const input = Object.assign({},
{ query: ctx.request.query || {} },
{ body: ctx.request.body || {} },
{ params: ctx.params || {} });

const koa=require('koa')
const {middleware: validator} = require('koa-json-schema')

koa()
    .use(validator(schema, options))
    .use(function (ctx){
       // do something with safe input
    });

koa()
    .use(async function (ctx, next){
        try {
            await next();
        } catch(e){
           if(e.status === 422){
                console.log(e.error_description);
           }
        }
    })
    .use(validator(schema, options))
    .use(function (ctx){
       // do something with safe input
    });