Resume FTP download after timeout

Question

I'm downloading files from a flaky FTP server that often times out during file transfer and I was wondering if there was a way to reconnect and resume the download. I'm using Python's ftplib. Here is the code that I am using:

#! /usr/bin/python

import ftplib
import os
import socket
import sys

#--------------------------------#
# Define parameters for ftp site #
#--------------------------------#
site           = 'a.really.unstable.server'
user           = 'anonymous'
password       = 'someperson@somewhere.edu'
root_ftp_dir   = '/directory1/'
root_local_dir = '/directory2/'

#---------------------------------------------------------------
# Tuple of order numbers to download. Each web request generates 
# an order numbers
#---------------------------------------------------------------
order_num = ('1','2','3','4')

#----------------------------------------------------------------#
# Loop through each order. Connect to server on each loop. There #
# might be a time out for the connection therefore reconnect for #
# every new ordernumber                                          #
#----------------------------------------------------------------#
# First change local directory
os.chdir(root_local_dir)

# Begin loop through 
for order in order_num:
    
    print 'Begin Proccessing order number %s' %order
    
    # Connect to FTP site
    try:
        ftp = ftplib.FTP( host=site, timeout=1200 )
    except (socket.error, socket.gaierror), e:
        print 'ERROR: Unable to reach "%s"' %site
        sys.exit()
    
    # Login
    try:
        ftp.login(user,password)
    except ftplib.error_perm:
        print 'ERROR: Unable to login'
        ftp.quit()
        sys.exit()
     
    # Change remote directory to location of order
    try:
        ftp.cwd(root_ftp_dir+order)
    except ftplib.error_perm:
        print 'Unable to CD to "%s"' %(root_ftp_dir+order)
        sys.exit()

    # Get a list of files
    try:
        filelist = ftp.nlst()
    except ftplib.error_perm:
        print 'Unable to get file list from "%s"' %order
        sys.exit()
    
    #---------------------------------#
    # Loop through files and download #
    #---------------------------------#
    for each_file in filelist:
        
        file_local = open(each_file,'wb')
        
        try:
            ftp.retrbinary('RETR %s' %each_file, file_local.write)
            file_local.close()
        except ftplib.error_perm:
            print 'ERROR: cannot read file "%s"' %each_file
            os.unlink(each_file)
        
    ftp.quit()
    
    print 'Finished Proccessing order number %s' %order
    
sys.exit()

The error that I get:

socket.error: [Errno 110] Connection timed out

Any help is greatly appreciated.

user_850848 · Answer

A simple example for implementing a resumable FTP download using Python ftplib:

def connect():

ftp = None

with open('bigfile', 'wb') as f:
    while (not finished):
        if ftp is None:
            print("Connecting...")
            FTP(host, user, passwd)

        try:
            rest = f.tell()
            if rest == 0:
                rest = None
                print("Starting new transfer...")
            else:
                print(f"Resuming transfer from {rest}...")
            ftp.retrbinary('RETR bigfile', f.write, rest=rest)
            print("Done")
            finished = True
        except Exception as e:
            ftp = None
            sec = 5
            print(f"Transfer failed: {e}, will retry in {sec} seconds...")
            time.sleep(sec)

More fine-grained exception handling is advisable.

Similarly for uploads:
Handling disconnects in Python ftplib FTP transfers file upload

Resume FTP download after timeout

3 Answers