VB.NET

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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Dim success As Boolean = False

'  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.

Dim sftp As New Chilkat.SFtp

'  Connect, authenticate, and initialize the SFTP subsystem.
Dim port As Integer = 22
success = sftp.Connect("sftp.example.com",port)
If (success = False) Then
    Debug.WriteLine(sftp.LastErrorText)
    Exit Sub
End If


'  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.
Dim password As String = "mySshPassword"

success = sftp.AuthenticatePw("mySshLogin",password)
If (success = False) Then
    Debug.WriteLine(sftp.LastErrorText)
    Exit Sub
End If


success = sftp.InitializeSftp()
If (success = False) Then
    Debug.WriteLine(sftp.LastErrorText)
    Exit Sub
End If


Dim handle As String = sftp.OpenFile("subdir/data.txt","readOnly","openExisting")
If (sftp.LastMethodSuccess = False) Then
    Debug.WriteLine(sftp.LastErrorText)
    Exit Sub
End If


Dim reading As Boolean = True
Dim chunkSize As Integer = 4096
Dim bd As New Chilkat.BinData
While reading
    success = sftp.ReadFileBd(handle,chunkSize,bd)

    '  Distinguish an actual read failure from a normal EOF.  On EOF the read succeeds, returns
    '  zero bytes, and LastReadFailed is False.
    If (sftp.LastReadFailed(handle)) Then
        Debug.WriteLine("Read failed: " & sftp.LastErrorText)
        Exit Sub
    End If


    reading = Not sftp.Eof(handle)
End While

success = sftp.CloseHandle(handle)
If (success = False) Then
    Debug.WriteLine(sftp.LastErrorText)
    Exit Sub
End If

Debug.WriteLine("Read " & bd.NumBytes & " bytes with no read failures.")

sftp.Disconnect()