How to Parse Multipart Form Data in Python

import cgi
from io import BytesIO

def parse_multipart_form(headers, body_bytes):
    content_type = headers.get("Content-Type", "")
    content_length = int(headers.get("Content-Length", len(body_bytes)))
    
    # Create a file-like object from bytes for cgi.FieldStorage
    body_file = BytesIO(body_bytes)
    
    # Parse the multipart form data
    form = cgi.FieldStorage(
        fp=body_file,
        headers=headers,
        environ={
            "REQUEST_METHOD": "POST",
            "CONTENT_TYPE": content_type,
            "CONTENT_LENGTH": content_length,
        }
    )
    
    result = {}
    for field in form.list:
        if field.filename:
            # File upload
            result[field.name] = {
                "filename": field.filename,
                "content_type": field.type,
                "data": field.file.read() or b""
            }
        else:
            # Regular field
            result[field.name] = field.value
    
    return result

if __name__ == "__main__":
    # Simulate a multipart form upload
    boundary = "----WebKitFormBoundary7MA4YWxkTrZu0gW"
    
    # Build a simple multipart body
    body = (
        f"--{boundary}\r\n"
        f'Content-Disposition: form-data; name="username"\r\n\r\n'
        f"alice\r\n"
        f"--{boundary}\r\n"
        f'Content-Disposition: form-data; name="file"; filename="test.txt"\r\n'
        f"Content-Type: text/plain\r\n\r\n"
        f"Hello, World!\r\n"
        f"--{boundary}--\r\n"
    ).encode()
    
    headers = {
        "Content-Type": f"multipart/form-data; boundary={boundary}",
        "Content-Length": str(len(body)),
    }
    
    # Parse it
    parsed = parse_multipart_form(headers, body)
    
    # Show results
    import pprint
    pprint.pprint(parsed, width=80)