Removing key from session state

Question

( Noting that my total experience with Suave and back-end web-development in general can be measured in days and counted on one hand )

As part of my project, whenever a user successfully signs in a unique GUID is created and stored within the session state (using a SessionID key). Subsequent requests from that same user pass in that same GUID (from the session state) where it is looked up from a map held in server memory in order to confirm authority.

This part works perfectly using the approach from the Suave documentation . To clarify, my routing path uses statefulForSession along with setSessionValue and getSessionValue as defined in the documentation to set and read the SessionID key referred to above.

When a user logs-out or there has not been any activity for a certain period of time, the GUID will be removed from the server held map above. Is it possible to remove a key ( SessionID ) from the session state? ie... Is there a possible definition for a removeSessionValue ?

Given the underlying StateStore object only exposes set and get , it makes me wonder whether what I'm asking is (somewhat) non-sensical or whether they is some other mechanism I should be using.

From the Suave source code, I'm aware that the session state (which is held in a string -> object map) is ultimately serialised and encrypted within a cookie called st .

Answer 1

What you're asking for seems reasonable, but I don't think there's a clean way to do it given the current StateStore API. That said, you can hack the low-level cookie state as follows:

let removeSessionValue (key : string) : WebPart =
    context (fun ctx ->
        let cookieState =
            {
                serverKey      = ctx.runtime.serverKey
                cookieName     = StateCookie
                userStateKey   = StateStoreType
                relativeExpiry = Session
                secure         = false
            }
        updateCookies cookieState (function
            | None ->
                Map.empty
                    |> ctx.runtime.cookieSerialiser.serialise

            | Some data ->
                try
                    let m = ctx.runtime.cookieSerialiser.deserialise data
                    m
                    |> Map.remove key   // this is where we remove the key
                    |> ctx.runtime.cookieSerialiser.serialise
                with ex ->
                    Map.empty
                    |> ctx.runtime.cookieSerialiser.serialise))

I copied most of this from the Suave source code and tried it quickly to make sure it works, but I can't guarantee its correctness.