Websockets are hailed as a bi-directional process. However, whilst there are hundreds of websocket code examples on the web, they all require a request from the client(browser) to the server to get the data (like an echo server or chat).
So far, I have not found any code which will send new data (originating at the server end) to the client via an open websocket. Ideally, I would like to use a node.js server but I'm open to alternatives. Any ideas?
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I'm a beginner to TCP client-server architecture. I am making a client-server application in C++ I need the server to be able to accept messages from multiple clients at once. I used this IBM example as my starter for the server
server.
The client side is irrelevant but this is my source client.
The problem is with the server side it allows multiple clients to connect but not asynchronously, so the server will connect with the second client after the first one finishes. I want the server to watch for messages from both clients.
I tried to read about select() on the Internet but I couldn't find anything to make the IBM code async. How can I edit the server code to allow the clients to connect and interact at the same time?
I was experimenting hashicorp/yamux over gorilla/websocket, and got stuck.
I started with vanilla WebSocket using the echo example from Gorilla WebSocket project. It was very a straight forward client-server setup. Then image that the server is now behind a firewall, thus the client cannot make a direct connection to it. So I introduced a hub and an agent. The hub is supposed to be publicly visible and connectable for the client. The agent would run alongside the server, who would first make a WebSocket connection to the hub and then multiplex the connection using Yamux so that the hub can then initiate requests to the server. In this way, I effectively "exposed" the server beyond the firewall.
For normal HTTP endpoints, things are good. The client can make requests to the hub, who would proxy these requests to the agent using the WebSocket connection initiated by the hub, and then the hub would further proxy these requests to the server.
However, this trick failed to work with WebSocket endpoints. For the echo example, the client can access the HTML on / through the hub-agent-server chain, but would fail on the /echo path, which is a WebSocket endpoint.
My question is, is this WebSocker over Yamux over WebSocket fundamentally impossible, or do I just need some extra lines to get things work? Here's the code I've been experimenting with. Really appreciate your helps!
I have one api for stock trade.
this is the url for websocket communication with api server.
https://kite.trade/docs/connect/v3/websocket/
I've read about websocket for laravel, but almost are the content about sending socket request from client to server.
If then, in my case, I have to turn on browser all day long to get live market quote.
I want to make it possible to get live market data without turn on browser.
Till my understanding is, in node.js, using socket.io client, it is possible to send websocket request from server to socket server.
But in laravel, I could not find way.
If anyone has experience, please help me.
Thanks.
wss://www.mysite.ca/socket.io/?EIO=3&transport=websocket
This is how chrome webdevoloper tools shows the request url of a socket io.
I am trying to understand more about EIO=3&transport=websocket .
I have to invoke the url from an API tool
These are query parameters that the socket.io client sends to the socket.io server as part of the initial connection request.
EIO=3, I believe, is the version number of the engine.io sub-system in socket.io. If the server is not compatible with this version number, it will likely fail the attempt to connect.
transport=websocket says that socket.io wants to use the websocket protocol as the eventual transport. socket.io has several different transports it supports including web polling and a flash-based protocol.
To connect to socket.io server, you will need a full-fledged socket.io client. You can't make a socket.io connection by just sending a URL from a tool to the server. There's a lot more involved than that in establishing a working socket.io connection.
I'm trying to get a better understanding of how the server-side architecture works for WebSockets with the goal of implementing it in an embedded application. It seems that there are 3 different server-side software components in play here: 1) the web server to serve static HTTP pages and handle upgrade request, 2) a WebSockets library such as libwebsockets to handle the "nuts and bolts" of WebSockets communications, and 3) my custom application to actually figure out what to do with incoming data. How do all these fit together? Is it common to have a separate web server and WebSocket handling piece, aka a WebSocket server/daemon?
How does my application communicate with the web server and/or WebSockets library to send/receive data? For example, with CGI, the web server uses environmental variables to send info to the custom application, and stdout to receive responses. What is the equivalent communication system here? Or do you typically link in a WebSocket library into the customer application? But then how would communication with the web server to the WebSocket library + custom application work? Or all 3 combined into a single component?
Here's why I am asking. I'm using the boa web server on a uClinux/no MMU platform on a Blackfin processor with limited memory. There is no native WebSocket support in boa, only CGI. I'm trying to figure out how I can add WebSockets support to that. I would prefer to use a compiled solution as opposed to something interpreted such as JavaScript, Python or PHP. My current application using long polling over CGI, which does not provide adequate performance for planned enhancements.
First off, it's important to understand how a webSocket connection is established because that plays into an important relationship between webSocket connections and your web server.
Every webSocket connection starts with an HTTP request. The browser sends an HTTP request to the host/port that the webSocket connection is requested on. That request might look something like this:
GET /chat HTTP/1.1
Host: example.com:8000
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Sec-WebSocket-Version: 13
What distinguishes this request from any other HTTP request to that server is the Upgrade: websocket header in the request. This tells the HTTP server that this particular request is actually a request to initiate a webSocket connection. This header also allows the web server to tell the difference between a regular HTTP request and a request to open a webSocket connection. This allows something very important in the architecture and it was done this way entirely on purpose. This allows the exact same server and port to be used for both serving your web requests and for webSocket connections. All that is needed is a component on your web server that looks for this Upgrade header on all incoming HTTP connections and, if found, it takes over the connection and turns it into a webSocket connection.
Once the server recognizes this upgrade header, it responds with a legal HTTP response, but one that signals the client that the upgrade to the webSocket protocol has been accepted that looks like this:
HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
At that point, both client and server keep that socket from the original HTTP request open and both switch to the webSocket protocol.
Now, to your specific questions:
How does my application communicate with the web server and/or
WebSockets library to send/receive data?
Your application may use the built-in webSocket support in modern browsers and can initiate a webSocket connection like this:
var socket = new WebSocket("ws://www.example.com");
This will instruct the browser to initiate a webSocket connection to www.example.com use the same port that the current web page was connected with. Because of the built-in webSocket support in the browser, the above HTTP request and upgrade protocol is handled for you automatically from the client.
On the server-side of things, you need to make sure you are using a web server that has incoming webSocket support and that the support is enabled and configured. Because a webSocket connection is a continuous connection once established, it does not really follow the CGI model at all. There must be at least one long-running process handling live webSocket connections. In server models (like CGI), you would need some sort of webServer add-on that supports this long-running process for your webSocket connections. In a server environment like node.js which is already a long running process, the addition of webSockets is no change at all architecturally - but rather just an additional library to support the webSocket protocol.
I'd suggest you may find this article interesting as it discussions this transition from CGI-style single request handling to the continuous socket connections of webSocket:
Web Evolution: from CGI to Websockets (and how it will help you better monitor your cloud infrastructure)
If you really want to stick with the stdin/stdout model, there are libraries that model that for your for webSockets. Here's one such library. Their tagline is "It's like CGI, twenty years later, for WebSockets".
I'm trying to figure out how I can add WebSockets support to that. I
would prefer to use a compiled solution as opposed to something
interpreted such as JavaScript, Python or PHP.
Sorry, but I'm not familiar with that particular server environment. It will likely take some in-depth searching to find out what your options are. Since a webSocket connection is a continuous connection, then you will need a process that is running continuously that can be the server-side part of the webSocket connection. This can either be something built into your webServer or it can be an additional process that the webServer starts up and forwards incoming connections to.
FYI, I have a custom application at home here built on a Raspberry Pi that uses webSockets for real-time communication with browser web pages and it works just fine. I happen to be using node.js for the server environment and the socket.io library that runs on top of webSockets to give me a higher level interface on top of webSockets. My server code checks several hardware sensors on a regular interval and then whenever there is new/changed data to report, it sends messages down any open webSockets so the connected browsers get real-time updates on the sensor readings.
You would likely need some long-running application that incoming webSocket connections were passed from the web server to your long running process or you'd need to make the webSocket connections on a different port than your web server (so they could be fielded by a completely different server process) in which case you'd have a whole separate server to handle your webSocket requests and sockets (this server would also have to support CORS to enable browsers to connect to it since it would be a different port than your web pages).