Delphi DLL

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

See more HTTP Examples

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. Delphi DLL

uses
    Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
    Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Task, Http;

...

procedure TForm1.Button1Click(Sender: TObject);
var
success: Boolean;
http: HCkHttp;
url: PWideChar;
task: HCkTask;
waitMaxMs: Integer;
wasCanceled: Boolean;
responseStr: PWideChar;

begin
success := False;

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

http := CkHttp_Create();

// Set some timeouts, in seconds:
CkHttp_putConnectTimeout(http,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.
CkHttp_putReadTimeout(http,15);

url := 'https://your-url.com/something';
task := CkHttp_QuickGetStrAsync(http,url);
CkTask_Run(task);

// 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.
waitMaxMs := 20000;
CkTask_Wait(task,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.
wasCanceled := CkTask_Cancel(task);
if (wasCanceled = True) then
  begin
    Memo1.Lines.Add('The HTTP GET took too long and was canceled.');
  end
else
  begin
    // Find out what happened.
    if (CkTask_getStatusInt(task) = 7) then
      begin
        // The task completed, which means the background thread's call to QuickGetStr completed
        // with success or failure.  Find out which...
        if (CkTask_getTaskSuccess(task) = True) then
          begin
            // Get the string response for the call to QuickGetStr (which happened in Chilkat's background thread).
            responseStr := CkTask__getResultString(task);
            Memo1.Lines.Add(responseStr);
            Memo1.Lines.Add('HTTP GET successful!');
          end
        else
          begin
            Memo1.Lines.Add('HTTP GET failed prior to waitMaxMs...');
            Memo1.Lines.Add(CkTask__resultErrorText(task));
          end;
      end
    else
      begin
        // The task must've been canceled or aborted by some other means..
        Memo1.Lines.Add('Task did not complete.  Final status: ' + CkTask__status(task));
      end;
  end;

CkTask_Dispose(task);

CkHttp_Dispose(http);

end;