How to Read the Size of an Image Before Uploading it to Amazon S3 Using Python Flask

How to Read the Size of an Image Before Uploading it to Amazon S3 Using Python Flask

Python Flask is a powerful microframework that allows developers to build web applications. There are situations where we need to read the size of an image before uploading it to Amazon S3. In this blog post, we’ll guide you through the process.

Introduction

When dealing with file uploads, it is crucial to validate the file size before uploading it to your storage, in this case, Amazon S3. This helps in avoiding unnecessary costs and ensuring efficient usage of resources.

Prerequisites

To follow this guide, you’ll need:

1. Python installed on your machine
2. Basic understanding of Flask
3. An Amazon Web Services (AWS) account

The Flask Side of Things

First, let’s look at how to get the file size from the Flask side. Flask has a request object that allows us to access the file size. Here’s how you can do it:

from flask import Flask, request

app = Flask(__name__)

@app.route('/upload', methods=['POST'])
def upload_file():
    file = request.files['file']
    file_size = len(file.read())
    return f"File size is {file_size} bytes"

In this code snippet, we first import the necessary modules. We then create a Flask application instance. The @app.route decorator is used to bind a function to a URL route, in this case, ‘/upload’. When we get a POST request on this route, the upload_file function is called.

Inside the function, we access the uploaded file with request.files['file']. To get the file size, we read the file and then use the len function. The size is returned in bytes.

Uploading to Amazon S3

Now that we have the file size, let’s see how we can upload the file to Amazon S3 using the Boto3 library:

import boto3

def upload_file_to_s3(file, bucket_name, file_name):
    s3 = boto3.client('s3')
    try:
        s3.upload_fileobj(file, bucket_name, file_name)
        return "File uploaded successfully"
    except Exception as e:
        return(str(e))

In this function, we first create an S3 client. We then use the upload_fileobj method of the S3 client to upload the file to the specified bucket bucket_name with the specified file name file_name. If the upload is successful, we return a success message. If there’s an exception, we catch it and return the exception message.

Connecting the Dots

Let’s combine these two parts and create a full Flask application:

from flask import Flask, request
import boto3

app = Flask(__name__)

@app.route('/upload', methods=['POST'])
def upload_file():
    file = request.files['file']
    file_size = len(file.read())
    if file_size < 10485760:  # Limit file size to 10MB
        response = upload_file_to_s3(file, 'mybucket', file.filename)
        return response
    else:
        return "File size exceeds limit"

def upload_file_to_s3(file, bucket_name, file_name):
    s3 = boto3.client('s3')
    try:
        s3.upload_fileobj(file, bucket_name, file_name)
        return "File uploaded successfully"
    except Exception as e:
        return(str(e))

if __name__ == '__main__':
    app.run(debug=True)

In this final version, we added a condition to check if the file size exceeds 10MB. If it does, we return an error message. Otherwise, we upload the file to Amazon S3 and return the response of the upload function.

Conclusion

This guide explained how to read the size of an image before uploading it to Amazon S3 using Python Flask. This is a good practice to control the size of the files being uploaded to your storage, leading to better usage of resources and cost savings. Happy coding!

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