How to prohibit file downloading in PHP server

In the daily web development process, we often use PHP programs as server-side scripting languages ​​to process user requests. However, the security issues that come with it cannot be ignored. One of the more common security issues is that PHP servers prohibit file downloads, where when a user tries to download certain sensitive files on the server, the server denies their request.

File downloading is a very common feature for web applications. For example, on some websites, users may need to download PDF files, audio, video, software and other content. However, in some cases, making all files available for download may pose security risks. For example, if an unauthorized user downloads a sensitive spreadsheet or code file, the leakage of this information will pose a serious threat to the company's interests. Therefore, in order to ensure the security of the system, developers often need to prohibit certain files from being downloaded.

The file download of the PHP server is implemented through the HTTP protocol. When a user enters a URL and requests a file on a server, the server forwards the request to a PHP program, which then reads the file and sends it to the user. Therefore, if we want to prevent users from downloading certain files, we can do this by setting HTTP response headers. Specifically, we can add the following code to the PHP code to prohibit file downloads:

header('Content-Type: text/plain;');
header('Content-Disposition: attachment; filename=forbidden.txt');
readfile('/path/to/forbidden/file');

In the above code, header('Content-Type: text/plain;') Used to set the HTTP response header, indicating that the content type of the response is plain text. header('Content-Disposition: attachment; filename=forbidden.txt') means telling the browser that the file needs to be downloaded instead of opened in the browser. The last line of code readfile('/path/to/forbidden/file') is used to read the contents of the specified file and send it to the user.

If you do not want users to download the file, you can set the Content-Type in the header to a non-download type. For example:

header('Content-Type: application/pdf;');
readfile('/path/to/pdf/file');

Finally, it should be noted that although the above method can prohibit file downloading to a certain extent, more stringent control measures need to be taken for special file types such as executable files. At the same time, in actual development, if not handled properly, there may be security issues such as attackers bypassing restrictions on downloading and downloading sensitive files. Therefore, developers need to treat the file download function more carefully and implement comprehensive security protection.

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