I'm working on application running on JBossEAP 6.4 in domain mode. I need to handle multiple (up to 1000) parallel TCP connections from server to different hardware devices.
Connections have to be opened at server side and will be keept up to 90 seconds. All connections uses the same port and protocol, but destination IP adresses are different..
I wonder if JCA adapter is suitable for this use case. Should I create special Activation specification for every single device or use something else than JCA resource adapter?
The question is a bit old, but JCA is a not-that-popular technology so some knowledge about it would be useful despite of the fact you might have been implemented all the things already.
Firstly, JCA is a spec for writing your connector, it's not a connector implementation itself. If you need your application to work with external TCP it's up to you to implement a connector.
Whether JCA is suitable for your particular needs depends solely on the nature of your "different hardware devices". Resource adapters has been designed to be used on per-service basis with possible connections pooling. I.e. all the connections this particular adapter would fire should have quite similar nature and be interchangeable. However, JCA adapters also have sensible advantages outside of this scope, especially in EJB environment. EJB imposes quite harsh restrictions upon your code: no locking, threads spawning, etc. It might be quite difficult to implement TCP I/O without all those things. Here comes JCA and it's threading freedom (MDBs are capable of providing EJB-friendly scope on their activation despite of an underlying thread source).
In conclusion: you should consider using JCA for TCP networking if you're working in EJB environment (or if you're going to do so in observable future). If you're using Spring-powered environment upon Java EE stack it may worth to omit such a complicated technology and stick to some pure Netty networking.
If you choose to proceed with JCA, consider inspecting the JCA SocketConnector I am currently maintaining. It's build upon Netty stack and it could be a good start for you. You can also use it as a source of ideas how to build your own implementation instead.
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I've been asked to implement VPN capabilities in an existing software project on an embedded system, in order to make the device available via network to an external server while avoiding trouble with firewalls (no need for encryption, just to make it accessible).
Unfortunately, the embedded system is based on a Cortex-M4 MCU, therefore Linux, which would allow for VPN nearly out of the box, is not an option. All I've got is an RTOS and a working LwIP stack.
I've used VPNs in the past. However, my network knowledge is rather limited concerning implementing VPNs, so I'm rather stumped. As I think, I'd use the current LwIP instance for building up the tunnel connection, and the application would use a second instance for the actual network communication, while the network interface of the second instance is a virtual one (like a tap device on linux), encapsulating its low level data and tranceiving it via the tunnel connection of the first LwIP instance.
Maybe this way I'd be able to create a custom solution for the problem, but the solution should conform to any standards (as the server will be any kind of sophisticated system).
So I wonder if anyone has been confronted with a task like this, and would appreciate any hint what to do, at least a direction where to look at.
Thanks in advance!
I am new to SignalR and I try to understand the difference between consistent connection and long polling,Is there different use in methods ? is one better than the other? are there any diffrenet functions need to polling and other functions to use consistent connection?, I googled but didn't find a simple answer to this question, can someone help? need an explanation.
SignalR is a framework that allows us to build real-time web applications. Ideally, we would use web sockets for this. However, web sockets is a new protocol and requires support from both the browser and the server. Thus, web sockets are not generally available and SignalR tries to provide an abstract connection similar to web sockets but built upon existing technologies and techniques. This abstraction is called a Persistent Connection.
Persistent connection is the term used to describe SignalR's abstract connections.
Long polling is one of several techniques used to implement SignalR's persistent connections (the others are Forever Frame, Server-Sent Events and Web Sockets).
I'm writing a bit of desktop software which has two components. Component B queries component A. Creating a web service seems like an ideal way to do IPC in principle. The data model fits, there are ready-made client and server libraries, a well known way to encode and decode parameters etc.
But setting up an HTTP server on a network socket doesn't seem right for a local application. For example what port do I choose? I don't really want people to be able to scan and talk to the app from outside etc.
So I was thinking that I might be able to do HTTP over a domain socket. Does that make any sense? Is there any precedence for it? Is there an equivalent protocol that I could use for IPC which has the same properties as HTTP (requests for specified resources (URIs), encoded parameters, response)?
Looking for C libraries (and possibly Go and ObjC for bonus points).
Binding to the loopback interface only (127.0.0.1) solves your "external visibility" problem, only processes on the local machine will be able to connect.
It does not solve your port allocation problem though, the port number you choose might be taken by the time your app starts. Then your server can't bind and your client connects to the other process bound to your port.
Old, less hip, but CORBA implementations tend to have the problems you have not thought of yet figured out already.
I wonder if there exist any other technologies used to establish internet connection between applications. Are there any other? I am searching and so far I haven't found anything else described.
There are many abstractions on top of sockets, if you don't want to deal directly with a socket API. UDP, TCP/IP, various RPC protocols, HTTP (which is on top of TCP/IP), etc. Many programming languages have easy methods of doing, say, an HTTP request and getting the resulting document. You can use that to allow applications to talk to each other over the internet without using a socket API.
What are you trying to accomplish?
If you want to skip sockets you basically have to implement your own means of talking to the network card hardware and telling it to communicate with other devices. A socket is just the abstraction chosen for *nix and Windows machines.
I'm developing a multi-player game and I know nothing about how to connect from one client to another via a server. Where do I start? Are there any whizzy open source projects which provide the communication framework into which I can drop my message data or do I have to write a load of complicated multi-threaded sockety code? Does the picture change at all if teh clients are running on phones?
I am language agnostic, although ideally I would have a Flash or Qt front end and a Java server, but that may be being a bit greedy.
I have spent a few hours googling, but the whole topic is new to me and I'm a bit lost. I'd appreciate help of any kind - including how to tag this question.
If latency isn't a huge issue, you could just implement a few web services to do message passing. This would not be a slow as you might think, and is easy to implement across languages. The downside is the client has to poll the server to get updates. so you could be looking at a few hundred ms to get from one client to another.
You can also use the built in flex messaging interface. There are provisions there to allow client to client interactions.
Typically game engines send UDP packets because of latency. The fact is that TCP is just not fast enough and reliability is less of a concern than speed is.
Web services would compound the latency issues inherent in TCP due to additional overhead. Further, they would eat up memory depending on number of expected players. Finally, they have a large amount of payload overhead that you just don't need (xml anyone?).
There are several ways to go about this. One way is centralized messaging (client/server). This means that you would have a java server listening for udp packets from the clients. It would then rebroadcast them to any of the relevant users.
A second way is decentralized (peer to peer). A client registers with the server to state what game / world it's in. From that it gets a list of other clients in that world. The server maintains that list and notifies the other clients of people who join / drop out.
From that point forward clients broadcast udp packets directly to the other users.
If you look for communication framework with high performance try look at ACE C++ framework (it has Java bindings).
Official web-site is: http://www.cs.wustl.edu/~schmidt/ACE-overview.html
You could also look into Flash Media Interactive Server, or if you want a Java implementation, Wowsa or Red5. Those use AMF and provide native functionality for ShareObjects including synching of the ShareObjects among connected clients.
Those aren't peer to peer though (yet, it's coming soon I hear). They use centralized messaging managed by the server.
Good luck