首先创建一个文件流来读取要下载的文件，当然可以是动态产生的输入流
const fileStream = fs.createReadStream('test.zip');
然后创建响应头，指定响应的类型，同时也可以使用Content-Disposition设置浏览器下载时需要保存的文件名
const head = {'Content-Type': 'application/zip, application/octet-stream; charset=ISO-8859-1','Content-Disposition': 'attachment;filename=\"resources123.zip\"'};
res.writeHead(200, head);
最后通过文件流的pipe()方法输出到响应里
fileStream.pipe(res);
完整router代码如下
router.get('/download', function(req, res, next) {const fileStream = fs.createReadStream('test.zip');const head = {'Content-Type': 'application/zip, application/octet-stream; charset=ISO-8859-1','Content-Disposition': 'attachment;filename=\"test123.zip\"'};res.writeHead(200, head);fileStream.pipe(res);
});
最后说一下，express里的response也提供了一个attachment()方法，这个方法会设置Content-Disposition头，并且会通过res.type()来设置Content-Type头，代码如下
router.get('/download', function(req, res, next) {const fileStream = fs.createReadStream('test.zip');res.attachment('test123.zip');fileStream.pipe(res);
});
最后的最后，看一下如果出错了应该怎么处理
router.get('/download', function(req, res, next) {const fileStream = fs.createReadStream('test.zip');fileStream.on('open', () => {res.attachment('test123.csv');fileStream.pipe(res);});fileStream.on('error', err => {next(err);});
});
