SQL Server

Check Whether the Last SFTP Read Failed

Demonstrates the Chilkat SFtp.LastReadFailed method, which returns whether the most recent read for a handle failed. The only argument is the handle. A normal end-of-file is not a failure.

Background: A chunked read loop needs to tell three outcomes apart: more data, a clean end-of-file, and an actual error such as a dropped connection or a revoked handle. LastReadFailed isolates the error case — it is false on a normal EOF read (which succeeds with zero bytes) and true for an empty, malformed, or already-closed handle — so the loop can stop cleanly on EOF but bail out with an error message on a genuine failure.

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-- 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 @sTmp0 nvarchar(4000)
    DECLARE @success int
    SELECT @success = 0

    --  Demonstrates the SFtp.LastReadFailed method, which returns whether the most recent read for a
    --  handle failed.  The only argument is the handle.  A normal end-of-file is NOT a failure.

    DECLARE @sftp int
    EXEC @hr = sp_OACreate 'Chilkat.SFtp', @sftp OUT
    IF @hr <> 0
    BEGIN
        PRINT 'Failed to create ActiveX component'
        RETURN
    END

    --  Connect, authenticate, and initialize the SFTP subsystem.
    DECLARE @port int
    SELECT @port = 22
    EXEC sp_OAMethod @sftp, 'Connect', @success OUT, 'sftp.example.com', @port
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @sftp, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @sftp
        RETURN
      END

    --  Normally you would not hard-code the password in source.  You should instead obtain it
    --  from an interactive prompt, environment variable, or a secrets vault.
    DECLARE @password nvarchar(4000)
    SELECT @password = 'mySshPassword'

    EXEC sp_OAMethod @sftp, 'AuthenticatePw', @success OUT, 'mySshLogin', @password
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @sftp, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @sftp
        RETURN
      END

    EXEC sp_OAMethod @sftp, 'InitializeSftp', @success OUT
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @sftp, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @sftp
        RETURN
      END

    DECLARE @handle nvarchar(4000)
    EXEC sp_OAMethod @sftp, 'OpenFile', @handle OUT, 'subdir/data.txt', 'readOnly', 'openExisting'
    EXEC sp_OAGetProperty @sftp, 'LastMethodSuccess', @iTmp0 OUT
    IF @iTmp0 = 0
      BEGIN
        EXEC sp_OAGetProperty @sftp, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @sftp
        RETURN
      END

    DECLARE @reading int
    SELECT @reading = 1
    DECLARE @chunkSize int
    SELECT @chunkSize = 4096
    DECLARE @bd int
    EXEC @hr = sp_OACreate 'Chilkat.BinData', @bd OUT

    WHILE @reading
      BEGIN
        EXEC sp_OAMethod @sftp, 'ReadFileBd', @success OUT, @handle, @chunkSize, @bd

        --  Distinguish an actual read failure from a normal EOF.  On EOF the read succeeds, returns
        --  zero bytes, and LastReadFailed is 0.
        EXEC sp_OAMethod @sftp, 'LastReadFailed', @iTmp0 OUT, @handle
        IF @iTmp0
          BEGIN

            EXEC sp_OAGetProperty @sftp, 'LastErrorText', @sTmp0 OUT
            PRINT 'Read failed: ' + @sTmp0
            EXEC @hr = sp_OADestroy @sftp
            EXEC @hr = sp_OADestroy @bd
            RETURN
          END

        EXEC sp_OAMethod @sftp, 'Eof', @iTmp0 OUT, @handle
        SELECT @reading = Not @iTmp0
      END

    EXEC sp_OAMethod @sftp, 'CloseHandle', @success OUT, @handle
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @sftp, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @sftp
        EXEC @hr = sp_OADestroy @bd
        RETURN
      END

    EXEC sp_OAGetProperty @bd, 'NumBytes', @iTmp0 OUT

    PRINT 'Read ' + @iTmp0 + ' bytes with no read failures.'

    EXEC sp_OAMethod @sftp, 'Disconnect', NULL

    EXEC @hr = sp_OADestroy @sftp
    EXEC @hr = sp_OADestroy @bd


END
GO