We have a Java app, as well as a number of C#-based plugins for other apps (e.g. Excel) that can communicate with the main app. The communications layer is implemented using Apache MINA on the Java side and xsd for the .NET plugins. Typically things run on the same (Windows) machine, though it would be better not to assume that (e.g., allow the main app to run on a Mac and be able to communicate with Excel on a different machine).
The communication has to work regardless of whether the main app or the plugin(s) start up first. My question is how best to establish the link? Currently, our main Java app listens on a port that the plugins constantly poll for availability. This is obviously wasteful and inelegant. But it works.
An alternative would be to have each plugin listening on its own port, and when the app starts up it sends a "Hello" kind of message to each known port (on localhost), and then have the plugins establish the link at that point.
I've also looked a bit at multicast, but don't really know much about it. And of course, there could be multiple users on the same subnet all using the app.
Any other ideas or thoughts?
You should not be concerned with wasted attempts to connect to the server - it is not a resource intensive operation and the plugin requires the connection to work. There does not seems to be any real motivation to use anything different from a traditional client/server approach which you already are doing.
Related
I have been doing research for a few months now on the possibility of client-server communication. I have experimented with many methods such as WebORB and FluorineFX, which are both servers designed to deal with client/server authentication.
WebORB only runs on Windows for their .NET version as far as I can tell, and I would much rather use an open source system. I have tried using FluorineFX, but I think their must be a simpler way for me to build my own simple system from the ground up.
I have been using Dropbox for a while now, and I like the way that the client-server communication is instant. As far as I can tell (from some Google searches) the client doesn't open a port of its own, and just communicates with the Dropbox server through port 80. An example of its instant communication is where you may delete a file on Dropbox on their website, and instantly the server communicates with the client telling it what has happened. I don't know how this instant communication is possible without opening a port.
I can create a system that uses fetching from the client, asking the server every 10 seconds or so to see if there are any updates, but I would like a method to be able to push the information from the server to the client.
My server runs Linux so I don't think I can use WCF, and ideally I am looking for a way to make PHP and C# communicate with each other.
I would love to hear any advice that anyone has and how they deal with the problem.
Cheers.
You CAN use WCF to communicate with any platform. Just make sure you're using an endpoint which your target machine support: http://msdn.microsoft.com/en-us/library/ms733107.aspx
Have you tried the good old .NET Remoting which runs perfectly with Mono?
You can choose between a TcpChannel (for performance) and a HttpChannel (to pass proxy/firewall easily).
For push notifications, you can open a connection to your server and wait for an answer indefinitely.
I understand that trusted silverlight applications can communicate with each other over the LAN connection (peer to peer). Can they do this without an internet connection once installed out of browser? Do they need to first download some sort of Access Policy?
If not, is there some alternative way of doing this, perhaps with some kind of helper service on the computer?
Can they use similar techniques to talk to Local non-Silverlight devices, e.g. could a trusted silverlight application talk to an iPhone app over a local area network?
System.Net.Sockets.UdpAnySourceMulticastClient
Does allow you to connect between Multiple Silverlight applications on the same LAN. It does not require any internet connection after the application is installed out of browser.
I'm not clear if this could be used for communication with non-Silverlight applications althouh I believe it probably could since UDP Multicast is a standard protocol.
In situations where the network infrastructure is older it may not support UDP Multicast addresses. In this case, the best solution would be to install a separate local server on one of the client machines, to which all other silverlight applications could connect (once the user had typed in the IP address).
I'm not sure where you got your information from but as far as I'm aware there is no builtin way for Silverlight applications to connect to each other peer-to-peer. However it is possible to place a simple server application on the LAN through which Silverlight applications running on different nodes can communicate.
The plumbing needed to create peer-to-peer pipes is missing from Silverlight. It only has a means to connect to a specific TCP/IP port or to listen to Multicast UDP sources, it can't create a Listening port that waits for a connection nor generate UDP output.
You could go this by calling COM objects from Silverlight, however
Just because you can hammer in a nail
with a screw driver, does not make the
screw driver the best tool for the
job.
Have a look at using WPF so you get the full .net framework.
I would like to have a client-server application written in .NET which would do following:
server is running Linux
on the server there is SQL database (mySQL) containing document URLs
What we want:
- server side would regularly crawl all URLs and create a full text index for them
- client side would be able to perform a query into this index using GUI
The client application is written in .NET using C#. Besides of searching in documents it will be able to do a lot of other things which are not described here and which are done client-side very well.
We would like to use C# for the server side as well, but we have no experience in this area. How are things like this usually done?
Clarifying question now based on some answers:
The thing which is most unclear to me is how client-server communication is usually handled. Is client and server usually using sockets, caring about details like IP addresses, ports or NAT traversal? Or are there some common frameworks and patters, which would make this transparent, and make client-server messaging or procedure calling easy? Any examples or good starting points for this? Are there some common techniques how to handle the fact a single server is required to server multiple clients at the same time?
To use c# on Linux you will need to use Mono. This is an open source implementation of the CLR specification.
Next you need to decide on how to communicate between server and client, from the lowest level of just opening a TCP/IP socket and sending bits up and down, to .Net remoting, to WCF, to exposing webservices on the server. I do not know how compleat WCF implementation is on mono, also I think you may have issue with binary remoting between mono and MS .Net .
I would suggest RPC style WebServices offer a very good solution. WebServices also have the advantage of alowing clients from other platforms to connect easily.
EDIT
In response to the clarification of the question.
I would suggest using mono/ASP.NET/WebServices on the server, if you wish to use c# on both server and client.
One assumption I have made is that you can do a client pull model, where every message is initiated by the client. Using another approach could allow the server to push events to the client. Given the client has the ability to pole the server regularly I don't consider this much of a draw back but it may be depending on the type of application you are developing.
Mono allow execution of c# (compiled to IL) on a Linux box. Mono ASP.NET allows you to use the standard ASP.NET and integrate into Apache see http://www.mono-project.com/ASP.NET and finally WebServices allow you to communicate robustly in a strongly typed manner between you client and your server.
Using this approach negates most of the issues raised in your clarification and makes them someone else's problem.
Sockets/SSL - is taken care of by standard .Net runtime on the client and Apache on the server.
IPAddress/ports/NAT traversal - Is all taken care of. DNS look up will get the servers IP. Open socket will allow the server to respond through any firewall and NAT setup.
Multiple Clients - Apache is built to handle multiple clients processing at the same time as is ASP.NET, so you should not encounter any problems there.
As many have already mentioned there are a number of thing that you have mentioned which are going to cause you pain. I'm not going to go into those, instead I will answer your original question about communication.
The current popular choice in this kind of communication is web services. These allow you to make remote calls using the HTTP protocol, and encoding the requests and responses in XML. While this method has its critics I have found it incredibly simple to get up and running, and works fine for nearly all applications.
The .NET framework has built in support for web services which can definitely be called by your client. A brief look at the mono website indicates that it has support for web services also, so writing your server in C# and running it under mono should be fine. Googling for "C# Web Service Tutorial" shows many sites which have information about how to get started, here is a random pick from those results:
http://www.codeguru.com/Csharp/Csharp/cs_webservices/tutorials/article.php/c5477
have a look at Grasshopper:
"With Grasshopper, you can use your favorite development environment from Microsoft® to deploy applications on Java-enabled platforms such as Linux"
Or see here
The ideea is to convert your app to Java and then run it on Tomcat or JBoss.
Another approach: use the Mod_AspDotNet module for Apache, as described here.
This Basic Client/Server Chat Application in C# looks like a kind of example which might be a starting point for me. Relevant .NET classes are TcpClient and TcpListener
I have 50+ kiosk style computers that I want to be able to get a status update, from a single computer, on demand as opposed to an interval. These computers are on a LAN in respect to the computer requesting the status.
I researched WCF however it looks like I'll need IIS installed and I would rather not install IIS on 50+ Windows XP boxes -- so I think that eliminates using a webservice unless it's possible to have a WinForm host a webservice?
I also researched using System.Net.Sockets and even got a barely functional prototype going however I feel I'm not skilled enough to make it a solid and reliable system. Given this path, I would need to learn more about socket programming and threading.
These boxes are running .NET 3.5 SP1, so I have complete flexibility in the .NET version however I'd like to stick to C#.
What is the best way to implement this? Should I just bite the bullet and learn Sockets more or does .NET have a better way of handling this?
edit:
I was going to go with a two way communication until I realized that all I needed was a one way communication.
edit 2:
I was avoiding the traditional server/client and going with an inverse because I wanted to avoid consuming too much bandwidth and wasn't sure what kind of overhead I was talking about. I was also hoping to have more control of the individual kiosks. After looking at it, I think I can still have that with WCF and connect by IP (which I wasn't aware I could connect by IP, I was thinking I would have to add 50 webservices or something).
WCF does not have to be hosted within IIS, it can be hosted within your Winform, as a console application or as windows service.
You can have each computer host its service within the winform, and write a program in your own computer to call each computer's service to get the status information.
Another way of doing it is to host one service in your own computer, and make the 50+ computers to call the service once their status were updated, you can use a database for the service to persist the status data of each node within the network. This option is easier to maintain and scalable.
P.S.
WCF aims to replace .net remoting, the alternatives can be net.tcp binding or net.pipe
Unless you have plans to scale this to several thousand clients I don't think WCF performance will even be a fringe issue. You can easily host WCF services from windows services or Winforms applications, and you'll find getting something working with WCF will be fairly simple once you get the key concepts.
I've deployed something similar with around 100-150 clients with great success.
There's plenty of resources out on the web to get you started - here's one to get you going:
http://msdn.microsoft.com/en-us/library/aa480190.aspx
Whether you use a web service or WCF on your central server, you only need to install and configure IIS on the server (and not on the 50+ clients).
What you're trying to do is a little unclear from the question, but if the clients need to call the server (to get a server status, for example), then they just call a method on the webservice running on the server.
If instead you need to have the server call the clients from time to time, then you'll need to have each client call a sign-in method on the server webservice each time the client starts up. The sign-in method would take a delegate method from the client as a parameter. The server would then call this delegate when it needed information from the client.
Setting up each client with its own web service would represent an inversion of the traditional (one server, multiple clients) client/server architecture, and as you've already noted this would be impractical.
Do not use remoting.
If you want robustness and scalability you end up ruling out everything but what are essentially stateless remote procedure calls. Since this is exactly the capability of web services, and web services are simpler and easier to build, remoting is an essentially pointless technology.
Callbacks with remote delegates are on the performance/reliability forbidden list, so if you were thinking of using remoting for that, think again.
Use web services.
I know you don't want to be polling, but I don't think you need to. Since you say all your units are on a single network segment then I suggest UDP for broadcast change notifications, essentially setting a dirty flag, and allowing the application to (re-)fetch on demand. It's still not reliable but it's easy and very fast because it's broadcast.
As others have said you don't need IIS, you can self-host. See ServiceHost class for details on how to do this.
I'd suggest using .NET Remoting. It's quite easy to implement and doesn't require anything else.
For me its is better to learn networking.. or the manual way of socket communication.. web services are mush slower because it contains metadata..
your clients and the servers can transform to multithreaded application. just imitate the request and response architecture. it is much easy to implement a network application like this..
If you just need a status update, you can use much simpler solution, such as simple tcp server/client messaging or like orrsella said, remoting. WCF is kinda overkill here.
One note though, if all your 50+ kiosk is connected via internet, then you might need use VPN or have an open port on each kiosk(which is a security risk) so that your server can retrieve status update from each kiosk.
We had a similiar situation, but the status is send to our server periodically, so we only have 1 port to protect/secure. The frequency of the update is configurable as to accomodate slower clients.
As someone who implemented something like this with over 500+ clients and growing:
Message Queing is the way to go.
We have gone from an internal developed TCP server and client to WCF polling and ended up with Message queing. It's the only guaranteed way to get data to and from clients and servers over the internet. As a bonus, many of these solutions have an extensive framework makeing it trivial to implement publish-subscribe, Send-one-way, point-to-point sending, Request-reply. Some of these are possible with WCF but it will involve crying, shouting, whimpering and long nights not to mention gallons of coffee.
A couple of important remarks:
Letting a process poll the clients instead of the other way around = Bad idea.. it is not scalable at all and you will soon be running in to trouble when the process is take too long to complete.. Not to mention having to handle all the ip addresses ( do you have access to all clients on the required ports ? What happpens when the ip changes etc..)
what we have done: The clients sends status updates to a central message queue on a regular interval ( you can easily implement live updates in the UI), it also listens on it's own queue for a GetStatusRequest message. if it receives this, it answers ( has a timeout).. this way, we can see overal status of all clients at all times and get a specific status of a specific client when needed.
Concerning bandwidth: kiosk usually show images/video etc.. 1Kb or less status messages will not be the big overhead.
I CANNOT stress enough that the current design you present will have a very intensive development cycle AND will not scale or extend well ( trust me, we have learned this lesson). Next to this, building a good client/server protocol for this type of stuff is a hard job that will be totally useless afterwards if you make a design error ( migrating a protocol is not easy)
We have built our solution ontop of ActiveMQ ( using NMS library c#) and are currently extending Simple Service Bus for our internal workings.
We only use WCF for the communication between our winforms app and the centralized service(s)
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.