Bagaimana untuk melaksanakan bar kemajuan muat turun dalam php

<?php
// 当前文件：download.php

$action = @$_GET[&#39;action&#39;];

// 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 &#39;prepare-download&#39;:
        // 下载缓存文件夹
        $download_cache = __DIR__."/download_cache";

        if (!is_dir($download_cache)) {
            if (false === mkdir($download_cache)) {
                exit(&#39;创建下载缓存文件夹失败，请检查目录权限。&#39;);
            }
        }

        $tmp_path = $download_cache."/update_".time().".zip";

        save_tmp_path(); // 这里保存临时文件地址

        return json(compact(&#39;remote_url&#39;, &#39;tmp_path&#39;, &#39;file_size&#39;));

        break;

    case &#39;start-download&#39;:

        // 这里检测下 tmp_path 是否存在

        try {
            set_time_limit(0);

            touch($tmp_path);

            // 做些日志处理

            if ($fp = fopen($remote_url, "rb")) {

                if (!$download_fp = fopen($tmp_path, "wb")) {
                    exit;
                }

                while (!feof($fp)) {

                    if (!file_exists($tmp_path)) {
                        // 如果临时文件被删除就取消下载
                        fclose($download_fp);

                        exit;
                    }

                    fwrite($download_fp, fread($fp, 1024 * 8 ), 1024 * 8);
                }

                fclose($download_fp);
                fclose($fp);

            } else {
                exit;
            }

        } catch (Exception $e) {
            Storage::remove($tmp_path);

            exit(&#39;发生错误：&#39;.$e->getMessage());
        }

        return json(compact(&#39;tmp_path&#39;));

        break;

    case &#39;get-file-size&#39;:

        // 这里检测下 tmp_path 是否存在

        if (file_exists($tmp_path)) {
            // 返回 JSON 格式的响应
            return json([&#39;size&#39; => filesize($tmp_path)]);
        }

        break;

    default:
        # code...
        break;
}

// 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() {
            $(&#39;#update-button&#39;).html(&#39;<i class="fa fa-spinner fa-spin"></i> 正在准备&#39;).prop(&#39;disabled&#39;, &#39;disabled&#39;);
        },
    })
    .done(function(json) {
        console.log(json);

        file_size = json.file_size;

        $(&#39;#file-size&#39;).html(file_size);

        // 显示进度条

        console.log("started downloading");
        $.ajax({
            url: &#39;./download.php?action=start-download&#39;,
            type: &#39;POST&#39;,
            dataType: &#39;json&#39;
        })
        .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() {

            $(&#39;#imported-progress&#39;).html(progress);
            $(&#39;.progress-bar&#39;).css(&#39;width&#39;, progress+&#39;%&#39;).attr(&#39;aria-valuenow&#39;, 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: &#39;./download.php?action=get-file-size&#39;,
                    type: &#39;GET&#39;
                })
                .done(function(json) {
                    progress = (json.size / file_size * 100).toFixed(2);

                    updateProgress(progress);

                    console.log("Progress: "+progress);
                })
                .fail(showAjaxError);
            }

        }, 300);

    })
    .fail(showAjaxError);

}