ring-apigw-lambda-proxy

Ring middleware for handling AWS API Gateway Lamdbda proxy Requests and responses

Note! UTF-8 is used as encoding everywhere. HTTP response contains always message-body, so using HEAD should be avoided.

Installation

Add the following to your project.clj :dependencies:

[ring-apigw-lambda-proxy "0.4.0"]

Usage

This library can be used to wrap AWS Lambda API Gateway request and response so that they can be used together with Ring. It takes AWS API Gateway request as input parameter (parsed from JSON with keywords) and creates Ring compatible request map. Same way it transforms Ring response map to AWS API Gateway response map which can be marshaled to JSON back.

Note! This is not a standard Ring Middleware because this has to be always first middleware in a chain.

AWS Lambda JSON Rest API example.

Add ring/ring-core, ring/ring-json,compojure,lambdada and cheshire dependencies.

(ns example
  (:require [uswitch.lambada.core :refer [deflambdafn]]
            [cheshire.core :refer [parse-stream generate-stream]]
            [clojure.java.io :as io]
            [ring.middleware.apigw :refer [wrap-apigw-lambda-proxy]]
            [ring.middleware.params :refer [wrap-params]]
            [ring.middleware.keyword-params :refer [wrap-keyword-params]]
            [ring.middleware.json :refer [wrap-json-params
                                          wrap-json-response]]
            [ring.util.response :as r]
            [compojure.core :refer :all]))

(defroutes app
  (GET "/v1/hello" {params :params}
    (let [name (get params :name "World")]
      (-> (r/response {:message (format "Hello, %s" name)})))))

(def handler (wrap-apigw-lambda-proxy
               (wrap-json-response
                 (wrap-json-params
                   (wrap-params
                     (wrap-keyword-params
                       app))))))

(deflambdafn example.LambdaFn [is os ctx]
  (with-open [writer (io/writer os)]
    (let [request (parse-stream (io/reader is :encoding "UTF-8") true)]
      (generate-stream (handler request) writer))))

It is a common to use AWS Scheduled Events to warmup the Lambda function. For this case ring-apigw-lambda-proxy provides a configuration where Scheduled Event can be mapped to regular Ring GET route like this:

(wrap-apigw-lambda-proxy app {:scheduled-event-route "/warmup"})

(defroutes app
  (GET "/warmup" request {:status 200 :body "Scheduled event for warmup"}))

If you have not configured :scheduled-event-route and Lambda function is called via Scheduled Event the error will be thrown.

Design

This is a tiny library with zero dependencies. That is the reason why JSON parsing of AWS API Gateway request/response is not included.