What are the common file upload and download operations in PHP programming?

With the gradual maturity of Internet technology and website applications, file uploading and downloading have become essential functions in website development. As a programming language widely used in network development, PHP provides a series of file upload and download operations. This article will introduce common file upload and download operations in PHP programming.

1. File upload

File upload is the process of uploading files on the local computer to the Web server. PHP provides a variety of ways to implement file upload operations, including uploading through HTML forms, asynchronous uploading using Ajax, uploading files through FTP, etc. Among them, the most common method is to upload through HTML forms.

1. Upload files through HTML forms

Use in HTML forms to implement the file upload function. In the back-end PHP program, you can obtain relevant information about the uploaded file, such as file name, type, temporary file name, etc., through the information in the $_FILES array. The following is a sample code for file upload:

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

<?php
if($_SERVER["REQUEST_METHOD"] == "POST"){
  if($_FILES["file"]["error"] > 0){
    echo "上传发生错误：" . $_FILES["file"]["error"];
  }else{
    echo "文件名：" . $_FILES["file"]["name"] . "<br>";
    echo "文件类型：" . $_FILES["file"]["type"] . "<br>";
    echo "文件大小：" . ($_FILES["file"]["size"] / 1024) . " KB<br>";
    echo "临时文件名：" . $_FILES["file"]["tmp_name"] . "<br>";
  }
}
?>

2. Limit uploaded file types and sizes

In order to prevent users from uploading unsafe file types and overly large files, we It is often necessary to limit the type and size of uploaded files. In PHP, restrictions can be imposed by judging the type and size of uploaded files. The following is a sample code that limits the type and size of uploaded files:

$allowed_types = array("image/jpeg", "image/png", "application/pdf");
$max_size = 1024 * 1024; // 1MB

if(in_array($_FILES["file"]["type"], $allowed_types) && $_FILES["file"]["size"] < $max_size){
  // 执行上传操作
}else{
  echo "上传失败！文件类型不允许或文件大小超过限制！";
}

2. File download

File downloading is the process of downloading files from the Web server to the local computer. In PHP, commonly used file download methods include reading the file content and then outputting it, sending a response header through header(), and using the readfile() function to read and output the file.

1. Output after reading the file content

In PHP, you can read the file content through the file reading function (such as fread(), fgets(), etc.) , and then output it to the browser through echo. The following is a sample code output after reading the file content:

$file_path = "path/to/file.pdf";
$file_size = filesize($file_path);

header("Content-Type: application/octet-stream");
header("Content-Disposition: attachment; filename=file.pdf");
header("Content-Length: " . $file_size);

$handle = fopen($file_path, "r");
if($handle){
  while(!feof($handle)){
    echo fread($handle, 1024);
  }
  fclose($handle);
}

2. Send the response header through header()

In PHP, you can also use the header() function Set the response header information to let the browser download the file. The following is a sample code for sending response headers through header():

$file_path = "path/to/file.pdf";

header("Content-Type: application/octet-stream");
header("Content-Disposition: attachment; filename=file.pdf");
header("Content-Length: " . filesize($file_path));

readfile($file_path);

3. Use the readfile() function to read and output the file

In PHP, you can also directly Use the readfile() function to read content from a file and output it to the browser. The following is a sample code that uses the readfile() function to read and output a file:

$file_path = "path/to/file.pdf";

header("Content-Type: application/octet-stream");
header("Content-Disposition: attachment; filename=file.pdf");
header("Content-Length: " . filesize($file_path));

readfile($file_path);

Summary

File uploading and downloading is one of the common functions in web development. With the support of PHP, We can implement these functions easily. When writing file upload and download code, you need to pay attention to file type, size, security and other issues to ensure that users enjoy a better experience.

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