package session

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A session manager for your everyday needs


Dune Dependency






ocaml-session is an session manager that handles cookie headers and backend storage for HTTP servers. The library supports CoHTTP and Webmachine; Async and Lwt; and pluggable backing stores based on a functor interface.


Install the library and its depenencies via OPAM:

opam install session

Basic Usage

Below is a simplified implementation of session-based user authentication, one of the most common use-cases of sessions. The server will respond with 401 Unauthorized for every path until the client visits /authenticate, after which all paths will respond with 200 OK.

module Session = struct
  module Backend = Session_postgresql_lwt
  include Session
  include Session_cohttp_lwt.Make(Backend)

let cookie_key = "__session"

let callback conn { Request.headers; uri } body =
  Session.of_header backend cookie_key headers
  >>= function
    | Ok (Some session) when authorized session ->
      Server.respond ~status:`OK ()
    | _ ->
      if Uri.path = "/authenticate" then
        let session = Session.generate backend "<user_id>" in
        let headers = Header.of_list (Session.to_cookie_hdrs cookie_key session) in
        Server.respond ~headers ~status:`OK ()
        Server.respond ~status:`Unauthorized ()

There are additional examples for both CoHTTP and webmachine in the examples subdirectory of this project. These examples use a session to count the number of HTTP requests that the server has received from a client. To build them, reconfigure the build to enable examples, an i/o library of our choice (e.g., Async or Lwt), as well as the library you're using to build your server (e.g., CoHTTP or Webmachine):

./configure --enable-examples --enable-async --enable-cohttp


To install development versions of the library, pin the package from the root of the repository:

opam pin add .

You can install the latest changes by committing them to the local git repository and running:

opam upgrade session

For building and running the tests during development, you will need to install the oUnit package and reconfigure the build process to enable tests:

opam install oUnit
./configure --enable-tests
make && make test


BSD3, see LICENSE file for its text.