Introduction
In this article, I will discuss how to receive and process multipart/form-data with AWS Chalice, including handling the incoming requests, parsing the data, and extracting files and form fields.
Creating a Route for Form Submission
First, create a new route in your app.py file to handle form submissions. This route will listen for POST requests and accept content of type multipart/form-data:
app = Chalice(app_name='my_chalice_app')
@app.route('/submit-form', methods=['POST'], content_types=['multipart/form-data'])
def submit_form():
pass
Using the CGI Library to Parse Multipart Data
Next, you'll need to modify the submit_form() function to parse the incoming multipart form data using the CGI library. To do this, you will need to create a FieldStorage instance and pass it the app.current_request.raw_body and the request's content type.
from io import BytesIO
def submit_form():
content_type = app.current_request.headers['content-type']
content_length = int(app.current_request.headers['content-length'])
raw_body = app.current_request.raw_body
environ = {
'REQUEST_METHOD': 'POST',
'CONTENT_TYPE': content_type,
'CONTENT_LENGTH': content_length,
'wsgi.input': BytesIO(raw_body),
}
form_data = cgi.FieldStorage(fp=environ['wsgi.input'], environ=environ, keep_blank_values=True)
Extracting Form Data and Files
Once the form data has been parsed, you can access the submitted fields and files using the form_data object. For example, you can retrieve the value of a text field named description like this:
description = form_data.getvalue('description')
To access uploaded files, you can use the form_data['file_field'] syntax. For instance, to retrieve a file uploaded under the field name file, you can use the following code:
uploaded_file = form_data['file']
filename = uploaded_file.filename
file_content = uploaded_file.file.read()
Handling Errors and Validation
To ensure that your application properly handles errors and edge cases, you should validate the incoming form data before processing it. For instance, you can check if a required field is missing or if the file size exceeds a certain limit.
def validate_form_data(form_data):
if 'description' not in form_data:
raise BadRequestError('Missing description field.')
if 'file' not in form_data:
raise BadRequestError('Missing file field.')
if len(form_data['file'].file.read()) > MAX_FILE_SIZE:
raise BadRequestError('File size exceeds the allowed limit.')
def submit_form():
# ... (previous code)
validate_form_data(form_data)
Remember to define the MAX_FILE_SIZE constant with an appropriate value at the beginning of your app.py file.
MAX_FILE_SIZE = 10 * 1024 * 1024 # 10 MB
By following these steps, you'll be able to receive and process multipart form data using AWS Chalice and the CGI library.
Complete Code
Here's the complete code.
import cgi
import json
from io import BytesIO
from chalice import Chalice, BadRequestError
app = Chalice(app_name='my_chalice_app')
MAX_FILE_SIZE = 10 * 1024 * 1024 # 10 MB
@app.route('/submit-form', methods=['POST'], content_types=['multipart/form-data'])
def submit_form():
content_type = app.current_request.headers['content-type']
content_length = int(app.current_request.headers['content-length'])
raw_body = app.current_request.raw_body
environ = {
'REQUEST_METHOD': 'POST',
'CONTENT_TYPE': content_type,
'CONTENT_LENGTH': content_length,
'wsgi.input': BytesIO(raw_body),
}
form_data = cgi.FieldStorage(fp=environ['wsgi.input'], environ=environ, keep_blank_values=True)
validate_form_data(form_data)
description = form_data.getvalue('description')
uploaded_file = form_data['file']
filename = uploaded_file.filename
file_content = uploaded_file.file.read()
# Process and handle the form data and uploaded file as needed
# ...
return {'status': 'success'}
def validate_form_data(form_data):
if 'description' not in form_data:
raise BadRequestError('Missing description field.')
if 'file' not in form_data:
raise BadRequestError('Missing file field.')
if len(form_data['file'].file.read()) > MAX_FILE_SIZE:
raise BadRequestError('File size exceeds the allowed limit.')
Ryusei Kakujo
Focusing on data science for mobility
Bench Press 100kg!