koa中间层 文件下载的请求转发

背景：

前端用a标签发起下载文档的get请求

node中间层接到get请求后将请求转发到java后端

java后端返回文档流传递给node中间层

好处：

后端的java业务逻辑层接口、数据库不向外部暴露，node中间层进行安全验证及请求转发

1.前端发起请求

 <a download={`${filename}文件.doc`} href={`${domain}/api/word/download?a=${fileid}&b=${filename}>
    下载文件
</a>

2.koa 中间层转发

router.get('/word/download',async (ctx,next)=>{
    let {a,b,date} = ctx.query;
    date = date || timeStamp2String(false,'short');
    let file = await request({
        uri:'word',
        qs:{
            orgNo:a
        }
    });
    let s = new Readable;
    s.push(file);
    s.push(null);
    let docx = 'application/vnd.openxmlformats-officedocument.wordprocessingml.document';
    let doc = 'application/msword';
    ctx.set('content-type',docx);
    ctx.set('content-disposition',`attachment;filename*=UTF-8''${encodeURIComponent(b)}.docx`);
    ctx.body = s;
});

3.request方法请求java后端

import request from 'request-promise';
function reqGetStreamData(params){
    let {uri,qs} = params;
    return new Promise((resolve,reject)=>{
        request({
            uri:`${domain}api/jgs/${uri}`,
            qs,
            encoding:null,
            headers: {
                'User-Agent': 'Request-Promise',
                'Content-type':docx
            },
            json: false
        }).then(data => {
            resolve(data);
        }, err => {
            let errData = {
                status:1,
                data:err,
                statusInfo:'失败'
            }
            reject(errData);
        }).catch(err => {
            let obj = {
                status: 1,
                data: err,
                statusInfo: '未知错误！'
            };
            reject(obj);
        });
    });
}

原理就是：将java后端返回的文件流被request转换为buffer对象，然后用stream.Readable将buffer对象转换为流，直接返回给前端即可