Unify Request and Response representation

option-b.cs

namespace Owin
{
    public delegate void AppDelegate(
        IDictionary<string, object> env,
        IDictionary<string, string[]> headers,
        Stream body,
        ResultDelegate result,
        Action<Exception> fault);

    public delegate void ResultDelegate(
        string status,
        IDictionary<string, string[]> headers,
        Func<Stream, CancellationToken, Task> body,
        IDictionary<string, object> properties);

    public delegate Task<Tuple<string /* status */, IDictionary<String, string[]> /* headers */, Func<Stream, CancellationToken, Task> /* body */, IDictionary<string, object> /*properties*/>>
        AppTaskDelegate(IDictionary<string, object> env);

    public interface IAppBuilder
    {
        IAppBuilder Use<TApp>(Func<TApp, TApp> middleware);
        TApp Build<TApp>(Action<IAppBuilder> fork);

        IAppBuilder AddAdapters<TApp1, TApp2>(Func<TApp1, TApp2> adapter1, Func<TApp2, TApp1> adapter2);
        IDictionary<string, object> Context { get; }
    }
}

option-c.cs

namespace Owin
{
    public struct CallParameters
    {
        public IDictionary<string, object> Environment;
        public IDictionary<string, string[]> RequestHeaders;
        public Stream RequestBody;
    }

    public struct ResultParameters
    {
        public string StatusCode;
        public IDictionary<string, string[]> ResponseHeaders;
        public Func<Stream, CancellationToken, Task> ResponseBody;
        public IDictionary<string, object> ResponseProperties;
    }

    public delegate void AppDelegate(CallParameters call, Action<ResultParameters> result, Action<Exception> fault);

    public delegate Task<ResultParameters> AppTaskDelegate(CallParameters call);

    public interface IAppBuilder
    {
        IAppBuilder Use<TApp>(Func<TApp, TApp> middleware);
        TApp Build<TApp>(Action<IAppBuilder> fork);

        IAppBuilder AddAdapters<TApp1, TApp2>(Func<TApp1, TApp2> adapter1, Func<TApp2, TApp1> adapter2);
        IDictionary<string, object> Properties { get; }
    }
}

option-c.fs

namespace Owin

open System
open System.Collections.Generic
open System.Threading
open System.Threading.Tasks
open FSharp.Control  // from FSharpx.Core

//type BodyDelegate = (ArraySegment<byte> -> (unit -> unit) -> bool) -> (exn -> unit) -> CancellationToken -> unit
//type BodyObservable = IObservable<ArraySegment<byte> * (unit -> unit) * (unit -> unit)>
type MessageBody = AsyncSeq<ArraySegment<byte>>

[<Struct>]
type CallParameters =
    val Environment     : IDictionary<string, obj>
    val RequestHeaders  : IDictionary<string, string[]>
    val RequestBody     : MessageBody

[<Struct>]
type ResultParameters = {
    val StatusCode          : int
    val ResponseHeaders     : IDictionary<string, string[]>
    val ResponseBody        : MessageBody
    val ResponseProperties  : IDictionary<string, obj>

type AppDelegate = CallParameters -> Async<ResultParameters>

[<Interface>]
type IAppBuilder =
    abstract member Use         : 'a -> 'a -> IAppBuilder
    abstract member Build       : IAppBuilder -> unit
    abstract member AddAdapters : ('a -> 'b) * ('b -> 'a) -> IAppBuilder
    abstract member Properties  : IDictionary<string, obj> with get

option-d.cs

namespace Owin
{
    public delegate void AppDelegate(IDictionary<string,object> env, Action<IDictionary<string,object>> result, Action<Exception> fault);

    public delegate Task<IDictionary<string,object>> AppTaskDelegate(IDictionary<string,object> env);

    public interface IAppBuilder
    {
        IAppBuilder Use<TApp>(Func<TApp, TApp> middleware);
        TApp Build<TApp>(Action<IAppBuilder> fork);

        IAppBuilder AddAdapters<TApp1, TApp2>(Func<TApp1, TApp2> adapter1, Func<TApp2, TApp1> adapter2);
        IDictionary<string, object> Properties { get; }
    }
}