HTTP in a Background Thread (Asynchronous HTTP)

This example shows the technique one would follow to run any Chilkat HTTP method in a background task. (Only HTTP methods that communicate with an HTTP server are background-enabled. Methods that perform no HTTP communications return immediately and never need to be backgrounded.)

Download Chilkat HTTP ActiveX

CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @sTmp1 nvarchar(4000)
    DECLARE @http int
    EXEC @hr = sp_OACreate 'Chilkat.Http', @http OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    DECLARE @success int

    --  Any string unlocks the component for the 1st 30-days.
    EXEC sp_OAMethod @http, 'UnlockComponent', @success OUT, 'Anything for 30-day trial'
    IF @success <> 1
      BEGIN
        EXEC sp_OAGetProperty @http, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        RETURN
      END

    --  To run an HTTP method asynchronously in a background thread, set
    --  the UseBgThread property equal to 1
    EXEC sp_OASetProperty @http, 'UseBgThread', 1

    --  For those programming languages that support event callbacks:
    --  events are not fired when a task is running in the background thread.
    --  Instead, Chilkat has added the "event log" mechanism.  While the
    --  background task is running, events that normally would've been fired
    --  are accumulated in the event log.  Your application may periodically check
    --  the event log to keep track of the progress of the background task.
    --  To enable event logging, set the KeepEventLog property = 1
    EXEC sp_OASetProperty @http, 'KeepEventLog', 1

    --  Start an asynchronous HTTP download in a background thread.
    --  The method will return cktrue if the task was successfully started.
    --  Note: When the UseBgThread property = 1, all methods involving
    --  HTTP communications will be asynchronous.  These methods include:
    --  SynchronousRequest, QuickGetStr, QuickGet, PostUrlEncoded, XmlRpc,
    --  XmlRpcPut, QuickPutStr, QuickGetObj, QuickDeleteStr, PutText,
    --  PutBinary, PostBinary, PostMime, GetHead, DownloadAppend, etc.
    EXEC sp_OAMethod @http, 'Download', @success OUT, 'http://www.chilkatsoft.com/download/ChilkatJava.zip', 'ChilkatJava.zip'
    IF @success <> 1
      BEGIN
        EXEC sp_OAGetProperty @http, 'LastErrorText', @sTmp0 OUT

        PRINT @sTmp0
        RETURN
      END
    ELSE
      BEGIN

        PRINT 'Initiated asynchronous HTTP download...'
      END

    --  Write a loop to wait for the background task to complete.
    --  Your application would typically do something different than this --
    --  after all... there's no point in doing the task asynchronously if your application
    --  is simply going to wait for it to complete -- that's the same as doing it synchronously,
    --  and that could've been achieved by a single call to the http.Download method
    --  with the UseBgThread = 0.
    --  However... we do this here for the purpose of demonstration...
    EXEC sp_OAGetProperty @http, 'BgTaskRunning', @sTmp0 OUT
    WHILE (@sTmp0 = 1)
      BEGIN
        --  Show the events in the event log that have accumulated so far...
        DECLARE @n int

        EXEC sp_OAGetProperty @http, 'EventLogCount', @n OUT

        IF @n > 0
          BEGIN
            DECLARE @i int

            SELECT @i = 0
            WHILE @i <= @n - 1
              BEGIN
                EXEC sp_OAMethod @http, 'EventLogName', @sTmp0 OUT, @i

                EXEC sp_OAMethod @http, 'EventLogValue', @sTmp1 OUT, @i
                PRINT @sTmp0 + ': ' + @sTmp1
                SELECT @i = @i + 1
              END
            EXEC sp_OAMethod @http, 'ClearEventLog', NULL
          END

        --  In some programming languages, you might wish to handle user-interface events
        --  For example, in C#  you might call Application.DoEvents()

        --  Sleep .1 seconds -- to keep the CPU from being 100% busy...
        EXEC sp_OAMethod @http, 'SleepMs', NULL, 100
      END

    --  Once the background task has completed, check it for success/failure:
    EXEC sp_OAGetProperty @http, 'BgTaskSuccess', @sTmp0 OUT
    IF @sTmp0
      BEGIN

        PRINT 'Background task completed successfully.'
      END

END
GO