上传的图片已损坏，但未损坏txt文件

Question

我正在尝试使用AWS lambdas上传图像，但是图像损坏了，我使用txt文件进行了测试，效果很好。函数checkImage是处理程序

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
    }

当我从python打印文件时，我得到了

我使用了diff，二进制文件不同。我认为图像文件被解析成两倍或类似的东西 我猜这里我做错了什么

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

我尝试了不同的形式，例如

fp = io.BytesIO(event['body'].encode('utf-8'))

但基本相同。