php语言实现上传文件和下载文件

上传文件：

<?php
if(isset($_FILES['file'])) {
    $errors = array();
    $file_name = $_FILES['file']['name'];
    $file_size = $_FILES['file']['size'];
    $file_tmp = $_FILES['file']['tmp_name'];
    $file_type = $_FILES['file']['type'];
    $file_ext = strtolower(end(explode('.', $_FILES['file']['name'])));
    
    $extensions = array("jpeg", "jpg", "png");
    
    if(in_array($file_ext, $extensions) === false) {
        $errors[] = "extension not allowed, please choose a JPEG or PNG file.";
    }
    
    if($file_size > 2097152) {
        $errors[] = 'File size must be exactly 2 MB';
    }
    
    if(empty($errors) == true) {
        move_uploaded_file($file_tmp, "uploads/" . $file_name);
        echo "Success";
    } else {
        print_r($errors);
    }
}
?>
<form action="" method="POST" enctype="multipart/form-data">
    <input type="file" name="file" />
    <input type="submit" />
</form>

下载文件：

<?php
$file = 'example.txt';

if(file_exists($file)) {
    header('Content-Description: File Transfer');
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename="' . basename($file) . '"');
    header('Expires: 0');
    header('Cache-Control: must-revalidate');
    header('Pragma: public');
    header('Content-Length: ' . filesize($file));
    readfile($file);
    exit;
} else {
    echo "File not found.";
}
?>