Routing

Routing is responsible for matching incoming HTTP requests and dispatching those requests to the app's HttpHandlers. The breakdown of Endpoint Routing is simple. Associate a specific route pattern and an HTTP verb to an HttpHandler which represents the ongoing processing (and eventual return) of a request.

Bearing this in mind, routing can practically be represented by a list of these "mappings" known in Falco as an HttpEndpoint which bind together: a route, verb and handler.

Note: All of the following examples are fully functioning web apps.

open Falco
open Falco.Routing
open Falco.HostBuilder

webHost [||] {
    endpoints [
        get "/" (Response.ofPlainText "Hello World!")
    ]
}

The preceding example includes a single HttpEndpoint:

The following example shows a more sophisticated HttpEndpoint:

open Falco
open Falco.Routing
open Falco.HostBuilder

webHost [||] {
    endpoints [
        get "/hello/{name:alpha}" (fun ctx ->
            let route = Request.getRoute ctx
            let name = route.GetString "name" ""
            let message = sprintf "Hello %s" name
            Response.ofPlainText message ctx)
    ]
}

The string /hello/{name:alpha} is a route template. It is used to configure how the endpoint is matched. In this case, the template matches:

The second segment of the URL path, {name:alpha}:

An alternative way to express the HttEndpoint above is seen below. Note the omission of the ctx parameter, made possible by the Request module:

open Falco
open Falco.Routing
open Falco.HostBuilder

webHost [||] {
    endpoints [
        get "/hello/{name:alpha}"
            (Request.mapRoute
                (fun route -> route.GetString "name" "John Doe")
                Response.ofPlainText)
    ]
}

Multi-method Endpoints

There are scenarios where you may want to accept multiple HTTP verbs to single a URL. For example, a GET/POST form submission.

To create a "multi-method" endpoint, the all function accepts a list of HTTP Verb and HttpHandler pairs.

open Falco
open Falco.Routing
open Falco.HostBuilder

let form =
    Templates.html5 "en" [] [
        [ Elem.form [ Attr.method "post" ] [
            Elem.input [ Attr.name "name" ]
            Elem.input [ Attr.type' "submit" ] ] ]

webHost [||] {
    endpoints [
        get "/hello" (Response.ofPlainText "/hello")
        all "/form"  [GET, Response.ofHtml form
                      POST, Request.debug] // useful development tool
    ]
}