VB.NET

Cancel HTTP Get Async Task if not Completed after a Max Time

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Demonstrates how to wait a maximum amount of time for an asynchronous task to completed. If not completed in the allotted amount of time, the task is cancelled. VB.NET

Dim success As Boolean = False

' This example requires the Chilkat API to have been previously unlocked.
' See Global Unlock Sample for sample code.

Dim http As New Chilkat.Http

' Set some timeouts, in seconds:
http.ConnectTimeout = 15
' ReadTimeout specifies the max number of seconds that must elapse when no additional data is received before
' timing out.  For example, if a server sends a 300 byte response at the rate of 1 byte per second, then
' ReadTimeout would never cause a timeout because there is never a 15 second interval when nothing arrives.
http.ReadTimeout = 15

Dim url As String = "https://your-url.com/something"
Dim task As Chilkat.Task = http.QuickGetStrAsync(url)
task.Run()

' Wait a maximum of waitMaxMs for the task (i.e. the HTTP GET) to complete.
' The Wait method returns when the task has been canceled, aborted, or completed, or when the max allotted time has passed.
Dim waitMaxMs As Integer = 20000
task.Wait(waitMaxMs)

' At this point, the GET may or may not have completed.  
' Rather than checking the Task status, we can call task.Cancel because
' if the Task is no longer running (because it already completed, was canceled or aborted), then the 
' call to Cancel is a NO-OP (meaning it does nothing and the Task's status is unaffected).
' Also, task.Cancel returns True if the task was in the "queued" or "running" state and was canceled or aborted. 
' The method returns False if the task has any other status.
Dim wasCanceled As Boolean = task.Cancel()
If (wasCanceled = True) Then
    Debug.WriteLine("The HTTP GET took too long and was canceled.")
Else
    ' Find out what happened.
    If (task.StatusInt = 7) Then
        ' The task completed, which means the background thread's call to QuickGetStr completed
        ' with success or failure.  Find out which...
        If (task.TaskSuccess = True) Then
            ' Get the string response for the call to QuickGetStr (which happened in Chilkat's background thread).
            Dim responseStr As String = task.GetResultString()
            Debug.WriteLine(responseStr)
            Debug.WriteLine("HTTP GET successful!")
        Else
            Debug.WriteLine("HTTP GET failed prior to waitMaxMs...")
            Debug.WriteLine(task.ResultErrorText)
        End If

    Else
        ' The task must've been canceled or aborted by some other means..
        Debug.WriteLine("Task did not complete.  Final status: " & task.Status)
    End If

End If