The Functional Web
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The HTTP protocol adheres to the functional programming paradigm. This talk looks at HTTP on .NET and illustrates how F# allows for a more direct correlation to the patterns of composition inherent in the design of HTTP.
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The Functional Web
- 2. Ryan Riley O Logos Bible Software O Community for F# O F# MVP O OSS: FSharpx, Fracture, Frank O @panesofglass
- 3. Outline O The State of HTTP on .NET O Composition Patterns in HTTP O Identifying Problems O Examining a Solution
- 4. The State of HTTP on .NET
- 5. Current Options O http.sys O HttpListener O IIS (IHttpModule & IHttpHandler) O Web Forms O MVC O WCF HTTP & Data Services
- 6. Future Options O System.Net.Http (BETA) O .NET 4.5 O Available on NuGet O ASP.NET Web API (BETA) O Builds on System.Net.Http O Integrated with MVC 4
- 7. OSS Options Frameworks Servers O FubuMVC O Firefly (OWIN) O MonoRail O Fracture (F#) O NancyFx O Kayak (OWIN) O OpenRasta O Manos de Mono O OWIN/Gate O ServiceStack.NET O Mono XSP O WebSharper O ⊠and many more!
- 8. Composition Patterns in HTTP
- 9. Component Parts O Request/Response Lines O Methods, URIs, Status Codes O Headers O General, Request, Response, Content O Resources O Representations O Hypermedia
- 10. Simplest HTTP Application HttpRequestMessage -> HttpResponseMessage
- 11. Resources GET /item/1 + POST /item/1 + PUT /item/1 + OPTIONS /item/1 = Resource at / with GET, POST, PUT, & OPTIONS
- 12. HTTP Applications / + /items + /item/{itemId} + /help = Typical HTTP âapplicationâ
- 13. Content Negotiation Client Accepts Server Supports application/xml;q=0.9 application/json application/json;q=0.8 text/plain text/plain;q=0.5 text/html application/json
- 15. HttpListener O Low-level O Defines the signature for a single application only O HttpListenerContext provides a singleton; no chance to intercept and chain behavior O Routing requests requires custom handling; typically by using imperative if-then-else O No means of chaining or composing multiple listeners
- 16. HttpListener HttpListener.Start ("http://localhost:8082/", (fun (request, response) -> async { match request.Url.LocalPath with | "/post" -> // Send message to the chat room room.SendMessage(request.InputString) response.Reply("OK") | "/chat" -> // Get messages from the chat room (asynchronously!) let! text = room.AsyncGetContent() response.Reply(text) | s -> // Handle an ordinary file request let file = root + (if s = "/" then "chat.html" else s.ToLower()) if File.Exists(file) then let typ = contentTypes.[Path.GetExtension(file)] response.Reply(typ, File.ReadAllBytes(file)) else response.Reply(sprintf "File not found: %s" file) }), cts.Token)
- 17. IHttpModule & IHttpHandler O Low-level O HttpContext has the same problems as HttpListenerContext O IHttpHandler could represent a Resource, but method mapping is imperative O IHttpModule provides a middleware layer for routing or hosting multiple IHttpHandlers O System.Web.Routing surfaces the routing component
- 18. IHttpModule & IHttpHandler interface IHttpModule { void Dispose(); void Init(HttpApplication context); } interface IHttpHandler { bool IsReusable { get; } void ProcessRequest(HttpContext context); }
- 19. ASP.NET Web Forms O HTML composition via MasterPages, Pages, and Controls O Suffers many problems associated with IHttpModule and IHttpHandler O Evented model allows for interception O No built-in support for other representations O Pages loosely correlate to Resources O Application composition and routing by file path
- 20. ASP.NET MVC O Suffers many problems associated with IHttpModule and IHttpHandler O Primarily HTML generation but allows for better HTTP control O Built-in support for handling Ajax requests O ActionFilters allow for behavior composition at different points: Authorize, ActionExecuting, ActionExecuted, Resul tExecuting, ResultExecuted
- 21. ASP.NET MVC, cont. O Content Negotiation is still very manual O ViewEngines and Serializers can be made to render various representations O ViewEngines offer representation composition O Controllers ~ Resources, but not quite O Areas and Routing allow for Nested Resources, to a degree
- 22. Problem Summary O Have: O Limited interception for cross-cutting concerns O Representation composition O Do not have: O No easy resource composition O No built-in content negotiation
- 23. Composition for Conneg O Rendering O Imperative if-then-else O Serializers O Location O Within the specific method handler (common for imperative) O Top-level (common for serializers) O Why not both?
- 24. Nested Resources O Imperative if-then-else O Routing O MVC Areas offer another level O What about more than one level? O Rails â problem with deep URIs O System.Web.Routing does everything at the top-level, so tracking deeper resource trees is difficult.
- 26. Function Composition O Functional programming offers solutions to these problems O Filter O Map O Reduce
- 27. Frank O F# DSL using System.Net.Http O Headers composition O Follows the natural composition of HTTP O Frank Resources == HTTP Resources O Define your own conventions!
- 28. Simplest HTTP Frank Application HttpRequestMessage -> HttpResponseMessage HttpRequestMessage -> Async<HttpResponseMessage>
- 29. Define a Method Handler // handler let echo request = async { let! body = request.Content.AsyncReadAsString() return HttpResponseMessage.ReplyTo(request, body) } // method handler get echo
- 30. Define a Resource let helloworld request = async { ⊠} let echo request = async { ⊠} let resource = route â/â (get helloworld <|> post echo)
- 31. Define an Application let todoListResource = route â/â (get todoList <|> âŠ) let todoItemResource = route â/item/{1}â (put âŠ) let app = merge [ todoListResource; todoItemResource ]
- 32. Leverage Conneg val negotiateMediaType = formatters -> HttpRequestMessage -> string -> Async<HttpResponseMessage> let echo = negotiateMediaType formatters <| fun request -> request.Content.AsyncReadAsString())
- 33. WebSharper O One language for both client and server O Can leverage to cleanly separate parts O Use WebSharper to generate code-on- demand to send to the client O Plays well with existing tools
- 34. Summary
- 35. Resources O ASP.NET Web Forms in F# O ASP.NET MVC in F# O Figment DSL for MVC O Frank DSL for Web API O WebSharper O Pit FW
- 36. Thank you! O Please rate this talk: http://speakerrate.com/talks/9293-the- functional-web
Hinweis der Redaktion
- HTTP defines several components that allow distributed, loosely-coupled agents to communicate. The first lines of requests and responses are standardized to ensure that loosely-coupled components can understand one another, yet they allow for extension either by standards bodies or for internal, proprietary use.
- This may be new to some, but this resource is not the same as the collection of items at /items.
- The aggregate of many resources is generally what we refer to as an HTTP, or Web, Application. A single resource is enough, as is a single method.
- Resources may be directly returned in a response. In the beginning, when most HTTP applications served static files, this was common. However, Resources are not equivalent to the representation returned to the client, even if they appear identical. Unlike editing files locally, if you were to edit a file returned from an HTTP application, you would not be editing the original file. You would need to re-submit the file to the server, if allowed, and then the server would need to take the content you supplied and update the original Resource.It is thus reasonable to understand that a Resource can be represented in more than one way. A JSON representation is just as valid as XML, HTML, or even an image.Content negotiation, or âconneg,â is a cross-cutting concern that allows HTTP applications to select an appropriate representation to send in the response message. The actual execution of this selection could occur either at the top-level or at the lowest-level of a composed HTTP application.
- Itâs also important to note that the request and response headers are just NameValueCollections, so you donât have easy, typed access to common header values. This isnât critical for composition but odd for a statically-typed language platform.DEMO: In spite of its short-comings, you can still do some interesting things with HttpListener. Tomas Petricek created a really interesting project where he uses HttpListener as the base for a chat server.
- Itâs also important to note that the request and response headers are just NameValueCollections, so you donât have easy, typed access to common header values. This isnât critical for composition but odd for a statically-typed language platform.DEMO: In spite of its short-comings, you can still do some interesting things with HttpListener. Tomas Petricek created a really interesting project where he uses HttpListener as the base for a chat server.
- Itâs important to note here that these interfaces are exposed by IIS and can be used to modify that server directly, though they are also tied directly to that server. Mono offers additional options for hosting, but you should understand that you are generally tied to IIS.
- Itâs important to note here that these interfaces are exposed by IIS and can be used to modify that server directly, though they are also tied directly to that server. Mono offers additional options for hosting, but you should understand that you are generally tied to IIS.
- ASP.NET Web Forms 4.0 provided a hook intoSystem.Web.Routing.Also of note:Web Forms has historically been demonized by itâs poor HTML output, requiring a <form> element to scope control usage.Many server controls have weird behavior. Anchor tags, which generally perform GET requests instead POST back to server, even just to navigate to another page. Some of this is of course avoidable, but the designer-centric focus often leads to ill-advised HTTP use.FSharpCodeDomProvider has limitations.
- Also difficult to use F# for View Models. You will have a difficult time using records and discriminated unions as types, and youâll be forced into mutability.
- Current frameworks typically choose to lean on one or the other of the above sets of options. However, there really should be no reason to require only one or the other. In fact, you should be free to define various boundaries where you might use a serializer approach over a subset of resources.
- Routing is nothing more than filtering down a set of handlers to select the appropriate one and return a response.A Response is nothing more than a map function over a request, though it is true that some HTTP methods are destructive (e.g. POST).Pulling handlers into resources or applications is nothing more than a reduce function. Frank uses merge; WebSharper uses Sum.
- For those with a stronger bent towards building web sites, Mauricio Schefferâs Figment may be a closer match to your taste.
- Compare the Frank application signature with the simplest app signature we used above. The only addition is that we are stating that an application is non-blocking. This is the same idea as is used in node.js. Itâs also sort-of required since Frank sits on System.Net.Http via MessageHandlers. The signature for the MessageHandler.SendAsync is the same but for Task rather than Async. This signature extends all the way through all layers of composition.
- A resource is the only current location that does not conform solely to the Frank application signature. A resource holds both a Uri Template (its name) as well as a HttpRequestMessage -> Async<HttpResponseMessage> option. Why the option? The resource will respond with a 405 Method Not Allowed if it does not respond to the method thrown its way. Thus the option allows the programmer to define the methods for the resource without having to manually hook up the 405 response.
- Similar to resource, merge is a function of HttpRequestMessage -> Async<HttpResponseMessage> option. When a resource uri is not found, a 404 Not Found response is returned. The result, however, is a Frank application.
- Frank currently uses Mauricio SchefferâsFsConneg library, now in FSharpx.Http. System.Net.Http has a similar mechanism, but itâs currently still a little heavy as they work out the kinks in preparation for the RC. FsConneg provides a mechanism for submitting the Accept headers and a list of supported formats and returns the best match. negotiateMediaType wraps that with the selection of the appropriate formatter, of type System.Net.Http.Formatting.MediaTypeFormatter, and returns the formatted content.
- Another option is Pit FW, which was featured on the Community for F# on 2/21/2012 (today). It also compiles F# to JavaScript. You can learn more at http://pitfw.org/.
- Using F# for web projects isnât just about code size. Yes, youâll save some lines of code, but more importantly, youâll work closer to the guts of HTTP. You can leverage the power of composition to build applications that will be more maintainable and much clearer to understand.