Executive Summary

Sinatra like web toolkit for OCaml based on cohttp & lwt

Design Goals

• Opium should be very small and easily learnable. A programmer should be instantly productive when starting out.
• Opium should be extensible using independently developed plugins. This is a Rack inspired mechanism borrowed from Ruby. The middleware mechanism in Opium is called Rock.
• It should maximize use of creature comforts people are used to in other languages. Such as sexplib, fieldslib, cow, a decent standard library.

Installation

NOTE: At this point there's a good chance this library will only work against cohttp master. Once cohttp 1.0 is released then this library will always be developed against OPAM version.

Stable

The latest stable version is available on opam

$ opam install opium

Master

If you'd like to live on the bleeding edge (which is sometimes more stable than stable)

$ opam pin add opium --dev-repo

Examples

All examples are built once the necessary dependencies are installed (cow). $ make will compile all examples. The binaries are located in _build/examples/

Hello World

Here's a simple hello world example to get your feet wet:

$ cat hello_world.ml

#include "examples/hello_world.ml"

compile with:

$ ocamlbuild -pkg opium.unix hello_world.native

and then call

    ./hello_world.native &
curl http://localhost:3000/person/john_doe/42

You should see a JSON message.

Middleware

The two fundamental building blocks of opium are:

• Handlers: Rock.Request.t -> Rock.Response.t Deferred.t
• Middleware: Rock.Handler.t -> Rock.Handler.t

Almost every all of opium's functionality is assembled through various middleware. For example: debugging, routing, serving static files, etc. Creating middleware is usually the most natural way to extend an opium app.

Here's how you'd create a simple middleware turning away everyone's favourite browser.

#include "examples/middleware_ua.ml"

Compile with:

$ ocamlbuild -pkg opium.unix middleware_ua.native

Here we also use the ability of Opium to generate a cmdliner term to run your app. Run your executable with the -h to see the options that are available to you. For example:

# run in debug mode on port 9000
$ ./middleware_ua.native -p 9000 -d