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.NET Cross platform Functional Web Request Handlers for F#
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Oryx is a high performance .NET cross platform functional HTTP request handler library for writing HTTP web clients in F#.

An SDK for writing HTTP web clients or SDKs.

This library enables you to write Web and REST clients and SDKs for various APIs and is currently used by the .NET SDK for Cognite Data Fusion (CDF).

Oryx is heavily inspired by the Giraffe web framework, and applies the same ideas to the client making the web requests. You can think of Oryx as the client equivalent of Giraffe, and you could envision the HTTP request processing pipeline starting at the client and going all the way to the server and back again.


The main building blocks in Oryx is the Context and the HttpHandler. The Context stores all the state needed for making the request and any response or error received from the server:

type Context<'a> = {
    Request: HttpRequest
    Response: 'a

The Context may be transformed by series of HTTP handlers. The HttpHandler takes a Context (and a NextFunc) and returns a new Context wrapped in a Result and Task.

type HttpFuncResult<'b> =  Task<Result<Context<'b>, ResponseError>>

type HttpFunc<'a, 'b> = Context<'a> -> HttpFuncResult<'b>
type NextFunc<'a, 'b> = HttpFunc<'a, 'b>

type HttpHandler<'a, 'b, 'c> = NextFunc<'b, 'c> -> Context<'a> -> HttpFuncResult<'c>

// For convenience
type HttpHandler<'a, 'b> = HttpHandler<'a, 'a, 'b>
type HttpHandler<'a> = HttpHandler<HttpResponseMessage, 'a>
type HttpHandler = HttpHandler<HttpResponseMessage>

An HttpHandler is a plain function that takes two curried arguments, a NextFunc and a Context, and returns a new Context (wrapped in a Result and Task) when finished. On a high level the HttpHandler function takes and returns a context object, which means every HttpHandler function has full control of the outgoing HttpRequest and also the resulting response.

Each HttpHandler usually adds more info to the HttpRequest before passing it further down the pipeline by invoking the next NextFunc or short circuit the execution by returning a result of Result<Context<'a>, ResponseError>. E.g if an HttpHandler detects an error, then it can return Result.Error to fail the processing.

The easiest way to get your head around a Oryx HttpHandler is to think of it as a functional Web request processing pipeline. Each handler has the full Context at its disposal and can decide whether it wants to fail the request by returning an Error, or continue the request by passing on a new Context to the "next" handler, NextFunc.

The more complex way to think about a HttpHandler is that there are in fact 3 different ways it may process the request:

  1. Call the next handler with an Ok result value, and return what the next handler is returning.
  2. Return an Errorresult to fail the request.
  3. Return Ok to short circuit the processing. This is not something you would normally do.


The fact that everything is an HttpHandler makes it easy to compose handlers together. You can think of them as lego bricks that you can fit together. Two HttpHandler functions may be composed together using Kleisli composition, i.e using the fish operator >=>.

let (>=>) a b = compose a b

The compose function is the magic that sews it all togheter and explains how you can curry the HttpHandler to generate a new NextFunc that you give to next HttpHandler. If the first handler fails, the next handler will be skipped.

let compose (first : HttpHandler<'a, 'b, 'd>) (second : HttpHandler<'b, 'c, 'd>) : HttpHandler<'a,'c,'d> =
    fun (next: NextFunc<_, _>) (ctx : Context<'a>) ->
        let func =
            |> second
            |> first

        func ctx

This enables you to compose your web requests and decode the response, e.g as we do when listing Assets in the the Cognite Data Fusion SDK:

    let listAssets (options: AssetQuery seq) (filters: AssetFilter seq) (fetch: HttpHandler<HttpResponseMessage, 'a>) =
        let decodeResponse = Decode.decodeContent AssetItemsReadDto.Decoder id
        let request : Request = {
            Filters = filters
            Options = options

        >=> setVersion V10
        >=> setContent (Content.JsonValue request.Encoder)
        >=> setResource Url
        >=> fetch
        >=> Decode.decodeError
        >=> decodeResponse

Thus the function listAssets is now also an HttpHandler and may be composed with other handlers to create complex chains for doing series of multiple requests to a web service.

There is also a retry that retries HTTP handlers using max number of retries and exponential backoff.

val retry : (initialDelay: int<ms>) -> (maxRetries: int) -> (handler: HttpHandler<'a,'b,'c>) -> (next: NextFunc<'b,'c>) -> (ctx: Context<'a>) -> Task<Context<'c>>

And a concurrent operator that runs a list of HTTP handlers in parallel.

val concurrent : (handlers: HttpHandler<'a, 'b, 'b> seq) -> (next: NextFunc<'b list, 'c>) -> (ctx: Context<'a>) -> Task<Context<'c>>

JSON and Protobuf

Oryx will serialize (and deserialize) JSON using Thoth.Json.Net or Protobuf using Google.Protobuf.

Both encode and decode uses streaming so no large strings or arrays will be allocated in the process.

Computational Expression Builder

Working with Context objects can be a bit painful since the actual result will be available inside a Task effect that has a Result that can be either Ok with the response or Error. To make it simpler to handle multiple requests using handlers you can use the oryx builder that will hide the complexity of both the Context and the Result.

    oryx {
        let! a = fetchData "service1"
        let! b = fetchData "service2"

        return a + b

To run a handler u can use the runHandler function.

val runHandler : (handler: HttpHandler<'a,'b,'b>) -> (ctx : Context<'a>) -> Task<Result<'b, ResponseError>>


  • The library currently depends on Thoth.Json.Net. This should at some point be split into a separate library.

  • The library also assumes the type of the error response. This should perhaps be made more generic.

Code of Conduct

This project follows, see our Code of Conduct.


Apache v2, see LICENSE.

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