How can upload and download web applications ensure security and reliability and control permissions?

For example, the backend of a common web application is php. How to design a file upload/download class. 1. security: Malicious users may upload attack scripts. 2. reliability: the backend of PHP development. Generally, http is used for downloading. How to Improve the download reliability? 3. permission control: for download permissions of different users, the general web application backend is php. How to design a file upload/download class.
1. Security: Malicious users may upload attack scripts
2. Reliability: PHP backend development. Generally, http is used for downloading. How to Improve the download reliability?
3. Permission control: designed for different users to download Permissions

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For example, the backend of a common web application is php. How to design a file upload/download class.
1. Security: Malicious users may upload attack scripts
2. Reliability: PHP backend development. Generally, http is used for downloading. How to Improve the download reliability?
3. Permission control: designed for different users to download Permissions

In terms of security, we must ensure that scripts cannot be executed in the upload directory. The reliability and permissions are used to determine whether the user has the permission to download the files. If yes, a decrypted encrypted link is generated, the link should include the downloaded file information and expiration time, and then jump to the download file, which can basically prevent leeching and permission problems.