PowerBuilder

Resume an Interrupted FTP Transfer

Demonstrates the RestartNext and PartialTransfer properties, which request that the next transfer resume from existing content and report whether a download was incomplete.

Note: The local paths are relative to the application's current working directory. Absolute paths may also be used. Supply the paths appropriate to your own environment.

Background: For a large transfer over a flaky link, restarting from zero after a drop is wasteful. Setting RestartNext makes the next download continue from the current local file size (and the next upload from the remote size); the flag is consumed by that one transfer and then reset. Afterward PartialTransfer tells you whether the download got only part of the file — the signal to set RestartNext again and resume once more.

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PowerBuilder

integer li_rc
integer li_Success
oleobject loo_Ftp

li_Success = 0

loo_Ftp = create oleobject
li_rc = loo_Ftp.ConnectToNewObject("Chilkat.Ftp2")
if li_rc < 0 then
    destroy loo_Ftp
    MessageBox("Error","Connecting to COM object failed")
    return
end if

loo_Ftp.Hostname = "ftp.example.com"
loo_Ftp.Username = "myFtpLogin"

//  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.
loo_Ftp.Password = "myPassword"

li_Success = loo_Ftp.Connect()
if li_Success = 0 then
    Write-Debug loo_Ftp.LastErrorText
    destroy loo_Ftp
    return
end if

//  RestartNext requests that the NEXT transfer resume from existing content rather than starting
//  over.  It is consumed by that transfer and then automatically reset.
loo_Ftp.RestartNext = 1

//  Resume a partially-downloaded file.  Because RestartNext is set, the download continues from
//  the current local file size.
li_Success = loo_Ftp.GetFile("public_html/bigfile.zip","qa_output/bigfile.zip")
if li_Success = 0 then
    Write-Debug loo_Ftp.LastErrorText
    destroy loo_Ftp
    return
end if

//  PartialTransfer indicates whether the most recent download received some, but not all, of the
//  remote file -- distinguishing a mid-transfer failure from other outcomes.
if loo_Ftp.PartialTransfer then
    Write-Debug "Only part of the file was received; another resume may be needed."
else
    Write-Debug "The file was fully received."
end if

li_Success = loo_Ftp.Disconnect()
if li_Success = 0 then
    Write-Debug loo_Ftp.LastErrorText
    destroy loo_Ftp
    return
end if



destroy loo_Ftp