What I want to do is create a WCF service just to get the availability of a user. I have gone through the following quick-start example:
Name: SubscribePresence
http://msdn.microsoft.com/en-us/library/office/dn454835(v=office.15).aspx
I have managed to do this but i feel that its not the most efficient way to just get a users availability.
At the moment I create a end point subscribe to a users presence and wait for the response to come back and from that i get the users availability. (I'm simplifying this down).
What I would ideally like though is just to quickly get a users availability without subscribing to a users presence and close the connection as soon as i have retrieved the availability.
I was wondering if anyone knows of an example that i can have a look at or that they have implemented themselves
any advice would be appreciated
You can also do a one-time presence query. From MSDN:
If a one-time presence query to a remote presentity is desired, creating a view and tearing it down is a suboptimal solution for an application. In addition, the application needs to wait and track whether all presence information has been received.
An alternative is to use the BeginPresenceQuery(IEnumerable<String>, [], EventHandler<RemotePresentitiesNotificationEventArgs>, AsyncCallback, Object) and EndPresenceQuery(IAsyncResult) methods on the endpoint’s PresenceServices property.
See http://msdn.microsoft.com/en-us/library/office/hh383136%28v=office.14%29.aspx
Example
You can call the presence query like this. The null argument on 3rd position is the event handler which will fire when presence is recieved, it's not required since we process the results of the EndPresenceQuery instead. You could also pass an eventhandler and not care about the results of the EndPresenceQuery, thats up to you.
endpoint.PresenceServices.BeginPresenceQuery(
new[] { "sip:user#example.com" }, // Collection of sip addresses to query
new[] { "state" }, // Collection of presence catrgories to query
null, // The eventhandler to call when presence is recieved
(ar) => {
var result = endpoint.PresenceServices.EndPresenceQuery(ar);
// process the recieved containers in 'result' here.
},
null); // The state object
However, when you run a WCF service for presence which will be queried multiple times, I would say it might be better to subscribe to presence than to do single queries every time. I build a similar system once with the following logic:
Get an incoming presence request on WCF.
If this SIP uri presence is known to the WCF service (is subscribed), return immediately the cached presence.
If it is not known, subscribe to the presence.
When presence is recieved, return the result and add the presence to the cache.
Any time a subscribed user updates their presence, an event is fired to update the cache.
If no presence queries are recieved for a single user for a certain period of time, unsubscribe from the presence and remove from cache.
The main advantage here is that for multiple subsequent queries for the same user's presence, you do not query the Lync server each time. Your service responses will be a lot faster, and you get presence pushed rather than having to poll for it each time.
Related
I'm learning how to design a RESTful API and I've come across a quandary.
Say I have a POST endpoint to perform an action. The action has a certain cost associated with it. The cost depends on what the action is, particularly, on the body of the POST. For example, given these two requests:
POST /flooblinate
{"intensity": 50, "colorful": true, "blargs": [{"norg": 43}]}
POST /flooblinate
{"intensity": 100, "colorful": false, "blargs": []}
Say the first one costs 500 and the second one costs 740.
I want to create a method which will tell me what the cost of posting the action will be. Since I am not creating or updating anything, it seems that GET is the most appropriate verb. However, a request body with GET should not have any meaning. This means that I'd have to put the data in the query string, say by URL encoding the request body to be passed to the POST:
GET /flooblinate/getCost?body=%7B%22intensity%22%3A+50%2C+%22colorful%22%3A+true%2C+%22blargs%22%3A+%5B%7B%22norg%22%3A+43%7D%5D%7D
This seems less than ideal since it's two data formats for the same thing. But the following:
POST /flooblinate/getCost
{"intensity": 50, "colorful": true, "blargs": [{"norg": 43}]}
This also seems less than ideal since it's abusing the POST verb to query information, instead of to create or update something.
What's the correct choice to make, here? Is there any third alternative? Is there a way to rethink this design fundamentally which will obviate the need to make this choice?
Personally I'm not for adding dryRyn flags. I try to avoid boolean flags in general unless they're really required.
I've two ideas to cover this scenario:
One is to introduce state on the backend site, e.g. STARTED, FINISHED. When given resource action is submitted it has STARTED state and calculated cost which cam be viewed via GET method. Such resource may be modified with PUT and PATCH methods and is submitted when given method changes its state to FINISHED. Resources that didn't change its state for given amount of time are removed are their state is changed to other terminal value.
Second idea is to introduce a new endpoint called e.g. /calculations. If you need to calculate the cost of given action you just send the same payload (via POST) to this endpoint and in return a cost is given. Then resource send may be kept on server for some established TTL or kept forever.
In all the scenarios given (including yours) there's a need to make at least two requests.
The nicest choice here seems to be to have the endpoints return the info that need querying, and add a dryRun parameter to those endpoints. Thus:
POST /flooblinate?dryRun=true
{"intensity": 50, "colorful": true, "blargs": [{"norg": 43}]}
Returns:
{"cost": 500, /* whatever else */
And then posting with dryRun=false actually commits the action.
I am trying to write a control panel to
Inform about certain KPIS
Enable the user to init certain requests / jobs by pressing a button that then runs a stored proc on the DB or sets a specific setting etc
So far, so good, except I would like to run some bigger jobs where the length of time that the job is running for is unknown and could run over both the script timeout period AND the time the user is willing to wait for a response.
What I want is a "fire and forget" process so the user hits the button and even if they kill the page or turn off their phone they know the job has been initiated and WILL complete.
I was looking into C# BeginExecuteNonQuery which is an async call to the query so the proc is fired but the control doesn't have to wait for a response from it to carry on. However I don't know what happens when the page/app that fired it is shut.
Also I was thinking of some sort of Ajax command that fires the code in a page behind the scenes so the user doesn't know about it running but then again I believe if the user shuts the page down the script will die and the command will die on the server as well.
The only way for certain I know of is a "queue" table where jobs are inserted into this table then an MS Agent job comes along every minute or two checking for new inserts and then runs the code if there is any. That way it is all on the DB and only a DB crash will destroy it. It won't help with multiple jobs waiting to be run concurrently that both take a long time but it's the only thing I can be sure of that will ensure the code is run at all.
Any ideas?
Any language is okay.
Since web browsers are unconnected, requests from them always take the full amount of time. The governing factor isn't what the browser does, but how long the web site itself will allow an action to continue.
IIS (and in general, web servers) have a timeout period for requests, where if the work being done takes simply too long, the request is terminated. This would involve abruptly stopping whatever is taking so long, such as a database call, running code, and so on.
Simply making your long-running actions asynchronous may seem like a good idea, however I would recommend against that. The reason is that in ASP and ASP.Net, asynchronously-called code still consumes a thread in a way that blocks other legitimate request from getting through (in some cases you can end up consuming two threads!). This could have performance implications in non-obvious ways. It's better to just increase the timeout and allow the synchronously blocking task to complete. There's nothing special you have to do to make such a request complete fully, it will occur even if the sender closes his browser or turns off his phone immediately after (presuming the entire request was received).
If you're still concerned about making certain work finish, no matter what is going on with the web request, then it's probably better to create an out-of-process server/service that does the work and to which such tasks can be handed off. Your web site then invokes a method that, inside the service, starts its own async thread to do the work and then immediately returns. Perhaps it also returns a request ID, so that the web page can check on the status of the requested work later through other methods.
You may use asynchronous method and call the query from this method.
Your simple method can be changed in to a asynch method in the following manner.
Consider that you have a Test method to be called asynchronously -
Class AsynchDemo
{
public string TestMethod(out int threadId)
{
//call your query here
}
//create a asynch handler delegate:
public delegate string AsyncMethodCaller(out int threadId);
}
In your main program /or where you have to call the Test Method:
public static void Main()
{
// The asynchronous method puts the thread id here.
int threadId;
// Create an instance of the test class.
AsyncDemo ad = new AsyncDemo();
// Create the delegate.
AsyncMethodCaller caller = new AsyncMethodCaller(ad.TestMethod);
// Initiate the asychronous call.
IAsyncResult result = caller.BeginInvoke(
out threadId, null, null);
// Call EndInvoke to wait for the asynchronous call to complete,
// and to retrieve the results.
string returnValue = caller.EndInvoke(out threadId, result);
Console.WriteLine("The call executed on thread {0}, with return value \"{1}\".",
threadId, returnValue);
}
From my experience a Classic ASP or ASP.NET page will run until complete, even if the client disconnects, unless you have something in place for checking that the client is still connected and do something if they are not, or a timeout is reached.
However, it would probably be better practice to run these sorts of jobs as scheduled tasks.
On submitting your web page could record in a database that the task needs to be run and then when the scheduled task runs it checks for this and starts the job.
Many web hosts and/or web control panels allow you to create scheduled tasks that call a URL on schedule.
Alternately if you have direct access to the web server you could create a scheduled task on the server to call a URL on schedule.
Or, if ASP.NET, you can put some code in global.asax to run on a schedule. Be aware though, if your website is set to stop after a certain period of inactivity then this will not work unlesss there is frequent continuous activity.
I'm creating a web API based on the new ASP.NET Web API. I'm trying to understand the best way to handle people submitting multiple data-sets at the same time. If they have 100,000 requests it would be nice to let them submit 1,000 at a time.
Let's say I have a create new Contact method in my Contacts Controller:
public string Put(Contact _contact)
{
//add new _contact to repository
repository.Add(_contact);
//return success
}
What's the proper way to allow users to "Batch" submit new contacts? I'm thinking:
public string BatchPut(IEnumerable<Contact> _contacts)
{
foreach (var contact in _contacts)
{
respository.Add(contact);
}
}
Is this a good practice? Will this parse a GET request with a JSON array of Contacts (assuming they are correctly formatted)?
Lastly, any tips on how best to respond to Batch requests? What if 4 out of 300 fail?
Thanks a million!
When you PUT a collection, you are either inserting the whole collection or replacing an existing collection as if it was a single resource. It is very similar to GET, DELETE or POST a collection. It is an atomic operation. Using is as a substitute for individual calls to PUT a contact may not be very RESTfull (but that is really open for debate).
You may want to look at HTTP pipelining and send multiple PutContact requests of the same socket. With each request you can return standard HTTP status for that single request.
I implemented batch updates in the past with SOAP and we encountered a number of unforeseen issues when the system was under load. I suspect you will run into the same issues if you don't pay attention.
For example, the database may timeout in the middle of the batch update and the all hell broke loose in terms of failures, reliability, transactions etc. And the poor client had to figure out what was actually updated and try again.
When there was too many records to update, the HTTP request would time out because we took too long. That opened another can of worms.
Another concern was how much data would we accept during the update? Was 10MB of contacts enough? Perhaps 1MB? Larger buffers has numerous implications in terms of memory usage and security.
Hence my suggestion to look at HTTP pipelining.
Update
My suggestion would to handle batch creation of contacts as an async process. Just assume that a "job" is the same as a "batch create" process. So the service may look as follows:
public class JobService
{
// Post
public void Create(CreateJobRequest job)
{
// 1. Create job in the database with status "pending"
// 2. Save job details to disk (or S3)
// 3. Submit the job to MSMQ (or SQS)
// 4. For 20 seconds, poll the database to see if the job completed
// 5. If the job completed, return 201 with a URI to "Get" method below
// 6. If not, return 202 (aka the request was accepted for processing, but has not completed)
}
// Get
public Job Get(string id)
{
// 1. Fetch the job from the database
// 2. Return the job if it exists or 404
}
}
The background process that consumes stuff from the queue can update the database or alternatively perform a PUT to the service to update the status of Job to running and completed.
You'll need another service to navigate through the data that was just processed, address errors and so forth.
You background process may be need to be tolerant of validation errors. If not, or if your service does validation (assuming you are not doing database calls etc for which response times cannot be guaranteed), you can return a structure like CreateJobResponse that contains enough information for your client to fix the issue and resubmit the request. If you have to do some validation that is time consuming, do it in the background process, mark the job as failed and update the job with the information that will allow a client to fix the errors and resubmit the request. This assumes that the client can do something with the fact that the job failed.
If the Create method breaks the job request into many smaller "jobs" you'll have to deal with the fact that it may not be atomic and pose numerous challenges to monitor whether jobs completed successfully.
A PUT operation is supposed to replace a resource. Normally you do this against a single resource but when doing it against a collection that would mean you replace the original collection with the set of data passed. Not sure if you are meaning to do that but I am assuming you are just updating a subset of the collection in which case a PATCH method would be more appropriate.
Lastly, any tips on how best to respond to Batch requests? What if 4 out of 300 fail?
That is really up to you. There is only a single response so you can send a 200 OK or a 400 Bad Request and put the details in the body.
I've got a real lemon on my hands. I hope someone who has the same problem or know how to fix it could point me in the right direction.
The Setup
I'm trying to create a WCF data service that uses an ADO Entity Framework model to retrieve data from the DB. I've added the WCF service reference and all seems fine. I have two sets of data service calls. The first one retrieves a list of all "users" and returns (this list does not include any dependent data (eg. address, contact, etc.). The second call is when a "user" is selected, the application request to include a few more dependent information such as address, contact details, messages, etc. given a user id. This also seems to work fine.
The Lemon
After some user selection change, ie. calling for more dependent data from the data service, the application stops to respond.
Crash error:
The request channel timed out while waiting for a reply after 00:00:59.9989999. Increase the timeout value passed to the call to Request or increase the SendTimeout value on the Binding. The time allotted to this operation may have been a portion of a longer timeout.
I restart the debugging process but the application will not make any data service calls until after about a minute or so, VS 08 displays a message box with error:
Unable to process request from service. 'http://localhost:61768/ConsoleService.svc'. Catastrophic failure.
I've Googled the hell out of this error and related issues but found nothing of use.
Possible Solutions
I've found some leads as to the source of the problem. In the client's app.config:
maxReceivedMessageSize > Set to a higher value, eg. 5242880.
receiveTimeout > Set to a higher value, eg. 00:30:00
I've tried these but all in vain. I suspect there is an underlying problem that cannot be fixed by simply changing some numbers. Any leads would be much appreciated.
I've solved it =P.
Cause
The WCF service works fine. It was the data service calls that was the culprit. Every time I made the call, I instantiated a new reference to the data service, but never closed/disposed the service reference. So after a couple of calls, the data service reaches its maximum connection and halts.
Solution
Make sure to close/dispose of any data service reference properly. Best practice would be to enclose in a using statement.
using(var dataService = new ServiceNS.ServiceClient() )
{
// Use service here
}
// The service will be disposed and connection freed.
Glad to see you fixed your problem.
However, you need to be carefull about using the using statement. Have a look at this article:
http://msdn.microsoft.com/en-us/library/aa355056.aspx
I have a WCF function that is executing long time, so I call the function in UI with backgraundworker... I want to give a feature to cancel the execution, so I abort IComunicationObject, the problem is that Service execution is not stoping, Is there any way to stop Service execution in this case?
You may not need a BackgroundWorker. You can either make the operation IsOneWay, or implement the asynchronous pattern. To prevent threading issues, consider using the SynchronizationContext. Programming WCF Services does a great job at explaining these.
Make a CancelOperation() method which sets some static ManualResetEvent in your service. Check this event in your Operation method frequently. Or it can be CancelOperation(Guid operationId) if your service can process multiple operation calls concurrently.
One important thing to understand if you're using the Async calls is that there's still no way to cancel a request and prevent a response coming back from the service once it's started. It's up to your UI to be intelligent in handling responses to avoid race conditions. Fortunately there's a simple way of doing this.
This example is for searching orders - driven by a UI. Lets assume it may take a few seconds to return results and the user is running two searches back to back.
Therefore if your user runs two searches and the first search returns after the second - you need to make sure you don't display the results of the first search.
private int _searchRequestID = 0; // need one for each WCF method you call
// Call our service...
// The call is made using the overload to the Async method with 'UserToken'.
// When the call completes we check the ID matches to avoid a nasty
// race condition
_searchRequestID = _searchRequestID++;
client.SearchOrdersCompleted += (s, e) =>
{
if (_searchRequestID != (int)e.UserState))
{
return; // avoid nasty race condition
}
// ok to handle response ...
}
client.SearchOrdersAsync(searchMessage, _searchRequestID);