Transmitting commands from a client to a server in Clojure/Java

Question

I'm working on Clojure app where a client needs to send some commands to a server. These will happen in quite large volumes, so I'd like it to be reasonably efficient, both in terms of processing and over-the-wire serialised size.

What would be the best way of doing this in Clojure?

Currently I'm thinking of:

• Creating a simple standard representation e.g. {:command-id 1, :params [1 2 3 "abc"]}
• Serialising using some efficient Java library such as Kryo, and configuring it to understand the Clojure data types
• Hacking together an appropriate Client/Server socket implementation using the Java NIO libraries for the transmission over TCP/IP

However this seems a little convoluted and I'm sure other people have come up with smarter approaches. Any ideas / advice much appreciated!

Answer 1

My answer is not Clojure-specific, but I tend to prefer strings over http - it's reasonably standard and reasonably efficient.

There are libraries for JSON in pretty much every language, I'd go with that (along with your simple standard command format) unless the data volume is massive.

My experience is that the less you need to fiddle with specialized formats, sockets and protocols the more likely it is that you can spend the weekend on the beach :).

I'd reserve anything more complicated than JSON over http until after benchmarking shows a need for something else.

Answer 2

How about Google's protocol buffers? There's a library for dealing with them from Clojure: clojure-protobuf. I remember someone on Freenode #clojure is doing a Haskell vs. OCaml vs. Clojure comparison on a serious task (processing loads of Twitter data); s/he's been lavishing praise on the lib.

Update: Here's the relevant utterance from the #clojure conversation I had in mind.

Answer 3

If parameters aren't too big and source is trusted, why not send s-expressions back and fort,

(eval (read-string "(println \"Hello World\")"))

Clojure being a LISP dialect code is data.

EDIT:

For safety, after reading the string you check the command against a valid set of commands,

(contains? #{'println} 
           (first (read-string "(println \"Hello World\")")))

or you can use a library designed for this such as

http://github.com/Licenser/clj-sandbox