Websocket Frames

gistfile1.fs

namespace Tsunami.Server

open System
open System.IO
open System.Linq
open System.Net
open System.Net.Sockets
open System.Text
open System.Threading
open System.Runtime.Serialization

module WebSockets =

    type WebsocketFrame =
        | ContinuationFrame         //%x0
        | TextFrame                 //%x1
        | BinaryFrame               //%x2
        | ReservedNonControl        //%x3-7
        | ConnectionClosed          //%x8
        | Ping                      //%x9
        | Pong                      //%xA
        | ReservedControl           //%xB-F

    /// Swaps the Endian only if the Machine Is Little Endian
    let swapEndian (bs : byte array) = if BitConverter.IsLittleEndian then Array.rev bs else bs

    let unwrapFrame (stream:Stream) =
        async {
            let! firstByte_t = stream.AsyncRead(1)
            let firstByte = firstByte_t.[0]
            let final = firstByte &&& 128uy <> 0uy
            let opcode = 
                match firstByte &&& 15uy with
                | 0uy -> ContinuationFrame
                | 1uy -> TextFrame
                | 2uy -> BinaryFrame
                | 3uy | 4uy | 5uy | 6uy | 7uy -> ReservedNonControl
                | 8uy -> ConnectionClosed
                | 9uy -> Ping
                | 10uy -> Pong
                | 11uy | 12uy | 13uy | 14uy | 15uy -> ReservedControl 
                | _ -> failwith "given the mask above this cannot happen"
        
            let! secondByte_t = stream.AsyncRead(1)
            let secondByte = secondByte_t.[0]
            let mask = secondByte &&& 128uy <> 0uy
     
            let! payloadLength =
                match secondByte &&& 127uy with
                | 127uy -> 
                    async {
                        let! int64Bytes = stream.AsyncRead(8)
                        return BitConverter.ToUInt64(int64Bytes |> swapEndian, 0)
                    }
                | 126uy -> 
                    async {
                        let! int16Bytes = stream.AsyncRead(2)
                        return uint64 (BitConverter.ToUInt16(int16Bytes |> swapEndian, 0))
                    }
                | x -> async { return uint64 (Convert.ToUInt16(x)) }
        
            let payloadLength' = int32 payloadLength // TODO support int64 payloads....
        
            let! data = 
                if mask 
                then
                    async {
                        let! mask = stream.AsyncRead(4)
                        let! data = stream.AsyncRead(payloadLength')
                        return data |> Array.mapi (fun i b -> b ^^^ mask.[i % 4])
                    }
                else
                    stream.AsyncRead(payloadLength')
            return (opcode, data, final)
        }


    let wrapFrame (opcode : WebsocketFrame, data:byte array, final : bool, mask : uint32 option) =
        let firstByte =
            match opcode with
            | ContinuationFrame -> 0uy 
            | TextFrame -> 1uy 
            | BinaryFrame -> 2uy 
            | ReservedNonControl -> failwith "Use of reserved unsuported opcode \"ReservedNonControl\""
            | ConnectionClosed -> 8uy 
            | Ping -> 9uy
            | Pong -> 10uy 
            | ReservedControl -> failwith "Use of reserved unsuported opcode \"ReservedControl\""
            |> fun x -> if final then x  ||| 128uy else x
    
        let length = data |> Array.length // NOTE  Length cannot be > int32 but can be > int16
        let lengthBytes =
            if length < 126 then [Convert.ToByte(length)]
            else if length < int32 UInt16.MaxValue then 126uy :: (BitConverter.GetBytes(length) |> swapEndian |> Seq.skip 2 |> Seq.toList)
            else 127uy :: ([0uy;0uy;0uy;0uy] @ ((BitConverter.GetBytes(length) |> swapEndian |> Seq.toList)))  // TODO support 64 bit lengths
            |> function
            | (x::xs) as ys -> if mask.IsSome then (x ||| 128uy) :: xs else ys // Set the mask bit if one is available
            | _ -> failwith "Should not happen - should have at least one byte in the list"

        let maskedData = 
            match mask with 
            | None -> data
            | Some(m) ->
                let maskBits = BitConverter.GetBytes(m) |> swapEndian // Note order really does not matter for this
                Array.append maskBits (data |> Array.mapi (fun i b -> b ^^^ maskBits.[i % 4]))
        Array.append (firstByte :: lengthBytes |> List.toArray) maskedData

    let echo (ns:NetworkStream) : Async<unit> =
        async {
            while true do
                let! msg = unwrapFrame(ns)
                match msg with
                | (TextFrame, data, true) -> 
                    do! ns.AsyncWrite(wrapFrame (TextFrame, data, true, None))
                | _ -> () 
        }

Apache 2.0 licensed...