PHP and FTP: Implement differential and incremental backup of remote files

PHP and FTP: Implement differential and incremental backup of remote files

1. Introduction
When developing web applications, we often encounter situations where we need to interact with remote FTP servers. For example, we need to download files from an FTP server or upload local files to an FTP server. In this process, how to implement differential and incremental backup of remote files becomes an important issue. This article will introduce how to use PHP to implement differential and incremental backup of remote files, and attach corresponding code examples.

2. Realize the difference of remote files
When we need to download files from the FTP server, usually we only need to download the parts that are different from the local files to reduce the amount of data transmitted over the network and time. The following is a sample code that uses PHP to implement differential download of remote files:

<?php
function downloadFile($remoteFile, $localFile)
{
    $ftpServer = "ftp.example.com";
    $ftpUsername = "username";
    $ftpPassword = "password";
    
    $ftpConn = ftp_connect($ftpServer);
    ftp_login($ftpConn, $ftpUsername, $ftpPassword);
    
    $localFileSize = file_exists($localFile) ? filesize($localFile) : 0;
    $ftpFileSize = ftp_size($ftpConn, $remoteFile);
    
    if ($localFileSize !== $ftpFileSize) {
        if (ftp_get($ftpConn, $localFile, $remoteFile, FTP_BINARY)) {
            echo "文件下载成功！";
        } else {
            echo "文件下载失败！";
        }
    } else {
        echo "本地文件与远程文件一致，无需下载！";
    }
    
    ftp_close($ftpConn);
}

// 调用示例
downloadFile("/remote/path/file.txt", "/local/path/file.txt");
?>

3. Implement incremental backup of remote files
In some cases, we need to upload local files to the FTP server and Make incremental backups. That is, only upload parts that do not exist on the remote server or are different from the local file. The following is a sample code that uses PHP to implement incremental backup:

<?php
function uploadFile($localFile, $remoteFile)
{
    $ftpServer = "ftp.example.com";
    $ftpUsername = "username";
    $ftpPassword = "password";
    
    $ftpConn = ftp_connect($ftpServer);
    ftp_login($ftpConn, $ftpUsername, $ftpPassword);
    
    $remoteFileSize = ftp_size($ftpConn, $remoteFile);
    $localFileSize = filesize($localFile);
    
    if ($remoteFileSize !== $localFileSize) {
        if (ftp_put($ftpConn, $remoteFile, $localFile, FTP_BINARY)) {
            echo "文件上传成功！";
        } else {
            echo "文件上传失败！";
        }
    } else {
        echo "远程文件与本地文件一致，无需上传！";
    }
    
    ftp_close($ftpConn);
}

// 调用示例
uploadFile("/local/path/file.txt", "/remote/path/file.txt");
?>

IV. Summary
Through the above sample code, we can see how to use PHP to implement remote file differences and Incremental backup. When downloading a file, we will only download the parts that are different from the local file to improve efficiency. When uploading files, we only upload the parts that are different from the remote file to achieve incremental backup. In this way, we can reduce the amount of data and time transferred over the network while maintaining file integrity. I hope this article will be helpful for you to interact with FTP servers in developing web applications!

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