Clojure + Ring + API Gateway + Lambda

Serverless is all the rage right now, so I’ve been playing with AWS Lambda, and just by the name itself what could possibly be a better fit for lambda than using Clojure on it? Since I’m mostly interested in webapps I decied to give API Gateway a spin with lambda, sadly it does not immedialty work with the awesome Ring library for building web applications in clojure. Luckily it is reasonably easy to map between the two, and inspired by ring-aws-lambda-adapter some time later I now have a working version of Ring + API Gateway. Together with AWS SAM and AWS SAM CLI this makes for quite a nice, local or cloud, development and hacking experience. And all it took is about 90 lines of Clojure

(ns playground.core
  (:require [ :as json]
            [ :as io]
            [clojure.string :as s]
            [ring.util.codec :as codec]
            [ring.util.response :as r])
   :name playground.core.Handler
   :implements [])
  (:import [ RequestStreamHandler]
           [ InputStream File]
           [clojure.lang ISeq]))

(defn sample-handler
  (r/response "Hello Lambda, from ring!"))

(defn stream->event
  (json/read (io/reader in) :key-fn keyword))

(defn str->int
    (Integer/parseInt s)
    (catch NumberFormatException _)))

(defn maybe-remote-address
  "Take a guess at the remote client ip based on the X-FORWARDED-FOR header.
  This is not perfect as the X-FORWARDED-FOR can easily be spoofed. "
  (some-> x-forwarded-for
          (s/split #"," 2)

(defn maybe-http-version
  "Take http version frim VIA header if present"
  (some-> via
          (s/split #" " 2)

(defn api-gw-event->ring-request
  ([ev] (api-gw-event->ring-request ev nil))
  ([ev ctx]
   (let [headers (get ev :headers {})]
     {:server-port (str->int (:X-Forwarded-Port headers))
      :body (:body ev)
      :server-name (:Host headers)
      :remote-addr (maybe-remote-address (:X-Forwarded-For headers))
      :uri (:path ev)
      :query-string (codec/form-encode (get ev :queryStringParameters {}))
      :scheme (maybe-http-version (:Via headers))
      :request-method (:httpMethod ev)
      :protocol (:X-Forwarded-Proto headers)
      :headers headers
      :event ev
      :context ctx})))

(defmulti wrap-body class)
(defmethod wrap-body String [body] body)
(defmethod wrap-body ISeq [body] (s/join body))
(defmethod wrap-body File [body] (slurp body))
(defmethod wrap-body InputStream [body] (slurp body))

(defn ring-response->api-gw-response
  {:statuCode (:status response)
   :headers (:headers response)
   :body (wrap-body (:body response))})

(defn handle-request
  "Handle an api-gateway request from IN via a RING-HANDLER writing
  response to OUT."
  [ring-handler in out ctx]
  (let [event (stream->event in)
        request (api-gw-event->ring-request event ctx)
        response (ring-handler request)
        event-response (ring-response->api-gw-response response)]
    (with-open [w (io/writer out)]
      (json/write event-response w))))

(defn -handleRequest
  "Implementation for RequestStreamHandler handleRequest using IN
  instream OUT outstream and CTX context object, delegating to
  handle-request to handle request using ring"
  [_ in out ctx]
(handle-request sample-handler in out ctx))

All I want for XMas … is a Brainfuck interpreter in Clojure?

Over the holidays I felt it was time to play with a little Clojure, and since I recently became interested in compilers and interpreters I felt like it was a good idea to start extremly simple, it is the holidays after all. So I built the simplest possible interpreter, a Brainfuck interpreter. It is quite a need excercise and most certainly made me more interesting in building more complex ones.

So here it goes clojure-brainfuck for anyone interested.

First class functions over channels


Inspired by reading go-cache and reading about core.async I was interested how well sending functions over a channel can work, here is the quick hacky result.


Clojure with its access to a very concise way to construct functions lends itself very nicely to the idea of using CSP with first class functions as messages passed over a channel.

(let [c (chan)]
  (>!! c #(zero? %)))

Given that a channel is only consumed by one thread, this provides an interesting way to sync on a data structure without the need for explicit locking as the channel with by itself serialize the operations. This could be quite performant depending on the consumer as multiple operations could be pipelined for example by polling the channel for a batch of operations to be dispatched to different workers.

Why not?

This is mainly an idea taken from playing with go-lang and implemented in clojure, for access to a basic data structure like a map, even so it can now be a transient map, the built in transactions will provide much better performance.