PHP form processing: file uploads and restrictions

PHP form processing: file upload and restrictions

In web development, file upload is a common functional requirement. As a widely used server-side language, PHP provides a wealth of functions and methods to handle file uploads. This article will introduce how to use PHP to implement the file upload function and limit the size and type of files.

1. Basic steps for file upload

To implement the file upload function, you need to go through the following basic steps:

1. Create an HTML form and specify the enctype attribute of the form as "multipart /form-data" for uploading files.

<form action="upload.php" method="post" enctype="multipart/form-data">
    <input type="file" name="file">
    <input type="submit" value="上传">
</form>

2. Write a PHP script and use the $_FILES global variable in the script to obtain the uploaded file information.

$targetDir = "uploads/";  // 上传文件保存的目录
$targetFile = $targetDir . basename($_FILES["file"]["name"]);  // 上传文件保存的路径

if (move_uploaded_file($_FILES["file"]["tmp_name"], $targetFile)) {
    echo "文件上传成功";
} else {
    echo "文件上传失败";
}

$_FILES here is an associative array that contains information about uploaded files, such as file size, file type, temporary file name, etc.

3. Set the upload target path of the file, and use the move_uploaded_file() function to move the file from the temporary directory to the specified directory.

2. File size limit

In order to ensure the security and performance of the server, we need to limit the size of uploaded files. PHP provides two related configuration options: upload_max_filesize and post_max_size.

upload_max_filesize is used to control the maximum size of a single file. Its value can be an integer in bytes, or a string in units of K, M, or G. For example:

ini_set("upload_max_filesize", "10M");

post_max_size is used to limit the maximum size of the entire HTTP request. Its value can also be an integer or a string. We need to set its value to a value greater than or equal to upload_max_filesize. For example:

ini_set("post_max_size", "10M");

3. File type restrictions

In actual projects, we may only want users to upload specific types of files, for example, only image files are allowed to be uploaded. PHP provides the finfo_file() function to obtain the file type.

First, we need to enable the fileinfo extension in the php.ini file:

extension=php_fileinfo.dll  // Windows环境下
extension=php_fileinfo.so  // Linux环境下

Then, use the finfo_file() function to get the file type:

$finfo = finfo_open(FILEINFO_MIME_TYPE);
$fileType = finfo_file($finfo, $_FILES["file"]["tmp_name"]);
finfo_close($finfo);

Next, we You can use conditional statements to determine whether the file type meets the requirements and perform corresponding operations:

if ($fileType == "image/jpeg" || $fileType == "image/png") {
    // 上传文件操作
} else {
    echo "只允许上传JPEG和PNG图片文件";
}

4. Complete code example

<?php
$targetDir = "uploads/";
$targetFile = $targetDir . basename($_FILES["file"]["name"]);

if ($_FILES["file"]["size"] > 1024 * 1024) {
    echo "文件过大";
} elseif ($_FILES["file"]["error"] != 0) {
    echo "文件上传失败";
} elseif ($_FILES["file"]["type"] != "image/jpeg" && $_FILES["file"]["type"] != "image/png") {
    echo "只允许上传JPEG和PNG图片文件";
} elseif (move_uploaded_file($_FILES["file"]["tmp_name"], $targetFile)) {
    echo "文件上传成功";
} else {
    echo "文件上传失败";
}
?>

Summary:

This article introduces the use of PHP Basic steps to implement the file upload function, with restrictions on file size and type. By setting configuration options appropriately, we can ensure the security and performance of the server. In addition, by using the finfo_file() function to obtain the file type, we can further restrict the file types uploaded by users to meet specific needs. I hope this article can help readers understand and implement the file upload function.

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