PowerShell

Read Text at a 32-bit Offset from a Remote SFTP File

Demonstrates the Chilkat SFtp.ReadFileText32 method, which reads up to a number of bytes from a specific 32-bit byte offset of an open handle and decodes them to text. The arguments are the handle, the offset, the maximum number of bytes, and the charset.

Background: Reading from an explicit offset lets you fetch just the part of a file you need — a header, a record at a known position, a slice of a large log — without downloading everything before it. As with offset writes, the offset counts bytes rather than characters, so it must respect the encoded width of any multibyte content.

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

$success = $false

#  Demonstrates the SFtp.ReadFileText32 method, which reads up to a number of bytes from a
#  specific 32-bit byte offset of an open handle and decodes them to text.  The 1st argument is
#  the handle, the 2nd is the offset, the 3rd is the maximum number of bytes, and the 4th is the
#  charset.

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

#  Read 5 bytes starting at byte offset 10, without first reading the bytes before it.
$offset = 10
$numBytes = 5
$text = $sftp.ReadFileText32($handle,$offset,$numBytes,"utf-8")
if ($sftp.LastMethodSuccess -eq $false) {
    $($sftp.LastErrorText)
    exit
}

$($text)

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

$sftp.Disconnect()