A functional ASP.NET Core micro web framework for building rich web applications.

Read this blog post on functional ASP.NET Core for more information.

Windows	Linux

Giraffe was formerly known as ASP.NET Core Lambda and has been later renamed to Giraffe to better distinguish from AWS Lambda and to establish its own unique brand.

The old NuGet package has been unlisted and will no longer receive any updates. Please use the Giraffe NuGet package going forward.

• About
• Basics
  • HttpHandler
  • Combinators
    • compose (>=>)
    • choose
  • Tasks
• Default HttpHandlers
  • GET, POST, PUT, PATCH, DELETE
  • mustAccept
  • challenge
  • signOff
  • requiresAuthentication
  • requiresRole
  • requiresRoleOf
  • clearResponse
  • route
  • routef
  • routeCi
  • routeCif
  • routeBind
  • routeStartsWith
  • routeStartsWithCi
  • subRoute
  • subRouteCi
  • setStatusCode
  • setHttpHeader
  • setBody
  • setBodyAsString
  • text
  • json
  • xml
  • negotiate
  • negotiateWith
  • htmlFile
  • renderHtml
  • redirectTo
  • warbler
• Additional HttpHandlers
  • Giraffe.Razor
    • razorView
    • razorHtmlView
  • Giraffe.DotLiquid
    • dotLiquid
    • dotLiquidTemplate
    • dotLiquidHtmlView
• Custom HttpHandlers
• Model Binding
  • BindJson
  • BindXml
  • BindForm
  • BindQueryString
  • BindModel
• Error Handling
• Installation
• Sample applications
• Benchmarks
• Building and developing
• Contributing
• Contributors
• Blog posts
• License
• Contact and Slack Channel

Giraffe is an F# micro web framework for building rich web applications. It has been heavily inspired and is similar to Suave, but has been specifically designed with ASP.NET Core in mind and can be plugged into the ASP.NET Core pipeline via middleware. Giraffe applications are composed of so called HttpHandler functions which can be thought of a mixture of Suave's WebParts and ASP.NET Core's middleware.

If you'd like to learn more about the motivation of this project please read my blog post on functional ASP.NET Core (some code samples in this blog post might be outdated today).

Giraffe is intended for developers who want to build rich web applications on top of ASP.NET Core in a functional first approach. ASP.NET Core is a powerful web platform which has support by Microsoft and a huge developer community behind it and Giraffe is aimed at F# developers who want to benefit from that eco system.

It is not designed to be a competing web product which can be run standalone like NancyFx or Suave, but rather a lean micro framework which aims to complement ASP.NET Core where it comes short for functional developers. The fundamental idea is to build on top of the strong foundation of ASP.NET Core and re-use existing ASP.NET Core building blocks so F# developers can benefit from both worlds.

You can think of Giraffe as the functional counter part of the ASP.NET Core MVC framework.

The main building block in Giraffe is a so called HttpHandler:

type HttpFuncResult = Task<HttpContext option>
type HttpFunc = HttpContext -> HttpFuncResult
type HttpHandler = HttpFunc -> HttpContext -> HttpFuncResult

A HttpHandler is a simple function which takes two curried arguments, a HttpFunc and a HttpContext, and returns a HttpContext (wrapped in an option and Task workflow) when finished.

Given that a HttpHandler receives and returns an ASP.NET Core HttpContext there is literally nothing which cannot be done from within a Giraffe web application which couldn't be done from a regular ASP.NET Core (MVC) application either.

Each HttpHandler can process an incoming HttpRequest before passing it further down the pipeline by invoking the next HttpFunc or short circuit the execution by returning an option of Some HttpContext.

If a HttpHandler decides to not process an incoming HttpRequest at all, then it can return None instead. In this case another HttpHandler might pick up the incoming HttpRequest or the middleware will defer to the next RequestDelegate from the ASP.NET Core pipeline.

The easiest way to get your head around a Giraffe HttpHandler is to think of it like a functional ASP.NET Core middleware. Each handler has the full HttpContext at its disposal and can decide whether it wants to return Some HttpContext, None or pass it on to the "next" HttpFunc.

Please check out the sample applications for a demo as well as a real world example.

The compose combinator combines two HttpHandler functions into one:

let compose (handler1 : HttpHandler) (handler2 : HttpHandler) : HttpHandler =
    fun (next : HttpFunc) ->
        let func = next |> handler2 |> handler1
        fun (ctx : HttpContext) ->
            match ctx.Response.HasStarted with
            | true  -> next ctx
            | false -> func ctx

It is the main combinator as it allows composing many smaller HttpHandler functions into a bigger web application.

If you would like to learn more about the >=> (fish) operator then please check out Scott Wlaschin's blog post on Railway oriented programming.

let app = route "/" >=> setStatusCode 200 >=> text "Hello World"

The choose combinator function iterates through a list of HttpHandler functions and invokes each individual handler until the first HttpHandler returns a result.

let app =
    choose [
        route "/foo" >=> text "Foo"
        route "/bar" >=> text "Bar"
    ]

Another important aspect to Giraffe is that it natively works with .NET's Task and Task<'T> objects instead of relying on F#'s async {} workflows. The main benefit of this is that it removes the necessity of converting back and forth between tasks and async workflows when building a Giraffe web application (because ASP.NET Core works only with tasks out of the box).

For this purpose Giraffe has it's own task {} workflow which comes with the Giraffe.Tasks module. Syntactically it works identical to F#'s async workflows:

open Giraffe.Tasks
open Giraffe.HttpHandlers

let personHandler =
    fun (next : HttpFunc) (ctx : HttpContext) ->
        task {
            let! person = ctx.BindModel<Person>()
            return! json person next ctx
        }

The task {} workflow is not strictly tied to Giraffe and can be used from anywhere in an F# application:

open Giraffe.Tasks

let readFileAndDoSomething (filePath : string) =
    task {
        use stream = new FileStream(filePath, FileMode.Open)
        use reader = new StreamReader(stream)
        let! contents = reader.ReadToEndAsync()

        // do something with contents

        return contents
    }

If you were to write the same code with F#'s async workflow it would look something like this:

let readFileAndDoSomething (filePath : string) =
    async {
        use stream = new FileStream(filePath, FileMode.Open)
        use reader = new StreamReader(stream)
        let! contents =
            reader.ReadToEndAsync()
            |> Async.AwaitTask

        // do something with contents

        return contents
    }

Apart from the convenience of not having to convert from a Task<'T> into an Async<'T> workflow and then back again into a Task<'T> when returning back to the ASP.NET Core pipeline it also proved to improve overall performance by two figure % in comparison to F#'s async implementation.

The original code for Giraffe's task implementation has been taken from Robert Peele's TaskBuilder.fs and gradually modified to better fit Giraffe's use case for a highly scalable ASP.NET Core web application.

GET, POST, PUT, PATCH, DELETE filters a request by the specified HTTP verb.

let app =
    choose [
        GET  >=> route "/foo" >=> text "GET Foo"
        POST >=> route "/foo" >=> text "POST Foo"
        route "/bar" >=> text "Always Bar"
    ]

mustAccept filters a request by the Accept HTTP header. You can use it to check if a client accepts a certain mime type before returning a response.

let app =
    mustAccept [ "text/plain"; "application/json" ] >=>
        choose [
            route "/foo" >=> text "Foo"
            route "/bar" >=> json "Bar"
        ]

challenge challenges an authentication with a specified authentication scheme (authScheme).

let mustBeLoggedIn =
    requiresAuthentication (challenge "Cookie")

let app =
    choose [
        route "/ping" >=> text "pong"
        route "/admin" >=> mustBeLoggedIn >=> text "You're an admin"
    ]

signOff signs off the currently logged in user.

let app =
    choose [
        route "/ping" >=> text "pong"
        route "/logout" >=> signOff "Cookie" >=> text "You have successfully logged out."
    ]

requiresAuthentication validates if a user is authenticated/logged in. If the user is not authenticated then the handler will execute the authFailedHandler function.

let mustBeLoggedIn =
    requiresAuthentication (challenge "Cookie")

let app =
    choose [
        route "/ping" >=> text "pong"
        route "/user" >=> mustBeLoggedIn >=> text "You're a logged in user."
    ]

requiresRole validates if an authenticated user is in a specified role. If the user fails to be in the required role then the handler will execute the authFailedHandler function.

let accessDenied = setStatusCode 401 >=> text "Access Denied"

let mustBeAdmin =
    requiresAuthentication accessDenied
    >=> requiresRole "Admin" accessDenied

let app =
    choose [
        route "/ping" >=> text "pong"
        route "/admin" >=> mustBeAdmin >=> text "You're an admin."
    ]

requiresRoleOf validates if an authenticated user is in one of the supplied roles. If the user fails to be in one of the required roles then the handler will execute the authFailedHandler function.

let accessDenied = setStatusCode 401 >=> text "Access Denied"

let mustBeSomeAdmin =
    requiresAuthentication accessDenied
    >=> requiresRoleOf [ "Admin"; "SuperAdmin"; "RootAdmin" ] accessDenied

let app =
    choose [
        route "/ping" >=> text "pong"
        route "/admin" >=> mustBeSomeAdmin >=> text "You're an admin."
    ]

clearResponse tries to clear the current response. This can be useful inside an error handler to reset the response before writing an error message to the body of the HTTP response object.

let errorHandler (ex : Exception) (logger : ILogger) =
    clearResponse
    >=> setStatusCode 500
    >=> text ex.Message

let webApp =
    choose [
        route "/foo" >=> text "Foo"
        route "/bar" >=> text "Bar"
    ]

type Startup() =
    member __.Configure (app : IApplicationBuilder)
                        (env : IHostingEnvironment)
                        (loggerFactory : ILoggerFactory) =
        app.UseGiraffeErrorHandler errorHandler
        app.UseGiraffe webApp

route compares a given path with the actual request path and short circuits if it doesn't match.

let app =
    choose [
        route "/"    >=> text "Index path"
        route "/foo" >=> text "Foo"
        route "/bar" >=> text "Bar"
    ]

routef matches a given format string with the actual request path. On success it will resolve the arguments from the format string and invoke the given HttpHandler with them.

The following format placeholders are currently supported:

• %b for bool
• %c for char
• %s for string
• %i for int32
• %d for int64 (this is custom to Giraffe)
• %f for float/double

let app =
    choose [
        route  "/foo" >=> text "Foo"
        routef "/bar/%s/%i" (fun (name, age) ->
            // name is of type string
            // age is of type int
            text (sprintf "Name: %s, Age: %i" name age))
    ]

routeCi is the case insensitive version of route.

// "/FoO", "/fOO", "/bAr", etc. will match as well

let app =
    choose [
        routeCi "/"    >=> text "Index path"
        routeCi "/foo" >=> text "Foo"
        routeCi "/bar" >=> text "Bar"
    ]

routeCif is the case insensitive version of routef.

let app =
    choose [
        route  "/foo" >=> text "Foo"
        routeCif "/bar/%s/%i" (fun (name, age) ->
            text (sprintf "Name: %s, Age: %i" name age))
    ]

routeBind matches and parses a request path with a given object model. On success it will resolve the arguments from the route and create an instance of type 'T and invoke the given HttpHandler with it.

type Person =
    {
        FirstName : string
        LastName : string
    }

let app =
    choose [
        route  "/foo/{firstName}/{lastName}" >=> routeBind<Person> (fun person ->
            sprintf "%s %s" person.FirstName person.LastName
            |> text)
    ]

routeStartsWith checks if the current request path starts with the given string. This can be useful when combining with other http handlers, e.g. to validate a subset of routes for authentication.

let app =
    routeStartsWith "/api/" >=>
        requiresAuthentication (challenge "Cookie") >=>
            choose [
                route "/api/v1/foo" >=> text "Foo"
                route "/api/v1/bar" >=> text "Bar"
            ]

routeStartsWithCi is the case insensitive version of routeStartsWith.

let app =
    routeStartsWithCi "/api/v1/" >=>
        choose [
            route "/api/v1/foo" >=> text "Foo"
            route "/api/v1/bar" >=> text "Bar"
        ]

subRoute checks if the current path begins with the given path and will invoke the passed in handler if it was a match. The given handler (and any nested handlers within it) should omit the already applied path for subsequent route evaluations.

let app =
    subRoute "/api"
        (choose [
            subRoute "/v1"
                (choose [
                    route "/foo" >=> text "Foo 1"
                    route "/bar" >=> text "Bar 1" ])
            subRoute "/v2"
                (choose [
                    route "/foo" >=> text "Foo 2"
                    route "/bar" >=> text "Bar 2" ]) ])

subRouteCi is the case insensitive version of subRoute.

let app =
    subRouteCi "/api"
        (choose [
            subRouteCi "/v1"
                (choose [
                    route "/foo" >=> text "Foo 1"
                    route "/bar" >=> text "Bar 1" ])
            subRouteCi "/v2"
                (choose [
                    route "/foo" >=> text "Foo 2"
                    route "/bar" >=> text "Bar 2" ]) ])

setStatusCode changes the status code of the HttpResponse.

let app =
    choose [
        route  "/foo" >=> text "Foo"
        setStatusCode 404 >=> text "Not found"
    ]

setHttpHeader sets or modifies a HTTP header of the HttpResponse.

let app =
    choose [
        route  "/foo" >=> text "Foo"
        setStatusCode 404 >=> setHttpHeader "X-CustomHeader" "something" >=> text "Not found"
    ]

setBody sets or modifies the body of the HttpResponse. This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more.

let app =
    choose [
        route  "/foo" >=> setBody (Encoding.UTF8.GetBytes "Some string")
    ]

setBodyAsString sets or modifies the body of the HttpResponse. This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more.

let app =
    choose [
        route  "/foo" >=> setBodyAsString "Some string"
    ]

text sets or modifies the body of the HttpResponse by sending a plain text value to the client.. This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more.

The different between text and setBodyAsString is that this http handler also sets the Content-Type HTTP header to text/plain.

let app =
    choose [
        route  "/foo" >=> text "Some string"
    ]

json sets or modifies the body of the HttpResponse by sending a JSON serialized object to the client. This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more. It also sets the Content-Type HTTP header to application/json.

type Person =
    {
        FirstName : string
        LastName  : string
    }

let app =
    choose [
        route  "/foo" >=> json { FirstName = "Foo"; LastName = "Bar" }
    ]

xml sets or modifies the body of the HttpResponse by sending an XML serialized object to the client. This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more. It also sets the Content-Type HTTP header to application/xml.

[<CLIMutable>]
type Person =
    {
        FirstName : string
        LastName  : string
    }

let app =
    choose [
        route  "/foo" >=> xml { FirstName = "Foo"; LastName = "Bar" }
    ]

negotiate sets or modifies the body of the HttpResponse by inspecting the Accept header of the HTTP request and deciding if the response should be sent in JSON or XML or plain text. If the client is indifferent then the default response will be sent in JSON.

This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more.

[<CLIMutable>]
type Person =
    {
        FirstName : string
        LastName  : string
    }
    // The ToString method is used to serialize the object as text/plain during content negotiation
    override this.ToString() =
        sprintf "%s %s" this.FirstName this.LastNam

let app =
    choose [
        route  "/foo" >=> negotiate { FirstName = "Foo"; LastName = "Bar" }
    ]

negotiateWith sets or modifies the body of the HttpResponse by inspecting the Accept header of the HTTP request and deciding in what mimeType the response should be sent. A dictionary of type IDictionary<string, obj -> HttpHandler> is used to determine which obj -> HttpHandler function should be used to convert an object into a HttpHandler for a given mime type.

This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more.

[<CLIMutable>]
type Person =
    {
        FirstName : string
        LastName  : string
    }

// xml and json are the two HttpHandler functions from above
let rules =
    dict [
        "*/*"             , xml
        "application/json", json
        "application/xml" , xml
    ]

let app =
    choose [
        route  "/foo" >=> negotiateWith rules { FirstName = "Foo"; LastName = "Bar" }
    ]

htmlFile sets or modifies the body of the HttpResponse with the contents of a physical html file. This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more.

This http handler takes a relative path of a html file as input parameter and sets the HTTP header Content-Type to text/html.

let app =
    choose [
        route  "/" >=> htmlFile "index.html"
    ]

renderHtml is a more functional way of generating HTML by composing HTML elements in F# to generate a rich Model-View output.

It is based on Suave's Experimental Html and bears some resemblance with Elm.

Create a function that accepts a model and returns an XmlNode:

open Giraffe.XmlViewEngine

let model = { Name = "John Doe" }

let layout (content: XmlNode list) =
    html [] [
        head [] [
            title [] (encodedText "Giraffe")
        ]
        body [] content
    ]

let partial () =
    p [] (encodedText "Some partial text.")

let personView model =
    [
        div [] [
                h3 [] (sprintf "Hello, %s" model.Name |> encodedText)
            ]
        div [] [partial()]
    ] |> layout

let app =
    choose [
        route "/" >=> (personView model |> renderHtml)
    ]

redirectTo uses a 302 or 301 (when permanent) HTTP response code to redirect the client to the specified location. It takes in two parameters, a boolean flag denoting whether the redirect should be permanent or not and the location to redirect to.

let app =
    choose [
        route "/"          >=> redirectTo false "/foo"
        route "/permanent" >=> redirectTo true "http://example.org"
        route "/foo"       >=> text "Some string"
    ]

If your route is not returning a static response, then you should wrap your function with a warbler.

// unit -> string
let time() =
    System.DateTime.Now.ToString()

let webApp =
    choose [
        GET >=>
            choose [
                route "/once"      >=> (time() |> text)
                route "/everytime" >=> warbler (fun _ -> (time() |> text))
            ]
    ]

Functions in F# are eagerly evaluated and the /once route will only be evaluated the first time. A warbler will help to evaluate the function every time the route is hit.

// ('a -> 'a -> 'b) -> 'a -> 'b
let warbler f a = f a a

There's a few additional HttpHandler functions which you can get through referencing extra NuGet packages.

The Giraffe.Razor NuGet package adds additional HttpHandler functions to render Razor views from Giraffe.

razorView uses the official ASP.NET Core MVC Razor view engine to compile a page and set the body of the HttpResponse. This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more.

The razorView handler requires the view name, an object model and the contentType of the response to be passed in. It also requires to be enabled through the AddRazorEngine function during start-up.

Add the razor engine service during start-up:

open Giraffe.Razor.Middleware

type Startup() =
    member __.ConfigureServices (services : IServiceCollection, env : IHostingEnvironment) =
        let viewsFolderPath = Path.Combine(env.ContentRootPath, "views")
        services.AddRazorEngine(viewsFolderPath) |> ignore

Use the razorView function:

open Giraffe.Razor.HttpHandlers

let model = { WelcomeText = "Hello World" }

let app =
    choose [
        // Assuming there is a view called "Index.cshtml"
        route  "/" >=> razorView "text/html" "Index" model
    ]

razorHtmlView is the same as razorView except that it automatically sets the response as text/html.

Add the razor engine service during start-up:

open Giraffe.Razor.Middleware

type Startup() =
    member __.ConfigureServices (services : IServiceCollection, env : IHostingEnvironment) =
        let viewsFolderPath = Path.Combine(env.ContentRootPath, "views")
        services.AddRazorEngine(viewsFolderPath) |> ignore

Use the razorView function:

open Giraffe.Razor.HttpHandlers

let model = { WelcomeText = "Hello World" }

let app =
    choose [
        // Assuming there is a view called "Index.cshtml"
        route  "/" >=> razorHtmlView "Index" model
    ]

The Giraffe.DotLiquid NuGet package adds additional HttpHandler functions to render DotLiquid templates in Giraffe.

dotLiquid uses the DotLiquid template engine to set or modify the body of the HttpResponse. This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more.

The dotLiquid handler requires the content type and the actual template to be passed in as two string values together with an object model. This handler is supposed to be used as the base handler for other http handlers which want to utilize the DotLiquid template engine (e.g. you could create an SVG handler on top of it).

open Giraffe.DotLiquid.HttpHandlers

type Person =
    {
        FirstName : string
        LastName  : string
    }

let template = "<html><head><title>DotLiquid</title></head><body><p>First name: {{ firstName }}<br />Last name: {{ lastName }}</p></body></html>

let app =
    choose [
        route  "/foo" >=> dotLiquid "text/html" template { FirstName = "Foo"; LastName = "Bar" }
    ]

dotLiquidTemplate uses the DotLiquid template engine to set or modify the body of the HttpResponse. This http handler triggers a response to the client and other http handlers will not be able to modify the HTTP headers afterwards any more.

This http handler takes a relative path of a template file, an associated model and the contentType of the response as parameters.

open Giraffe.DotLiquid.HttpHandlers

type Person =
    {
        FirstName : string
        LastName  : string
    }

let app =
    choose [
        route  "/foo" >=> dotLiquidTemplate "text/html" "templates/person.html" { FirstName = "Foo"; LastName = "Bar" }
    ]

dotLiquidHtmlView is the same as dotLiquidTemplate except that it automatically sets the response as text/html.

open Giraffe.DotLiquid.HttpHandlers

type Person =
    {
        FirstName : string
        LastName  : string
    }

let app =
    choose [
        route  "/foo" >=> dotLiquidHtmlView "templates/person.html" { FirstName = "Foo"; LastName = "Bar" }
    ]

Defining a new HttpHandler is fairly easy. All you need to do is to create a new function which matches the signature of HttpFunc -> HttpContext -> Task<HttpContext option>. Through currying your custom HttpHandler can extend the original signature as long as the partial application of your function will still return a function of HttpFunc -> HttpContext -> Task<HttpContext option> (HttpFunc -> HttpFunc).

Defining a custom HTTP handler to partially filter a route:

(After creating this example I added the routeStartsWith HttpHandler to the list of default handlers as it turned out to be quite useful)

let routeStartsWith (subPath : string) =
    fun (next : HttpFunc) (ctx : HttpContext) ->
        if ctx.Request.Path.ToString().StartsWith subPath
        then next ctx
        else Task.FromResult None

Defining another custom HTTP handler to validate a mandatory HTTP header:

let requiresToken (expectedToken : string) (handler : HttpHandler) =
    fun (next : HttpFunc) (ctx : HttpContext) ->
        let token    = ctx.Request.Headers.["X-Token"].ToString()
        let response =
            if token.Equals(expectedToken)
            then handler
            else setStatusCode 401 >=> text "Token wrong or missing"
        response next ctx

Composing a web application from smaller HTTP handlers:

let app =
    choose [
        route "/"       >=> htmlFile "index.html"
        route "/about"  >=> htmlFile "about.html"
        routeStartsWith "/api/v1/" >=>
            requiresToken "secretToken" (
                choose [
                    route "/api/v1/foo" >=> text "something"
                    route "/api/v1/bar" >=> text "bar"
                ]
            )
        setStatusCode 404 >=> text "Not found"
    ] : HttpHandler

The Giraffe.HttpContextExtensions module exposes a default set of model binding functions which extend the HttpContext object.

ctx.BindJson<'T>() can be used to bind a JSON payload to a strongly typed model.

Define an F# record type with the CLIMutable attribute which will add a parameterless constructor to the type:

[<CLIMutable>]
type Car =
    {
        Name   : string
        Make   : string
        Wheels : int
        Built  : DateTime
    }

Then create a new HttpHandler which uses BindJson and use it from an app:

open Giraffe.HttpHandlers
open Giraffe.HttpContextExtensions

let submitCar =
    fun (next : HttpFunc) (ctx : HttpContext) ->
        task {
            // Binds a JSON payload to a Car object
            let! car = ctx.BindJson<Car>()

            // Serializes the Car object back into JSON
            // and sends it back as the response.
            return! json car next ctx
        }

let webApp =
    choose [
        GET >=>
            choose [
                route "/"    >=> text "index"
                route "ping" >=> text "pong" ]
        POST >=> route "/car" >=> submitCar ]

You can test the bind function by sending a HTTP request with a JSON payload:

POST http://localhost:5000/car HTTP/1.1
Host: localhost:5000
Connection: keep-alive
Content-Length: 77
Cache-Control: no-cache
Content-Type: application/json
Accept: */*

{ "Name": "DB9", "Make": "Aston Martin", "Wheels": 4, "Built": "2016-01-01" }

ctx.BindXml<'T>() can be used to bind an XML payload to a strongly typed model.

Define an F# record type with the CLIMutable attribute which will add a parameterless constructor to the type:

[<CLIMutable>]
type Car =
    {
        Name   : string
        Make   : string
        Wheels : int
        Built  : DateTime
    }

Then create a new HttpHandler which uses BindXml and use it from an app:

open Giraffe.HttpHandlers
open Giraffe.HttpContextExtensions

let submitCar =
    fun (next : HttpFunc) (ctx : HttpContext) ->
        task {
            // Binds an XML payload to a Car object
            let! car = ctx.BindXml<Car>()

            // Serializes the Car object back into JSON
            // and sends it back as the response.
            return! json car next ctx
        }

let webApp =
    choose [
        GET >=>
            choose [
                route "/"    >=> text "index"
                route "ping" >=> text "pong" ]
        POST >=> route "/car" >=> submitCar ]

You can test the bind function by sending a HTTP request with an XML payload:

POST http://localhost:5000/car HTTP/1.1
Host: localhost:5000
Connection: keep-alive
Content-Length: 104
Cache-Control: no-cache
Content-Type: application/xml
Accept: */*

<Car>
    <Name>DB9</Name>
    <Make>Aston Martin</Make>
    <Wheels>4</Wheels>
    <Built>2016-01-01</Built>
</Car>

ctx.BindForm<'T>() can be used to bind a form urlencoded payload to a strongly typed model.

Define an F# record type with the CLIMutable attribute which will add a parameterless constructor to the type:

[<CLIMutable>]
type Car =
    {
        Name   : string
        Make   : string
        Wheels : int
        Built  : DateTime
    }

Then create a new HttpHandler which uses BindForm and use it from an app:

open Giraffe.HttpHandlers
open Giraffe.HttpContextExtensions

let submitCar =
    fun (next : HttpFunc) (ctx : HttpContext) ->
        task {
            // Binds a form urlencoded payload to a Car object
            let! car = ctx.BindForm<Car>()

            // Serializes the Car object back into JSON
            // and sends it back as the response.
            return! json car next ctx
        }

let webApp =
    choose [
        GET >=>
            choose [
                route "/"    >=> text "index"
                route "ping" >=> text "pong" ]
        POST >=> route "/car" >=> submitCar ]

You can test the bind function by sending a HTTP request with a form payload:

POST http://localhost:5000/car HTTP/1.1
Host: localhost:5000
Connection: keep-alive
Content-Length: 52
Cache-Control: no-cache
Content-Type: application/x-www-form-urlencoded
Accept: */*

Name=DB9&Make=Aston+Martin&Wheels=4&Built=2016-01-01

ctx.BindQueryString<'T>() can be used to bind a query string to a strongly typed model.

Define an F# record type with the CLIMutable attribute which will add a parameterless constructor to the type:

[<CLIMutable>]
type Car =
    {
        Name   : string
        Make   : string
        Wheels : int
        Built  : DateTime
    }

Then create a new HttpHandler which uses BindQueryString and use it from an app:

open Giraffe.HttpHandlers
open Giraffe.HttpContextExtensions

let submitCar =
    fun (next : HttpFunc) (ctx : HttpContext) ->
        task {
            // Binds a query string to a Car object
            let car = ctx.BindQueryString<Car>()

            // Serializes the Car object back into JSON
            // and sends it back as the response.
            return! json car next ctx
        }

let webApp =
    choose [
        GET >=>
            choose [
                route "/"    >=> text "index"
                route "ping" >=> text "pong"
                route "/car" >=> submitCar ]

You can test the bind function by sending a HTTP request with a query string:

GET http://localhost:5000/car?Name=Aston%20Martin&Make=DB9&Wheels=4&Built=1990-04-20 HTTP/1.1
Host: localhost:5000
Cache-Control: no-cache
Accept: */*

ctx.BindModel<'T>() can be used to automatically detect the method and Content-Type of a HTTP request and automatically bind a JSON, XML,or form urlencoded payload or a query string to a strongly typed model.

Define an F# record type with the CLIMutable attribute which will add a parameterless constructor to the type:

[<CLIMutable>]
type Car =
    {
        Name   : string
        Make   : string
        Wheels : int
        Built  : DateTime
    }

Then create a new HttpHandler which uses BindModel and use it from an app:

open Giraffe.HttpHandlers
open Giraffe.HttpContextExtensions

let submitCar =
    fun (next : HttpFunc) (ctx : HttpContext) ->
        task {
            // Binds a JSON, XML or form urlencoded payload to a Car object
            let! car = ctx.BindModel<Car>()

            // Serializes the Car object back into JSON
            // and sends it back as the response.
            return! json car next ctx
        }

let webApp =
    choose [
        GET >=>
            choose [
                route "/"    >=> text "index"
                route "ping" >=> text "pong" ]
        // Can accept GET and POST requests and
        // bind a model from the payload or query string
        route "/car" >=> submitCar ]

Similar to building a web application in Giraffe you can also set a global error handler, which can react to any unhandled exception of your web application.

The ErrorHandler is a function which accepts an exception object and a default logger and returns a HttpHandler function which is the same as all other HttpHandler functions in Giraffe:

type ErrorHandler = exn -> ILogger -> HttpHandler

For example you could create an error handler which logs the unhandled exception and returns a HTTP 500 response with the error message as plain text:

let errorHandler (ex : Exception) (logger : ILogger) =
    logger.LogError(EventId(), ex, "An unhandled exception has occurred while executing the request.")
    clearResponse
    >=> setStatusCode 500
    >=> text ex.Message

In order to enable the error handler you have to configure the error handler in your application startup:

type Startup() =
    member __.Configure (app : IApplicationBuilder)
                        (env : IHostingEnvironment)
                        (loggerFactory : ILoggerFactory) =
        app.UseGiraffeErrorHandler errorHandler
        app.UseGiraffe webApp

It is recommended to set the error handler as the first middleware in the pipeline, so that any unhandled exception from a later middleware can be caught and processed by the error handling function.

The easiest way to get started with Giraffe is by installing the giraffe-template NuGet package, which adds a new template to your dotnet new command:

dotnet new -i "giraffe-template::*"

Afterwards you can create a new Giraffe application by running dotnet new giraffe.

Install the Giraffe NuGet package:

PM> Install-Package Giraffe

Create a web application and plug it into the ASP.NET Core middleware:

open Giraffe.HttpHandlers
open Giraffe.Middleware

let webApp =
    choose [
        route "/ping"   >=> text "pong"
        route "/"       >=> htmlFile "/pages/index.html" ]

type Startup() =
    member __.Configure (app : IApplicationBuilder)
                        (env : IHostingEnvironment)
                        (loggerFactory : ILoggerFactory) =

        app.UseGiraffe webApp

There are two basic sample applications in the /samples folder. The IdentityApp demonstrates how ASP.NET Core Identity can be used with Giraffe and the SampleApp is a generic sample application covering multiple features.

An example of a live website which uses Giraffe is https://buildstats.info. It uses the XmlViewEngine to build dynamically rich SVG images and Docker to run the application in the Google Container Engine (see GitHub repository).

More sample applications will be added in the future.

Currently Giraffe has only been tested against a simple plain text route and measured the total amount of handled requests per second. The latest result yielded an average of 79093 req/s over a period of 10 seconds, which was only closely after plain Kestrel which was capable of handling 79399 req/s on average.

Please check out Jimmy Byrd's dotnet-web-benchmarks for more details.

Giraffe is built with the latest .NET Core SDK.

You can either install Visual Studio 2017 which comes with the latest SDK or manually download and install the .NET SDK 1.1.

After installation you should be able to run the .\build.ps1 script to successfully build, test and package the library.

The build script supports the following flags:

• -IncludeTests will build and run the tests project as well
• -IncludeSamples will build and test the samples project as well
• -All will build and test all projects
• -Release will build Giraffe with the Release configuration
• -Pack will create a NuGet package for Giraffe and giraffe-template.
• -OnlyNetStandard will build Giraffe only targeting the NETStandard1.6 framework (see known issues)

Examples:

Only build the Giraffe project in Debug mode:

PS > .\build.ps1

Build the Giraffe project in Release mode:

PS > .\build.ps1 -Release

Build the Giraffe project in Debug mode and also build and run the tests project:

PS > .\build.ps1 -IncludeTests

Same as before, but also build and test the samples project:

PS > .\build.ps1 -IncludeTests -IncludeSamples

One switch to build and test all projects:

PS > .\build.ps1 -All

Build and test all projects, use the Release build configuration and create all NuGet packages:

PS > .\build.ps1 -Release -All -Pack

Currently the best way to work with F# on .NET Core is to use Visual Studio Code with the Ionide extension. Intellisense and debugging is supported with the latest versions of both.

Currently there is a known issue with Ionide where Intellisense breaks when a project targets multiple frameworks.

This issue affects Giraffe because it targets more than one framework and therefore breaks Intellisense when building the project with the default configuration.

During development you can workaround this issue by invoking the build script with the -OnlyNetStandard flag:

PS > .\build.ps1 -OnlyNetStandard

This switch will override the default configuration and allow a frictionless development experience.

The official build by the build server doesn't use this setting and builds the project against all supported target frameworks as you would expect it.

Help and feedback is always welcome and pull requests get accepted.

When contributing to this repository, please first discuss the change you wish to make via an open issue before submitting a pull request. For new feature requests please describe your idea in more detail and how it could benefit other users as well.

Please be aware that Giraffe strictly aims to remain as light as possible while providing generic functionality for building functional web applications. New feature work must be applicable to a broader user base and if this requirement cannot be met sufficiently then a pull request might get rejected. In the case of doubt the maintainer will rather reject a potentially useful feature than adding one too many. This measure is to protect the repository from feature bloat over time and shall not be taken personally.

When making changes please use existing code as a guideline for coding style and documentation. If you intend to add or change an existing HttpHandler then please update the README.md file to reflect these changes there as well. If applicable unit tests must be be added or updated and the project must successfully build before a pull request can be accepted.

If you have any further questions please let me know.

You can file an issue on GitHub or contact me via https://dusted.codes/about.

Special thanks to all developers who helped me by submitting pull requests with new feature work, bug fixes and other improvements to keep the project in good shape (in no particular order):

• slang25 (Added subRoute feature and general help to keep things in good shape)
• Nicolás Herrera (Added razor engine feature)
• Dave Shaw (Extended sample application and general help to keep things in good shape)
• Tobias Burger (Fixed issues with culture specific parsers)
• David Sinclair (Created the dotnet-new template for Giraffe)
• Florian Verdonck (Ported Suave's experimental Html into Giraffe, implemented the warbler and general help with the project)
• Roman Melnikov (Added redirectTo route)
• Diego B. Fernandez (Added support for the Option<'T> type in the query string model binding)
• Jimmy Byrd (Added Linux builds)
• Jon Canning (Moved the Razor and DotLiquid http handlers into separate NuGet packages and added the routeBind handler as well as some useful HttpContext extensions)
• Andrew Grant (Fixed bug in the giraffe-template NuGet package)
• Gerard (Changed the API to continuations instead of binding HttpHandlers and to tasks from async)

If you submit a pull request please feel free to add yourself to this list as part of the PR.

• Functional ASP.NET Core
• Functional ASP.NET Core part 2 - Hello world from Giraffe
• Carry On! … Continuation over binding pipelines for functional web

If you have blogged about Giraffe, demonstrating a useful topic or some other tips or tricks then please feel free to submit a pull request and add your article to this list as a reference for other Giraffe users. Thank you!

Apache 2.0

If you have any further questions feel free to reach out to me via any of the mentioned social media on https://dusted.codes/about or join the #giraffe Slack channel in the Functional Programming Slack Team. Please use this link to request an invitation to the Functional Programming Slack Team.