middlewares

Middlewares Guide

Middlewares are used to execute code before and after the handler is called in API Steps.

The middleware is a handler that receives three arguments:

• Request: this is the same request object received by API Step handlers, if modified by the middleware, it will be the same object passed to the handler and any subsequent middleware. Be careful to not cause any side effects to the request object.
• Context: this is the same context object received by API Step handlers, if modified by the middleware, it will be the same object passed to the handler and any subsequent middleware. Be careful to not cause any side effects to the context object.
• Next: this is a function that you need to call to invoke the next middleware in the stack. If you don't call it, the request will be halted—the handler and any subsequent middlewares will not be called.

Next function

Next function is a way to either continue the execution flow or stop it. For example, in authentication middlewares, if the user is not authenticated, you can return a 401 response and not call next().

It can also be used to enrich data returned back to the HTTP response. Like adding a header parameter or so after calling next().

Adding middlewares to a step

TypeScript/JavaScript Example

import { ApiRouteConfig } from 'motia'
import { coreMiddleware } from '../middlewares/core.middleware'

export const config: ApiRouteConfig = {
  type: 'api',
  name: 'SampleRoute',
  description: 'Sample route',
  path: '/sample',
  method: 'GET',
  emits: [],
  flows: [],
  middleware: [coreMiddleware],
}

Python Example

async def enrich_data_middleware(req, context, next_fn):
    context.logger.info("enriching data")
    req["enriched"] = "yes"
    return await next_fn()

config = {
    "type": "api",
    "name": "SampleRoute",
    "description": "Sample route",
    "path": "/sample",
    "method": "GET",
    "emits": [],
    "flows": [],
    "middleware": [enrich_data_middleware],
}