如何使用koa-graphql设置graphql-upload？

const { graphqlUploadKoa } = require('graphql-upload');

const graphqlUpload = graphqlUploadKoa();

async function graphqlUpload(ctx, next) {
  await graphqlUpload(ctx.req, ctx.res);
  await next();
}

const Koa = require('koa');
const { graphqlHTTP } = require('koa-graphql');
const { buildSchema } = require('graphql');

const schema = buildSchema(`
  type Query {
    hello: String
  }
`);

const root = {
  hello: () => 'Hello World!'
};

const app = new Koa();

app.use(graphqlUpload); // 使用自定义的graphqlUpload中间件

app.use(
  graphqlHTTP({
    schema: schema,
    rootValue: root,
    graphiql: true
  })
);

app.listen(3000, () => {
  console.log('GraphQL server running at http://localhost:3000');
});