I'm using a duplex WCF contract in this chat-like application that i have running. (obviously not really a chat, but for the interest of thinking about it you can assume it's similar enough).
the problem is that many of the clients that talk over this contract are running dhcp, and there's not really anything i can do about this.
What's the best way to handle duplex communication with dhcp? I found a setting <compositeDuplex clientBaseAddress="Uri"/> which means i could update this value at runtime.... seems a bit kludgy.
Update
I found that in my WCF server logs, part of the problem is that it was putting hostname in the response address. what am i doing wrong here?
thanks
To be blunt, the first thing that you're doing wrong is using DualHttpBinding to do duplex. That whole binding is a giant kludge and is prone to problems like this (and firewalls, oh god firewalls).
If you were to use something like net.tcp instead then the clients establish a single bidirectional connection to the server instead of needing two connections, and thus the server doesn't care if the client is on DHCP anymore.
Related
does someone know if it possible to use one WCF Data Service as data source of another WCF Data Service? If so, how?
So the short answer is yes. Actually I have consumed one WCF service in another (HttpBinding coming to a service on computer, then that service had a NamedPipesBinding service to communicate with multiple desktop apps, but it did some data transformation in the middle). That would not be an issue at all, you would set up a proxy/client just like you would in a desktop client, and handle everything in your new service as if it was just passing information along, you could even create a shared library for the DataContracts and such.
HOWEVER I would not suggest the leapfrog method in your implementation. Depending on how many customers you are potentially opening the door too, you may be introducing a bottlekneck, if you have a singleton service, or overload your existing service in the case of many connections from the new one. Since you have a SQL server, why would you not have a WCF service on your web/app server (public) that connected to it and provided the data you need? I'm only thinking this because your situation can become exponentially complicated when you start trying to pass credentials for authentication and authorization between the two, depending on your security settings. Another thing to consider is the complexity in debugging this new service and the old one, and a client at the same time, as if it wasn't a pain just to do server and client, since you are opening it to a public facing port, there are different things to set up, and debugging everything on the same machine is not the same as a public facing application server.
Sorry if this goes against what you were hoping to hear. I'm just saying that it is possible, but not suggested (at least by me) in your particular case.
I'd like to create a web service that an application server can contact to add itself to a list of servers implementing the application. Clients could then contact the service to get a list of servers. Something similar to how minecraft's heartbeats work for adding your server to the main server list.
I could implement it myself pretty easily, but I'm hoping someone has already created something like this.
Advanced features would be useful. Things like:
Allowing a client to perform queries on application-specific properties like the number of users currently connected to the server
Distributing the server list across more than one machine
Timing out a server's entry in the list if it hasn't sent a heartbeat within some amount of time
Does anyone know of a service like this? I know there are open protocols and servers for doing local-LAN service discovery, but this would be a WAN service.
The protocols I could find that had any relevance to your intended application are these:
XRDS (eXtensible Resource Descriptor Sequence).
XMPP Service Discovery protocol.
The XRDS documentation is obtuse, but you may be able to push service descriptions in XML format. The service type specification might be generic, but I get a headache from trying to decipher committee-speak.
The XMPP Service Discovery protocol (part of the protocol Formerly Known As Jabber) also looked promising, but it seems that even though you could push your service description, they expect it to be one of the services mentioned on this list. Extending it would make it nonstandard.
Finally, I found something called seap (SErvice Announcement Protocol). It's old, it's rickety, the source may be propriety, it's written in C and Perl, it's a kludge, but it seems to do what you want, kind-of.
It seems like pushing a service announcement pulse is such an application-specific and trivial problem, that almost nobody has considered solving the general case.
My advice? Read the protocols and sources mentioned above for inspiration (I'd start with seap), and then write, implement, and publish a generic (probably xml-based) protocol yourself. All the existing ones seem to be either application-specific, incomprehensible, or a kludge.
Basically, you can write it yourself though I am not aware if anyone has one for public (I wrote one over 10 yrs ago, but for a company).
database (TableCols: auto-counter, svr_name, svr_ip, check_in_time, any-other-data)
code to receive heartbeat (http://<you-app.com>?svr_name=XYZ&svr_ip=P.Q.R.S)
code to list out servers within certain check_in_time
code to do some housecleaning once a while (eg: purge old records)
To send a heartbeat out, you only need to send a http:// call, on Linux use wget* with crontab, on windows use wget.exe with task scheduler.
It is application specific, so even if you wrote one yourself, others can't use it without modifying the source code.
I'm working on shipping in a change for my lab that will hopefully help diagnose some weird channel-faulting weirdness we're seeing. There's a test application that uses DuplexChannelFactory to connect to a couple windows services, and for some reason the channels on this test application seem to be faulting quite a bit. I have plans to implement some retry logic in there, but it would be great to figure out why exactly they're faulting.
I know that channel factories and proxy objects all implement a lot of interfaces, and I've used reflector to crawl through some of them, but I haven't found anything like what I'm looking for. Is there a way to query these objects after they've faulted in order to get some information about what caused the fault?
Edit: The configuration is very basic--the binding is just the default-constructed NetTcpBinding, the service implementation has [ServiceBehavior(InstanceContextMode = InstanceContextMode.Single, ConcurrencyMode = ConcurrencyMode.Reentrant)], and no special attributes are on any of the operations in the service contract. However, I'm asking more about general techniques in diagnosing channel faults, not diagnosing this specific case. I wouldn't expect configuration specifics to have too much impact on that; if anything, the configuration details would be something returned by said diagnostics, right?
Ladislav and Shiraz answers are all good and I have gave them +1.
All I can add to them is that normally a faulted channel is the result of unhandled exception on the server. When that happens, WCF thinks that there is somethig fundamentally wrong with the server and faults the channel so that it cannot be used.
The correct approach - which I believe should have been default and come for free - is for the service to catch the exception and create a FaultException and return it (look at this form example http://www.c-sharpcorner.com/UploadFile/ankithakur/ExceptionHandlingWCF12282007072617AM/ExceptionHandlingWCF.aspx)
The reason WCF does not make as default is that it changes the contract and the WSDL so the client has to get the updated WSDL.
So if I were you, I would catch the exceptions, log them and then return a fault exception and this way I would know what the problem is and channels are not faulted.
First thing is it this test application, or are the specific services used by other clients.
Assuming that it is the test client that is causing the problem. There could be 2 problems:
Not closing proxies, therefore hitting max connections to the server.
Not aborting proxies when they are in a failed state.
Diagnostic tool you are looking for is called WCF Tracing. It usually shows why the channel has faulted. You can configure it on both client and server and use SvcTraceViewer.exe to browse collected traces.
Have you hooked on to the ICommunicationObject.OnFauled
I'm trying to set up a client-server architecture. I have one GKSession configured as a server, and two others as clients.
When either client uses the sendData:toAllPeers:WithDataMode:error method, it sends it not only to the server but to the other client.
I guess I could use the display name to exclude clients, so client data only goes to the server, but I'm not quite following why this is happening.
My server explicitly accepts a connection, via acceptConnectionFromPeer:error: But my client isn't accepting anything from anybody, it seems to be just silently finding the other client.
Should this be happening? I understand in a peer-peer setup you'd want peers to just find others; but in client-server, this seems a little weird.
Any clarification or advice would be greatly appreciated.
While a client cannot explicitly connect to another client, but the method sendData:toPeers:withDataMode:error: should allows you to send data directly from one client to another given that you have the correct peerId.
Are there any bindings to communicate on Serial port using WCF?
OK I couldn't find any workable solution. Thus started to build a custom channel.
http://wcfserialchannels.codeplex.com
Interested developers please join.
i dont know how to do it ,but here is a Codeproject article on how to make your own transport for WCF. You could make one for to use a serial port. I am not familiar with WCF so i dont know if this article can help you, but it looks promising.
Hard to say without knowing more about what you're up to, but probably easiest to take it down a layer. If you're just talking about two machines where you control both sides, set up a Dialup Networking PPP connection between the machines over a null modem and use WCF with standard HTTP or NetTcp over the pipe.