counter = 0
while True:
# Allow the server to read up to 1024 bytes.
data = self.conn.recv(1024)
chunk_counter += 1
# To minimize lag, read guess in chunks.
if chunk_counter < 5:
result += data.decode()
# If reading the guess is done,
# break out of loop.
if not data:
break
# Send.
self.socket.send("Test from python".encode())
# Close
self.socket.close()
def send_data(self):
"""Send data"""
pass
def receive_data(self):
"""Receive data"""
pass
Communicator('::1', 14654)

It seems like I didn't search the StackOverflow forum enough.
I found a solution in the code and answer given in this StackOverflow answer.
I didn't need to use the actual localhost loopback address and instead needed to get the HOSTNAME address through C#'s DNS function:
Dns.GetHostName()
I also used socket.gethostname() in Python so that they would have same addresses when connecting.
I also changed the whole thing to use IPv4 addresses and found out in the answer of the linked question that the first element in host.AddressList contains IPv6 addresses while the second AND last element contained IPv4 addresses, and that was the missing piece.
UPDATED CODE
C# Code:
using UnityEngine;
using System;
using System.Net;
using System.Net.Sockets;
using System.Collections;
using System.Text;
public class PyCommunicator : MonoBehaviour {
private int port = 14654;
public string dataStringToSend
{
get { return dataStringToSend; }
set { dataStringToSend = value; }
}
private void Start()
{
StartCoroutine(RequestServerCoroutine());
}
IEnumerator RequestServerCoroutine()
{
while (true)
{
RequestServer();
yield return new WaitForSecondsRealtime(10);
}
}
public void RequestServer()
{
byte[] bytes = new byte[1024]; // 1 KiloByte
try
{
// Connect to a Remote server,
// and get host IP Address that is used to establish a connection.
// In this case, we get one IP address of localhost that is IP : 127.0.0.1
// If a host has multiple addresses, you will get a list of addresses
IPHostEntry host = Dns.GetHostEntry(Dns.GetHostName());
IPAddress ipAddress = host.AddressList[1];
IPEndPoint remoteEP = new IPEndPoint(ipAddress, port);
// Create a TCP/IP socket.
Socket sender = new Socket(ipAddress.AddressFamily,
SocketType.Stream, ProtocolType.Tcp);
// Connect the socket to the remote endpoint. Catch any errors.
try
{
// Connect to Remote EndPoint
sender.Connect(remoteEP);
Debug.Log("Successfully established a connection between Unity and Python.");
// Encode the data string into a byte array.
dataStringToSend = "Test from C#";
if (dataStringToSend != "")
{
byte[] msg = Encoding.ASCII.GetBytes(dataStringToSend);
// Send the data through the socket.
int bytesSent = sender.Send(msg);
// Reset.
dataStringToSend = "";
}
// Receive the response from the remote device.
int bytesRec = sender.Receive(bytes);
Debug.LogFormat("Echoed test = {0}",
Encoding.ASCII.GetString(bytes, 0, bytesRec));
// Release the socket.
sender.Shutdown(SocketShutdown.Both);
sender.Close();
}
catch (ArgumentNullException ane)
{
Debug.LogFormat("ArgumentNullException: {0}", ane.ToString());
}
catch (SocketException se)
{
Debug.LogFormat("SocketException: {0}", se.ToString());
}
catch (Exception e)
{
Debug.LogFormat("Unexpected exception: {0}", e.ToString());
}
}
catch (Exception e)
{
Debug.LogFormat("Exception from setup: {0}", e.ToString());
}
}
}
Python Code:
import socket
from time import sleep
class Communicator():
def __init__(self, ip, port):
self.ip = ip
self.port = port
self.data_to_send = None
self.socket = None
self.socket_conn = None
self.socket_addr = None
# Start listening right away.
self.start()
def start(self):
"""Start listening and accept connection."""
self.socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
self.socket.bind((self.ip, self.port))
# Begin listening for 1 connection.
self.socket.listen(1)
print("Socket is listening on ip (" + str(self.ip) + ") and port " + str(self.port))
self.socket_conn, self.socket_addr = self.socket.accept()
print("Connection between Unity and Python established. Unity-C# is at: " + str(self.socket_addr))
sleep(5) # TESTING PURPOSES
# Receive.
result = ""
chunk_counter = 0
while True:
# Allow the server to read up to 1024 bytes.
data = self.conn.recv(1024)
chunk_counter += 1
# To minimize lag, read guess in chunks.
if chunk_counter < 5:
result += data.decode()
# If reading the guess is done,
# break out of loop.
if not data:
break
# Send.
self.socket.send("Test from python".encode())
# Close
self.socket.close()
def send_data(self):
"""Send data"""
pass
def receive_data(self):
"""Receive data"""
pass
Communicator(socket.gethostname(), 14654)

Communicating between Raspberry Pi and Arduino over LAN

I'm doing image processing with a raspberry pi, and I want it to be able to talk to my arduino over LAN to steer a light beam based on the pi's instructions. The only things I've seen a lot are direct connections between the Pi and the Arduino. It may seem naive of me, but I was trying to have them communicate using the Arduino as a server, programmed with the Ethernet library, and the Raspberry Pi as the client through the socket library. I gave them both static IP's on my router, and used the following code to try and get through, but I was met with socket.error: [Errno 113] No route to host when my python line came to the command to connect to the Arduino's IP through a specific port.
Any ideas on how I could more properly do this connection? The main goal for me is to be able to do this over LAN, so the USB connections and the direct I2C connections aren't helpful, though they would definitely get the job done.
Raspberry Pi:
from socket import *
import select
data = None
timeout = 3 # timeout in seconds
msg = "test"
host = "192.168.1.113"
print ("Connecting to " + host)
port = 23
s = socket(AF_INET, SOCK_STREAM)
print "Socket made"
ready = select.select([s],[],[],timeout)
s.connect((host,port))
print("Connection made")
while True:
if data != None:
print("[INFO] Sending message...")
s.sendall(msg)
data = None
print("[INFO] Message sent.")
continue
if ready[0]: #if data is actually available for you
data = s.recv(4096)
print("[INFO] Data received")
print data
continue
Arduino:
//90-a2-da-0f-25-E7
byte mac[] = {0x90, 0xA2, 0xDA, 0x0f, 0x25, 0xE7};
//ip Address for shield
byte ip[] = {192,168,1,113};
//Use port 23
EthernetServer server = EthernetServer(23);
void setup() {
//init device
Ethernet.begin(mac,ip);
//start listening for clients
server.begin();
Serial.begin(9600); //For visual feedback on what's going on
while(!Serial){
; //cause Leonardo
}
delay(1000);
if(server.available()){
Serial.write("Client available");
}
}
void loop() {
// put your main code here, to run repeatedly:
EthernetClient client = server.available();
if (client == true){
Serial.write("Client Connected.");
if(client.read() > 0){
Serial.write(client.read());
}
else{
server.write("ping");
}
}
else{
Serial.println("No one's here yet...");
}
delay(1500);
}

After digging around, I found my solution, and some more details. So both the R-Pi and the Arduino can do TCP, and I found the source of my errors.
1) I believe the delay I set after server.begin() in my Arduino Code was giving me the error, since it pauses the program and so probably pauses the listening process.
2) The while loop in my R-Pi client code was giving me a broken pipe error.
3) The if (client == True) test in my Arduino's loop() was not working. The R-Pi could connect and send messages with no error, but the Arduino didn't seem to be responding properly. Once I pulled everything out of the if statement, the R-Pi started receiving my messages and I saw everything respond. Here's my final code:
R-Pi:
from socket import *
import select
data = None
timeout = 3 # timeout in seconds
msg = "test"
host = "192.168.1.113"
print ("Connecting to " + host)
port = 23
s = socket(AF_INET, SOCK_STREAM)
print "Socket made"
ready = select.select([s],[],[],timeout)
s.connect((host,port))
print("Connection made")
if ready[0]: #if data is actually available for you
print("[INFO] Sending message...")
s.sendall(msg)
print("[INFO] Message sent.")
data = s.recv(4096)
print("[INFO] Data received")
print data
Arduino:
#include <SPI.h>
#include <Ethernet.h>
//90-a2-da-0f-25-E7
byte mac[] = {0x90, 0xA2, 0xDA, 0x0f, 0x25, 0xE7};
//ip Address for shield
byte ip[] = {192,168,1,113};
//Use port 23 for telnet
EthernetServer server = EthernetServer(23);
void setup() {
Serial.begin(9600); //For visual feedback on what's going on
while(!Serial){
; //wait for serial to connect -- needed by Leonardo
}
Ethernet.begin(mac,ip); // init EthernetShield
delay(1000);
server.begin();
if(server.available()){
Serial.println("Client available");
}
}
void loop() {
// put your main code here, to run repeatedly:
EthernetClient client = server.available();
message = client.read();
server.write(message);
server.write("Testu ");
Serial.println(message);
// if (client == true){ <----- This check screwed it up. Not needed.
// Serial.println("Client Connected.");
// server.write(client.read()); //send back to the client whatever the client sent to us.
// }
}