Uploading images from multipart/data/-from get corrupted

[jdc18]

I am trying to upload images using aws lambdas, I am testing locally with serverless offline. When I upload an image it gets corrupted, but when I upload a txt file it works ok. So I guess it has to do something with the encoding

import json
import os
from cgi import FieldStorage
from io import BytesIO


def parse_into_field_storage(fp, ctype, clength):
    fs = FieldStorage(
        fp=fp,
        environ={'REQUEST_METHOD': 'POST'},
        headers={
            'content-type': ctype,
            'content-length': clength
        },
        keep_blank_values=True
    )
    form = {}
    files = {}
    for f in fs.list:
        if f.filename:
            files.setdefault(f.name, []).append(f)
        else:
            form.setdefault(f.name, []).append(f.value)
    return form, files
  
def checkImage(event, context):
    body_file = BytesIO(bytes(event["body"], "utf-8"))
    form, files = parse_into_field_storage(
        body_file,
        event['headers']['Content-Type'],
        body_file.getbuffer().nbytes
    )
    fileitem = files['file'][0]

    print(fileitem.filename)

    # Test if the file was uploaded
    if fileitem.filename:
        fn = os.path.basename(fileitem.filename)
        open('/tmp/' + fn, 'wb').write(fileitem.file.read())
        message = 'The file "' + fn + '" was uploaded successfully'
    else:
        message = 'No file was uploaded'
    
    return {
        "statusCode": 200,
        "body": message
    }

checkImage is the main handler that. I have tried different approaches but the result is the same. I am guessing this is the problem

body_file = BytesIO(bytes(event["body"], "utf-8"))

Maybe I shoul use another encoding.