download.php

<?php 
 // 当前文件：download.php
 
 $action = @$_GET@['action'];
 
 // 自己获取这些信息
 $remote_url  = get_remote_file_url();
 $file_size   = get_remote_file_size($remote_url);
 $tmp_path    = get_tmp_path();
 
 switch ($action) {
     case 'prepare-download':
         // 下载缓存文件夹
         $download_cache = __DIR__."/download_cache";
 
         if (!($download_cache)) {
             if (false === ($download_cache)) {
                 exit('创建下载缓存文件夹失败，请检查目录权限。');
             }
         }
 
         $tmp_path = $download_cache."/update_".().".zip";
 
         save_tmp_path(); // 这里保存临时文件地址
 
         return json(('remote_url', 'tmp_path', 'file_size'));
 
         break;
 
     case 'start-download':
 
         // 这里检测下 tmp_path 是否存在
 
         try {
             (0);
 
             ($tmp_path);
 
             // 做些日志处理
 
             if ($fp = ($remote_url, "rb")) {
 
                 if (!$download_fp = ($tmp_path, "wb")) {
                     exit;
                 }
 
                 while (!($fp)) {
 
                     if (!($tmp_path)) {
                         // 如果临时文件被删除就取消下载
                         ($download_fp);
 
                         exit;
                     }
 
                     ($download_fp, ($fp, 1024 * 8 ), 1024 * 8);
                 }
 
                 ($download_fp);
                 ($fp);
 
             } else {
                 exit;
             }
 
         } catch (Exception $e) {
             Storage::remove($tmp_path);
 
             exit('发生错误：'.$e->getMessage());
         }
 
         return json(('tmp_path'));
 
         break;
 
     case 'get-file-size':
 
         // 这里检测下 tmp_path 是否存在
 
         if (($tmp_path)) {
             // 返回 JSON 格式的响应
             return json(['size' => ($tmp_path)]);
         }
 
         break;
 
     default:
         # code...
         break;
 }

js

// 咋触发这个函数我就不举例了
 function downloadFile() {
     var file_size = 0;
     var progress  = 0;
 
     console.log("Prepared to download");
 
     $.ajax({
         url: './download.php?action=prepare-download',
         type: 'GET',
         dataType: 'json',
         beforeSend: function() {
             $('#update-button').html('<i class="fa fa-spinner fa-spin"></i> 正在准备').prop('disabled', 'disabled');
         },
     })
     .done(function(json) {
         console.log(json);
 
         file_size = json.file_size;
 
         $('#file-size').html(file_size);
 
         // 显示进度条
 
         console.log("started downloading");
         $.ajax({
             url: './download.php?action=start-download',
             type: 'POST',
             dataType: 'json'
         })
         .done(function(json) {
             // set progress to 100 when got the response
             progress = 100;
 
             console.log("Downloading finished");
             console.log(json);
         })
         .fail(showAjaxError);
 
         var interval_id = window.setInterval(function() {
 
             $('#imported-progress').html(progress);
             $('.progress-bar').css('width', progress+'%').attr('aria-valuenow', progress);
 
             if (progress == 100) {
                 clearInterval(interval_id);
               
                 // 到此远程文件下载完成，继续其他逻辑
             } else {
                 $.ajax({
                     url: './download.php?action=get-file-size',
                     type: 'GET'
                 })
                 .done(function(json) {
                     progress = (json.size / file_size * 100).toFixed(2);
                   
                     updateProgress(progress);
 
                     console.log("Progress: "+progress);
                 })
                 .fail(showAjaxError);
             }
 
         }, 300);
 
     })
     .fail(showAjaxError);
 
 }