I am basically writing an almost purely clientside application (there is a webserver which can be used to store some persistent data, but its easier to forget about it), but as part of this I was looking to add some functionality akin to hosting a game.
The scenario would be 1 person would host the game via their browser (open a TCP socket awaiting connections), then X other people would connect to that server and join. The server would be in charge of receiving and sending data between clients.
So in this scenario is it possible to host a websocket server within a webpage?
I was looking at trying to do something peer to peer style, but I don't think it is currently supported, but its not a major problem as its only going to be for sending small amounts of text and some update messages between clients.
The WebSocket browser API is client only (for the foreseeable future).
In some sense, WebRTC us peer-to-peer, but even if the WebRTC API adds the ability to send arbitrary data, you still need a STUN/TURN server to establish the initial connection.
Related
I have a realtime HTML5 canvas game that runs off a node backend. Players are connected via Websocket (socket.io). The problem is sometimes I need to deploy new code (hotfixes for instance) and restart the server but I don't want to disconnect players.
My idea for this was to divide the websocket server and application server into separately deployable components and add a message queue in the middle to decouple the 2 components. That way if the application server was rebooting there would just be a short delay while the messages bunch up but nothing would be lost. Is this a good strategy? Is there an alternative?
It's very possible for websocket based applications to be restarted without the user noticing anything (that's the case for my chat server for example).
To make that possible, the solution isn't to have a websocket application isolated and never restarted. In fact this would be very optimistic (are you sure you could ensure its API is never changed ?).
A solution is
to ensure the client reconnects if disconnected (this is standard if you use socket.io for websocketing)
to make the server ask the client its id (or session id) on client initiated reconnection
to persists the state of the application. This is usually done with a database. If your server has no other state than the queue between clients (which is a little unlikely) then you might look for an existing persistent queue implementation or build your own over a fast local storage (redis comes to mind)
I'm new websocket streaming application.
I'm trying to evaluate kaazing and solace streaming vendor products.
I'm trying to put a layer or interface application infornt of kaazing publisher before it creates the socket connection.
The client would make request to the interface for the socket connection , the interface plays the role to authenticate and authorize and do some business changes before the creation of socket.
The interface establish the secured socket connection with kazzing or streaming application and transfer the connection object to the client in response.
The client use the established connection from the reponse and retains the connection for streaming the data to client from the streaming server.
The objective is to hide the topic info and connection established from the client side for secured process.
So the infterace creates the secured connection and transfers the connection to authorized client which continue the streaming from the streaming server until the session expires.
Please let me designing such an application is possible.
The client receives data but it doesn't establish connection of its own, its created from server side and transfered to client side after all necessary validation.
Guide me to proceed further with the design and I'm inneed of expert's valuable suggestion.
Thanks in advance and appriciated for directing me to the right path in designing the streaming appliation.
My aim is not to introduce a new layer between the gateway and client. Altimate aim is to customize the gateway for my product, For example the user(client) connects to gateway and tries to access the topic say stock(eligible to subscribe) then he will be able to get the data streaming. If he needs share he would register is some place and after approval only he will be eligible to view, So authorization would play a role and maintaince a session and loads the customized data and allows to stream.
Typically am trying to have a dashboard of data streaming. So only authorized streaming is allowed for user. Also he will be able to see all the topic name. whether its possible to use proxy name , example 1, or 2 might be the value he would use from client side, when it reaches the gateway it verify the authorization and replace the value with real topic name and establish the data.
Please let me know whether I've my question clear. Your valuable suggestions and guidance will be more helpful to continue with my research.
Thanks
Krish
in case you wonder how the world has changed over the last five year to address this kind of need, now you could give a try to streamdata.io, a proxy which uses SSE protocol (unidirectional) and is available in minutes. It would perfectly fit what's needed in the example given, because Im not sure WebSocket is the ideal answer here. Tho it should work, it's basically like buying a harvester to go get your kids at school.
As a disclaimer, I need to say that I work for Streamdata, and we see this kind of thing every day.
WebSocket is great if you need bidirectional streams of data, like in chats or games. Most of the time, when the clients mainly expect updated data from the server, instead of polling AF or deploying WebSocket, SSE is the best alternative as it's easier to deploy (http, etc.). The rest of the settings (for security) can be done through the proxy interface.
Boom: it's available before you even realize it, it's secure, easy to maintain and more efficient than before. You have more time available to answer questions from the community over here; your team is happy; your boss loves you more than before and might even give you a raise. Life can be so simple sometimes!
or any other type of realtime data feed from server to client... I'm talking about a bunch of realtime data from server to client. i.e., an informational update every second.
Does the server magically push the data to the client, or does the client need to continuously poll the server for updates? And under what protocol does this usually work? (http, socket communication, etc?)
In server-side financial applications used by brokers/banks etc. market data (quotes,trades etc) is transmitted over TCP via some application-level protocol which most probably won't be HTTP. Of course, there's no polling. Client is establishing TCP connection with server, server pushes data to client. One of common approaches to distribute market data is FIX.
Thomson-Reuters have bunch of cryptic proprietary protocols dating from mainframe days to distribute such data.
HTTP can be used for SOAP/RESTful to transmit/request data of not-so-large volume, like business news.
UPDATE Actually, even FIX is not enough in some cases, as it has big overhead because of it's "text" nature. Most brokers and exchanges transmit high-volume streams, such as quotes, using binary-format protocols (FAST or some proprietary).
In a simple case:
Create a server with a listening socket.
On the client, connect to the server's socket.
Have the client do a while(data = recv(socket)) (pseudocode)
When the server has something exciting to tell the client, it simply send(...)s on the socket.
You can even implement this pattern over HTTP (there is no real upper time limit to an HTTP socket). The server need not even read from the socket - it can be trying to write to the firehose only.
Usually a TCP socket is employed - messages arrive in order, and are best-effort. If latency is more important and dropped or out of order is not an issue, UDP can be used.
I have one app. that consists of "Manager" and "Worker". Currently, the worker always initiates the connection, says something to the manager, and the manager will send the response.
Since there is a LOT of communication between the Manager and the Worker, I'm considering to have a socket open between the two and do the communication. I'm also hoping to initiate the interaction from both sides - enabling the manager to say something to the worker whenever it wants.
However, I'm a little confused as to how to deal with "collisions". Say, the manager decides to say something to the worker, and at the same time the worker decides to say something to the manager. What will happen? How should such situation be handled?
P.S. I plan to use Netty for the actual implementation.
"I'm also hoping to initiate the interaction from both sides - enabling the manager to say something to the worker whenever it wants."
Simple answer. Don't.
Learn from existing protocols: Have a client and a server. Things will work out nicely. Worker can be the server and the Manager can be a client. Manager can make numerous requests. Worker responds to the requests as they arrive.
Peer-to-peer can be complex with no real value for complexity.
I'd go for a persistent bi-directional channel between server and client.
If all you'll have is one server and one client, then there's no collision issue... If the server accepts a connection, it knows it's the client and vice versa. Both can read and write on the same socket.
Now, if you have multiple clients and your server needs to send a request specifically to client X, then you need handshaking!
When a client boots, it connects to the server. Once this connection is established, the client identifies itself as being client X (the handshake message). The server now knows it has a socket open to client X and every time it needs to send a message to client X, it reuses that socket.
Lucky you, I've just written a tutorial (sample project included) on this precise problem. Using Netty! :)
Here's the link: http://bruno.linker45.eu/2010/07/15/handshaking-tutorial-with-netty/
Notice that in this solution, the server does not attempt to connect to the client. It's always the client who connects to the server.
If you were thinking about opening a socket every time you wanted to send a message, you should reconsider persistent connections as they avoid the overhead of connection establishment, consequently speeding up the data transfer rate N-fold.
I think you need to read up on sockets....
You don't really get these kinds of problems....Other than how to responsively handle both receiving and sending, generally this is done through threading your communications... depending on the app you can take a number of approaches to this.
The correct link to the Handshake/Netty tutorial mentioned in brunodecarvalho's response is http://bruno.factor45.org/blag/2010/07/15/handshaking-tutorial-with-netty/
I would add this as a comment to his question but I don't have the minimum required reputation to do so.
If you feel like reinventing the wheel and don't want to use middleware...
Design your protocol so that the other peer's answers to your requests are always easily distinguishable from requests from the other peer. Then, choose your network I/O strategy carefully. Whatever code is responsible for reading from the socket must first determine if the incoming data is a response to data that was sent out, or if it's a new request from the peer (looking at the data's header, and whether you've issued a request recently). Also, you need to maintain proper queueing so that when you send responses to the peer's requests it is properly separated from new requests you issue.
First let me explain the data flow I need
Client connects and registers with server
Server sends initialization JSON to client
Client listens for JSON messages sent from the server
Now all of this is easy and straightforward to do manually, but I would like to leverage a server of some sort to handle all of the connection stuff, keep-alive, dead clients, etc. etc.
Is there some precedent set on doing this kind of thing? Where a client connects and receives JSON messages asynchronously from a server? Without using doing manual socket programming?
A possible solution is known as Comet, which involves the client opening a connection to the server that stays open for a long time. Then the server can push data to the client as soon as it's available, and the client gets it almost instantly. Eventually the Comet connection times out, and another is created.
Not sure what language you're using but I've seen several of these for Java and Scala. Search for comet framework and your language name in Google, and you should find something.
In 'good old times' that would be easy, since at the first connection the server gets the IP number of the client, so it could call back. So easy, in fact, that it was how FTP does it for no good reason.... But now we can be almost certain that the client is behind some NAT, so you can't 'call back'.
Then you can just keep the TCP connection open, since it's bidirectional, just make the client wait for data to appear. The server would send whatever it wants whenever it can.... But now everybody wants every application to run on top of a web browser, and that means HTTP, which is a strictly 'request/response' initiated by the client.
So, the current answer is Comet. Simply put, a JavaScript client sends a request, but the server doesn't answer for a looooong time. if the connection times out, the client immediately reopens it, so there's always one open pipe waiting for the server's response. That response will contain whatever message the server want's to send to the client, and only when it's pertinent. The client receives it, and immediately sends a new query to keep the channel open.
The problem is that HTTP is a request response protocol. The server cannot send any data unless a requests is submitted by the client.
Trying to circumvent this by macking a request and then continously send back responses on the same, original, requests is flawed as the behavior does not conform with HTTP and it does not play well with all sort of intermediaries (proxies, routers etc) and with the browser behavior (Ajax completion). It also doesn't scale well, keeping a socket open on the server is very resource intensive and the sockets are very precious resources (ordinarly only few thousand available).
Trying to circumvent this by reversing the flow (ie. server connects to the client when it has somehting to push) is even more flawed because of the security/authentication problems that come with this (the response can easily be hijacked, repudiated or spoofed) and also because often times the client is unreachable (lies behind proxies or NAT devices).
AFAIK most RIA clients just poll on timer. Not ideal, but this how HTTP works.
GWT provides a framework for this kind of stuff & has integration with Comet (at least for Jetty). If you don't mind writing at least part of your JavaScript in Java, it might be the easier approach.