We have designed an Android and iOS application for a client using their WCF created backend.
We have a method that allows users to checkin for their appointments if they are with in a certain geo location.
Both apps are able to find the server and grab data however the android application only works about 50% of the time (the iOS version works 100%). I have tried on Wifi and Cellular and get the same results.
The biggest issue is I can't even determine if the issue is with the client or server or how should i handle it?
I have read that it could be due to an unclosed httpURLConnection but thats my only real lead at the moment.
Please help!!!
Thanks
Since it works half of the time on android and for iOS always, the problem can be only the network problem by my opinion. It just happens in some network environments and on some of the devices or on some of the device with certain android-java version. I think you will not be able to do anything.
When I started to have those problems, I just always bumped into a simple fact about fallacy of network programming and CAP theorem: Network is reliable. So the fact is that network is NOT reliable and you should consider it in your solutions.
http://en.wikipedia.org/wiki/Fallacies_of_Distributed_Computing
http://en.wikipedia.org/wiki/CAP_theorem
It could be that this problem sometimes gets also into succeeded request but no response problem. Again almost the same network failure problem as above and what you can do is handle the possible timeout exceptions etc. and handle it appropriately on the server and client. So in case of having methods like submittingSomePayment, not use a normal WCF methods, but use enterprise service buses which store the messages into queues and process them and then have additional call that checks the results. See CQRS pattern for example.
http://msdn.microsoft.com/en-us/library/jj591573.aspx
Not very helpful, I know. But a possible answer and my thought about it. Because it annoyed me too. So it could be that you will not be able to do anything about it (except end users handling their network issue by themselves).
I would also log the request in the core beginning of the WCF service method call to exclude any internal WCF behavior (to exclude guessing is a problem in your code). All possible Logging on server and client would be a possible way to go in case you are still convinced the problem is in a code. And also see is this happening on all android devices (LG,... etc.) or only certain with certain java versions.
Related
I've tried to find a solution at stackoverflow but can't seem to find one quite like mine so here it goes. I have a computer in the lab that is connected to various devices like pan/tilt units, cameras, and light sensors and has all their drivers installed. I have C# code on the lab computer that knows how to talk to the hardware. The C# code can set an exposure time, ask for a picture, get one back, and display it in a picture box. I can tell the pan/tilt to move to a location and have it respond when done. If I am in the lab, it all works just the way I want.
The problem is that I want it to feel like I am at the lab computer when I am really at another computer. Most likely, I will be running the code that is on the non lab computer from inside Visual Studio. The program running in the lab will not be running from Visual Studio. With Remoting, this is a piece of cake. Put the code that talks to the hardware into a class, use MarshalByRefObject along with an interface I create, add RegisterWellKnownServiceType and presto I can use GetObject to get a reference and control it like I was sitting at the computer in the lab. So I know that remoting will work.
However, remoting is being phased out for WCF not to mention its not real safe out in the real world. It appears to me that WCF is going to make a local copy (by value) of the remote object which means it will not be on the lab computer and therefore unable to interact with the hardware that is attached. Someday this lab computer and all the sensor equipment is going to be moved away and I will have to access it remotely using the internet. A couple of years ago I did this exact thing but I was using remoting. Since remoting is so insecure, how do I do this without using remoting? Does WCF not have something equivalent to MarshalByRefObject? If WCF only uses by value, then it seems like they are phasing something out without providing functionality to replace it. Is there a way to use remoting that is not insecure? Is there something else besides WCF I should use?
This may be long winded but I see lots of people get dinged for asking questions that aren't very clear so I am trying to be clear. If there is already a post that truly provides me the best answer to my question, I must first apologize for not finding it myself but ask that a link be provided so I can get the answer there.
It appears to me that WCF is going to make a local copy (by value) of
the remote object which means it will not be on the lab computer and
therefore unable to interact with the hardware that is attached
This is almost entirely incorrect. There is no "copying" being done across machines. In fact the whole terminology around the "remote object" no longer has much meaning with WCF.
There is no remote object, simply a service. The service exposes operations across it's boundary. Service consumers can call those operations. When a consumer calls an operation, that call passes into the service and can cause the state of the service to change (for example, to talk to some hardware devices).
The service can also send a response to the caller, which can then cause the caller state to change (for example, to display output from the hardware device).
In order to make this happen you first need to create a service definition. Then you need to host your service on the lab machine. Then you need to create a service client, which you can then use on your local machine to call the service operations.
(How to) handle the situation where the port connected to the hardware
on the lab computer fires a DataReceived event that needs to be picked
up by my application
This is a more complex requirement but yes, WCF supports duplex communications with it's clients.
When you are defining your service contract you can specify that consuming clients implement a callback contract. This forces clients to define a callback operation which is exposed over the communication channel between service and client, and which the service can then call to "push" information to the client.
You should have your service use the WSDualHttpBinding WCF channel binding, which will use port 80 in both directions, allowing this to go across the internet.
Scenario
I have a Windows service that is in charge of listening for various things and act accordingly. Most of the time this service modifies the database in some fashion (adding, removing and cancelling items). This is on the servers side and requires no user involvement. The client side is quite simple. Each user (5-10) each use an application to work on the items inserted by the Windows service.
Problem
The issue is that the clients are working in a disconnected state. What I mean by that a client could reload their list of items needing to be worked on and 5 minutes later actually begin their work.
Also, due to various issues no administrative assistance must be required in order to install the client application. This rules out libraries such NServiceBus (or any library requiring the use of MSMQ) and WCF (seems like so because it requires the use of opening up URLs using netsh http add urcl.
I'm not looking to send messages to clients. All I'm looking for is an easy way to have the Windows service poke each subscribed client instructing them to reload their list. I do realize that I could simply create a background thread (or the like) and refresh every n minutes but there's really no sense in doing that (IMO) if nothing has happened in the last few hours.
Edit
Researching some more it appears I can use raw sockets for this. Will update once I get something working.
Take a look at 0MQ, it might meet your requirements.
I'm currently working on a Windows service (my first) and I'm wondering how to handle disconnect events and the like. In essence, this Windows service polls our Exchange servers for new emails. Once an email is received we parse it and insert it into a database. Now, I have everything working so long as everything is working in my favour. Since that is impossible to maintain I need to look for ways to ensure my service stays on line regardless of what may happen that is out of my control (minus the server hosting the service that is).
The main issues I can foresee are our Exchange servers going down for whatever reason or losing internet connectivity. Two problems which can happen several times a year.
Currently, if an exception is thrown regarding connectivity issues I keep attempting to connect every n minutes with a 30 second time out. So say our Exchange servers go down (either planned maintenance or unforeseen events) for 2 hours then the service would try and reconnect every n minutes until a connection is made.
Is this a sustainable strategy to ensure my service always stays online? If not, what is a better way?
What I want to avoid is my service going down because Exchange had issues making me have to manually restart my Windows service.
Thank you.
Your strategy sounds like the only thing that's practical.
It may also be worth considering adding the ability to view event logs from the service remotely so you can diagnose issues that you don't currently know about. If you're really paranoid, a second "watcher" service could be used to periodically check the primary service and report if it fails.
So I'm working on a project for my internship and have hit a bit of a brick wall. Unfortunately, the only people I know who are qualified to help me at the office are on vacation at the moment, and Google has been unfortunately unhelpful (or my search skills inadequate), so I thought I'd ask here.
The project is basically to make a server to mimic one that the company (which makes phone apps) already has. What I need to do is have one of their apps send a request to my server (I will have to modify the app to do this, but don't know how), and have my server reply with an XML response that the app already knows how to process. (The main purpose is so that we can see how the app responds when the real server sends it an error by simulating it on my server.)
Now, I already have a few sample HTTP requests and their associated XML responses handy, taken from simulations with the app and the real server. The app is written in C#, and currently sends HTTP web requests to the real server's online location, which responds to these HTTP web requests with XML. My server, however, will not have an online location, so the app will have to be modified to work with sockets on a local host.
My questions:
1) My boss said to create an XML file to associate certain requests with certain XML responses, but I have no idea what he means or how to do this. (He said it could also be done with a .ini file.) Does anyone know?
2) Once I have this XML file that can make these associations, how can I incorporate it into my server so that my server can check the request it received against its table of valid requests and figure out which response to send back?
3) How can one modify the app from using HTTP web requests and responses to using sockets?
If you have any questions/clarifications that you need in order to better answer this, please don't hesitate to ask me.
Thanks!
What you're describing is a web service. Unfortunately, his advice to change a setting in an .ini file make it sound like they have a proprietary system for doing this, rather than using a standard ASMX (which requires IIS) or WCF (which can either run in IIS or as a standalone service, which it sounds like is what you'd want) service.
Without more information about what they're using, I don't know that you'll be able to get much help here.
In response to question #3:
HTTP is a protocol that already runs on a specific socket (normally using port 80).
An internet socket is an endpoint that is used to transport data between processes. If you want to run your own protocol, you will need to create a new socket (with TCP or UDP) on a specific port.
This will however require you to create your own client and server in order to exchange data between them.
To get started, here is a very simple client-server example in C# using a custom socket.
Good luck!
Ask your boss if this client communicates with soap, if so then just go to MSDN and find tutorials on implementing an ASMX webservice, follow the tutorial through and you'll have a shell to start with.
First I'd like to say that it sounds like you have some unclear requirements that you should probably clarify with your boss. If you're not exactly sure what he means you should find out because nothing sucks more than having to support someone's creative interpretation of requirements.
1) It sounds like your boss just wants a way to easily change associations for testing without having to rebuild the app so he's asking you to store those associations in an xml/ini file that can easily be modified. In c# you can easily go between XML and DataSet objects so this should be trivial. I would create the data structure in a DataSet first and then use the GetXml method of the DataSet to output the xml format.
2) In .NET you can store objects in Cache and create a Cache Dependency that is a file association. Thus whenever the file is modified the Cache is purged. Whenever your program handles a request it pulls the object from Cache, if the object isn't in Cache then you have a condition block rebuild it from the xml/ini file on disk. I would have that condition block call out to a function that then loads the above mentioned xml format into a dataset that is then stored in the Cache with a Cache Dependency.
3) If you are trying to test an applications i/o, modifying it to use a different transport layer sounds like a bad idea. If the app currently works over HTTP to send requests then just route the HTTP request. I would suspect that the app probably has a configuration somewhere defining the path of the webservice it currently calls out to, once you know what that path is you can either change it, or if that's not possible setup a DNS rule on the server running the app to route it to the location of your application. On windows this is as simple as adding a line to the hosts file.
I am writing you because of a new problem I need to solve, and I have now been banging my head against a wall for too long now.
Basically, I need to create an application that can take care of the following:
A user starts an app, which sends a broadcast to the subnet, and recieves a response of all servers there with their IP (and some additional info). The user can then select what server he wants to connect to.
Making it work is simple enough, with identifying the subnet, and broadcasting with UDP, and then having a different server application recieving it and sending back a response . The problem lies with these restrictions, that I need to take into consideration:
There will most likely also be clients on the server machines in the network, meaning that we can assume that the application is present on all machines. Every machine needs to have the listener running, and every machine can launch the GUI for selecting a server.
I am only allowed to add one exception to the firewall - an exception that handles both sending out the broadcasts, recieving broadcasts, sending answers and recieving answers.
I should also only be adding one Windows Service
on a server machine, the listener should run as a windows service, so the user won't notice it. Nor will the user notice, that the response is sent back to the client.
On the client machine, the user can start an application, which will notify the application to emmit the broadcast, and will get all the server responses, so the user can choose one to connect to.
Besides from the application that the user launches in order to select a server, there should be no interaction with the user whatsoever. Not even a popup, requesting the user to allow traffic trough the firewall - it should all be automatically
It needs to work on and in between Win XP, Win Vista and Win 7.
I don't know if I am putting too many constrains on myself, but I really hope that I can make the application with these requirements.
I have a few ideas - I just need to figure out how to do it:
Should i make everything into one application, that I add to the firewall exception list, so it will take care of the traffic on both the server and the client machines?
Should I add a custom exception to the firewall, allowing UDP traffic on a specific port, and then have all traffic flow trough that?
Is there a third and better option for managing that?
It is OK to have the service running on both client and server machines. But can it take care of everything for me - like it handling both the broadcast send/recieve and answer send/recieve? And is there any way to extract the information about servers on the network from a service?
I know it is a lot, but I really hope that you will be able to help me out.
let me know if I wasn't clear enough, or if you need further explanations.
I am coding in C# .Net, and I can utilize all I want from the .Net framework. As soon as I have this functionality implemented
All the best
/Sagi
The kind of peer-to-peer networking problems become simple to the point of being trivial if you designate one machine as the master server. It should have a well-known name that all sub-servers can connect to so they can publish (and withdraw) their availability. A client can then send a query request to the same server and get a list of known servers in return.
This can also solve your firewall problem, the master server could be listening on port 80.
Look into the System.Net.PeerToPeer namespace for a p2p solution supported by the framework.
Maybe a UPnP server and client may be a solution to your problem?