Function download

（改）网盘直链下载助手.user.js:1240–1446

* 下载文件 * @author hmjz100 * @description 发送 GET 请求，一般用于文件下载，支持进度监控、自动重试、断点续传、非断回退 * @param {String} url - 请求地址 * @param {Object} headers - 请求头配置 * @param {Number} [size=0] - 响应类型 * @param {Object} [extra] - 附加参数（必须 `name`、`index`、`size` 属性；可选 `thread`、`retry` 属性） * @return

(url, headers, extra)

		 * @returns {Promise} 包含响应数据的 `Promise` 对象
		 */
		async download(url, headers, extra) {
			headers = this.standHeaders(headers);
			// 初始化全局共享状态
			this.download.active = this.download.active || 0; // 全局活跃线程数
			this.download.taskCount = this.download.taskCount || 0; // 当前正在运行的 download 任务数
			var global_maxThreads = 8; // 整个允许的最大并发数

			if (extra) base.console.log(`【LinkSwift】Download\n收到数据：`, extra);
			if (!extra || !extra.index || !extra.name || !extra.size) throw new Error("extra 缺少内容。");

			let status = {
				aborted: false,
				requests: new Set(),
				results: [],
				active: 0,
				maxSpeed: 0
			};

			let promise = new Promise(async (resolve, reject) => {
				this.download.taskCount++; // 任务进入

				try {
					var finalHead = await base.getFinal(url, headers, false, false).catch(reject);
					if (!finalHead) return;
					url = finalHead.finalUrl;

					var responseHeaders = finalHead.responseHeaders;
					let size = parseInt(extra.size || responseHeaders?.["Content-Length"] || 0, 10);
					if (responseHeaders?.["Content-Range"]) {
						size = parseInt((responseHeaders["Content-Range"]?.match(/\/(\d+)$/)?.[1] || size), 10);
					}

					if (!status.aborted && typeof extra?.onProgress === "function") extra.onProgress(0, 0, size);
					if (!(finalHead.status >= 200 && finalHead.status < 400)) return reject(finalHead);
					if (finalHead.status == 204 && finalHead.statusText === "IDM") return reject(finalHead);

					var supportRange = finalHead.status == 206 && (responseHeaders?.["Accept-Ranges"]?.includes("bytes") || responseHeaders?.["Content-Range"]?.includes("bytes"));

					if (!!supportRange || size > 0) {
						base.console.log(`【LinkSwift】Download(Start)\n文件名称：${extra.name}\n断点续传：支持`);

						var maxRetry = extra.retry || 10;
						let index = 0;
						let offset = 0;
						let totalLoaded = 0;

						var worker = async () => {
							var minChunk = extra.minChunk || 50 * 1024; // 最小 50KB
							var maxChunk = extra.maxChunk || 1 * 1024 * 1024; // 最大 1MB
							let chunk = Math.floor(minChunk + (maxChunk - minChunk) * 0.37);

							while (offset < size && !status.aborted) {
								// 如果全局线程满了，且当前任务已经抢到了 1 条以上的线程，则 “让路” 给后来的任务
								let fairShare = Math.max(1, Math.floor(global_maxThreads / this.download.taskCount));
								while (!status.aborted && this.download.active >= global_maxThreads && status.active >= fairShare) {
									await new Promise(r => setTimeout(r, 200)); // 等待，直到其他任务释放或有空位
								}