I am new to node.js. How to detect client is disconnected from node.js server .
Here is my code:
var net = require('net');
var http = require('http');
var host = '192.168.1.77';
var port = 12345;//
var server = net.createServer(function (stream) {
stream.setEncoding('utf8');
stream.on('data', function (data) {
var comm = JSON.parse(data);
if (comm.action == "Join_Request" && comm.gameId =="game1") // join request getting from client
{
var reply0 = new Object();
reply0.message = "WaitRoom";
stream.write(JSON.stringify(reply0) + "\0");
}
});
stream.on('disconnect', function() {
});
stream.on('close', function () {
console.log("Close");
});
stream.on('error', function () {
console.log("Error");
});
});
server.listen(port,host);
How to know client side internet disconnection.
The best way to detect "dead sockets" is to send periodic application-level ping/keepalive messages. What that message looks like depends on the protocol you're using for communicating over the socket. Then it's just a matter of using a timer or other means of checking if you've received a "ping response" within a certain period of time after you sent the ping/keepalive message to the client.
On a semi-related note, it looks like you're using JSON messages for communication, but you're assuming a complete JSON string on every data event which is a bad assumption. Try using a delimiter (a newline is pretty common for something like this, and it makes debugging the communication more human-readable) instead.
Here is a simple example of how to achieve this:
var PING_TIMEOUT = 5000, // how long to wait for client to respond
WAIT_TIMEOUT = 5000; // duration of "silence" from client until a ping is sent
var server = net.createServer(function(stream) {
stream.setEncoding('utf8');
var buffer = '',
pingTimeout,
waitTimeout;
function send(obj) {
stream.write(JSON.stringify(obj) + '\n');
}
stream.on('data', function(data) {
// stop our timers if we've gotten any kind of data
// from the client, whether it's a ping response or
// not, we know their connection is still good.
clearTimeout(waitTimeout);
clearTimeout(pingTimeout);
buffer += data;
var idx;
// because `data` can be a chunk of any size, we could
// have multiple messages in our buffer, so we check
// for that here ...
while (~(idx = buffer.indexOf('\n'))) {
try {
var comm = JSON.parse(buffer.substring(0, idx));
// join request getting from client
if (comm.action === "Join_Request" && comm.gameId === "game1") {
send({ message: 'WaitRoom' });
}
} catch (ex) {
// some error occurred, probably from trying to parse invalid JSON
}
// update our buffer
buffer = buffer.substring(idx + 1);
}
// we wait for more data, if we don't see anything in
// WAIT_TIMEOUT milliseconds, we send a ping message
waitTimeout = setTimeout(function() {
send({ message: 'Ping' });
// we sent a ping, now we wait for a ping response
pingTimeout = setTimeout(function() {
// if we've gotten here, we are assuming the
// connection is dead because the client did not
// at least respond to our ping message
stream.destroy(); // or stream.end();
}, PING_TIMEOUT);
}, WAIT_TIMEOUT);
});
// other event handlers and logic ...
});
You could also just have one interval instead of two timers that checks a "last data received" timestamp against the current timestamp and if it exceeds some length of time and we have sent a ping message recently, then you assume the socket/connection is dead. You could also instead send more than one ping message and if after n ping messages are sent and no response is received, close the connection at that point (this is basically what OpenSSH does).
There are many ways to go about it. However you may also think about doing the same on the client side, so that you know the server didn't lose its connection either.
Related
I'm currently developing a NodeJS WebSocket server. To detect broken connections I've followed this guide here:
https://github.com/websockets/ws#how-to-detect-and-close-broken-connections
The server side works really good but the client makes problems because I can't find a ping function.
Does anyone has an idea how I can get the client part done without the library?
const WebSocket = require('ws');
function heartbeat() {
clearTimeout(this.pingTimeout);
// Use `WebSocket#terminate()`, which immediately destroys the connection,
// instead of `WebSocket#close()`, which waits for the close timer.
// Delay should be equal to the interval at which your server
// sends out pings plus a conservative assumption of the latency.
this.pingTimeout = setTimeout(() => {
this.terminate();
}, 30000 + 1000);
}
const client = new WebSocket('wss://echo.websocket.org/');
client.on('open', heartbeat);
client.on('ping', heartbeat);
client.on('close', function clear() {
clearTimeout(this.pingTimeout);
});
One main problem is that there is no ping method I think:
client.on('open') -> client.onopen available in JavaScript
client.on('close') -> client.onclose available in JavaScript
client.on('ping') -> How? Just how?
There is no Javascript API to send ping frames or receive pong frames. This is either supported by your browser, or not. There is also no API to enable, configure or detect whether the browser supports and is using ping/pong frames.
https://stackoverflow.com/a/10586583/7377682
Sad but true, in case of the ping frame, the API does not support it as mentioned in previous answers.
The most popular workaround is to listen to the close event and try to reconnect to the server using an interval.
This tutorial is easy to understand and contains most use-cases to begin with WS:
var ws = new WebSocket("ws://localhost:3000/ws");
let that = this; // cache the this
var connectInterval;
var check = () => {
const { ws } = this.state;
if (!ws || ws.readyState == WebSocket.CLOSED) this.connect(); //check if websocket instance is closed, if so call `connect` function.
};
// websocket onopen event listener
ws.onopen = () => {
console.log("connected websocket main component");
this.setState({ ws: ws });
that.timeout = 250; // reset timer to 250 on open of websocket connection
clearTimeout(connectInterval); // clear Interval on on open of websocket connection
};
// websocket onclose event listener
ws.onclose = e => {
console.log(
`Socket is closed. Reconnect will be attempted in ${Math.min(
10000 / 1000,
(that.timeout + that.timeout) / 1000
)} second.`,
e.reason
);
that.timeout = that.timeout + that.timeout; //increment retry interval
connectInterval = setTimeout(this.check, Math.min(10000, that.timeout)); //call check function after timeout
};
// websocket onerror event listener
ws.onerror = err => {
console.error(
"Socket encountered error: ",
err.message,
"Closing socket"
);
ws.close();
};
I think what you are look for on the client is onmessage:
client.onmessage = function (event) {
console.log(event.data);
}
All messages sent from the server can be listened to this way. See https://developer.mozilla.org/en-US/docs/Web/API/WebSockets_API/Writing_WebSocket_client_applications
I am currently trying to setup a server stream with the gRPC Node.js API. For that I want to achieve that when I write on server side to the stream that the client immediately receives the data event.
At the moment I don't receive anything on client side if I only call write on server side. However as soon as I call the end function on the server the client receives all data events.
To test this I used an endless while loop for writing messages on server side. Then the client does not receive messages (data events). If instead I use a for loop and call end afterwards the client receives all the messages (data events) when end is called.
My .proto file:
syntax = "proto3";
message ControlMessage {
enum Control {
Undefined = 0;
Start = 1;
Stop = 2;
}
Control control = 1;
}
message ImageMessage {
enum ImageType {
Raw = 0;
Mono8 = 1;
RGB8 = 2;
}
ImageType type = 1;
int32 width = 2;
int32 height = 3;
bytes image = 4;
}
service StartImageTransmission {
rpc Start(ControlMessage) returns (stream ImageMessage);
}
On the server side I implement the start function and try to endlessly write messages to the call:
function doStart(call) {
var imgMsg = {type: "Mono8", width: 600, height: 600, image: new ArrayBuffer(600*600)};
//for(var i = 0; i < 10; i++) {
while(true) {
call.write(imgMsg);
console.log("Message sent");
}
call.end();
}
I register the function as service in the server:
var server = new grpc.Server();
server.addService(protoDescriptor.StartImageTransmission.service, {Start: doStart});
On client side I generate an appropriate call and register the data and end event:
var call = client.Start({control: 0});
call.on('data', (imgMessage) => {
console.log('received image message');
});
call.read();
call.on('end', () => {console.log('end');});
I also tried to write the server side in python. In this case the node client instantly receives messages and not only after stream was ended on server side. So I guess this should be also possible for the server written with the Node API.
It seems that the problem was that the endless while loop is blocking all background tasks in node. A possible solution is to use setTimeout to create the loop. The following code worked for me:
First in the gRPC call store the call object in an array:
function doStart(call) {
calls.push(call);
}
For sending to all clients I use a setTimeout:
function sendToAllClients() {
calls.forEach((call) => {
call.write(imgMsg);
});
setTimeout(sendToAllClients, 10);
}
setTimeout(sendToAllClients, 10);
Helpful stackoverflow atricle: Why does a while loop block the event loop?
I was able to use uncork which comes from Node.js's Writable.
Here is an example. Pseudocode, but pulled from across a working implementation:
import * as grpc from '#grpc/grpc-js';
import * as proto from './src/proto/generated/organizations'; // via protoc w/ ts-proto
const OrganizationsGrpcServer: proto.OrganizationsServer = {
async getMany(call: ServerWritableStream<proto.Empty, proto.OrganizationCollection>) {
call.write(proto.OrganizationCollection.fromJSON({ value: [{}] }));
call.uncork();
// do some blocking stuff
call.write(proto.OrganizationCollection.fromJSON({ value: [{}] }));
call.uncork();
// call.end(), or client.close() below, at some point?
},
ping(call, callback) {
callback(null);
}
};
const client = new proto.OrganizationsClient('127.0.0.1:5000', grpc.credentials.createInsecure());
const stream = client.getMany(null);
stream.on('data', data => {
// this cb should run twice
});
export default OrganizationsGrpcServer;
//.proto
service Organizations {
rpc GetMany (google.protobuf.Empty) returns (stream OrganizationCollection) {}
}
message OrganizationCollection {
repeated Organization value = 1;
}
Versions:
#grpc/grpc-js 1.4.4
#grpc/proto-loader 0.6.7
ts-proto 1.92.1
npm 8.1.4
node 17
When I try to initialize a websocket connection to the server running on localhost with
var webSocket = new WebSocket("ws://localhost:8025/myContextRoot");
in javascript, but the server hasn't completed starting up yet, I get the error
SCRIPT12029: WebSocket Error: Network Error 12029, A connection with the server could not be established
How can I prevent this? I.e. how do I check if the server has already started or how can I force the WebSocket client to wait for the server?
What about:
var webSocketFactory = {
connectionTries: 3,
connect: function(url) {
var ws = new WebSocket(url);
ws.addEventListener("error", e => {
// readyState === 3 is CLOSED
if (e.target.readyState === 3) {
this.connectionTries--;
if (this.connectionTries > 0) {
setTimeout(() => this.connect(url), 5000);
} else {
throw new Error("Maximum number of connection trials has been reached");
}
}
});
}
};
var webSocket = webSocketFactory.connect("ws://localhost:8025/myContextRoot");
When you get a connection error, you can do a limited number of trial-errors to try to re-connect. Or you can endlessly try to reach the server.
The accepted answer is perfectly fine. I just would like to extend it a little bit further with promises.
var wsFactory = { tryCount: 3,
connect : function(url){
var ctx = this,
ws = new WebSocket(url);
return new Promise(function(v,x){
ws.onerror = e => { console.log(`WS connection attempt ${4-ctx.tryCount} -> Unsuccessful`);
e.target.readyState === 3 && --ctx.tryCount;
if (ctx.tryCount > 0) setTimeout(() => v(ctx.connect(url)), 1000);
else x(new Error("3 unsuccessfull connection attempts"));
};
ws.onopen = e => { console.log(`WS connection Status: ${e.target.readyState}`);
v(ws);
};
ws.onmessage = m => console.log(m.data);
});
}
};
wsFactory.connect("ws://localhost:8025/myContextRoot")
.then(ws => ws.send("Hey..! This is my first socket message"))
.catch(console.log);
You can't prevent (or put on hold) the WebSocket from starting / establish a connection. WebSocket automatically establishes a connection with the server when its declared. What you can do is place all your code inside onopen event handler that you want to execute on successful connection. So it would be like...
var webSocket = new WebSocket("ws://localhost:8025/myContextRoot");
webSocket.onopen = function() {
// code you want to execute
};
check this article to know more about WebSocket.
Hence the protocol can't get queried by the server if it is not started, the only option is trial and error.
Or you could let the WebSocket server create a simple textfile with the timestamp of the startup in your web space directory where the javascript can retrieve it and than try to establish a connection. You can retrieve the textfile with XMLHttpRequest.
I'm trying to create a basic game (only text) using Node.js, and it's 'net' library.
I'm hitting a bit of a wall. I can't seem to figure out how to prompt the user to enter some information, and wait for the user to enter said information.
Here's the code I have so far. It's fairly basic, and will print out 2 lines for you when you run the client, and then hang. It's at that point I want the user to be able to enter information. I'm unsure of a few things here:
1. How do I enable the user to type? (more specifically, is it client or server side)
2. How do I send that data to the server when enter is pressed?
I have read up on some documentation as far as Telnet goes, and it leads me to my last question: is the Telnet module in Node really the right one for this, or is there a better alternative for client/server creation and communication?
Client Code:
var connect = require('net');
var client = connect.connect('80', 'localhost');
console.log('Connection Success!\n\n');
client.on('data', function(data) {
// Log the response from the HTTP server.
console.log('' + data);
}).on('connect', function() {
// Manually write an HTTP request.
//I'm assuming I could send data at this point here, on connect?
}).on('end', function() {
console.log('Disconnected');
});
Server Code:
var net = require('net');
var sockets = [];
function cleanInput(data) {
return data.toString().replace(/(\r\n|\n|\r)/gm,"");
}
function receiveData(socket, data) {
var cleanData = cleanInput(data);
if(cleanData === "quit") {
socket.end('Goodbye!\n');
}
else {
for(var i = 0; i<sockets.length; i++) {
if (sockets[i] !== socket) {
sockets[i].write(data);
}
}
}
}
function closeSocket(socket) {
var i = sockets.indexOf(socket);
if (i != -1) {
sockets.splice(i, 1);
}
}
function newSocket(socket) {
sockets.push(socket);
socket.write('Welcome to the Battleship Server!\n\n');
socket.write('Please enter a username: ');
socket.on('data', function(data) {
receiveData(socket, data);
})
socket.on('end', function() {
closeSocket(socket);
})
}
var server = net.createServer(newSocket);
server.listen(80);
Thanks in advance!
you want to use process.stdin and process.stdout to interact with input/output from/to the terminal. Have a look here.
You can send data to the server when enter is pressed with process.stdin.once('data', function(data){ /* ... */ }). The .once method ensures that the callback is called just once when the user hits enter.
The client code should look like:
var connect = require('net');
var client = connect.connect('80', 'localhost');
client.on('data', function(data) {
console.log('' + data);
process.stdin.once('data', function (chunk) {
client.write(chunk.toString());
});
}).on('connect', function() {
client.write('Hello');
}).on('end', function() {
console.log('Disconnected');
});
How would you go to create a streaming API with Node? just like the Twitter streaming API.
What I want to do ultimately is get the first update from the FriendFeed api, and stream when a new one becomes available (if the id is different), and later on expose it as a web service so I can use it with WebSockets on my website :).
So far I have this:
var sys = require('sys'),
http = require('http');
var ff = http.createClient(80, 'friendfeed-api.com');
var request = ff.request('GET', '/v2/feed/igorgue?num=1',
{'host': 'friendfeed-api.com'});
request.addListener('response', function (response) {
response.setEncoding('utf8'); // this is *very* important!
response.addListener('data', function (chunk) {
var data = JSON.parse(chunk);
sys.puts(data.entries[0].body);
});
});
request.end();
Which only gets the data from FriendFeed, creating the Http server with node is easy but it can't return a stream (or I haven't yet found out how).
You would want to set up a system that keeps track of incoming requests and stores their response objects. Then when it's time to stream a new event from FriendFeed, iterate through their response objects and responses[i].write('something') out to them.
Check out LearnBoost's Socket.IO-Node, you may even just be able to use that project as your framework and not have to code it yourself.
From the Socket.IO-Node example app (for chat):
io.listen(server, {
onClientConnect: function(client){
client.send(json({ buffer: buffer }));
client.broadcast(json({ announcement: client.sessionId + ' connected' }));
},
onClientDisconnect: function(client){
client.broadcast(json({ announcement: client.sessionId + ' disconnected' }));
},
onClientMessage: function(message, client){
var msg = { message: [client.sessionId, message] };
buffer.push(msg);
if (buffer.length > 15) buffer.shift();
client.broadcast(json(msg));
}
});