Easiest form of process communication in Scala

Question

What I want to do: I want to add communication capabilities to a couple of applications (soon to be jar libraries for Java) in Scala, and I want to do it in the most painless way, with no Tomcat, wars, paths for GET requests, RPC servers, etc.

What I have done: I've been checking a number of libraries, like Jetty, JAX-RS, Jackson, etc. But then I see the examples and they usually involve many different folders for configuration, WSDL files, etc. Most of the examples lack a main method and I don't have a clear picture about how many additional requirements may they have (e.g. Tomcat).

What I am planning to do: I'm considering to simply open a socket on the "server" to listen, then connect with the "client" and transfer some JSON, in both directions. This should be fairly standard so that I can use other programming languages in compatible ways (e.g. Python).

What I am asking: I would like to know whether there is some library that makes this easier. Not necessarily using raw sockets, but setting up some process communication in just a few lines, maybe not as simple as Node.js, but something similar.

Bonus: It would be cool to

• be able to use other programming languages (e.g. Python) by using open standards
• have authentication

But I don't really need any of those at this point.

Funiculus

Answer 1

I think you need RPC client/server system, I would suggest to take one of these two:

1. Finagle - super flexible and powerful RPC client/server from Finagle. You can define your service with Thrift, and it will generate stubs for client/server in scala. With Thrift it should be straightforward to add Python support.

2. Spray - much smaller library, focused on creating REST services. It's not so powerful as Finagle, however much easier. And REST allows you to use any other clients

3. Remotely - an elegant RPC system for reasonable people. Interesting and very promising project, however maybe difficult to start with because of extensive Scalaz+Shapeless+Macro usage

Protozoal

Answer 2

Honestly if you want something that is cross-language compatible, simple, straightforward, and concise then you do not want to use plain old sockets!

Check out dropwizard. It is amazing and I use it for small and large projects alike! It is usually configured by no more than a single configuration file. It supports authentication too!

Out of the box it gives you really great inter-process communication over JSON (using Jackson) and much much more. There is also pretty decent Scala support for dropwizard.

If you must roll your own then I'd recommend using Jackson for JSON parsing. It's super simple to use and also has great scala support.

Statue

Answer 3

If you've got a "controlled" use case where the client and server are on the same LAN and deployed in tandem, I'd (controversially) recommend Java RMI; it's dumb and JVM-specific (and uses a Java-specific protocol), but it's very simple to use.

If you need something more robust and cross-language, I'd recommend Apache Thrift. You write your interfaces in a platform-independent interface definition language, and it's very clear which changes are compatible and which are not; the thrift compiler generates skeleton interfaces for you to use, and then you just write an implementation of that interface and a couple of lines to start the server (as you can see from the example on the homepage). It's also got good support for async implementations if you need the performance. Thrift itself is reasonably standard and cross-platform, with its own binary protocol, or you can use JSON as a transport if you really want to (I'd recommend against that though).

Araby

Answer 4

RabbitMQ provides one easy way to do what you want without writing a server and implementing your own persistence, flow control, authentication, etc. You can brew or apt-get install it.

• You start up a broker daemon process (i.e. manages message queues)
• In the Scala producer, you can use Maven-provided Java API to send JSON strings without any fuss (e.g. no definition languages) to specified queues
• Then in your other Scala program, connect to the broker, and listen for messages on the queue, and parse the incoming JSON

Because it is so popular, there are many tutorials online for different patterns you may want to use to distribute the messages, e.g. pub/sub, one-to-one, exactly-once delivery, etc.

Immobile