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Write Text at a 32-bit Offset in a Remote SFTP File

Demonstrates the Chilkat SFtp.WriteFileText32 method, which encodes text and writes it at a specific 32-bit byte offset in an open handle. The arguments are the handle, the offset, the charset, and the text.

Background: Explicit-offset writes enable random access — patching a fixed-length record in place, for instance, without rewriting the whole file. The offset is a byte position, not a character position, so with a variable-width encoding like UTF-8 you must account for the encoded size of preceding characters to land where you intend. After the write, the sequential position continues just past the bytes written.

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

$success = $false

#  Demonstrates the SFtp.WriteFileText32 method, which encodes text and writes it at a specific
#  32-bit byte offset in an open handle.  The 1st argument is the handle, the 2nd is the offset,
#  the 3rd is the charset, and the 4th is the text.

$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
}

#  Open the remote file for read/write so an existing file can be modified in place.
$handle = $sftp.OpenFile("subdir/record.dat","readWrite","openOrCreate")
if ($sftp.LastMethodSuccess -eq $false) {
    $($sftp.LastErrorText)
    exit
}

#  Overwrite 5 bytes starting at offset 10.  The offset is a byte position, not a character
#  position, so it must account for the encoded size of any multibyte characters.
$offset = 10
$success = $sftp.WriteFileText32($handle,$offset,"utf-8","HELLO")
if ($success -eq $false) {
    $($sftp.LastErrorText)
    exit
}

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

$("Wrote at the specified offset.")

$sftp.Disconnect()