This package allows you to create reusable middleware functions, with a function signature that is similar to express. You are then able to order them however you want. The middlewares are executed left to right, the last one will invoke your handler.
This package has no external dependencies. Therefore, it wont add any bloat to your lambda functions.
Here are some examples on how this package can be used. The middlewares are only for demo purposes.
import { withMiddlewares } from 'lambda-express-middlewares'
const authenticate = async (token) => {
const user = await authenticaitonService.getUser(token)
return user
}
// Create a middleware for adding a custom user object to your lambda context.
const authMiddleware = async (event, context, next) => {
const user = await authenticate()
const userContext = { ...context, user }
return await next(event, userContext)
}
// Create a middleware that relies on the user being there, and fetches additional information.
const orderMiddleware = async (event, context, next) => {
const { user } = context
const orders = await orderService.getOrders(user.email)
const orderContext = { ...context, orders }
return await next(event, orderContext)
}
// Your regular lambda handler.
const apiHandler = async (event, context) => {
const { user, orders } = context
// ... your specific logic
return { statusCode: 200, body: JSON.stringify({ message: 'success' }) }
}
// Export your handler with middlewares.
export const handler = withMiddlewares([authMiddleware, orderMiddleware], apiHandler)
import { withMiddlewares } from 'lambda-express-middlewares'
const orderRegex = new RegExp(/^[0-9A-F]{8}-[0-9A-F]{4}-4[0-9A-F]{3}-[89AB][0-9A-F]{3}-[0-9A-F]{12}$/i)
// Your custom middleware, takes in an additional next function, similar to express.
const validateOrderMiddleware = async (event, context, next) => {
const orderId = event.pathParameters.orderId
if !(orderRegex.test(orderId)) {
// Validation failed, you can therefore exit early by returning and not invoking the *next* function.
return { statusCode: 400, body: JSON.stringify(null) }
}
// Validation passed, invoke the handler!
return await next(event, context)
}
// Your regular lambda handler.
const apiHandler = async (event, context) => {
// At this point you know that the orderId has been validated
const orderId = event.pathParameters.orderId
// ... your specific logic
return { statusCode: 200, body: JSON.stringify({ message: 'success' }) }
}
// Export your handler with middlewares.
export const handler = withMiddlewares([validateOrderMiddleware], apiHandler)
import { withMiddlewares } from 'lambda-express-middlewares'
// Your custom middleware, takes in an additional next function, similar to express.
const cleanupMiddleware = async (event, context, next) => {
try {
const res = await next(event, context)
return res
} catch (e) {
console.log()
return { statusCode: 500, body: { message: 'e.message' } }
} finally {
// Some code to cleanup
}
}
// Your regular lambda handler.
const apiHandler = async (event, context) => {
const result = await someService(event)
return { statusCode: 200, body: JSON.stringify({ message: 'success' }) }
}
// Export your handler with middlewares.
export const handler = withMiddlewares([validateOrderMiddleware], apiHandler)
For examples in typescript, check out the test file in this project. There you will find some examples on how to type your middleware functions.