Using WebSockets with React Native

We’re going to create a React Native application that will act as a Websockets client and communicate with a remote server. WebSockets is a popular, simple and robust web communication protocol enabling real-time communication between client and server.

Hardware

• Android device
• Computer for programming
• USB cable to connect Android device to PC

React Native project configuration

To communicate via Websocket, we’re going to use the Websocket library, react-use-websocket

npm install --save react-use-websocket

Utilisation de la librairie

From the library, we import the objects and functions we are interested in

import useWebSocket, { ReadyState } from 'react-use-websocket';

• ReadyState server connection status
• useWebScoket to initialize a websockets connection

We then create a functional component with the desired states

  const [ipAddress, setIpAddress] = useState('');
  const [ipServer, setIpServer] = useState('ws://192.168.1.52:8765');
  const [messageText, setMessageText] = useState("");
  const [messageHistory, setMessageHistory] = useState([]);
  const { sendMessage, sendJsonMessage, lastMessage, lastJsonMessage, readyState } = useWebSocket(ipServer);

  const connectionStatus = {
    [ReadyState.CONNECTING]: 'Connecting',
    [ReadyState.OPEN]: 'Open',
    [ReadyState.CLOSING]: 'Closing',
    [ReadyState.CLOSED]: 'Closed',
    [ReadyState.UNINSTANTIATED]: 'Uninstantiated',
  }[readyState];

  const paramCmd = {
    type: 'setParam',
    param1: 30,
    param2: 2.3,
  }

In the states we retrieve the functions and states of useWebSokcet

• sendMessage the function for sending messages in String format
• sendJsonMessage for sending messages in JSON format
• lastMessage contains the server response in String format
• lastJsonMessage contains the last server message in JSON format
• readyState contains the connection state

We also define a constant in Json paramCmd format.

We use a useEffect hook to retrieve the device’s IP address and manage the messages received from the server.

  useEffect(() => {
    const fetchIpAddress = async () => {
      const ip = await NetworkInfo.getIPV4Address();
      setIpAddress(ip);
      console.log("ip adresses ; ", ip)
    };

    fetchIpAddress();
	
    if (lastMessage !== null) {
      setMessageHistory((prev) => prev.concat(lastMessage));
    }
    if (lastJsonMessage !== null) {
      console.log(JSON.stringify(lastJsonMessage));
    }
    return () => {
    };
  }, [lastMessage, setMessageHistory,lastJsonMessage]);

Finally, we create the application rendering with the following elements

  return (
    <View style={styles.mainBody}>
      <Text
        style={styles.mainTitle}>
        AC Websocket Terminal
      </Text>
      <ScrollView>

      <View style={styles.deviceItem}>
                      <View style={{flex:2}}>
                        <Text style={styles.deviceName}>{ipAddress}</Text>
                        <Text style={styles.deviceInfo}>{connectionStatus}</Text>
                      </View>
                      <TouchableOpacity
                        onPress={() => sendJSON()}
                        disabled={readyState !== ReadyState.OPEN}
                        style={styles.deviceButton}>
                        <Text
                          style={styles.buttonText}>
                          Send JSON
                        </Text>
                      </TouchableOpacity>
                    </View>


      <View
              style={styles.inputBar}>        
              <TextInput
                style={styles.textInput}
                placeholder="Enter a message"
                value={messageText}
                onChangeText={(text) =>    setMessageText(text)
                }
              />
              <TouchableOpacity
                        onPress={() => sendMessage(messageText)}
                        disabled={readyState !== ReadyState.OPEN}
                        style={[styles.sendButton]}>
                        <Text
                          style={styles.buttonText}>
                          SEND
                        </Text>
                      </TouchableOpacity>
        </View>

      <TextInput
        placeholder="Server IP"
        onChangeText={setIpServer}
        value={ipServer}
      />
      <View style={{flex:1,minHeight:200}}>
      <Text>Received Message:</Text>
              <ScrollView style={styles.textOutput}>
                {lastMessage ? <Text>last message : {lastMessage.data}</Text> : null}
                
                {messageHistory.map((message, idx) => (
                  <Text key={idx}>{message ? message.data : null}</Text>
                ))}
              </ScrollView>
              </View>
      </ScrollView>
    </View>
  );

Creating a WebSockets server with Python

To test our application, we create a websockets server on the PC

#!/usr/bin/env python
# python3 -m pip install websockets

import json
import asyncio
from websockets.server import serve

def getIpAddress():
    import socket
    s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
    s.connect(("8.8.8.8", 80))
    ipaddress = s.getsockname()[0]
    s.close()
    return ipaddress

ipaddress = getIpAddress()
port = 8765

async def echo(websocket):
    async for message in websocket:
        print("received from {}:{} : ".format(websocket.remote_address[0],websocket.remote_address[1]) + message)
        
        if('{' not in message):
            await websocket.send(message)
        else:
            request = json.loads(message)
            answer = {}
            if(request['type'] == 'setParam'):
                answer['type'] = request['type']
                if(request['param1']<100 and request['param2']>1.2):
                    answer['valid'] = True
                    for key, val in request.items():
                        print("\t"+key+": ", val)
                else:
                    answer['valid'] = False
            else:
                answer['type'] = 'unknown'
                answer['valid'] = False
                
            await websocket.send(json.dumps(answer))

async def main():
    print("Server is activated on ws://{}:{}".format(ipaddress,port))
    #async with serve(echo, "localhost", 8765):
    async with serve(echo, "0.0.0.0", port):
        await asyncio.Future()  # run forever

asyncio.run(main())

Results

Thanks to this application, we can send Strings and JSON to the server and display its responses.

Complete code for WebSockets communication with React Native

/**
 * https://reactnative.dev/docs/network
 * https://www.npmjs.com/package/react-use-websocket
 * https://github.com/robtaussig/react-use-websocket
 * test on python
 * https://websockets.readthedocs.io/en/stable/
 */

import React, {useState, useEffect, useCallback} from 'react';
import {   
  View, 
  ScrollView, 
  Text,
  TextInput,
  TouchableOpacity, 
  StyleSheet} from 'react-native';
import { NetworkInfo } from 'react-native-network-info'
import useWebSocket, { ReadyState } from 'react-use-websocket';



const WebsocketTerminal = () =>  {

  const [ipAddress, setIpAddress] = useState('');
  const [ipServer, setIpServer] = useState('ws://192.168.1.52:8765');
  const [messageText, setMessageText] = useState("");
  const [messageHistory, setMessageHistory] = useState([]);
  const { sendMessage, sendJsonMessage, lastMessage, lastJsonMessage, readyState } = useWebSocket(ipServer);


  useEffect(() => {
    const fetchIpAddress = async () => {
      const ip = await NetworkInfo.getIPV4Address();
      setIpAddress(ip);
      console.log("ip adresses ; ", ip)
    };

    fetchIpAddress();
	
    if (lastMessage !== null) {
      setMessageHistory((prev) => prev.concat(lastMessage));
    }
    if (lastJsonMessage !== null) {
      console.log(JSON.stringify(lastJsonMessage));
    }
    return () => {
    };
  }, [lastMessage, setMessageHistory,lastJsonMessage]);

  const connectionStatus = {
    [ReadyState.CONNECTING]: 'Connecting',
    [ReadyState.OPEN]: 'Open',
    [ReadyState.CLOSING]: 'Closing',
    [ReadyState.CLOSED]: 'Closed',
    [ReadyState.UNINSTANTIATED]: 'Uninstantiated',
  }[readyState];

  const sendJSON = () => {
    const paramCmd = {
      type: 'setParam',
      param1: 30,
      param2: 2.3,
    }

    sendJsonMessage(paramCmd);

  }
  
  return (
    <View style={styles.mainBody}>
      <Text
        style={styles.mainTitle}>
        AC Websocket Terminal
      </Text>
      <ScrollView>

      <View style={styles.deviceItem}>
                      <View style={{flex:2}}>
                        <Text style={styles.deviceName}>{ipAddress}</Text>
                        <Text style={styles.deviceInfo}>{connectionStatus}</Text>
                      </View>
                      <TouchableOpacity
                        onPress={() => sendJSON()}
                        disabled={readyState !== ReadyState.OPEN}
                        style={styles.deviceButton}>
                        <Text
                          style={styles.buttonText}>
                          Send JSON
                        </Text>
                      </TouchableOpacity>
                    </View>


      <View
              style={styles.inputBar}>        
              <TextInput
                style={styles.textInput}
                placeholder="Enter a message"
                value={messageText}
                onChangeText={(text) =>    setMessageText(text)
                }
              />
              <TouchableOpacity
                        onPress={() => sendMessage(messageText)}
                        disabled={readyState !== ReadyState.OPEN}
                        style={[styles.sendButton]}>
                        <Text
                          style={styles.buttonText}>
                          SEND
                        </Text>
                      </TouchableOpacity>
        </View>

      <TextInput
        placeholder="Server IP"
        onChangeText={setIpServer}
        value={ipServer}
      />
      <View style={{flex:1,minHeight:200}}>
      <Text>Received Message:</Text>
              <ScrollView style={styles.textOutput}>
                {lastMessage ? <Text>last message : {lastMessage.data}</Text> : null}
                
                {messageHistory.map((message, idx) => (
                  <Text key={idx}>{message ? message.data : null}</Text>
                ))}
              </ScrollView>
              </View>
      </ScrollView>
    </View>
  );
}

export default WebsocketTerminal;


let BACKGROUND_COLOR = "#161616"; //191A19
let BUTTON_COLOR = "#346751"; //1E5128
let ERROR_COLOR = "#C84B31"; //4E9F3D
let TEXT_COLOR = "#ECDBBA"; //D8E9A8
var styles = StyleSheet.create({

  mainBody: { flex: 1, justifyContent: 'center',  backgroundColor: BACKGROUND_COLOR},

  mainTitle:{
    color: TEXT_COLOR,
    fontSize: 30,
    textAlign: 'center',
    borderBottomWidth: 2,
    borderBottomColor: ERROR_COLOR,
  },

  backgroundVideo: {
    borderWidth: 2,
    borderColor: 'red',
    position: 'absolute',
    top: 0,
    left: 0,
    bottom: 0,
    right: 0,
  },

  webVideo: {
    borderWidth: 2,
    borderColor: 'green',
    position: 'absolute',
    top: 0,
    left: 0,
    bottom: 0,
    right: 0,
  },

  buttonText: {
    color: TEXT_COLOR,
    fontWeight: 'bold',
    fontSize: 12,
	  textAlign: 'center',
    textAlignVertical: 'center',
  },

  sendButton: {
    backgroundColor: BUTTON_COLOR,
    padding: 15,
    borderRadius: 15,
    margin: 2,
    paddingHorizontal: 20,
    },

    deviceItem: {
      flexDirection: 'row',
      flex: 3,
      marginBottom: 2,
    },
    deviceName: {
      fontSize: 14,
      fontWeight: 'bold',
    },
    deviceInfo: {
      fontSize: 8,
    },
    deviceButton: {
      backgroundColor: '#2196F3',
      padding: 10,
      borderRadius: 10,
      margin: 2,
      paddingHorizontal: 20,
    },

  inputBar:{
    flexDirection: 'row',
    justifyContent: 'space-between',
    margin: 5,
  },  

  textInput:{
    backgroundColor: '#888888',
    margin: 2,
    borderRadius: 15,
    flex:3,
  },

  textOutput:{
    backgroundColor: '#333333',
    margin: 10,
    borderRadius: 2,
    borderWidth: 1,
    borderColor: '#EEEEEE',
    textAlignVertical: 'top',
  }

});

Sources

• react-use-websockets Documentation
• react-use-websockets Github
• Creating a React Native application
• Using Websockets with Python