B4X

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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B4X

Dim success As Boolean = 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.

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


'  Open the remote file for read/write so an existing file can be modified in place.
Dim handle As String = sftp.OpenFile("subdir/record.dat", "readWrite", "openOrCreate")
If sftp.LastMethodSuccess = False Then
    Log(sftp.LastErrorText)
    Return
End If


'  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.
Dim offset As Int = 10
success = sftp.WriteFileText32(handle, offset, "utf-8", "HELLO")
If success = False Then
    Log(sftp.LastErrorText)
    Return
End If


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

Log("Wrote at the specified offset.")

sftp.Disconnect