Adding New VB .NET Module

At this stage we already completed the VB .NET web service project. Next, let add another project for the asynchronous web access. Add a new project.

Select Class Library project template and you can use AsyncModuleVB as the project name.

Imports System

Imports System.Web

Imports System.Threading

Imports System.Text.RegularExpressions

Public Class AsyncModule

    Implements IHttpModule

    ' shared data members

    Shared counter As Integer = 0

    Shared modCounter As Integer = 0

    Const RedirectLocation As String = "accessdenied.aspx"

    ' instance data members

    Dim instanceCounter As Integer

    Dim isAuthorized As Boolean

    Dim ctx As HttpContext

    Dim locationRegex As Regex = New Regex(RedirectLocation, RegexOptions.IgnoreCase)

    Public Sub Dispose() Implements IHttpModule.Dispose

        ' nothing to do

    End Sub

    Public Sub Init(ByVal app As HttpApplication) Implements IHttpModule.Init

        ' register for our async event

        app.AddOnAuthorizeRequestAsync(New BeginEventHandler(AddressOf AsyncBeginHandler), New EndEventHandler(AddressOf AsyncEndHandler))

        ' add a sync EndRequest handler to explain what happened if

        ' access is denied

        AddHandler app.EndRequest, New EventHandler(AddressOf OnEndRequest)

        Dim modCount As Integer = Interlocked.Increment(modCounter)

        TraceHelper.WriteLine("AsyncModule.Init: Initializing the module instance...", modCount)

    End Sub

    Public Function AsyncBeginHandler(ByVal src As Object, ByVal e As EventArgs, ByVal cb As AsyncCallback, ByVal extraData As Object) As IAsyncResult

        Dim app As HttpApplication = CType(src, HttpApplication)

        ' per-request init

        instanceCounter = Interlocked.Increment(counter)

        isAuthorized = False

        ctx = app.Context

        ' let anyone into the access denied page

        Dim m As Match = locationRegex.Match(ctx.Request.FilePath)

        ' is it something other than accessdenied.aspx? Check authorization...

        If Not m.Success Then

            ' create service proxy, async result, and callback

            Dim authServ As New AuthorizationService.Service1

            Dim myAr As MyAsyncResult = New MyAsyncResult(cb, authServ, instanceCounter)

            Dim myCb As New AsyncCallback(AddressOf WebServiceAsyncCallback)

            ' start async call

            TraceHelper.WriteLine("AsyncModule.AsyncBeginHandler: Begin the authorization...", instanceCounter)

            authServ.BeginIsAuthorized(ctx.User.Identity.Name, myCb, myAr)

            Return myAr

            ' otherwise, complete synchronously

        Else

            isAuthorized = True

            TraceHelper.WriteLine("AsyncModule.AsyncBeginHandler: Request for accessdenied.aspx page, skipping...", instanceCounter)

            Return New MyAsyncResult(Nothing, Nothing, True, True, Nothing, instanceCounter)

        End If

    End Function

    Public Sub AsyncEndHandler(ByVal ar As IAsyncResult)

        Dim myAr As MyAsyncResult = CType(ar, MyAsyncResult)

        TraceHelper.WriteLine("AsyncModule.AsyncEndHandler: Ending the authorization...", instanceCounter)

        ' if this user isn't authorized, then bail out

        If Not isAuthorized Then

            ctx.Response.StatusCode = 403

            ctx.ApplicationInstance.CompleteRequest()

            TraceHelper.WriteLine("AsyncModule.AsyncEndHandler: Request Rejected...", instanceCounter)

        End If

        ' clear variables

        ctx = Nothing

        instanceCounter = -1

        isAuthorized = False

        myAr.EndOp() ' throw if necessary

    End Sub

    Public Sub WebServiceAsyncCallback(ByVal ar As IAsyncResult)

        Dim myAr As MyAsyncResult = CType(ar.AsyncState, MyAsyncResult)

        Dim authServ As AuthorizationService.Service1 = CType(myAr.AsyncState, AuthorizationService.Service1)

        ' get back result

        isAuthorized = authServ.EndIsAuthorized(ar)

        TraceHelper.WriteLine("AsyncModule.WebServiceAsyncCallback: WebService call completed...", instanceCounter)

        ' tell ASP.NET we're done

        Dim cnt As Integer = instanceCounter

        TraceHelper.WriteLine("AsyncModule.WebServiceAsyncCallback: Begin notifing ASP.NET...", cnt)

        myAr.Complete(False, isAuthorized, Nothing)

        TraceHelper.WriteLine("AsyncModule.WebServiceAsyncCallback: End notifing ASP.NET...", cnt)

    End Sub

    Public Sub OnEndRequest(ByVal src As Object, ByVal E As EventArgs)

        Dim app As HttpApplication = CType(src, HttpApplication)

        ' did we block someone?

        If app.Response.StatusCode = 403 Then

            app.Response.Redirect(RedirectLocation, False)

        End If

    End Sub

End Class

Imports System

Imports System.Threading

Imports System.Diagnostics

' Implementation of IAsyncResult

Public Class MyAsyncResult

    Implements IAsyncResult

    ' data members

    Dim cb As AsyncCallback

    Dim state As Object

    Dim completed As Boolean

    Dim completedSync As Boolean

    Dim result As Object

    Dim err As Exception

    Dim counter As Integer

    Public Sub New(ByVal callb As AsyncCallback, ByVal st As Object, ByVal cnt As Integer)

        Me.cb = callb

        Me.state = st

        Me.counter = cnt

    End Sub

    ' constructor with predefined results,

    ' useful for errors that occur before async work is done

    Public Sub New(ByVal callb As AsyncCallback, ByVal st As Object, ByVal complete As Boolean, ByVal res As Object, ByVal e As Exception, ByVal cnt As Integer)

        Me.cb = callb

        Me.state = st

        Me.completed = complete

        Me.completedSync = Me.completed

        Me.result = res

        Me.err = e

        Me.counter = cnt

        If Not IsNothing(cb) Then

            cb(Me)

        End If

        If Me.completed Then

            TraceHelper.WriteLine("MyAsyncResult.New: MyAsyncResult completed sync", counter)

        End If

    End Sub

    Public ReadOnly Property AsyncState() As Object Implements System.IAsyncResult.AsyncState

        Get

            Return state

        End Get

    End Property

    Public ReadOnly Property AsyncWaitHandle() As System.Threading.WaitHandle Implements System.IAsyncResult.AsyncWaitHandle

        Get

            Return Nothing ' Wait not Supported

        End Get

    End Property

    Public ReadOnly Property CompletedSynchronously() As Boolean Implements System.IAsyncResult.CompletedSynchronously

        Get

            Return completedSync

        End Get

    End Property

    Public ReadOnly Property IsCompleted() As Boolean Implements System.IAsyncResult.IsCompleted

        Get

            Return completed

        End Get

    End Property

    ' non IAsyncResult Stuff

    Public ReadOnly Property AsyncError() As Exception

        Get

            Return err

        End Get

    End Property

    Public Sub Complete(ByVal sync As Boolean, ByVal res As Object, ByVal e As Exception)

        TraceHelper.WriteLine("MyAsyncResult.Complete: MyAsyncResult.Complete called", counter)

        completed = True

        completedSync = sync

        result = res

        err = e

        If Not IsNothing(cb) Then

            cb(Me)

        End If

    End Sub

    Public Function EndOp() As Object

        If Not IsNothing(err) Then

            Throw New Exception("AsyncOperation failed", err)

        End If

        Return result

    End Function

End Class

Imports System

Imports System.Threading

Imports System.Diagnostics

Public Class TraceHelper

    Public Shared Sub WriteLine(ByVal msg As String, ByVal cnt As Integer)

        Dim tid As Integer = Thread.CurrentThread.ManagedThreadId

        Trace.WriteLine(String.Format("TraceHelper.WriteLine: ThreadId: {0} Counter: {1} Msg: {2}", tid, cnt, msg))

    End Sub

End Class