B4X

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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B4X

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 ChilkatSFtp
sftp.Initialize("sftp")

'  Connect, authenticate, and initialize the SFTP subsystem.
Dim port As Int = 22
success = sftp.Connect("sftp.example.com", port)
If success = False Then
    Log(sftp.LastErrorText)
    Return
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
    Log(sftp.LastErrorText)
    Return
End If


success = sftp.InitializeSftp
If success = False Then
    Log(sftp.LastErrorText)
    Return
End If


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


Dim reading As Boolean = True
Dim chunkSize As Int = 4096
Dim bd As ChilkatBinData
bd.Initialize
Do 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
        Log("Read failed: " & sftp.LastErrorText)
        Return
    End If


    reading = Not(sftp.Eof(handle))
Loop

success = sftp.CloseHandle(handle)
If success = False Then
    Log(sftp.LastErrorText)
    Return
End If

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

sftp.Disconnect