SQL Server

Resume an Interrupted SFTP Upload

Demonstrates the Chilkat SFtp.ResumeUploadFileByName method, which resumes an interrupted upload. The first argument is the remote file path and the second is the local file path. Chilkat uses the existing remote file size as the local starting offset.

Note: This example uses relative local paths, which are resolved against the application's current working directory. Absolute local paths may also be used. Supply the paths appropriate to your own environment.

Background: For large transfers over unreliable links, restarting from zero after a dropped connection is wasteful. Resume picks up where it left off by comparing sizes: if the remote file is missing or empty it does a full upload, if it is smaller it appends the remaining local bytes, and if it is already the same size or larger it does nothing. The size-only check is simple and fast, but it assumes the partial remote file is a valid prefix of the local one — true for an interrupted transfer of the same file, but not a substitute for content verification if the file may have changed.

Chilkat SQL Server Downloads

Download Chilkat for SQL Server

SQL Server

-- Important: See this note about string length limitations for strings returned by sp_OAMethod calls.
--
CREATE PROCEDURE ChilkatSample
AS
BEGIN
    DECLARE @hr int
    DECLARE @sTmp0 nvarchar(4000)
    DECLARE @success int
    SELECT @success = 0

    --  Demonstrates the SFtp.ResumeUploadFileByName method, which resumes an interrupted upload.  The
    --  1st argument is the remote file path and the 2nd is the local file path.

    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

    --  Resume uploading the local file.  Chilkat uses the existing remote file size as the local
    --  starting offset, so only the remaining bytes are sent.  If the remote file is missing or
    --  empty, a normal full upload is performed.
    EXEC sp_OAMethod @sftp, 'ResumeUploadFileByName', @success OUT, 'subdir/largefile.zip', 'qa_data/largefile.zip'
    IF @success = 0
      BEGIN
        EXEC sp_OAGetProperty @sftp, 'LastErrorText', @sTmp0 OUT
        PRINT @sTmp0
        EXEC @hr = sp_OADestroy @sftp
        RETURN
      END

    PRINT 'Upload resumed and completed.'

    EXEC sp_OAMethod @sftp, 'Disconnect', NULL

    EXEC @hr = sp_OADestroy @sftp


END
GO