WebContext.md

Web Context

Both in Sitelets and Rpc functions, WebSharper provides a value of type WebSharper.Web.IContext that gives some contextual information about the current request.

Retrieving the context

Sitelets

In Sitelets, the context provided by content-generating functions such as PageContent or CustomContent and by SiteletBuilder.With() implements Web.IContext, so you can use it directly.

Rpc functions

In Rpc functions, the context can be retrieved using the function WebSharper.Web.Remoting.GetContext(). A typical Rpc has the following structure:

// F#:
open WebSharper
open WebSharper.Web

[<Rpc>]
let MyRpcFunction () =
    // Retrieve the context outside of the async {} expression.
    let context = Remoting.GetContext()
    async {
        // Once retrieved, use the context at will here.
        do! Async.Sleep 1000
        return System.IO.File.ReadAllText(context.RootFolder + "/someContent.txt")
    }

// C#:
using WebSharper;
using WebSharper.Web;

[Rpc]
public static async Task<string> MyRpcFunction ()
{
    // Retrieve the context before using await.
    var context = Remoting.GetContext();
    // Once retrieved, use the context at will here.
    await Task.Delay(1000);
    return System.IO.File.ReadAllText(context.RootFolder + "/someContent.txt");
}

Be careful to only call Remoting.GetContext() from the thread from which your function was called. In F#, this means calling it before entering async {}. In C#, this means calling it before any await.

User Sessions

The main reason to use the context is to manage user sessions. The member UserSession has the following members:

• LoginUser : username: string * ?persistent: bool -> Async<unit>

  Logs in the user with the given username. This sets a cookie that is uniquely associated with this username. Set persistent to true if the user session should last beyond the user's current browser session.

• GetLoggedInUser : unit -> Async<string option>

  Retrieves the currently logged in user's username, or None if the user is not logged in.

• Logout : unit -> unit

  Logs the user out.

The implementation of these functions relies on cookies and thus requires that the browser has enabled cookies.

Other Context functionality

• context.RootFolder returns the physical folder on the server machine from which the application is running.