The project is to build a messaging mechanism between a Python and C# program via ZeroMQ .
I want messages to be able to travel in/out from both ends at any time, which is NOT a basic request-reply model a.k.a. REQ/REP.
One way I can think of is to build a PUB/SUB model on two ports, i.e. two one way channels.
Is there any method to get a real duplex channel?
There are several ways to do this with ZeroMQ. I suggest using a DEALER/ROUTER socket pair:
Choose one program to be the "server", the other the "client".
The server will bind a ROUTER socket on a port.
The client will connect a DEALER socket to the server's ROUTER port.
(Note: this implies that the client must know the server's IP and port in advance.)
At this point the client can send messages to the server, but the server has no way to send to the client.
The client sends a "HELLO" message to the server.
The server will receive a message that includes the client's address and the HELLO message. Now the server can send messages to the client using the client's address.
DEALER/ROUTER is considered an "advanced" socket pair in ZeroMQ. My description here is very high level. You'll really need to read the docs to get the most out of ZeroMQ.
Oh yes, Sir!
Use the PAIR-PAIR or even the XREQ-XREP ought make it.
The best next step is to carefully read the respective Scalable Formal Communication Pattern archetypes' access-points' API documentation, so as to cross-check, that all pieces of pre-wired behavioural logic meet your Project needs and voilá, harness them in your messaging setup and tune-up the settings so as to meet you performance and latency needs.
That is this simple ( thanks to all the genuine knowhow hidden in these builtins ).
Using for years this very sort of inter-platforms integration among Python + C/MQL4 and other computing nodes, so well worth one's time to learn the powers and strengths of ZeroMQ.
Related
I have the same dilemma as the one who posted this topic, Real-time communication with WCF
except that my problem is not about games programming. I would like to know what's the best method to use to be able to have a real time communication in between two windows applications (server-client). I am using visual c++/c# to date and i would like to be able to display all the Feeds that are being received by my server to the client in real time.
I have started trying to use .NET remoting but in my continuous research, it appears that it will use SOAP-http, and might affect the speed of the communication. My server and client will communicate using the internet and .NET remoting does not permit the use of TCP Channel when communicating in between a firewall or the internet.
Your inputs will be greatly appreciated.
I guess it depends on your escenario, if you want "real-time" and you are willing to lose some packages in the process you are better with UDP, take a video conferencing tool for example, by the time you recover your slow packages you will have to move and display the next frame in the video or audio; that is a good example for the use of UDP. This is the reason why UDP is much faster than TCP.
If however, you are not willing to lose a single bit of your message, then TCP was made for you because if you lost a package the protocol will request it again to have your complete message as complete as possible.
Additionally it depends on the way the communication is being sustained, is the information flowing from one to many?, from many to many?, one to tone?
Take NetNamedPipeBinding for instance, this will be much faster process, but is only deployed in a single machine but accross processes. Whereas NetMsmqBinding will help you to build queues and it will be amazingly reliable and scalable for scenarios where your load will be a massive number of connections.
In the end, it all boils down to your concrete escenario and your business goals.
Hope it helps
If you are willing to do your own message parsing, you can use standard TCP sockets with the TcpClient and TcpListener classes. If your data is already a serializable object, you could serialize it into a text stream and just send it over the socket, deserializing it on the client side.
To get it to work over the internet, the server needs to have the port forwarded on your router, the client would just attach to the server's public IP. You would obviously need to add an exception in your firewall for this port as well.
The biggest problem with WCF and large data is setting up the streaming, by default WCF sends everything at once, which isn't practical for large files.
I am currently new to C# and I need to understand simple server-client architecture!
I am currently trying to write a simple server/client program where basically a client can send a variable to a server and the server can send it to another client. Problem is that I am really blind to this as I am still very new to C# although I have some experience with Java (But still not with networking).
My question is:
How many files will i Have to write?
Can anybody be nice enough to provide me with a framework or example for a program like this?
What is a TCP server?
This is intended to be for an online game. One client will roll the dice and the server must show all the other clients that this is the value the first client rolled.
Any help would be greatly appreciated!
Answer to all of your questions: MSDN - Network Programming (.NET 4)
Since you are planning on TCP (because you want state) you need to develop a strategy. You'll get plenty of information about establishing a connection and moving some sort of data back and forth. Google will give you more than you can handle. Without doing all the work, here are a few steps to get you oriented.
1) Connection Registration - When a client comes online and wants to communicate with the server it first needs to say "Hey I'm here and want to role some dice." This initial handshake could be a connection id that is used for a heart beat and/or transactions. The server will use this to identify data and the respective thread if open.
2) Heart Beat - Now that the client has registered with the server the client is responsible for providing a heart beat saying it's still there and still planning to continue work. Typically every 3 - 10 seconds is good.
3) Develop the Request/Response protocol - For "every command" there will be a formal process. This formal process will include the connection id but also a request id. The client will not accept a response unless it receives the corresponding request id. Furthermore, every request will require a success or fail response to identify if it conforms to the API or what not. Within the request will be the command or action to perform. Some people use int's to dispatch a command id then use a switch on the id to call an entry-point method (cmd id = 1 is connect(), cmd id = 2 is rolldice(), etc). You might include additional payload that identifies the result from the command.
In short, 1 is the handshake, 2 is the keep-alive and 3 is passing data back and forth.
Now whether to use socket or WCF, I'd recommend to have a basic understanding of TcpClient programming then run with WCF. You'll be amazed how simple socket programming is but the overhead is a killer. Nothing to be intimidated by. It's a lot of work to coordinate calls, threads and not to mention security. WCF on the other hand does shave some of this overhead off.
I'd check out this question...
How to use socket based client with WCF (net.tcp) service?
1) The number of files will depend on your particular implementation. You can create this architecture as simply as 1 class for the server and 1 class for the client (you can have more than one class in a file). Depending on the complexity and choices you make during the design you could have many files or just a few.
2) A good tutorial for a simple TCP server / client can be found here
3) A TCP server is a process that waits for a connection from a TCP client. TCP stands for Transmission Control Protocol. From Wikipedia: TCP provides reliable, ordered delivery of a stream of bytes from a program on one computer to another program on another computer.
Lets say I have my C# app installed on 2 laptops connected to a WiFi Wireless Local Area Network.
How can these apps send messages to each other? What method or library can I use? I heard of using sockets but I have no idea how to work with these.
You could use WCF to build a communication pipe between the 2 applications. WCF encapsulates the sockets into a more manageable interface. You can start here.
Basically, you'll want to do it the same way you would in any other language. You'll open a network connection of one flavor or another (raw TCP or UDP, or a higher level protocol like HTTP) with one side acting as a server and the other acting as a client. Then each side can write data through or read data sent by the other side. It's can get pretty complicated from there. If you Google "C# Sockets" or "C# HTTP", etc, you'll find quite a few tutorials on the subject.
This is a very good article on sending C# objects (which could include whatever messages that you want to send) over a Socket connection using the Binary Formatter. Although it is not the most efficient, it is quite easy to grasp and get working.
What do I use for two way communication over the internet without the necessity to open ports on the client side?
Users won't agree to open ports and do port forwarding on the client side although everything is possible on the server side.
But,I need to accomplish two way communication..
How do I go about achieving this?
It doesn't matter whether its WCF or remoting or webservices...
I just need a quick and fast way to just get the concept to work out and distribute the application.
ofcourse,it's going to be through the internet.
Please help..
Thanks
Edit : Please note that i need to connect multiple clients and maintain a session for each client.
WCF supports duplex HTTP bindings.
As long as the initiating client can access the service, a callback contract can be defined to call the client. It simply keeps the HTTP connection once the client has initiated it.
It depends what you want to do. Duplex WCF can work, but through NAT and Proxies it becomes somewhat "iffy" because it depends on the client opening a WCF endpoint and maintaining the connection.
I wrote a beginners guide to WCF callbacks a while ago - it's simple enough to do, but you'll need to test it a lot, from various client setups.
Connect via TCP (raw sockets, or higher implementation) to a your central server.
Your server should have an application that listens to a specific, well known, TCP port.
Each client connects to your server, using the specific port, and "logs in".
Write an application protocol above the TCP (authentication, session management, etc.), and there you have it, since a TCP connection, once established, works for both directions.
I hope someone can guide me as I'm stuck... I need to write an emergency broadcast system that notifies workstations of an emergency and pops up a little message at the bottom of the user's screen. This seems simple enough but there are about 4000 workstations over multiple subnets. The system needs to be almost realtime, lightweight and easy to deploy as a windows service.
The problem started when I discovered that the routers do not forward UDP broadcast packets x.x.x.255. Later I made a simple test hook in VB6 to catch net send messages but even those didn't pass the routers. I also wrote a simple packet sniffer to filter packets only to find that the network packets never reached the intended destination.
Then I took a look and explored using MSMQ over HTTP, but this required IIS to be installed on the target workstation. Since there are so many workstations it would be a major security concern.
Right now I've finished a web service with asynchronous callback that sends an event to subscribers. It works perfectly on a small scale but once there are more than 15 subscribers performance degrades considerably. Polling a server isn't really an option because of the load it will generate on the server (plus I've tried it too)
I need your help to guide me as to what technology to use. has anyone used the comet way with so many clients or should I look at WCF?
I'm using Visual C# 2005. Please help me out of this predicament.
Thanks
Consider using WCF callbacks mechanism and events. There is good introduction by Juval Lowy.
Another pattern is to implement blocking web-service calls. This is how GMail chat works, for example. However, you will have to deal with sessions and timeouts here. It works when clients are behind NATs and Firewalls and not reachable directly. But it may be too complicated for simple alert within intranet.
This is exactly what Multicast was designed for.
A normal network broadcast (by definition) stays on the local subnet, and will not be forwarded through routers.
Multicast transmissions on the other hand can have various scopes, ranging from subnet local, through site local, even to global. All you need is for the various routers connecting your subnets together to be multicast aware.
This problem i think is best solved with socket.
Open a connection to the server, and keep it open.
Could you have a slave server in each subnet that was responsible for distributing the messages to all the clients in the subnet?
Then you could have just the slaves attached to the central server where the messages are initiated.
I think some of you are vastly overthinking this. There is already a service built into every version of Windows that provides this exact functionality! It is called the Messenger service. All you have to do is ensure that this service is enabled and running on all clients.
(Although you didn't specify in the question, I'm assuming from your choices of technology that the client population of this network is all Windows).
You can send messages using this facility from the command line using something like this:
NET SEND computername "This is a test message"
The NET SEND command also has options to send by Windows domain, or to specific users by name regardless of where they are logged in, or to every system that is connected to a particular Windows server. Those options should let you easily avoid the subnet issue, particularly if you use domain-based security on your network. (You may need the "Alerter" service enabled on certain servers if you are sending messages through the server and not directly to the clients).
The programmatic version of this is an API called NetMessageBufferSend() which is pretty straightforward. A quick scan of P/Invoke.net finds a page for this API that supplies not only the definitions you need to call out to the API, but also a C# sample program!
You shouldn't need to write any client-side code at all. Probably the most involved thing will be figuring out the best set of calls to this API that will get complete coverage of the network in your configuration.
ETA: I just noticed that the Messenger service and this API are completely gone in Windows Vista. Very odd of Microsoft to completely remove functionality like this. It appears that this vendor has a compatible replacement for Vista.