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rock 0.20.0


Rock provides finagle inspired Service/Filter abstractions to write HTTP services.


Services are simple functions that work on a request, and returns a promise representing the eventual result (or failure). Its represented with the following type:

type ('req, 'res) t = 'req -> 'res Lwt.t

Services can be used to represent any operation and not necessarily something related to HTTP. As an example we can have a service that works on integers and returns a string response:

let my_simple_service : (int, string) Service.t =
  fun request -> Lwt.return (string_of_int request)

In Rock HTTP handlers are also represented as services. They have the type:

type handler = (Request.t, Response.t) Service.t

With this type, one can have an HTTP server like:

open Rock.Rock

let http_service req =
  Lwt.return (Response.of_string "Hello World\n")

Services (For web services these are Rock.Handler) are used to implement an application's business logic.


Filters are also functions, instead of a request they work on services. They can be used to transform a service by performing some specific functions on the request or response, before/after the user's http service. This can be useful to enhance your application with some functionality that needs to shared by multiple services, things like logging, compression, authentication etc.

Example of a simple filter working on the service defined earlier in the page:

let add_two_filter service =
  fun req ->
    service (req + 2)

let new_service = add_two_filter my_simple_service;;

API documentation

  • Rock A tiny clone of ruby's Rack protocol in OCaml. Which is slightly more general and inspired by Finagle. It's not imperative to have this to for such a tiny framework but it makes extensions a lot more straightforward