Category Archives: Giraffe

Using Giraffe as a service pipeline in Kestrel

In the previous post we looked at using Kestrel to run an ASP.NET Core application, now we’re going to use Giraffe to build some services.

Giraffe is an F# library to let get started by creating our application code.

  • Create Visual F# | .NET Core | Console App
  • My project is named GiraffeTest
  • Add via NuGet Giraffe and Microsoft.AspNetCore

Replace Program.fs code with the following

open Giraffe
open Microsoft.Extensions.DependencyInjection
open Microsoft.AspNetCore.Builder
open Microsoft.AspNetCore.Hosting
open Microsoft.AspNetCore

let webApp =
    choose [
        GET >=>
            choose [
                routeCif "/hello/%s" (fun name -> text (sprintf "Hello %s" name))
            ]
    ]

type Startup() =
    member this.ConfigureServices (services : IServiceCollection) =
        services.AddGiraffe() |> ignore

    member this.Configure (app : IApplicationBuilder) =
        app.UseGiraffe webApp

[<EntryPoint>]
let main _ =
    WebHost.CreateDefaultBuilder()
        .UseKestrel()
        .UseStartup<Startup>()
        .Build()
        .Run()
    0

In the previous post we saw how to create the Kestrel server, so the code in main is exactly the same (apart from obviously being F#) which creates the server and calls the Startup class to configure our middleware. In this case we add Giraffe to the services and runs the Giraffe webApp HTTP handler.

The webApp HTTP handler is basically our filter and routing function.

Run this code up and navigate to localhost:5000/hello/World and we should get Hello World displayed.

We didn’t actually need the GET handler as by default the GET will be used, but it’s shown here to be a little more explicit in what is being implemented. We can also support POST methods using the same syntax as our GET code.

Extending our routes

Giraffe allows us to declare multiple routes which can include static pages. Let’s start off my adding an index.html page to the “Content root path” as displayed when running the application, in my case this is the folder containing Program.fs. I’m using the following index.html

<html>
    <body>
        Hello World
    </body>
</html>

Now add a new route to the route section of the webApp. i.e.

choose [
    routeCif "/hello/%s" (fun name -> text (sprintf "Hello %s" name))
    route "/" >=> htmlFile "index.html"
]

This has now added a route for localhost:5000/ which returns the contents of the index.html file.

A list of different routes can be seen in the source for Routing.fs.

Below is an example of using some different routes

let helloName name = text (sprintf "Hello %s" name)

let webApp =
    choose [
        GET >=>
            choose [
                // case insensitive using anonymous function
                routeCif "/hello/%s" (fun name -> text (sprintf "Hello %s" name))
                route "/"       >=> htmlFile "index.html" 
                route "/error"  >=> setStatusCode 404
                route "/ping"   >=> text "pong"
                // case sensitive use function
                routef "/hello2/%s" helloName
            ]
    ]

Return from the fish (>=>) operator can be marked as different types of result types.
The functions text, htmlFile and other response writes available here ResponseWriters.fs. These include the usual suspects such as XML and JSON. Giraffe also supports Razor, see the NuGet package Giraffe.Razor.

References

Giraffe GitHub repos.