Adjusting the max POST body size

[namooh]

I would like to adjust the POST max body size for my server, as 200KB default is pretty low for my use case. I have found the solution to modify the jetty server: https://wiki.eclipse.org/Jetty/Howto/Configure_Form_Size

The solution is basically to set the system property org.eclipse.jetty.server.Request.maxFormContentSize. This can be done in leiningen easily, but is not very production friendly.

Is there anyway to set this property in Ring? It would be great if run-jetty function accepts the argument above.

[weavejester]

You might be able to set this via .setAttribute on the server instance. So something like:

(run-jetty
 handler
 {:port 3000
  :configurator #(.setAttribute % "org.eclipse.jetty.server.Request.maxFormContentSize" -1)})

Let me know if that works.

[namooh]

@weavejester Thanks. I tried this but it did not affect the behavior of the server. I think the maxFormContentSize is first set from ContextHandler and falls back to the server attribute if there is no context.

From Jetty 7.6 Java Docs

The form content that a request can process is limited to protect from Denial of Service attacks. The size in bytes is limited by ContextHandler.getMaxFormContentSize() or if there is no context then the "org.eclipse.jetty.server.Request.maxFormContentSize" Server attribute. The number of parameters keys is limited by ContextHandler.getMaxFormKeys() or if there is no context then the "org.eclipse.jetty.server.Request.maxFormKeys" Server attribute.

Do you know if Ring uses a Context handler by default, and if so where to get it?

[weavejester]

Unfortunately I don't know. Jetty is labyrinthine in its class structure, and none of it is documented beyond a minimal set of Javadocs. I tried to figure out where the ContextHandler is introduced, but I think it'll require a significant investment of time going through the source code.

Also, the Jetty version is 9, so the Jetty 7.6 docs you have might be outdated.

[weavejester]

Perhaps the best option is simply to use another adapter, like Ring-Undertow or Http-Kit. It's a bit of a cop-out, but it might save you time in the long run.

[namooh]

@weavejester Thank you. I was lost in Jetty Docs and source code as well. I am thinking to change the adaptor to http-kit as it allows to explicitly set max-body-size.

[jszakmeister]

@namooh How do you know this is the right approach? What did you see that led you to this being the knob that needed to be adjusted? I ask because from my reading of the Jetty docs and examples, I don't think Jetty is introducing a ContextHandler itself. It sounds like the approach is to set a ContextHandler as the handler for the server instance. Perhaps something like this:

(let [server (create-server (dissoc options :configurator))
      proxyf (if (:async? options) async-proxy-handler proxy-handler)
      context-handler (ContextHandler. (proxyf handler))]
  (when-let [max-form-content-size (:max-form-content-size options)]
    (.maxFormContentSize context-handler max-form-content-size))
  (.setHandler server context-handler)
  (when-let [configurator (:configurator options)]
    (configurator server))
  (try
    (.start server)
    (when (:join? options true)
      (.join server))
    server
    (catch Exception ex
      (.stop server)
      (throw ex))))

Note: the above is completely untested, but seems to be what is suggested by the Jetty docs (though we may have to set a prefix too). This is what I'm basing this on: https://www.eclipse.org/jetty/documentation/9.3.x/embedding-jetty.html#_embedding_contexts

But, I'm not convinced that it's a ContextHandler problem. Perhaps in this case, it's really some other size that's not adjusted properly for your situation.