(SQL Server) Chaining Asynchronous Streams

The asynchronous functionality of Chilkat, combined with streams, can offer some interesting possibilities. This example demonstrates how to create two streams, call them streamA and streamB, where streamA feeds into streamB and both streams run in background threads. The examples demonstrates copying a file in this way:

sourceFile --> streamA --> streamB --> outputFile

This may seem pointless, but the possibilities become interesting when intermediate streams can perform tasks such as encryption or compression, or when a source or sink is a socket, a TLS connection, an SSH tunnel, etc. Or perhaps if a stream becomes the source for the file in an HTTP upload, or perhaps it is the source or sink for files in FTP, SFTP, etc. This is where Chilkat's Async standards in combination with Chilkat Stream can begin to offer powerful and simple-to-implement possibilities.

Chilkat ActiveX Downloads ActiveX for 32-bit and 64-bit Windows

-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @iTmp0 int
    DECLARE @iTmp1 int
    -- Important: Do not use nvarchar(max).  See the warning about using nvarchar(max).
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @sTmp1 nvarchar(4000)
    DECLARE @streamA int
    -- Use "Chilkat_9_5_0.Stream" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.Stream', @streamA OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    DECLARE @streamB int
    -- Use "Chilkat_9_5_0.Stream" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.Stream', @streamB OUT

    EXEC sp_OASetProperty @streamA, 'SourceFile', 'qa_data/hamlet.xml'

    -- streamA will feed into streamB. (streamA is the source for streamB)
    DECLARE @success int
    EXEC sp_OAMethod @streamB, 'SetSourceStream', @success OUT, @streamA

    EXEC sp_OASetProperty @streamB, 'SinkFile', 'qa_output/hamlet_copy.xml'

    -- Run each stream asynchronously in background threads:
    DECLARE @taskA int
    EXEC sp_OAMethod @streamA, 'RunStreamAsync', @taskA OUT
    DECLARE @taskB int
    EXEC sp_OAMethod @streamB, 'RunStreamAsync', @taskB OUT

    -- Start each task. (The call to Run returns immediately. 
    -- each task begins running in its own background thread.)
    EXEC sp_OAMethod @taskA, 'Run', @success OUT
    EXEC sp_OAMethod @taskB, 'Run', @success OUT

    -- Wait for each task to complete.
    -- Note: The SleepMs method is a utility method that puts the caller to sleep
    -- for a specified number of milliseconds.
    -- It is the caller's thread that sleeps (i.e. this foreground thread).
    -- It does not cause the background thread of the given task object to sleep.
    EXEC sp_OAGetProperty @taskA, 'Finished', @iTmp0 OUT
    EXEC sp_OAGetProperty @taskB, 'Finished', @iTmp1 OUT
    WHILE ((@iTmp0 <> 1) or (@iTmp1 <> 1))
      BEGIN
        EXEC sp_OAMethod @taskB, 'SleepMs', NULL, 20
      END

    -- At this point, each background task has finished. 
    -- Let's check to see if each stream succeeded.

    -- Did streamA succeed in reading the entire file?
    EXEC sp_OAGetProperty @taskA, 'TaskSuccess', @iTmp0 OUT
    IF @iTmp0 <> 1
      BEGIN

        PRINT 'streamA failed:'
        EXEC sp_OAGetProperty @taskA, 'ResultErrorText', @sTmp0 OUT
        PRINT @sTmp0
        SELECT @success = 0
      END

    -- Did streamB succeed in writing the entire file?
    EXEC sp_OAGetProperty @taskB, 'TaskSuccess', @iTmp0 OUT
    IF @iTmp0 <> 1
      BEGIN

        PRINT 'streamB failed:'
        EXEC sp_OAGetProperty @taskB, 'ResultErrorText', @sTmp0 OUT
        PRINT @sTmp0
        SELECT @success = 0
      END

    IF @success <> 1
      BEGIN
        EXEC @hr = sp_OADestroy @streamA
        EXEC @hr = sp_OADestroy @streamB
        RETURN
      END

    -- Let's double-check to see that the files are equal in size and content:
    DECLARE @fac int
    -- Use "Chilkat_9_5_0.FileAccess" for versions of Chilkat < 10.0.0
    EXEC @hr = sp_OACreate 'Chilkat.FileAccess', @fac OUT

    DECLARE @bFilesEqual int
    EXEC sp_OAGetProperty @streamA, 'SourceFile', @sTmp0 OUT
    EXEC sp_OAGetProperty @streamB, 'SinkFile', @sTmp1 OUT
    EXEC sp_OAMethod @fac, 'FileContentsEqual', @bFilesEqual OUT, @sTmp0, @sTmp1
    IF @bFilesEqual <> 1
      BEGIN

        PRINT 'The output file is not equal to the input file!'
      END
    ELSE
      BEGIN

        PRINT 'The file was successfully copied in a very roundabout way!'
      END

    EXEC @hr = sp_OADestroy @streamA
    EXEC @hr = sp_OADestroy @streamB
    EXEC @hr = sp_OADestroy @fac


END
GO