PowerShell

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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Add-Type -Path "C:\chilkat\ChilkatDotNet47-x64\ChilkatDotNet47.dll"

$success = $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.

$sftp = New-Object Chilkat.SFtp

#  Connect, authenticate, and initialize the SFTP subsystem.
$port = 22
$success = $sftp.Connect("sftp.example.com",$port)
if ($success -eq $false) {
    $($sftp.LastErrorText)
    exit
}

#  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.
$password = "mySshPassword"

$success = $sftp.AuthenticatePw("mySshLogin",$password)
if ($success -eq $false) {
    $($sftp.LastErrorText)
    exit
}

$success = $sftp.InitializeSftp()
if ($success -eq $false) {
    $($sftp.LastErrorText)
    exit
}

$handle = $sftp.OpenFile("subdir/data.txt","readOnly","openExisting")
if ($sftp.LastMethodSuccess -eq $false) {
    $($sftp.LastErrorText)
    exit
}

$reading = $true
$chunkSize = 4096
$bd = New-Object Chilkat.BinData
while ($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)) {
        $("Read failed: " + $sftp.LastErrorText)
        exit
    }

    $reading = !$sftp.Eof($handle)
}

$success = $sftp.CloseHandle($handle)
if ($success -eq $false) {
    $($sftp.LastErrorText)
    exit
}

$("Read " + $bd.NumBytes + " bytes with no read failures.")

$sftp.Disconnect()