Middlewares customization

Different types of middlewares

In Strapi, 3 middleware concepts coexist:

• Global middlewares are configured and enabled for the entire Strapi server application. These middlewares can be applied at the application level or at the API level.
  The present documentation describes how to implement them.
  Plugins can also add global middlewares (see Server API documentation).

• Route middlewares have a more limited scope and are configured and used as middlewares at the route level. They are described in the routes documentation.

• Document Service middlewares apply to the Document Service API and have their own implementation and related lifecycle hooks.

The diagram represents a simplified version of how a request travels through the Strapi back end, with global middlewares highlighted. The backend customization introduction page includes a complete, interactive diagram.

Implementation

A new application-level or API-level middleware can be implemented:

• with the interactive CLI command strapi generate
• or manually by creating a JavaScript file in the appropriate folder (see project structure):
  • ./src/middlewares/ for application-level middlewares
  • ./src/api/[api-name]/middlewares/ for API-level middlewares
  • ./src/plugins/[plugin-name]/middlewares/ for plugin middlewares

Middlewares working with the REST API are functions like the following:

JavaScript

./src/middlewares/my-middleware.js or ./src/api/[api-name]/middlewares/my-middleware.js

module.exports = (config, { strapi })=> {
  return (context, next) => {};
};

TypeScript

./src/middlewares/my-middleware.js or ./src/api/[api-name]/middlewares/my-middleware.ts

export default (config, { strapi })=> {
  return (context, next) => {};
};

Globally scoped custom middlewares should be added to the middlewares configuration file or Strapi won't load them.

API level and plugin middlewares can be added into the specific router that they are relevant to like the following:

./src/api/[api-name]/routes/[collection-name].js or ./src/plugins/[plugin-name]/server/routes/index.js

module.exports = {
  routes: [
    {
      method: "GET",
      path: "/[collection-name]",
      handler: "[controller].find",
      config: {
        middlewares: ["[middleware-name]"],
        // See the usage section below for middleware naming conventions
      },
    },
  ],
};

Example of a custom timer middleware

JavaScript

path: /config/middlewares.js

module.exports = () => {
  return async (ctx, next) => {
    const start = Date.now();

    await next();

    const delta = Math.ceil(Date.now() - start);
    ctx.set('X-Response-Time', delta + 'ms');
  };
};

TypeScript

/config/middlewares.ts

export default () => {
  return async (ctx, next) => {
    const start = Date.now();

    await next();

    const delta = Math.ceil(Date.now() - start);
    ctx.set('X-Response-Time', delta + 'ms');
  };
};

The GraphQL plugin also allows implementing custom middlewares, with a different syntax.

Usage

Middlewares are called different ways depending on their scope:

• use global::middleware-name for application-level middlewares
• use api::api-name.middleware-name for API-level middlewares
• use plugin::plugin-name.middleware-name for plugin middlewares

Tip

To list all the registered middlewares, run yarn strapi middlewares:list.

Restricting content access with an "is-owner policy"

It is often required that the author of an entry is the only user allowed to edit or delete the entry. In previous versions of Strapi, this was known as an "is-owner policy". With Strapi v4, the recommended way to achieve this behavior is to use a middleware.

Proper implementation largely depends on your project's needs and custom code, but the most basic implementation could be achieved with the following procedure:

1. From your project's folder, create a middleware with the Strapi CLI generator, by running the yarn strapi generate (or npm run strapi generate) command in the terminal.
2. Select middleware from the list, using keyboard arrows, and press Enter.
3. Give the middleware a name, for instance isOwner.
4. Choose Add middleware to an existing API from the list.
5. Select which API you want the middleware to apply.
6. Replace the code in the /src/api/[your-api-name]/middlewares/isOwner.js file with the following, replacing api::restaurant.restaurant in line 22 with the identifier corresponding to the API you choose at step 5 (e.g., api::blog-post.blog-post if your API name is blog-post):

src/api/blog-post/middlewares/isOwner.js

  "use strict";

  /**
   * `isOwner` middleware
   */

  module.exports = (config, { strapi }) => {
    // Add your own logic here.
    return async (ctx, next) => {
      const user = ctx.state.user;
      const entryId = ctx.params.id ? ctx.params.id : undefined;
      let entry = {};

      /** 
       * Gets all information about a given entry,
       * populating every relations to ensure 
       * the response includes author-related information
       */
      if (entryId) {
        entry = await strapi.documents('api::restaurant.restaurant').findOne(
          entryId,
          { populate: "*" }
        );
      }

      /**
       * Compares user id and entry author id
       * to decide whether the request can be fulfilled
       * by going forward in the Strapi backend server
       */
      if (user.id !== entry.author.id) {
        return ctx.unauthorized("This action is unauthorized.");
      } else {
        return next();
      }
    };
  };

7. Ensure the middleware is configured to apply on some routes. In the config object found in the src/api/[your-api–name]/routes/[your-content-type-name].js file, define the methods (create, read, update, delete) for which you would like the middleware to apply, and declare the isOwner middleware for these routes.
   
   For instance, if you wish to allow GET (i.e., read method) and POST (i.e., create method) requests to any user for the restaurant content-type in the restaurant API, but would like to restrict PUT (i.e., update method) and DELETE requests only to the user who created the entry, you could use the following code in the src/api/restaurant/routes/restaurant.js file:

   src/api/restaurant/routes/restaurant.js

   
   /**
    * restaurant router
    */
     
   const { createCoreRouter } = require("@strapi/strapi").factories;
   
   module.exports = createCoreRouter("api::restaurant.restaurant", {
     config: {
       update: {
         middlewares: ["api::restaurant.is-owner"],
       },
       delete: {
         middlewares: ["api::restaurant.is-owner"],
       },
     },
   });

Info

You can find more information about route middlewares in the routes documentation.