Monitor the status of a c# web service without using error handling

Question

Is there a good way to check if a web service is available that does not involve simply calling a served method?

That is, I was looking for something like a .TryConnect() or .IsAvailable() method I could call before calling my .TransferData(data) method.

I've tried reading the State variable of the service, but it even while the service is throwing EndpointNotFoundExceptions, it's reporting itself in the "Opened" state, and not "Faulted" like I had hoped.

I'm using synchronous data calls, and the web service implements IDataTransferService, if that helps. Also--.NET 3.5.

Answer 1

The only reliable way is to actually invoke the method and retry if it fails. No matter what preliminary checks you do the service could report that it is running and go offline at the moment you call it.

Answer 2

No, there is no better way. Just call the simplest WebMethod. Some services provide a dummy method or GetVersion() more or less for this purpose.

And then catch the TimeOut exception.

Answer 3

You can attempt to make a WebRequest that checks the wsdl of the web service. It's not a guarantee, but in most cases, if the service will serve the wsdl it'll serve the function as well. Here's one I wrote to test basic availability of a service.

Dim _streamReader As StreamReader
Dim responseString As New StringBuilder()

_streamReader = New StreamReader(Me.Response.GetResponseStream())
responseString.Append(_streamReader.ReadToEnd())
_streamReader.Close()
_streamReader = Nothing

If responseString.ToString().Contains("<wsdl:definitions") AndAlso _
    responseString.ToString().Contains("</wsdl:definitions>") Then
    wsdlVerified = True
Else
    Throw New Exception("The response did not generate valid wsdl.")
End If

Where the properties for this class serve the code above:

Public Property Url() As String
    Get
        Return _url.Trim()
    End Get
    Set(ByVal value As String)
        _url = value.Trim()
    End Set
End Property

Public ReadOnly Property Request() As System.Net.HttpWebRequest
    Get
        If _request Is Nothing AndAlso Me.Url.Trim.Length > 0 Then _
            _request = CType(System.Net.HttpWebRequest.Create(Me.Url & "?wsdl"), _
                System.Net.HttpWebRequest)
        Return _request
    End Get
End Property

Public ReadOnly Property Response() As System.Net.HttpWebResponse
    Get
        If _response Is Nothing AndAlso Me.Url.Trim().Length > 0 Then _
            _response = CType(Request.GetResponse(), System.Net.HttpWebResponse)
        Return _response
    End Get
End Property

EDIT: I'd refactor this into C# but it is fairly basic and should translate easily.

Answer 4

We are using a cached proxy client in one of our projects. In order to guarantee that the connection stays alive, we've created a simple Ping Operation in the Service. We call this method every x seconds, and report in the log if the Ping operation failed. You can expand this to also find the reason for the fail - timeouts or communication errors would indicate service unavailable. Of course this method is only possible when you have both service and client under your control.