Chilkat2-Python

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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Chilkat2-Python

import sys
import chilkat2

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 = chilkat2.SFtp()

# Connect, authenticate, and initialize the SFTP subsystem.
port = 22
success = sftp.Connect("sftp.example.com",port)
if (success == False):
    print(sftp.LastErrorText)
    sys.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 == False):
    print(sftp.LastErrorText)
    sys.exit()

success = sftp.InitializeSftp()
if (success == False):
    print(sftp.LastErrorText)
    sys.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 == False):
    print(sftp.LastErrorText)
    sys.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 == False):
    print(sftp.LastErrorText)
    sys.exit()

success = sftp.CloseHandle(handle)
if (success == False):
    print(sftp.LastErrorText)
    sys.exit()

print("Wrote at the specified offset.")

sftp.Disconnect()