let conditional = require('koa-conditional-get');

let etag = require('koa-etag');

exports.init = function(app) {

// use it upstream from etag so

// that they are present

// conditional triggers AFTER other middleware and returns 304/empty body if etag/modified matches

app.use(conditional());

// add etags AFTER every request (even POST), using file/body content and crc32

app.use(etag());

// set expires to ctx.expires

app.use(async function (ctx, next) {

await next();

if (!ctx.expires) return;

if (process.env.NODE_ENV === 'development') {

// override any value with 2 secs, we don't need long expires to block our changes in dev

ctx.expires = 2;

}

ctx.set('Expires', new Date(Date.now() + ctx.expires*1e3).toUTCString());

});

};