import snunit._
object HelloWorldExample {
  def main(args: Array[String]): Unit = {
    val server = SyncServerBuilder()
      .withRequestHandler(req =>
        req.send(
          statusCode = StatusCode.OK,
          content = s"Hello world!\n",
          headers = Seq("Content-Type" -> "text/plain")
        )
      )
      .build()

    server.listen()
  }
}

SNUnit is a Scala Native library to write HTTP server applications on top of NGINX Unit. It allows you to write both synchronous and asynchronous web servers with automatic restart on crashes, automatic load balancing of multiple processes, great performance and all the nice NGINX Unit features.

Once built your SNUnit binary, you need to deploy it to the unitd server.

You need to run unitd in a terminal with:

unitd --no-daemon --log /dev/stdout --control unix:control.sock

This will run unitd with a UNIX socket file named control.sock in your current directory.

Then, you need to create a json file with your configuration:

{
  "listeners": {
    "*:8081": {
      "pass": "applications/myapp"
    }
  },
  "applications": {
    "myapp": {
      "type": "external",
      "executable": "snunit/binary/path"
    }
  }
}

Where executable is the binary path which can be absolute or relative to the unitd working directory.

This configuration passes all requests sent to the port 8081 to the application myapp.

To know more about configuring NGINX Unit, refer to their documentation.

To deploy the setting you can use curl:

curl -X PUT --unix-socket control.sock -d @config.json localhost/config

If everything went right, you should see this response:

{
  "success": "Reconfiguration done."
}

In case of problems, you will get a 4xx response like this:

{
  "error": "Invalid configuration.",
  "detail": "Required parameter \"executable\" is missing."
}

Further informations can be found in unitd logs in the running terminal.

SNUnit has two different server implementations.

With SyncServerBuilder you need to call .listen() to start listening. It is a blocking operation so your process is stuck on listening and can't do anything else while listening. Moreover, all the request handlers need to respond directly and can't be implemented using Futures or any other asyncronous mechanism since no Future will run, being the process stuck on the listen() Unit event loop. With AsyncServerBuilder the server is automatically scheduled to run on the scala-native-loop event loop (based on the libuv library). This allows you to complete requests asyncronously using whatever mechanism you prefer. A process can accept multiple requests concurrently, allowing great parallelism.

SNUnit builder pattern allows to implement middlewares. Using middlewares it is possible to handle only some requests and skip others letting other layers to handle them. To pass a request to the next layer you need to call the next() method. Example:

AsyncServerBuilder()
  .withRequestHandler(req => {
    if(req.method == Method.GET) {
      // handle GET requests
    } else {
      req.next() // pass other requests to successive layers
    }
  })

Since ServerBuilders are immutable you can implement middlewares as functions:

def myMiddleware[T <: ServerBuilder](builder: T): T = builder.
  withRequestHandler(req => {
    if(req.method == Method.PUT && headers.get("Content-Type").contains("application/json")) {
      // handle only PUTs with json content
    } else {
      req.next() // pass other requests to successive layers
    }
  })

myMiddleware(AsyncServerBuilder()).build()

You can even implement them as extension methods:

implicit class ServerBuilderOps[T <: ServerBuilder](private val builder: T) extends AnyVal {
  def with404: T = builder.withRequestHandler(req => {
    req.send(StatusCode.NotFound, "Not found", Seq.empty)
  })
}

AsyncServerBuilder()
  .withRequestHandler(req => {
    if(req.method == GET && req.path == "/") {
      Future(req.send(200, "Hello world!", Seq("Content-Type" -> "text/plain")))
    } else req.next()
  })
  .with404
  .build()

SNUnit supports routes using the trail Scala library. You need to import the snunit-routes module and you can write handlers for specific routes:

import snunit._
import snunit.routes._
import trail._

val details  = Root / "details" / Arg[Int]
val userInfo = Root / "user" / Arg[String] & Param[Boolean]("show")

AsyncServerBuilder()
  .withRequestHandler(
    _.withMethod(Method.GET)
      .withRoute(details) { case (req, details) =>
        req.send(200, details, Seq.empty)
      }
  )
  .withRequestHandler(_.withRoute(userInfo) { case (req, (user, show)) =>
    req.send(200, s"User: $user, show: $show", Seq.empty)
  })
  .build()