I try to create OWIN(IIS Hosted) middleware that will ensure that all log4net events will have a particular property (CorrelationId) assigned per-request.
I tried to:
Use following middleware and use IOwinContext.
It works only when appender batching size is to 1. Otherwise, the whole batch of events is assigned the same CorrelationId.
public class CorrelationIdMiddleware : OwinMiddleware
{
public CorrelationIdMiddleware(OwinMiddleware next): base(next){}
public override async Task Invoke(IOwinContext context)
{
correlationId = Guid.NewGuid().ToString();
context.Set("CorrelationId", correlationId);
await Next.Invoke(context);
}
}
Middleware was paired with log4net active property:
public class CorrelationIdActiveLog4NetValue
{
public override string ToString()
{
var context = HttpContext.Current.GetOwinContext();
if (context != null)
{
var value = context.Get<string>("CorrelationId");
if (!string.IsNullOrEmpty(value))
{
return value;
}
}
return "N/A";
}
}
Use LogicalCallContext.
var stack = log4net.LogicalThreadContext.Stacks["CorrelationId"]
using (stack.Push(correlationId))
{
log4net.LogManager.GetLogger(typeof(CorrelationIdMiddleware))
.Info("TEST MESSAGE");
await Next.Invoke(context);
}
It worked for the message I produced in the middleware itself, but not when I logged from controllers.
For comparison, in Serilog such middleware code works universally in every case(ASP.NET core):
using (LogContext.PushProperty("BayCorrelationId", context.TraceIdentifier))
{
await next(context);
}
How can I pass along auditing information between clients and services in an easy way without having to add that information as arguments for all service methods? Can I use message headers to set this data for a call?
Is there a way to allow service to pass that along downstream also, i.e., if ServiceA calls ServiceB that calls ServiceC, could the same auditing information be send to first A, then in A's call to B and then in B's call to C?
There is actually a concept of headers that are passed between client and service if you are using fabric transport for remoting. If you are using Http transport then you have headers there just as you would with any http request.
Note, below proposal is not the easiest solution, but it solves the issue once it is in place and it is easy to use then, but if you are looking for easy in the overall code base this might not be the way to go. If that is the case then I suggest you simply add some common audit info parameter to all your service methods. The big caveat there is of course when some developer forgets to add it or it is not set properly when calling down stream services. It's all about trade-offs, as alway in code :).
Down the rabbit hole
In fabric transport there are two classes that are involved in the communication: an instance of a IServiceRemotingClient on the client side, and an instance of IServiceRemotingListener on the service side. In each request from the client the messgae body and ServiceRemotingMessageHeaders are sent. Out of the box these headers include information of which interface (i.e. which service) and which method are being called (and that's also how the underlying receiver knows how to unpack that byte array that is the body). For calls to Actors, which goes through the ActorService, additional Actor information is also included in those headers.
The tricky part is hooking into that exchange and actually setting and then reading additional headers. Please bear with me here, it's a number of classes involved in this behind the curtains that we need to understand.
The service side
When you setup the IServiceRemotingListener for your service (example for a Stateless service) you usually use a convenience extension method, like so:
protected override IEnumerable<ServiceInstanceListener> CreateServiceInstanceListeners()
{
yield return new ServiceInstanceListener(context =>
this.CreateServiceRemotingListener(this.Context));
}
(Another way to do it would be to implement your own listener, but that's not really what we wan't to do here, we just wan't to add things on top of the existing infrastructure. See below for that approach.)
This is where we can provide our own listener instead, similar to what that extention method does behind the curtains. Let's first look at what that extention method does. It goes looking for a specific attribute on assembly level on your service project: ServiceRemotingProviderAttribute. That one is abstract, but the one that you can use, and which you will get a default instance of, if none is provided, is FabricTransportServiceRemotingProviderAttribute. Set it in AssemblyInfo.cs (or any other file, it's an assembly attribute):
[assembly: FabricTransportServiceRemotingProvider()]
This attribute has two interesting overridable methods:
public override IServiceRemotingListener CreateServiceRemotingListener(
ServiceContext serviceContext, IService serviceImplementation)
public override IServiceRemotingClientFactory CreateServiceRemotingClientFactory(
IServiceRemotingCallbackClient callbackClient)
These two methods are responsible for creating the the listener and the client factory. That means that it is also inspected by the client side of the transaction. That is why it is an attribute on assembly level for the service assembly, the client side can also pick it up together with the IService derived interface for the client we want to communicate with.
The CreateServiceRemotingListener ends up creating an instance FabricTransportServiceRemotingListener, however in this implementation we cannot set our own specific IServiceRemotingMessageHandler. If you create your own sub class of FabricTransportServiceRemotingProviderAttribute and override that then you can actually make it create an instance of FabricTransportServiceRemotingListener that takes in a dispatcher in the constructor:
public class AuditableFabricTransportServiceRemotingProviderAttribute :
FabricTransportServiceRemotingProviderAttribute
{
public override IServiceRemotingListener CreateServiceRemotingListener(
ServiceContext serviceContext, IService serviceImplementation)
{
var messageHandler = new AuditableServiceRemotingDispatcher(
serviceContext, serviceImplementation);
return (IServiceRemotingListener)new FabricTransportServiceRemotingListener(
serviceContext: serviceContext,
messageHandler: messageHandler);
}
}
The AuditableServiceRemotingDispatcher is where the magic happens. It is our own ServiceRemotingDispatcher subclass. Override the RequestResponseAsync (ignore HandleOneWay, it is not supported by service remoting, it throws an NotImplementedException if called), like this:
public class AuditableServiceRemotingDispatcher : ServiceRemotingDispatcher
{
public AuditableServiceRemotingDispatcher(ServiceContext serviceContext, IService service) :
base(serviceContext, service) { }
public override async Task<byte[]> RequestResponseAsync(
IServiceRemotingRequestContext requestContext,
ServiceRemotingMessageHeaders messageHeaders,
byte[] requestBodyBytes)
{
byte[] userHeader = null;
if (messageHeaders.TryGetHeaderValue("user-header", out auditHeader))
{
// Deserialize from byte[] and handle the header
}
else
{
// Throw exception?
}
byte[] result = null;
result = await base.RequestResponseAsync(requestContext, messageHeaders, requestBodyBytes);
return result;
}
}
Another, easier, but less flexible way, would be to directly create an instance of FabricTransportServiceRemotingListener with an instance of our custom dispatcher directly in the service:
protected override IEnumerable<ServiceInstanceListener> CreateServiceInstanceListeners()
{
yield return new ServiceInstanceListener(context =>
new FabricTransportServiceRemotingListener(this.Context, new AuditableServiceRemotingDispatcher(context, this)));
}
Why is this less flexible? Well, because using the attribute supports the client side as well, as we see below
The client side
Ok, so now we can read custom headers when receiving messages, how about setting those? Let's look at the other method of that attribute:
public override IServiceRemotingClientFactory CreateServiceRemotingClientFactory(IServiceRemotingCallbackClient callbackClient)
{
return (IServiceRemotingClientFactory)new FabricTransportServiceRemotingClientFactory(
callbackClient: callbackClient,
servicePartitionResolver: (IServicePartitionResolver)null,
traceId: (string)null);
}
Here we cannot just inject a specific handler or similar as for the service, we have to supply our own custom factory. In order not to have to reimplement the particulars of FabricTransportServiceRemotingClientFactory I simply encapsulate it in my own implementation of IServiceRemotingClientFactory:
public class AuditedFabricTransportServiceRemotingClientFactory : IServiceRemotingClientFactory, ICommunicationClientFactory<IServiceRemotingClient>
{
private readonly ICommunicationClientFactory<IServiceRemotingClient> _innerClientFactory;
public AuditedFabricTransportServiceRemotingClientFactory(ICommunicationClientFactory<IServiceRemotingClient> innerClientFactory)
{
_innerClientFactory = innerClientFactory;
_innerClientFactory.ClientConnected += OnClientConnected;
_innerClientFactory.ClientDisconnected += OnClientDisconnected;
}
private void OnClientConnected(object sender, CommunicationClientEventArgs<IServiceRemotingClient> e)
{
EventHandler<CommunicationClientEventArgs<IServiceRemotingClient>> clientConnected = this.ClientConnected;
if (clientConnected == null) return;
clientConnected((object)this, new CommunicationClientEventArgs<IServiceRemotingClient>()
{
Client = e.Client
});
}
private void OnClientDisconnected(object sender, CommunicationClientEventArgs<IServiceRemotingClient> e)
{
EventHandler<CommunicationClientEventArgs<IServiceRemotingClient>> clientDisconnected = this.ClientDisconnected;
if (clientDisconnected == null) return;
clientDisconnected((object)this, new CommunicationClientEventArgs<IServiceRemotingClient>()
{
Client = e.Client
});
}
public async Task<IServiceRemotingClient> GetClientAsync(
Uri serviceUri,
ServicePartitionKey partitionKey,
TargetReplicaSelector targetReplicaSelector,
string listenerName,
OperationRetrySettings retrySettings,
CancellationToken cancellationToken)
{
var client = await _innerClientFactory.GetClientAsync(
serviceUri,
partitionKey,
targetReplicaSelector,
listenerName,
retrySettings,
cancellationToken);
return new AuditedFabricTransportServiceRemotingClient(client);
}
public async Task<IServiceRemotingClient> GetClientAsync(
ResolvedServicePartition previousRsp,
TargetReplicaSelector targetReplicaSelector,
string listenerName,
OperationRetrySettings retrySettings,
CancellationToken cancellationToken)
{
var client = await _innerClientFactory.GetClientAsync(
previousRsp,
targetReplicaSelector,
listenerName,
retrySettings,
cancellationToken);
return new AuditedFabricTransportServiceRemotingClient(client);
}
public Task<OperationRetryControl> ReportOperationExceptionAsync(
IServiceRemotingClient client,
ExceptionInformation exceptionInformation,
OperationRetrySettings retrySettings,
CancellationToken cancellationToken)
{
return _innerClientFactory.ReportOperationExceptionAsync(
client,
exceptionInformation,
retrySettings,
cancellationToken);
}
public event EventHandler<CommunicationClientEventArgs<IServiceRemotingClient>> ClientConnected;
public event EventHandler<CommunicationClientEventArgs<IServiceRemotingClient>> ClientDisconnected;
}
This implementation simply passes along anything heavy lifting to the underlying factory, while returning it's own auditable client that similarily encapsulates a IServiceRemotingClient:
public class AuditedFabricTransportServiceRemotingClient : IServiceRemotingClient, ICommunicationClient
{
private readonly IServiceRemotingClient _innerClient;
public AuditedFabricTransportServiceRemotingClient(IServiceRemotingClient innerClient)
{
_innerClient = innerClient;
}
~AuditedFabricTransportServiceRemotingClient()
{
if (this._innerClient == null) return;
var disposable = this._innerClient as IDisposable;
disposable?.Dispose();
}
Task<byte[]> IServiceRemotingClient.RequestResponseAsync(ServiceRemotingMessageHeaders messageHeaders, byte[] requestBody)
{
messageHeaders.SetUser(ServiceRequestContext.Current.User);
messageHeaders.SetCorrelationId(ServiceRequestContext.Current.CorrelationId);
return this._innerClient.RequestResponseAsync(messageHeaders, requestBody);
}
void IServiceRemotingClient.SendOneWay(ServiceRemotingMessageHeaders messageHeaders, byte[] requestBody)
{
messageHeaders.SetUser(ServiceRequestContext.Current.User);
messageHeaders.SetCorrelationId(ServiceRequestContext.Current.CorrelationId);
this._innerClient.SendOneWay(messageHeaders, requestBody);
}
public ResolvedServicePartition ResolvedServicePartition
{
get { return this._innerClient.ResolvedServicePartition; }
set { this._innerClient.ResolvedServicePartition = value; }
}
public string ListenerName
{
get { return this._innerClient.ListenerName; }
set { this._innerClient.ListenerName = value; }
}
public ResolvedServiceEndpoint Endpoint
{
get { return this._innerClient.Endpoint; }
set { this._innerClient.Endpoint = value; }
}
}
Now, in here is where we actually (and finally) set the audit name that we want to pass along to the service.
Call chains and service request context
One final piece of the puzzle, the ServiceRequestContext, which is a custom class that allows us to handle an ambient context for a service request call. This is relevant because it gives us an easy way to propagate that context information, like the user or a correlation id (or any other header information we want to pass between client and service), in a chain of calls. The implementation ServiceRequestContext looks like:
public sealed class ServiceRequestContext
{
private static readonly string ContextKey = Guid.NewGuid().ToString();
public ServiceRequestContext(Guid correlationId, string user)
{
this.CorrelationId = correlationId;
this.User = user;
}
public Guid CorrelationId { get; private set; }
public string User { get; private set; }
public static ServiceRequestContext Current
{
get { return (ServiceRequestContext)CallContext.LogicalGetData(ContextKey); }
internal set
{
if (value == null)
{
CallContext.FreeNamedDataSlot(ContextKey);
}
else
{
CallContext.LogicalSetData(ContextKey, value);
}
}
}
public static Task RunInRequestContext(Func<Task> action, Guid correlationId, string user)
{
Task<Task> task = null;
task = new Task<Task>(async () =>
{
Debug.Assert(ServiceRequestContext.Current == null);
ServiceRequestContext.Current = new ServiceRequestContext(correlationId, user);
try
{
await action();
}
finally
{
ServiceRequestContext.Current = null;
}
});
task.Start();
return task.Unwrap();
}
public static Task<TResult> RunInRequestContext<TResult>(Func<Task<TResult>> action, Guid correlationId, string user)
{
Task<Task<TResult>> task = null;
task = new Task<Task<TResult>>(async () =>
{
Debug.Assert(ServiceRequestContext.Current == null);
ServiceRequestContext.Current = new ServiceRequestContext(correlationId, user);
try
{
return await action();
}
finally
{
ServiceRequestContext.Current = null;
}
});
task.Start();
return task.Unwrap<TResult>();
}
}
This last part was much influenced by the SO answer by Stephen Cleary. It gives us an easy way to handle the ambient information down a hierarcy of calls, weather they are synchronous or asyncronous over Tasks. Now, with this we have a way of setting that information also in the Dispatcher on the service side:
public override Task<byte[]> RequestResponseAsync(
IServiceRemotingRequestContext requestContext,
ServiceRemotingMessageHeaders messageHeaders,
byte[] requestBody)
{
var user = messageHeaders.GetUser();
var correlationId = messageHeaders.GetCorrelationId();
return ServiceRequestContext.RunInRequestContext(async () =>
await base.RequestResponseAsync(
requestContext,
messageHeaders,
requestBody),
correlationId, user);
}
(GetUser() and GetCorrelationId() are just helper methods that gets and unpacks the headers set by the client)
Having this in place means that any new client created by the service for any aditional call will also have the sam headers set, so in the scenario ServiceA -> ServiceB -> ServiceC we will still have the same user set in the call from ServiceB to ServiceC.
what? that easy? yes ;)
From inside a service, for instance a Stateless OWIN web api, where you first capture the user information, you create an instance of ServiceProxyFactoryand wrap that call in a ServiceRequestContext:
var task = ServiceRequestContext.RunInRequestContext(async () =>
{
var serviceA = ServiceProxyFactory.CreateServiceProxy<IServiceA>(new Uri($"{FabricRuntime.GetActivationContext().ApplicationName}/ServiceA"));
await serviceA.DoStuffAsync(CancellationToken.None);
}, Guid.NewGuid(), user);
Ok, so to sum it up - you can hook into the service remoting to set your own headers. As we see above there is some work that needs to be done to get a mechanism for that in place, mainly creating your own subclasses of the underlying infrastructure. The upside is that once you have this in place, then you have a very easy way for auditing your service calls.
I structured my project into multiple mobile services, grouped by the application type eg:
my-core.azure-mobile.net (user, device)
my-app-A.azure-mobile.net (sales, order, invoice)
my-app-B.azure-mobile.net (inventory & parts)
I'm using custom authentication for all my services, and I implemented my own SSO by setting the same master key to all 3 services.
Things went well when I tested using REST client, eg. user who "logged in" via custom api at my-core.azure-mobile.net is able to use the returned JWT token to access restricted API of the other mobile services.
However, in my xamarin project, only the first (note, in sequence of creation) MobileServiceClient object is working properly (eg. returning results from given table). The client object are created using their own url and key respectively, and stored in a dictionary.
If i created client object for app-A then only create for app-B, I will be able to perform CRUD+Sync on sales/order/invoice entity, while CRUD+Sync operation on inventory/part entity will just hang there. The situation is inverse if I swap the client object creation order.
I wonder if there is any internal static variables used within the MobileServiceClient which caused such behavior, or it is a valid bug ?
=== code snippet ===
public class AzureService
{
IDictionary<String, MobileServiceClient> services = new Dictionary<String, MobileServiceClient>();
public MobileServiceClient Init (String key, String applicationURL, String applicationKey)
{
return services[key] = new MobileServiceClient (applicationURL, applicationKey);
}
public MobileServiceClient Get(String key)
{
return services [key];
}
public void InitSyncContext(MobileServiceSQLiteStore offlineStore)
{
// Uses the default conflict handler, which fails on conflict
// To use a different conflict handler, pass a parameter to InitializeAsync.
// For more details, see http://go.microsoft.com/fwlink/?LinkId=521416
var syncHandler = new MobileServiceSyncHandler ();
foreach(var client in services) {
client.Value.SyncContext.InitializeAsync (offlineStore, syncHandler);
}
}
public void SetAuthenticationToken(String uid, String token)
{
var user = new MobileServiceUser(uid);
foreach(var client in services) {
client.Value.CurrentUser = user;
client.Value.CurrentUser.MobileServiceAuthenticationToken = token;
}
}
public void ClearAuthenticationToken()
{
foreach(var client in services) {
client.Value.CurrentUser = null;
}
}
}
=== more code ===
public class DatabaseService
{
public static MobileServiceSQLiteStore LocalStore = null;
public static string Path { get; set; }
public static ISet<IEntityMappingProvider> Providers = new HashSet<IEntityMappingProvider> ();
public static void Init (String dbPath)
{
LocalStore = new MobileServiceSQLiteStore(dbPath);
foreach(var provider in Providers) {
var types = provider.GetSupportedTypes ();
foreach(var t in types) {
JObject item = null;
// omitted detail to create JObject using reflection on given type
LocalStore.DefineTable(tableName, item);
}
}
}
}
=== still code ===
public class AzureDataSyncService<T> : IAzureDataSyncService<T>
{
public MobileServiceClient ServiceClient { get; set; }
public virtual Task<List<T>> GetAll()
{
try
{
var theTable = ServiceClient.GetSyncTable<T>();
return theTable.ToListAsync();
}
catch (MobileServiceInvalidOperationException msioe)
{
Debug.WriteLine("GetAll<{0}> EXCEPTION TYPE: {1}, EXCEPTION:{2}", typeof(T).ToString(), msioe.GetType().ToString(), msioe.ToString());
}
catch (Exception e)
{
Debug.WriteLine("GetAll<{0}> EXCEPTION TYPE: {1}, EXCEPTION:{2}", typeof(T).ToString(), e.GetType().ToString(), e.ToString());
}
List<T> theCollection = Enumerable.Empty<T>().ToList();
return Task.FromResult(theCollection);
}
}
=== code ===
public class UserService : AzureDataSyncService<User>
{
}
public class PartService : AzureDataSyncService<Part>
{
}
const string coreApiURL = #"https://my-core.azure-mobile.net/";
const string coreApiKey = #"XXXXX";
const string invApiURL = #"https://my-inventory.azure-mobile.net/";
const string invApiKey = #"YYYYY";
public async void Foo ()
{
DatabaseService.Providers.Add (new CoreDataMapper());
DatabaseService.Providers.Add (new InvDataMapper ());
DatabaseService.Init (DatabaseService.Path);
var coreSvc = AzureService.Instance.Init ("Core", coreApiURL, coreApiKey);
var invSvc = AzureService.Instance.Init ("Inv", invApiURL, invApiKey);
AzureService.Instance.InitSyncContext (DatabaseService.LocalStore);
AzureService.Instance.SetAuthenticationToken("AAA", "BBB");
UserService.Instance.ServiceClient = coreSvc;
PartService.Instance.ServiceClient = invSvc;
var x = await UserService.GetAll(); // this will work
var y = await PartService.GetAll(); // but not this
}
It's ok to use multiple MobileServiceClient objects, but not with the same local database. The offline sync feature uses a particular system tables to keep track of table operations and errors, and it is not supported to use the same local store across multiple sync contexts.
I'm not totally sure why it is hanging in your test, but it's possible that there is a lock on the local database file and the other sync context is waiting to get access.
You should instead use different local database files for each service and doing push and pull on each sync context. With your particular example, you just need to move LocalStore out of DatabaseService and into a dictionary in AzureService.
In general, it seems like an unusual design to use multiple services from the same client app. Is there a particular reason that the services need to be separated from each other?
I have an Azure Mobile service coded in .net Web API. I have a TableController. I want that table controller to be able to insert multiple persons, not just one person with from the client with InsertAsync(myPerson). I have the following code in the TableController:
[RequiresAuthorization(AuthorizationLevel.Admin)]
public async Task<bool> InsertPersons(List<Person> values)
{
try
{
foreach (var item in values)
{
var current = await InsertAsync(item);
}
return true;
}
catch (System.Exception)
{
return false;
}
}
The problem is in the client. Because it is strongly typed it only allows me to insert one item at a time. How must I call the server from the client? Do I have to write a Custom Api Controller and call it with mobileService.InvokeApiAsync? If so, how can I get access to my database from a Custom API Controller that doesn't inherit from TableController?
Thank you so much!
The helper methods in the TableController<T> base class assume that the insert operations apply to a single object - and the InsertAsync method in the client also assumes the same. So even though you can define in a table controller a method that takes an array (or list) of Person, you won't be able to call it via the client SDK (at least not without some heavy-lifting using a handler, for example).
You can, however, create a custom API which takes such a list. And to insert the multiple items from the API, you can access the context directly, without needing to go through the helper methods from the table:
public class PersonController : ApiController
{
test20140807Context context;
protected override void Initialize(HttpControllerContext controllerContext)
{
base.Initialize(controllerContext);
this.context = new test20140807Context();
}
[HttpPost]
public async Task<bool> InsertPersons(List<Person> values)
{
foreach (var value in values)
{
if (string.IsNullOrEmpty(value.Id))
{
value.Id = Guid.NewGuid().ToString();
}
}
try
{
this.context.People.AddRange(values);
await this.context.SaveChangesAsync();
return true;
}
catch (System.Exception ex)
{
Trace.WriteLine("Error: " + ex);
return false;
}
}
}
And on the client:
private async void btnTest_Click(object sender, RoutedEventArgs e)
{
var items = new Person[]
{
new Person { Name = "John Doe", Age = 33 },
new Person { Name = "Jane Roe", Age = 32 }
};
try
{
var response = await App.MobileService.InvokeApiAsync<Person[], bool>("person", items);
Debug.WriteLine("response: " + response);
}
catch (Exception ex)
{
var str = ex.ToString();
Debug.WriteLine(str);
}
}
From Carlos Figueira's post on inserting multiple items at once in azure mobile services, it looks like what you need to do is create another table called AllPersons. In your client, the AllPersons object would have a Persons array member. In your server side script for the AllPersons insert, you iterate through the AllPersons.Persons and insert into the table one by one.
I am attempting to write a Validation attribute in MVC4.
The purpose is to check for the existence of an application reference (just a string that represents a key I wish to prevent a duplicate for).
My data is accessed via WebAPI and because I am using 4.5 I wish to make this asynchronous if possible.
I am perhaps not making the best or appropriate usage of async and await but I would like to know how to call my async method from the overridden IsValid method of the inherited Validation class.
public class UniqueApplicationReferenceAttribute : ValidationAttribute
{
public UniqueApplicationReferenceAttribute() : base(() => "The {0} already exists") { }
public int? ApplicationCount { get; set; }
public override bool IsValid(object value)
{
var myTask = GetApplicationRefCountAsync();
myTask.Wait();
this.ApplicationCount = this.ApplicationCount ?? 0;
if (ApplicationCount > 0)
{
return true;
}
else
{
return false;
}
}
public async Task GetApplicationRefCountAsync()
{
HttpClient client = new HttpClient();
client.BaseAddress = new Uri("http://localhost:11111/");
client.DefaultRequestHeaders.Accept.Add(new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
var apps = client.GetStringAsync("api/dataapplications");
await Task.WhenAll(apps);
var appList = apps.Result;
this.ApplicationCount = appList.Count();// apps.Count();
}
}
Many thanks,
Dan.
I recommend that you call your WebAPI methods synchronously. ValidationAttribute does not support asynchronous implementations natively, so any synchronous-over-asynchronous code you'll write is just going to be a hack and not actually provide any benefit as compared to the synchronous version.
I'm not able to test this in full, but you should be able to do something like this:
public bool IsValid(object value)
{
var appCount = GetApplicationRefCountAsync().Result;
return appCount > 0;
}
public async Task<int> GetApplicationRefCountAsync()
{
var client = new HttpClient();
client.BaseAddress = new Uri("http://localhost:11111/");
client.DefaultRequestHeaders.Accept.Add(
new System.Net.Http.Headers.MediaTypeWithQualityHeaderValue("application/json"));
return await client.GetStringAsync("api/dataapplications")
.ContinueWith(r => Convert.ToInt32(r))
.ConfigureAwait(false);
}
Be careful about using async/await methods in an ASP.NET thread. It's easy to create deadlocks.