Resolving File Size Differences After FTP Transfers: The Python Approach

When working with files and servers, maintaining data integrity is crucial. One common issue that many developers face is the unexpected change in file size after transferring files using FTP. If you’re migrating a PHP script to Python and encounter discrepancies in file sizes, you’re not alone. Let’s dive into the problem and its solution in detail.

The Problem: File Size Discrepancy

You’ve developed a PHP script to update a live web server by transferring files to a local directory. Everything works smoothly when you use PHP. However, after switching to Python, you notice that the size of the files on the server is different from the local version after using the PUT command via FTP.

After downloading the file from the server, you find that the only variation is in line endings (CR/LF marks). This may seem like a minor issue, but it can disrupt scripts that compare file sizes for updates, leading to potential synchronization problems.

Analyzing the Solution

The good news is that the problem can typically be resolved with a simple adjustment to how files are opened for upload. Let’s break this down into clear steps.

Step 1: Open the File in Binary Mode

In your Python script, the root of the problem lies in how you’re opening the local file for reading before uploading it to the server. By default, the file is opened in text mode, which can cause changes in the way line endings are handled. The solution is to open the file in binary mode. This ensures that there is no alteration to the file’s content during the upload process.

Here’s how you can correct the code:

• Change the line where you open the file from:

f = open(locfile, "r")

• To this:

f = open(locfile, "rb")

Full Updated Code

Here’s how your updated Python code will look after making this simple change:

from ftplib import FTP

ftpserver = "myserver"
ftpuser = "myuser"
ftppass = "mypwd"

locfile = "g:/test/style.css"
ftpfile = "/temp/style.css"

try:
    ftp = FTP(ftpserver, ftpuser, ftppass)
except:
    exit("Cannot connect")

f = open(locfile, "rb")  # Open file in binary mode
try:
    ftp.delete(ftpfile)
except:
    pass

ftp.storbinary("STOR %s" % ftpfile, f)
f.close()

ftp.dir(ftpfile)
ftp.quit()

Step 2: Verify the Transfer

Once you have made this change, upload the file again and check its size on the server against your local file. They should match now, and any changes in the CR/LF marks should be resolved, ensuring that your scripts can function correctly without any discrepancies.

Conclusion

Dealing with file size discrepancies after making FTP transfers can be discouraging, especially when switching between programming languages. However, the solution often involves a simple tweak: opening your files in binary mode. This approach preserves the integrity of your files, preventing unwanted changes during the upload process.

If you face any more issues or need further assistance with FTP in Python, feel free to reach out. Understanding these nuances will help you transition smoothly between programming languages and maintain efficient file handling in your projects.