Clojure Q&A - Recent questions tagged ring

Problem in production when removing wrap-reload

Sat, 25 Apr 2020 16:47:42 +0000

I'm setting up a service that returns a JSON, thanks to Ring, Compojure and Jetty. The problem I have is when I want to use Nginx as a reverse proxy. If I use the following handlers it doesn't work.

(def wrapped-handler
  ;; Handler middlewares
  (-> all-routes
      (wrap-defaults (assoc-in site-defaults [:security :anti-forgery] false))
      wrap-params
      wrap-session
      ))

The message I get back is

java.lang.NullPointerException
        at ring.adapter.jetty$proxy_handler$fn__6990.invoke(jetty.clj:26)
        at ring.adapter.jetty.proxy$org.eclipse.jetty.server.handler.AbstractHandler$ff19274a.handle(Unknown Source)
        at org.eclipse.jetty.server.handler.HandlerWrapper.handle(HandlerWrapper.java:132)
        at org.eclipse.jetty.server.Server.handle(Server.java:503)
        at org.eclipse.jetty.server.HttpChannel.handle(HttpChannel.java:364)
        at org.eclipse.jetty.server.HttpConnection.onFillable(HttpConnection.java:260)
        at org.eclipse.jetty.io.AbstractConnection$ReadCallback.succeeded(AbstractConnection.java:305)
        at org.eclipse.jetty.io.FillInterest.fillable(FillInterest.java:103)
        at org.eclipse.jetty.io.ChannelEndPoint$2.run(ChannelEndPoint.java:118)
        at org.eclipse.jetty.util.thread.QueuedThreadPool.runJob(QueuedThreadPool.java:765)
        at org.eclipse.jetty.util.thread.QueuedThreadPool$2.run(QueuedThreadPool.java:683)
        at java.base/java.lang.Thread.run(Thread.java:834)

But if I add wrap-reload everything goes right.

(def wrapped-handler
  ;; Handler middlewares
  (-> all-routes
      (wrap-defaults (assoc-in site-defaults [:security :anti-forgery] false))
      wrap-params
      wrap-session
      (#(if (config :debug) (wrap-reload %)))
      ))

My setup with Nginx is as follows.

server {        

        server_name domain.com;

        location / {
            proxy_pass http://localhost:9000/;
            proxy_set_header Host $http_host;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_set_header X-Forwarded-Proto $scheme;
            proxy_redirect  off;
        }
}

Is it safe to leave wrap-reload in production?
What have I left behind?

Thank you all in advance.

Role of application state in a Ring webserver

Thu, 19 Mar 2020 17:18:33 +0000

Getting started with Ring. I am most familiar with web development in php, in which the php application is booted afresh on every request, which is proxied to by the web server, e.g. apache.

That of course means it is not possible that the php application itself can maintain any in-memory state (PHP enforcing a "shared nothing" architecture). So, I do note that in other languages such as java and Clojure the server is a long running process and there is therefore an option for global state. I aim to stick to 12-factor principles, though, and so I understand application state should be avoided, as if I was programming in php, perhaps.

I've got initial awareness about the reloaded workflow and such like. Of course, that makes sense in many cases.

However, since I am aiming that the web app I now write have no global state, would that mean I don't actually need a reloaded workflow (and hence lein ring would be enough - just to reload the code, not the state).

I wonder if there is anything I am missing. e.g. what if I change a config variable, maybe that counts as 'state', and would require a reload. Yes, I'll test this myself in due course to find out.

But just looking for any general tips / discussion on these points to help get off on the right foot.

Redirection with Ring forcing GET

Fri, 20 Sep 2019 15:46:10 +0000

Hi! I'm having a problem doing a redirection with Ring. If I'm on a page with the POST method, doing the redirection will keep it. How can I force all my redirections to be GET? Thank you in advance.