求文件下载与合并脚本及基于现有PHP脚本的分块下载方案

Got it, let's revamp your basic download script to support chunked (resumable) downloads—perfect for large files where users might lose connection mid-transfer and need to pick up where they left off. Here's how to do it, with clear breakdowns of key changes:

Key Concepts for Resumable Downloads #

Resumable downloads rely on the HTTP Range header: the client tells the server which part of the file it wants, and the server responds with a 206 Partial Content status code plus the requested chunk. We'll build this logic alongside your existing POST trigger.

Modified Script with Chunk Support #

<?php
// Handle both POST (your original trigger) and GET (for chunked download requests)
if (isset($_POST['downloadButton']) || isset($_GET['filename'])) {
    $filename = isset($_POST["filename"]) ? $_POST["filename"] : $_GET["filename"];
    
    if (!file_exists($filename)) {
        http_response_code(404);
        echo "File not found";
        exit;
    }

    $fileSize = filesize($filename);
    $file = fopen($filename, 'rb');

    // Initialize range boundaries
    $start = 0;
    $end = $fileSize - 1;

    // Parse and validate Range header if present
    if (isset($_SERVER['HTTP_RANGE'])) {
        preg_match('/bytes=(\d+)-(\d+)?/', $_SERVER['HTTP_RANGE'], $matches);
        $start = intval($matches[1]);
        
        // Set end to file end if not specified in the request
        $end = !empty($matches[2]) ? intval($matches[2]) : $fileSize - 1;

        // Reject invalid range requests
        if ($start > $end || $start >= $fileSize || $end >= $fileSize) {
            http_response_code(416); // Requested Range Not Satisfiable
            header("Content-Range: bytes */$fileSize");
            exit;
        }
    }

    $chunkSize = $end - $start + 1;

    // Set critical response headers
    header("Content-Type: application/octet-stream");
    header("Content-Disposition: attachment; filename=\"" . basename($filename) . "\"");
    header("Content-Length: $chunkSize");
    header("Accept-Ranges: bytes"); // Tell clients resuming is supported
    
    // Send appropriate status code
    if (isset($_SERVER['HTTP_RANGE'])) {
        http_response_code(206); // Partial Content for chunked requests
        header("Content-Range: bytes $start-$end/$fileSize");
    } else {
        http_response_code(200); // OK for full file downloads
    }

    // Stream the requested chunk efficiently
    fseek($file, $start);
    while (!feof($file) && ($currentPos = ftell($file)) <= $end) {
        // Read in 1MB chunks to avoid memory overload with large files
        $readChunkSize = min(1024 * 1024, $end - $currentPos + 1);
        echo fread($file, $readChunkSize);
        flush(); // Push content to the client immediately
    }

    fclose($file);
    exit;
}
?>

What Changed & Why #

• Dual Request Support: Now works with your original POST button trigger and GET requests (most download managers use GET for resumable transfers)
• Range Header Handling: Parses client-requested file ranges, validates them, and adjusts output to match
• Proper Status Codes: Returns 206 Partial Content for chunks, 404 for missing files, and 416 for invalid range requests
• Memory Efficiency: Reads and outputs the file in 1MB chunks instead of loading the entire file into memory (critical for large files)
• Resumable Headers: Includes Accept-Ranges to signal support for resuming, and Content-Range to specify which chunk is being sent

Testing the Script #

You can test chunked downloads manually with curl:

# Download the first 1MB of the file
curl -r 0-1048575 http://your-domain.com/your-script.php?filename=your-large-file.zip -o chunk1.part

# Download the next 1MB
curl -r 1048576-2097151 http://your-domain.com/your-script.php?filename=your-large-file.zip -o chunk2.part

# Combine chunks (Linux/macOS)
cat chunk1.part chunk2.part > full-file.zip

Most modern browsers and download managers will automatically use resumable downloads if the server supports it—no extra client-side setup needed!

内容的提问来源于stack exchange，提问作者mohsen hasani