#Middleware

#How to Register Middleware?

Middleware registration methods are generally written in the load method

export class MyPlugin extends Plugin {
  load() {
    this.app.acl.use();
    this.app.resourcer.use();
    this.app.use();
  }
}

Explanation:

1. app.acl.use() Adds resource permission-level middleware, executed before permission judgment
2. app.resourcer.use() Adds resource-level middleware, only executed when a defined resource is requested
3. app.use() Adds application-level middleware, executed on every request

#Onion Model

app.use(async (ctx, next) => {
  ctx.body = ctx.body || [];
  ctx.body.push(1);
  await next();
  ctx.body.push(2);
});

app.use(async (ctx, next) => {
  ctx.body = ctx.body || [];
  ctx.body.push(3);
  await next();
  ctx.body.push(4);
});

Visit http://localhost:3000/api/hello to view, the browser response data is:

{"data": [1,3,4,2]}

#Built-in Middleware and Execution Order

1. bodyParser
2. cors
3. i18n
4. dataWrapping
5. db2resource
6. restApi actually resourcer
   1. auth
   2. acl
      1. Other middleware added by acl.use()
   3. Other middleware added by resourcer.use()
   4. action handler
7. Other middleware added by app.use()

You can also use before or after to insert middleware at a position marked by a tag, such as:

app.use(m1, { tag: 'restApi' });
app.resourcer.use(m2, { tag: 'parseToken' });
app.resourcer.use(m3, { tag: 'checkRole' });
// m4 will be placed before m1
app.use(m4, { before: 'restApi' });
// m5 will be inserted between m2 and m3
app.resourcer.use(m5, { after: 'parseToken', before: 'checkRole' });

If the position is not specifically specified, the execution order of newly added middleware is:

1. First execute those added by acl.use,
2. Then those added by resourcer.use, including middleware handler and action handler,
3. Finally those added by app.use.

Visit http://localhost:3000/api/hello to view, the browser response data is:

{"data": [1,2]}

Visit http://localhost:3000/api/test:list to view, the browser response data is:

{"data": [5,3,7,1,2,8,4,6]}

#Resource undefined, middleware added by resourcer.use() is not executed

app.use(async (ctx, next) => {
  ctx.body = ctx.body || [];
  ctx.body.push(1);
  await next();
  ctx.body.push(2);
});

app.resourcer.use(async (ctx, next) => {
  ctx.body = ctx.body || [];
  ctx.body.push(3);
  await next();
  ctx.body.push(4);
});

Visit http://localhost:3000/api/hello to view, the browser response data is:

{"data": [1,2]}

In the above example, the hello resource is undefined and will not enter the resourcer, so middleware in the resourcer will not be executed

#Helper Plugin

Enable dev tools to view the middleware execution order and related use stack addresses for the current request