File upload using PHP

In modern Internet applications, the file upload function has become an indispensable part. Whether it is a personal blog, social media or online mall, on many occasions we need to upload files to achieve specific functions. However, there may be problems during the implementation of this function, including file size limitations, file format limitations and security issues that require reasonable handling. This is also a common PHP file upload technology that will be introduced in this article.

1. Upload process

Before starting to understand PHP file upload in depth, let’s briefly understand the basic process of file upload. This process can be divided into the following steps:

1. Select the file to be uploaded

2. Submit the file to be uploaded to the server

3. The server processes the file and returns the upload result

4. Shows that the upload is successful or Failed feedback

Among them, the first and fourth steps are usually related to the browser side, while the server side is mainly responsible for the processing of the second and third steps.

2. Upload file limit

File size limit

For the upload file size limit, we can set it in the php.ini configuration file Upload_max_filesize, post_max_size are controlled by two values. Among them, upload_max_filesize indicates the maximum file size allowed to be uploaded, and post_max_size indicates the maximum number of bytes of the entire request (including files and other fields). If the uploaded file exceeds the limits of these two values, the server will return an error.

File type restrictions

In addition to size restrictions, for file type restrictions, we can filter the mimeType of the uploaded file. In PHP, you can use $_FILES'file' to get the mimeType of the received file. We can use the in_array() function to judge the mimeType of the file to confirm whether the upload is allowed to continue.

Security issues

Security issues are an important issue in the implementation process of file upload. For files uploaded by users, we need to perform certain security checks to prevent users from uploading unsafe files, such as Trojans, viruses, scripts, etc. To prevent this type of attack, we need to inspect and filter uploaded files.

3. PHP file upload code example

The following is a simple PHP file upload example to demonstrate the file upload process, as shown below:

<?php

$allow_exts = array('jpg', 'jpeg', 'gif', 'png', 'txt');
$upload_dir = 'uploads/';
$max_size = 1024 * 1024;

if ($_FILES['file']['error'] != UPLOAD_ERR_OK) {
    echo '上传失败，请稍后再试';
    exit;
}

$temp_file = $_FILES['file']['tmp_name'];
$file_name = $_FILES['file']['name'];
$file_ext = strtolower(pathinfo($file_name, PATHINFO_EXTENSION));

if (!in_array($file_ext, $allow_exts)) {
    echo '文件类型不符合要求，请上传指定类型的文件';
    exit;
}

if ($_FILES['file']['size'] > $max_size) {
    echo '文件大小不能超过1MB，请重新上传';
    exit;
}

if (!is_uploaded_file($temp_file)) {
    echo '非法上传，请重新上传';
    exit;
}

if (!file_exists($upload_dir)) {
    mkdir($upload_dir);
}

if (move_uploaded_file($temp_file, $upload_dir . $file_name)) {
    echo '上传成功';
    exit;
}

echo '上传失败，请稍后再试';

?>

In the above code, We used several PHP built-in functions to implement the basic functionality of file upload. Among them, the in_array() function is used to determine whether the uploaded file type meets the requirements. The pathinfo() function is used to obtain the suffix name of the uploaded file. The is_uploaded_file() function is used to verify whether the uploaded file is legal to prevent illegal uploading. The move_uploaded_file() function is used to move the uploaded cache file to the specified directory to complete the file upload process.

4. Summary

File uploading is an essential function for many websites. In PHP, implementing file upload requires us to restrict and check the uploaded files to ensure the safety and rationality of the upload process. This article mainly introduces the basic process and common techniques of file upload in PHP, hoping to be helpful to readers.

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