I have a requirement to close a tcp connection from the server when a client sends a http request, so that the server can send the next http request with a new tcp connection. Could someone please help me how to do that?
I have tried throwing an exception in a middleware but the tcp connection is not closed as I can see the same connection being used in the next http request in Wireshark.
Related
I have a webapp written in ReactJS.
And what I'm trying to do is communicate with a normal TCP Socket which is running on localhost. (The device which is listening for the requests is an Eftpos terminal). So I would like to send purchase commands and receive responses from it.
How can I communicate with the normal TCP socket from my webapp? From what I understand is that I cannot just communicate with the TCP socket from the webapp. Since webapps only support WebSockets which are different. Whats another way?
Javascript in a browser can do http, webSocket and webRTC. Browser Javascript (without custom add-ons that contain their own native code) cannot do a plain TCP connection.
If you want to connect to something that requires a plain TCP connection, then you need to connect to your server using either http or webSocket and have your server connect to the regular TCP socket and your server can translate between them. This is often referred to as a proxy.
So, for purposes of this explanation, let's imagine you want to connect to some service that uses a plain TCP socket and you need to send lines of text to it and get lines of text in response. Your client has to pick between http or webSocket for the browser-to-your-server transport so let's imagine you're using webSocket. The sequence of events could look like this:
Browser client connects to your server with a webSocket.
Your server receives incoming webSocket connection and since it knows it will be acting as a proxy to a server that uses a plain TCP socket, it opens that socket on behalf of that user.
Browser client sends first request over webSocket.
Your server receives that first request and translates it into whatever format is needed for the TCP socket and sends that over the TCP socket.
When your server gets a response from the TCP socket, it translates that response into a webSocket packet and sends that back to the client.
The client receives the response on its webSocket connection.
Repeat as long as you want.
When client closes webSocket connection, server will close TCP connection to other server.
The only way is to proxy the data server-side.
You can make that TCP connection server-side, and relay the data over a Websocket connection to the browser client.
I am trying to create a multi room chat application in node.js using socket.io and express. I am confused between use of server port and websocket port. I understand server port is used by the client to connect to server. But not sure about use of websocket port.
Thanks & Regards..
webSockets can share the same port as your web server and this is a common configuration. The reason this works is because of how a webSocket establishes a connection (all webSocket connections are initiated with an HTTP request). It works like this:
Client makes an HTTP request to a web server with a header specifying that they want to "upgrade" to the webSocket protocol and sends a security-related header.
Web server sees the upgrade request and, if it has support enabled for webSocket connections, it will respond with a 101 request (switching protocols) and another security related header.
Client gets the accepted upgrade and both ends switch to the webSocket protocol and the original TCP socket that started out using the HTTP protocol is now using the webSocket protocol.
In this manner, the same port and webServer can be used for regular HTTP requests or webSocket connection requests.
For a chat application it is common to use a webSocket connection because it is a continuous connection that more easily allows the server to send information directly to the client which is often needed in a chat application.
To understand more about how a webSocket connection and server work, see this reference on MDN: Writing WebSocket servers which shows the step by step process for initiating a webSocket connection.
Server socket is used by server... that keeps listening to coming sockets request in a loop... and websocket sends a request to server socket and bound a connection between two devices...
If you have / want to have web clients, WebSocket is going to be required, because there is no access to 'regular' TCP (or UDP) sockets from browser-based JavaScript (and I assume you do not want Flash, SilverLight or Java Applets, in 2017). WebSocket is not special because of the port number, but it is special because of the protocol: a WebSocket connection starts as a regular HTTP connection, and protocol upgrade reconfigures it afterwards, it is designed for the browser-world, and even capable of traversing HTTP proxies. After establishing the connection, it provides a full-duplex, bi-directional message stream, very usable for chat applications.
And because of being a Web-thing, you could simply use port 80, if you are allowed to.
I am using NodeJS server for HTTP request when request for a period with request per second, around 500 request, HTTP request in server stop working, when I open up netsat, TCP port on previous request didnt close, it is the reason causing the problem.
Is there any way to close TCP request port? or can I reuse the same TCP port for making request?
I have a node server and a web page connected via socket.io. I noticed in the browser console that it is outputting
XHR finished loading: GET "http://my_url/socket.io/?EIO=3&transport=polling&t=1418944327412-412&sid=vqLTUtW3QhNLwQG8AAAA".
and
XHR finished loading: POST "http://my_url/socket.io/?EIO=3&transport=polling&t=1418944385398-415&sid=vqLTUtW3QhNLwQG8AAAA".
every few seconds. Should it be doing this or am I missing a setting. I'm really only looking to send data back and forth explicitly via the socket. Perhaps I'm missing something in the set up.
Client side is basically
var socket = io("http://my_url");
with the usual event listeners. Server side is
var io = require('socket.io')(server);
I tried placing this on the server side
io.set('transports', ['websocket']);
but that seemed to kill it.
The socket.io implementation (when using webSockets) sends regular (every few seconds) heartbeat and response packets to constantly verify that the connection is alive and well. This is normal.
These packets are not actual http requests (they are websocket data packets) so there should not be full-on http packets going on unless socket.io is not actually using the webSocket protocol, but is instead using HTTP long polling. socket.io will use the webSocket protocol as long as it is supported in the client (which it should be in all modern browsers nowadays).
You may have to be careful about how you interpret requests in a debugger. A socket.io connection starts its life as an http request with some custom headers and all debuggers will show this initial http request. If webSocket is supported at both ends, then the server will return a response which "upgrades" the connection to the webSocket protocol. That same TCP socket which started out as a TCP request, then becomes a webSocket connection. Subsequent webSockets messages sent on the webSocket then flow over that TCP socket. It is up to the debugger on how it might display that traffic. In the Chrome debugger, you have to open the original http connection and then ask to see websocket traffic and only then can you actually see webSocket packets. But, I could imagine in other debuggers that weren't as webSocket saavy, they might show subsequent packets as related to that original HTTP connection (I haven't looked at how debuggers other than Chrome show webSocket traffic).
The only other reason I can think of that a client would be repeatedly sending HTTP connection requests is if the connection keeps dropping for some reason so the client keeps reconnecting every time the connection drops. socket.io has settings that can control how often/vigorously the client tries to reconnect when the connection is lost, though if you have connection issues, then you really need to figure out why there are connection issues rather than change the reconnect settings.
I'm new in node.js
So the question can be quite naive.
I want to use node.js as a proxy between the javascript client and a windows program which has a API working through a defined port.
So browser sends HTTP request to node.js.
Node.js opens connection with the windows program, sends request, get a respons and returns the response to the javascript that called node.js ( AJAX )
Actually it has been realized so and works.
The problem is that windows program wants to work persistent.
So once the connection is opened it should stay alive.
And my node.js script opens connection. And the next call to node.js try to open connection again. And that leads to error.
So the question - what is the right way and middles to reuse the TCP connection in node.js.
So that next call won't open new connection but go on with already opened one.
It is possible, but requires some coding on your side.
If it is not sticky (the same HTTP client does not require to use the same TCP connection):
Open an connection pools of TCP connections to the windows program
Listen to HTTP requests
If a HTTP request arrives find an unused TCP connection (if none is available, make a new one or wait)
Query the windows program, return the results to who ever called the HTTP request
Mark the TCP connection as free
If it is sticky (always use the same TCP connection for the same HTTP client):
If a HTTP clients connect and he hasn't one, give him session.
If not available for the session: create a TCP connection
Make the request, return the result
Store the TCP "connection" somewhere where you could reach it when the next request comes in and you could identify it by the HTTP clients session (Maybe make a timeout for clearing up)