Hi folks,
Mark McGranaghan and I have recently been working on new functionality
for Ring, a web application library for Clojure. Ring is similar to
Rack on Ruby, and provides a simple, functional interface for handling
HTTP requests.
We've recently added support for urlencoded parameters and cookies,
and next we plan on adding session support to the mix. What we'd like
is to get some feedback from the Clojure community on how best to
implement session support.
Currently we have two possible designs:
Design 1:
The session is stored as an mutable atom map in (request :session). To
update the session, use the standard Clojure swap! function, e.g.
(defn handler [request]
(let [session (request :session)
counter (@session :counter)]
(swap! session assoc :counter (inc counter))
{:status 200
:headers {}
:body (str "You've visited this page " counter " times!")}))
The reasoning behind this approach is that sessions are mutable maps
associated with the request, and thus the most natural way to
represent them is via an (atom {}) on the request.
Design 2:
The session is an immutable map in (request :session). To update the
session, add the updated session to the response, e.g.
(defn handler [request]
(let [session (request :session)
counter (session :counter)]
{:status 200
:headers {}
:session (assoc session :counter (inc counter))
:body (str "You've visited this page " counter " times!")}))
The reasoning behind this approach is that a more functional design
has more in common with other parts of Ring, and allows handlers to be
pure functions, even if they use sessions.
I favour design 1, whilst Mark favours design 2.
I've also had an email suggesting that instead of the session being
completely replaced by the session map on the response, it is instead
only updated. This could be achieved by adding an update function to
the :session key, or perhaps to merge the response session with the
existing session, removing any key with a value of nil.
Please let us know what you think is the best approach listed here, or
if you have an entirely new design we've not thought of.
Thanks in advance,
- James
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