Handling large file downloads with stream download to avoid timeout and other response errors

When working with large file downloads in web applications, one of the common issues developers face is timeouts, response time, memory overload errors. Most web servers and clients have limitations on how long they will wait for a response, and if the download process takes too long, you might encounter these errors. To mitigate this, streaming downloads is a more efficient and scalable solution.

In this article, we'll explore how using Python’s streaming capabilities to handle large file downloads can help avoid timeouts and response errors. Specifically, we will discuss chunked downloads, how they work, and how they can optimize performance when dealing with large files.

What is the Problem with Large File Downloads?

When a user requests a large file, your web server needs to:

• Open/Load the file on memory.
• Read it.
• Send the data back to the client in one large chunk as whole file.

While this process sounds simple, it becomes problematic as the file size increases. The issues you might encounter include:

• Timeouts: The server or client may time out if it takes too long to read and deliver the file.
• Memory overload: The server may try to load the entire file into memory, causing performance issues or even crashes, particularly with very large files.
• Network interruptions: Large files increase the risk of the connection dropping or encountering other network errors.

Solution: Stream the file in chunks, allowing the server to handle the file in smaller, manageable pieces, reducing the chances of these issues.

How Does Streaming Avoid Timeouts?

Instead of reading the entire file into memory and sending it in one large response, streaming breaks the file into smaller chunks that are read and transmitted sequentially. This allows the client to start receiving parts of the file earlier, rather than waiting for the entire file to be loaded before transmission starts.

Here’s why streaming is beneficial:

• Reduced memory footprint: Only a small part of the file is loaded into memory at a time.
• Avoid timeouts: By starting the transmission earlier and sending in chunks, you avoid long delays in initiating the download, reducing the likelihood of a timeout.
• Client experience: The client starts receiving data almost immediately, improving the perceived performance.

Example Implementing Chunked Downloads in Python

let assume you want to download the files from Google Drive or any other storage like SharePoint, GoogleCloudStorage etc. we can use generators for chunked based file downloading, here is how it will look like.

GoogleDrive:
    def generate_chunks(request, chunksize = 10 * 1024 * 1024): #10MB
        file_buffer = io.BytesIO()
        downloader = MediaIoBaseDownload(file_buffer, request, chunksize=chunksize)
        done = False
        previous_bytes = 0
        while not done:
            status, done = downloader.next_chunk()
            if status:
                new_bytes = downloader._progress - previous_bytes
                file_buffer.seek(previous_bytes)
                chunk_data = file_buffer.read(new_bytes)
                previous_bytes = downloader._progress
                yield chunk_data

    def file_loader(user_name, file_properties, credentials):
        file_uri = file_properties["file_uri"]
        # Your logic from Google Drive Doc to authenticate the user
        # and getting the file in request
        request = service.files().get_media(fileId=file_uri)
        return lambda: GoogleDrive.generate_chunks(request)

For stream download, you have to handle the response something like this

file = GoogleDrive.file_loader(user_name, file_properties, credentials)
response = Response(file(), content_type='application/octet-stream')
filename = "some example file.mp4"
response.headers['Content-Disposition'] = f"attachment; filename*=UTF-8''{quote(filename)}"
return response

Including the file name in the correct format for UTF-8 encoding will help to avoid issues when there is any emoji or special characters in file name in case you use dynamic file naming from db.

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